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- A device fitted around or in back of a projectile
in a gun barrel or launching tube to support or protect the projectile or to
prevent the escape of gas ahead of it.
- The sabot separates from the projectile after launching.
- Sagitta (abbr Sge, Sgte)
- See constellation.
- Sagittarius (abbr Sgr, Sgtr)
- See constellation.
- salvo launch
- Act of launching two or more rockets
- In statistics, a group of observations selected from a statistical population
by a set procedure. See random
- Samples may be taken at random or systematically. The sample is taken
in an attempt to estimate the population.
- Of sandwich
construction, as in sandwich panel, sandwich skin , etc.
- sandwich construction
- A type of construction in which two sheets, sides, or plates are separated
by a core of stiffening material, generally lightweight. See honeycomb
- (From search and rescue and homing). A radio homing device
originally designed for personnel rescue and now used in spacecraft recovery
operations at sea.
- The eclipse cycle
of about 18 years, almost the same length as 223 synodical
months. See lunar
- At the end of each saros the sun, moon, and line of nodes return to
approximately the same relative positions and another series of eclipses
begins, closely resembling the series just completed.
- 1. An attendant body that revolves about another body, the primary;
especially in the solar system, a secondary body, or moon, that revolves about
a planet. See table XIII for a list of satellites of the solar system.
- 2. A manmade object that revolves about a spatial body, such as Explorer I
orbiting about the earth. See spacecraft,
- 3. Such a body intended and designed for orbiting, as distinguished from a
companion body that may incidentally also orbit, as in the observer
actually saw the orbiting rocket rather than the satellite.
- 4. An object not yet placed in orbit, but designed or expected to be
launched into an orbit.
- A vehicle that
revolves about the earth or other body, but at such altitudes as to require
sustaining thrust to
- saturation-adiabatic lapse rate
- A special case of process
lapse rate, defined as the rate of decrease of temperature with height of
an air parcel
lifted in a saturation-adiabatic process through an atmosphere in hydrostatic
equilibrium. Also called moist-adiabatic lapse rate.
- Owing to the release of latent heat, this lapse rate is less than the
lapse rate, and the differential equation representing the process must be
integrated numerically. Wet-bulb potential temperature is constant with height
in an atmosphere with this lapse rate.
- saturation vapor pressure
- 1. The vapor
pressure of a system, at a given temperature, wherein the vapor of a
substance is in equilibrium with a plane surface of the pure liquid or solid
phase of that substance; that is, the vapor pressure of a system that has
attained saturation but not supersaturation. Compare equilibrium
vapor pressure, vapor
- The saturation vapor pressure of any pure substance, with respect to a
specified parent phase, is an intrinsic property of that substance and is a
function of temperature alone (see Clapeyron-Clausius
- 2. = equilibrium
- See planet, table.
- Referring to positions on Saturn measured in latitude from
Saturn's equator and in
from a reference meridian.
- A frequency
band used in radar extending
approximately from 1.55 to 5.2 kilomegacycles per second.
- Any physical quantity whose field can be described by a single numerical
value at each point in space.
- A scalar quantity is distinguished from a vector quantity
by the fact that a scalar quantity possesses only magnitude,
whereas a vector quantity possesses both magnitude and direction.
- scalar acceleration
- The square root of the sum of the squares of three orthogonal
components of an acceleration.
- scalar product
- A scalar
equal to the product of the magnitudes of any two vectors and the
cosine of the angle θ between their positive directions. Also called
dot product, direct product, inner product. See vector
- For two vectors A and B, the scalar product is most commonly written A
. B, read A dot B, and occasionally as (AB). If
the vectors A and B have the components Ax, Bx, Ay,
By, and Az, Bz along rectangular Cartesian, x, y, and z axes,
A . B = AxBx + AyBy + AzBz = |A||B|cosθ = AB cosθ
If a scalar product is zero, one of the vectors
is zero or else the two are perpendicular.
- scalar velocity
- The square root of the sum of the squares of three orthogonal
components of a velocity.
- scale effect
- Any variation in the nature of the flow and in the
force coefficients associated with a change in value of the Reynolds
number, i.e., caused by change is size without change in shape.
- scale height (symbol h, hs)
- A measure of the relationship between density and temperature of any point
in an atmosphere;
the thickness of a homogeneous
atmosphere which would give the observed temperature: h = kT/mg =
R*T/Mg where k is the Boltzmann
constant; T is the absolute temperature; m and M are
the mean molecular mass and weight, respectively, of the layer; g is
the acceleration of gravity; and R* is the universal gas constant.
- scale model
- A model of a different size from its prototype and having dimensions in
some constant ratio to the dimensions of the prototype, especially such a
model of smaller size than its prototype.
- scale of 10 counter = decade counter.
- A device that produces an output pulse whenever a
prescribed number of input pulses have been received. Also called scaling
- The number of input pulses per output pulse of a scaler is termed the
scaling factor. A binary scaler is a scaler whose scaling factor is 2. A
decade scaler is a scaler whose scaling factor is 10.
- scaling circuit = scaler.
- scaling factor
- See scalar, note.
- A radar mechanism incorporating a rotatable antenna, or radiator, motor
drives, mounting, etc., for directing a searching radar beam
through space and imparting target information to an indicator. See parabolic
- In radar,
the motion of the radar antenna
assembly when searching for targets.
- Scanning usually follows a systematic pattern involving one or more of
the following: (1) In horizontal scanning (or searchlighting), the antenna is
continuously rotated in azimuth around the horizon or in a sector (sector
scanning); used to generate plan-position-indicator-scope displays. (b)
Vertical scanning is accomplished by holding the azimuth constant but varying
the elevation angle of the antenna; used in height-finding radars to generate
the relative-height-indicator-scope display. (c) For conical scanning, a
somewhat offcenter radiating element is rotated while its parabolic reflectors
fixed in position so that the radiated beam generates a concially shaped
volume with the antenna at the apex; used to determine accurate bearing and
elevation angle of targets and employed in automatic tracking radars. (d) In
helical scanning (or spiral scanning) the azimuth and elevation angle of the
antenna are constantly varied so that at a given distance from the radar the
radiated beam generates the surface of a hemisphere; used for radio direction
finding, in certain types of search radars, and in tracking radars to search
areas for targets.
- scaphandre = full pressure suit.
- 1. = scattering.
- 2. The relative dispersion of points on a graph, especially with respect
to a mean value, or any curve used to represent the points. See dispersion.
- 3. To accomplish scattering.
- scatter angle
- The angle between any given ray of scattered
radiation and the incident ray. See relative
scatter intensity, scattering.
- Convention varies as to whether this angle is measured with respect to
the direction in which the incident radiation was advancing or with respect to
the direction from scatterer to radiation source.
- scatter communication
- See scatter
- scattered power = received power.
- scatterer = scattering particle.
- The process by which small particles suspended in a medium of a different
of refraction diffuse a portion of the incident radiation in
all directions. In scattering, no energy transformation results, only a change
in the spatial distribution of the radiation. Also called scatter.
- Along with absorption, scattering is a major cause of the attenuation
of radiation by the atmosphere. Scattering varies as a function of the ratio
of the particle diameter to the wavelength of the radiation. When this ratio
is less than about one-tenth, Rayleigh
scattering occurs in which the scattering coefficient varies inversely as
the fourth power of the wavelength. At larger values of the ratio of particle
diameter to wavelength, the scattering varies in a complex fashion described
by the Mie
theory; at a ratio of the order of 10, the laws of geometric optics begin
- scattering area coefficient
- The dimensionless ratio of the scattering
cross section to the geometric cross
section of a scattering
particle. Also called scattering area ratio.
- scattering area ratio = scattering area coefficient.
- scattering coefficient
- A measure of the attenuation
due to scattering
of radiation as it traverses a medium containing scattering
particles. Also called total scattering coefficient.
- scattering cross section
- The hypothetical area normal to the incident radiation
that would geometrically intercept the total amount of radiation actually
scattered by a scattering
particle. It is also defined, equivalently, as the cross-section area of
an isotropic scatterer (a sphere) which would scatter the same amount of
radiation as the actual amount. Also called extinction cross section,
- scattering function
- The intensity of
scattered radiation in
a given direction per lumen of flux incident upon the scattering
- scattering gage = scattering-type pressure gage.
- scattering loss
- That part of the transmission
loss which is due to scattering
within the medium or due to roughness of the reflecting surface.
- scattering particle
- The small particles
responsible for scattering.
- scattering power
- In radar terminology, the ratio of the total power scattered by a target to the
power in the incident wave, independent of the direction of scattering.
The scattering power measures the loss of energy by absorption
in the scatterers. Also called total scattering cross section. Compare
- scattering-type pressure gage
- An ionization
gage in which measurement is made of the electrons
scattered by collision of the gas molecules with the electrons from a
- scatter propagation
- Specifically, the long-range propagation
signals by scattering
due to index
of refraction inhomogeneities in the lower atmosphere. Also called tropospheric
- Recognition of this process and the development of specialized
equipment (basically, more powerful transmitters and sensitive receivers) has
greatly increased the range of VHF and UHF communication. The over-all
technique is known as scatter communication.
- (German, streaks, striae).
- 1. Regions of different density in a fluid, especially
as shown by special apparatus.
- 2. Pertaining to a method or apparatus for visualizing or photographing
regions of varying density in a field of flow. See schlieren
- Used in compounds, such as schlieren lens, schlieren method, schlieren
- schlieren method
- See schlieren.
- schlieren photography
- A method of photography for flow patterns that
take advantage of the fact that light passing through a density gradient in a
gas is refracted as
though it were passing through a prism. Compare shadowgraph.
- Schneider index
- A composite weighted index of pulse and blood-pressure response to
exercise, utilized as a test of physical efficiency.
- Schuler pendulum
- A hypothetical pendulum with a period of 84
- A simulated Schuler pendulum carried in a vehicle moving in the earth's
field would always indicate the true vertical.
- Schuler tuning
- Adjusting a system performing the function of a pendulum so that is has a
period of 84
minutes. See Schuler
- Schumann-Runge bands
- See absorption
- Schumann-Runge continuum
- See absorption
- scintillating counter = scintillation counter.
- 1. Generic term for rapid variations in apparent position, brightness, or
color of a distant luminous object viewed through the atmosphere.
- If the object lies outside the earth's atmosphere, as in the case of
stars and planets, the phenomenon is termed astronomical scintillation; if the
luminous source lies within the atmosphere, the phenomenon is termed
terrestrial scintillation. As one of the three principal factors governing
astronomical seeing, scintillation is defined as variations in luminance
only. It is clearly established that almost all scintillation effects are
caused by anomalous refraction occurring in rather small parcels or strata of
air, schlieren, whose temperatures and hence densities differ slightly from
those of their surroundings. Normal wind motions transporting such schlieren
across the observer's line of sight produce the irregular fluctuations
characteristic of scintillation. Scintillation effects are always much more
pronounced near the horizon than near the zenith. Parcels of the order of only
centimeters to decimeters are believed to produce most of the scintillatory
irregularities in the atmosphere.
- 2. A flash of light produced in a phosphor by an
event. See scintillation counter. 3. On a radar display, a rapid apparent
displacement of the target from its
mean position. Also called target glint or wander.
- This includes but is not limited to shift of effective reflection point
on the target.
- scintillation counter
- The combination of phosphor, photomultiplier
tube, and associated circuits for counting scintillations,
sense 2. Also called scintillating counter.
- scintillation meter = scintillometer.
- A type of photoelectric photometer
used in a method of determining high altitude winds on the assumption that
is caused by atmospheric inhomogeneities ( schlieren)
being carried along by the wind near tropopause
level. Also called scintillation meter.
- Scl, Scul
- International Astronomical Union abbreviations for Sculptor. See constellation.
- Sco, Scor
- International Astronomical Union abbreviations for Scorpius. See constellation.
- The general abbreviation for an instrument of viewing, such as telescope,
microscope, and oscilloscope. In radar installations, the cathode-ray
oscilloscope indicators are commonly referred to as scopes or
- Because of possible ambiguity this term should be avoided in formal
- International Astronomical Union abbreviation for Scorpius. See constellation.
- Scorpius (abbr Sco, Scor)
- See constellation.
- scotopic vision
- Vision associated with levels of illumination below approximately 0.01
foot-lambert, effective primarily in the detection of movement and low
luminous intensities. Compare photopic
vision. Also called parafoveal vision.
- Scotopic vision is associated with rod function.
- A form of combustion
instability, especially in a liquid-propellant
rocket engine, of relatively high frequency and characterized by a
- A form of combustion
instability, especially in an afterburner,
of relatively high frequency and characterized by a harsh, shrill noise.
- 1. A device to shield or separate one part of an apparatus from other
parts, or to separate the effects of one part on others.
- 2. A surface on which images are displayed, as the face of a cathode-ray
- To cancel a scheduled firing, either before or during countdown.
- Sct, Scut
- International Astronomical Union abbreviations for Scutum. See constellation.
- International Astronomical Union abbreviations for Sculptor. See constellation.
- Sculptor (abbr Scl, Scul)
- See constellation.
- Scutum (abbr Sct, Scut)
- See constellation.
- sea clutter
- See ground
- sealed cabin
- The occupied space of an aircraft or spacecraft
characterized by walls which do not allow any gaseous exchange between the
inner atmosphere and its surrounding atmosphere and containing its own
mechanisms for maintenance of the inside atmosphere.
- sea level = mean sea level.
- sea-level pressure
- The atmospheric
pressure at mean sea
level, either directly measured or, most commonly, empirically determined
from the observed station pressure.
scanning, in which the antenna beam is continuously rotated in azimuth.
- search radar
- A radar
designed for the approximate location of (usually airborne) objects. Search
radar beams are usually wide, wider in the vertical than in the horizontal,
making it possible to scan large volumes of space quickly. Compare tracking
- sea return
- See ground
- seat belt = lap belt.
- seat-to-head acceleration
- See physiological
- second (abbr s)
- The unit of time, the second, was defined originally as the fraction 1/86
400 of the mean solar day. The exact definition of the "mean solar day" was
left to astronomers, but their measurements have shown that on account of
irregularities in the rotation of the Earth, the mean solar day does not
guarantee the desired accuracy. In order to define the unit of time more
precisely, the 11th CGPM (1960) adopted a definition given by the
International Astronomical Union which was based on the tropical year [see ephemeris
second]. Experimental work had, however, already shown that an atomic
standard of time-interval, based on a transition between two energy levels of
an atom or a molecule, could be realized and reproduced much more accurately.
Considering that a very precise definition of the unit of time of the
International System, the second, is indispensable for the needs of advanced
metrology, the 13th CGPM (1967) decided to replaced the definition of the
second by the following:
- The second is the duration of 9 192 631 770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the ground
state of the cesium-133 atom (13th CGPM (1967), Resolution 1).
The previous is an excerpt (with the exception of the reference to
"ephemeris second") from WWW version of the National Institute of
Standards and Technology: Physics Laboratory's International System of Units
- 1. = secondary
- 2. A celestial body revolving around another body, its primary.
- 3. A particle emitted in secondary
- secondary circle = secondary great circle.
- secondary cosmic radiation = secondary cosmic ray.
- secondary cosmic rays
- Secondary emission in
stimulated by primary
cosmic rays. See air shower.
- secondary electron emission
- The release of electrons
from a surface which is bombarded by energetic electrons.
- The yield or ratio of secondary to primary electrons is a function of
the primary electron energy.
- secondary emission
- Emission of subatomic
particles or photons
stimulated by primary radiation; for example, cosmic rays impinging on other
particles and causing them, by disruption of their electron configurations or
even of their nuclei, to emit particles and photons or both in turn.
- secondary great circle
- A great
circle perpendicular to a primary
great circle, as a meridian. Also
called secondary circle, secondary.
- secondary instrument
- An instrument whose calibration is determined by comparison with an absolute
- secondary radar
- See radar,
- secondary radiation
or particulate radiation
resulting from absorption of other radiation in matter.
- secondary scattering
- See multiple
- second law of thermodynamics
- An inequality asserting that it is impossible to transfer heat from a colder
to a warmer system without the occurrence of other simultaneous changes in the
or in the environment.
- It follows from this law that during an adiabatic process, entropy
cannot decrease. For reversible adiabatic processes entropy remains constant,
and for irreversible adiabatic processes it increases. Another equivalent
formulation of the law is that it is impossible to convert the heat of a
system into work without the occurrence of other simultaneous changes in the
system or its environment. This version, which requires an engine to have a
cold source as well as a heat source, is particularly useful in engineering
applications. See first
law of thermodynamics.
- Secor (abbr) = sequential collation of range.
- (Sequential collation of range/distance measuring equipment). A distance
measuring system used in rocket tracking.
- One of the cross-section parts that a rocket
vehicle is divided into, each adjoining another at one or both of its end.
Usually described by a designating word, as in nose section, aft section,
center section, tail section, thrust section, tank section , etc.
- sectionalized vertical antenna
- A vertical antenna which
is insulated at one or more points along its length. The insertion of suitable
reactances or applications of a driving voltage across the insulated points
results in a modified current distribution giving a more desired radiation
pattern in the vertical plane.
- sector scanning
- See scanning.
- Pertaining to long periods of time on the order of a century, as
secular perturbations, secular terms.
- secular perturbations
- Changes in the orbit of a planet
or satellite that operate in extremely long cycles; long term perturbations.
- secular terms
- In the mathematical expression of an orbit, terms for very long period perturbations,
in contrast to periodic terms , terms of short period.
- Seebeck effect
- The establishment of an electric potential difference tending to produce a
flow of current in a circuit of two dissimilar metals the junctions of which
are at different temperatures.
- 1. The introduction of atoms, such as sodium, with a low ionization
potential into a hot gas for the purpose of increasing the electrical
- 2. = cloud
- A blanket term long used by astronomers for the disturbing effects
produced by the atmosphere
upon the image quality of an observed celestial body. Also called
- Recent studies show that seeing is a combination of three principal and
distinct effects that the human eye is not capable of distinguishing: (a)
scintillation, i.e., fluctuations in brightness; (b) transverse displacements
of the image; and (c) variations of the radius of curvature of the wavefront
rendering the image in an out of focus.
- seismic mass
- The element in an accelerometer
which is intended to serve as the force-summing member for applied
accelerations, gravitational forces, or both.
- selective absorption
which varies with the wavelength of radiation incident upon the absorbing
substance. See absorption
- A substance which absorbs in such fashion is called a selective
absorber and is to be contrasted with an ideal black body, white body, or gray
body. In reality, all substances are selective absorbers when due regard is
paid to their interaction with all wavelengths of the complete electromagnetic
- selective scattering
which varies with the wavelengths
of radiation incident upon the scattering particles.
- In general, the largest and most complex degree of selectivity is found
for wavelengths nearly equal to the diameter of the scattering particles.
- The degree of falling off in response of a resonant device with departure
- Relating to the center of the moon; referring to the moon as a center.
- 1. Of or pertaining to the physical geography of the moon.
- 2. Specifically, referring to positions on the moon measured in latitude from
the moon's equator and in
from a reference meridian.
- A satellite of
the earth's moon. (No such satellites are known).
- That branch of astronomy that treats of the moon, its magnitude, motion,
constitution, and the like. Selene is Greek for moon.
- self-adaptive control system
- A particular type of stability augmentation system which changes the
response of a given control input
by constantly sampling response and adjusting its gain, rather than having a
fixed or selective gain system.
- self-balancing potentiometer
- See potentiometer.
- self-excited vibration = self-induced vibration.
- self-induced vibration
- Vibration of
a mechanical system resulting
from conversion, within the system, of nonoscillatory excitation to
oscillatory excitation. Also called self-excited vibration.
- self-information = information content.
- (A trade name, from self-synchronous; often capitalized). An electrical
remote indicating instrument operating on direct current, in which the angular
position of the transmitter shaft, carrying a contact arm moving on a
resistance strip, controls the pointer on the indicator
- semiactive homing guidance
- Guidance in
which a craft or vehicle is directed toward a destination by means of
information received from the destination in response to transmissions from a
source other than the craft.
- In active homing guidance the information received is in response to
transmissions from the craft. In passive homing guidance natural radiations
from the destination are utilized.
- semiactive tracking system
- A trajectory
measuring system which tracks a signal source normally aboard the target
for other purposes, or a system that illuminates the target by use of a ground
transmitter but requires no special electronics on board the missile, e.g., telemetry
elsse, Cotat, Cotar, VHF/ ADF, pulse radar
- semicircular canals
- Structures of the inner ear,
the primary function of which is to register movement of the body in space.
They respond to change in the rate of movement.
- An electronic conductor,
in the range between metals and insulators, in which the electrical charge
carrier concentration increases with increasing temperature over some
temperature range. Certain semiconductors possess two types of carriers,
namely, negative electrons and
- semiconductor device
- An electron
device in which the characteristic distinguishing electronic conduction
takes place within a semiconductor.
- 1. The radius of a closed figure.
- 2. Half the angle at the observer subtended by the visible disk of a celestial
- semidiameter correction
- A correction due to semidiamter,
particularly that sextant altitude correction resulting from observation of
the upper or lower limb of a
celestial body, rather than the center of that body.
- Having a period of, occurring in, or related to approximately half a day.
- semimajor axis (symbol a )
- One-half the longest diameter of an ellipse.
- semiminor axis (symbol b )
- One-half the shortest diameter of an ellipse.
- A structural concept in which longitudinal members as well as formers
reinforce the skin and help carry the stresses. Compare with monocoque.
- semitransparent photocathode
- A photocathode
in which radiant
flux incident on one side produces photoelectric
emission from the opposite side. See phototube.
- sensation level
- The level of psychophysiologic stimulation above the threshold.
- sense antenna
- An antenna used to resolve a 180 degrees ambiguity in
- sense-reversing reflectivity
- The characteristic of a reflector
that reverses the sense of a circularly polarized incident ray. See polarization.
- For example, a perfect corner reflector is invisible to a circularly
polarized radar because it reverses the sense.
- In measurements, the smallest change that is reliably detectable.
- sensible atmosphere
- That part of the atmosphere
that offers resistance to a body passing through it.
- sensible horizon
- See horizon, note.
- sensible temperature
- The temperature at which average indoor air of moderate humidity would
induce, in a lightly clothed person, the same sensation of comfort as that
induced by the actual environment. Compare effective
- Sensible temperature depends on the air temperature; radiation from the
sun, sky, and surrounding objects; relative humidity; and air motion. The
wet-bulb temperature is often taken as an approximate measure.
- sensing element = sensor.
- 1. The ability of electronic equipment to amplify a signal, measured
by the minimum strength of signal input capable of
causing a desired value of output. The
lower the input signal for a given output, the higher the sensitivity.
- 2. In measurements, the derivative representing the change in instrument
indication produced by a change in the variable being measured.
- The measurement of the light response characteristics of photographic film
under specified conditions of exposure and development.
- 1. The component of an instrument that converts an input signal into
a quantity which is measured by another part of the instrument. Also called
- 2. The nerve endings or sense organs which receive information from the
environment, from the organism, or from both.
- 1. The action of a fallaway
section or companion
body as it casts off from the remaining body of a vehicle, or the
action of the remaining body as it leaves a fallaway section behind it.
- 2. The moment of this action.
- separation velocity
- The velocity at which a space vehicle is
moving when some part or section is separated from it; specifically, the
velocity of a space probe or satellite at the time of separation from the launch
- September equinox = autumnal equinox.
- A mechanical or electronic device that may be set to initiate a series of
events and to make the events follow in a given sequence. See program.
- sequential collation of range
- (abbr Secor) A spherical, long-baseline, phase-comparison trajectory
measuring system utilizing three or more ground stations, time sharing a
to provide nonambiguous range measurements to determine the instantaneous
position of a vehicle in flight.
- sequential control
by completion of a series of one or more events.
- Ser, Serp
- International Astronomical Union abbreviations for Serpens (Cap.
and Caud.). See constellation.
- Serpens (Cap. and Caud.) (abbr Ser, Serp)
- See constellation.
- 1. = servomechanism.
- 2 Pertaining to or incorporating a servomechanism.
- A control system
incorporating feedback in
which one or more of the system signals represent mechanical motion.
- It should be noted that servomechanism and regulator are not mutually
exclusive terms; their application to a particular system will depend on the
method of operation of that system.
- 1. To place a storage device
in a prescribed state.
- 2. To place a binary cell
in the one state.
- Sex, Sext
- International Astronomical Union abbreviations for Sextans. See constellation.
- sexidemical notation
- A positional
notation based on the integer sixteen.
- International Astronomical Union abbreviation for Sextans. See constellation.
- Sextans (abbr Sex, Sext)
- See constellation.
- A double-reflecting instrument for measuring angles, primarily altitudes of
- As originally used, the term applied only to instruments having an arc
of 60 degrees, a sixth of a circle, from which the instrument derived its
name. Such an instrument had a range of 120 degrees. In modern practice the
term applies to a similar instrument, regardless of its range, very few modern
instruments being sextants in the original sense.
- sextant altitude
- The altitude of a
body as actually measured by a sextant. See altitude
- 1. (Also spelled spherics ). The study of atmospherics,
especially from a meteorological point of view. This involves techniques of
locating and tracking atmospherics sources and evaluating received signals
(waveform, frequency, etc.) in terms of source.
- 2. = atmospherics.
- sferics fix
- The estimated location of a source of atmospherics,
presumably a lightning discharge.
- sferics observation
- An evaluation, from one or more sferics
receivers, of the location of weather conditions with which lightning is
- Such observations are more commonly obtained from networks of two or
three widely spaced stations. Simultaneous observations of the azimuth of the
discharge are made at all stations and the location of the storm is determined
- sferics receiver
- An instrument which measures, electronically, the direction of arrival,
intensity, and rate of occurrence of atmospherics.
In its simplest form the instrument consists of two orthogonally crossed
antennas. Their output signals are connected to an oscillograph so that one
loop measures the north-south component whereas the other measures the
east-west component. These are combined vertically to give the azimuth. Also
- Sge, Sgte
- International Astronomical Union abbreviation for Sagitta. See constellation.
- Sgr, Sgtr
- International Astronomical Union abbreviation for Sagittarius. See
- International Astronomical Union abbreviation for Sagitta. See constellation.
- International Astronomical Union abbreviation for Sagittarius. See
- Darkness in a region, caused by an obstruction between the source of light
and the region.
- By extension, the term is applied to a similar condition when any form
of radiant energy is cut off by an obstruction, as a radar shadow. The darkest
part of a shadow in which light is completely cut off is called the umbra; a
lighter part surrounding the umbra, in which the light is only partly cut off,
is called the penumbra.
- 1. A picture or image in which steep density gradients in
the flow about a body are made visible, the body itself being presented in
- 2. The optical method or technique by which this is done. A shadowgraph
differs from a schlieren photograph in that the schlieren method depends on
the first derivative of the refractive index while the shadow method depends
on the second derivative. Interference measurements give the refractive index
- shadow shield
- A shield
that is interposed between a radiation
source and a specific area to be protected.
- Useful in space, a shadow shield is less effective in the earth's
atmosphere because air scattering deflects radiation around it.
- An electromagnetic device capable of imparting known vibratory
acceleration to a given object.
- shake-table test
- A laboratory test for vibration
tolerance, in which the device to be tested is place in a vibrator.
- shaped-beam antenna
- A unidirectional
antenna whose major lobe differs
materially from that obtainable from an aperture of uniform phase. Also called
- shear strength
- In materials, the stress required
to produce fracture in the plane of cross section, the conditions of loading
being such that the directions of force and of resistance are parallel and
opposite although their paths are offset a specified minimum amount.
- shear wave
- A wave in
an elastic medium which causes an element of the medium to change its shape
without a change of volume. Mathematically, a shear wave is one whose velocity
field has zero divergence. Also called rotational wave.
- A shear plane wave in an isotropic medium is called a transverse wave.
- sheath = plasma sheath.
- A body one of whose dimensions is small compared with the others.
- A body of material used to prevent or reduce the passage of particles or
- A shield may be designated according to what it is intended to absorb,
as a gamma-ray shield or neutron shield, or according to the kind of
protection it is intended to give, as a background, biological, or thermal
shield. The shield of a nuclear reactor is a body of material designed to
prevent the escape of neutrons and radiation into a protected area, which
frequently is the entire space external to the reactor. It may be required for
the safety of personnel or to reduce radiation sufficiently to allow use of
- The arrangement of shields used
for any particular circumstances; the use of shields.
- shimmer = terrestrial scintillation.
- 1. = shock wave.
- 2. A blow, impact, collision, or violent jar.
- 3. A sudden agitation of the mental or emotional state or an event causing
- 4. The sudden stimulation caused by an electrical discharge on the animal
or human organism (e.g., electric shock).
- shock absorber
- A device for the dissipation of energy used to modify the response of a
mechanical system to applied shock.
- shock front
- 1. A shock wave
regarded as the forward surface of a fluid region
having characteristics different from those of the region ahead of the wave.
- 2. The front side of a shock wave.
- shock isolator
- A resilient support that tends to isolate a system from applied shock. Also
called shock mount.
- shock mount = shock isolator.
- shock spectrum
- A plot of the maximum acceleration experienced by a single-degree-of-freedom
system as a function of its own natural
frequency in response to an applied shock.
- shock tube
- A relatively long tube or pipe in which very brief high-speed gas flows
are produced by the sudden release of gas at very high pressure into a
low-pressure portion of the tube; the high-speed flow moves into the region of
low pressure behind a shock wave.
- shock tunnel
- A shock
tube used as a wind
- shock wave
- A surface or sheet of discontinuity (i.e., of abrupt changes in
conditions) set up in a supersonic
field or flow,
through which the fluid undergoes a finite decrease in velocity accompanied by
a marked increase in pressure, density, temperature, and entropy, as occurs,
e.g., in a supersonic flow about a body. Sometimes called a shock. See
shock wave, bow wave, condensation
shock wave, detached
shock wave, Mach wave, normal
shock wave, oblique
- Shodop (abbr) = short-range Doppler.
- shooting star = meteor.
- (From short-range navigation). A precision electronic position fixing
system using a pulse transmitter
and receiver and two transponder
beacons at fixed points. High- precision shoran is called hiran.
- short-baseline system
- A trajectory
measuring system using a baseline the
length of which is very small compared with the distance of the object being
- short-period error = random error.
- short-range Doppler (abbr Shodop)
- A short range trajectory
measuring system using the intersections of the ellipsoids of Dovap and the
hyperboloids of Dovap elsse
elsse during a rocket launch.
- short-range navigation = shoran.
- short-wave radiation
- In meteorology, a term used loosely to distinguish radiation in the
visible and near-visible portions of the electromagnetic
(roughly 0.4 to 1.0 micron in wavelength) from long-wave radiation ( infrared
- 1. An act or instance of firing a rocket,
especially from the earth's surface, as, the shot carried the rocket 200
- 2. The flight of a rocket, as, the rocket made a 200-mile shot.
- shoulder harness
- A harness that fastens over a person's shoulders to prevent his being
thrown forward in his seat. See lap belt.
- shower = air shower (cosmic rays).
- The process of decreasing engine thrust to zero.
- shutoff = fuel shutoff.
- SI (abbr) = International System of Units.
- SID (abbr) = sudden ionospheric disturbance.
- 1. Either of the two frequency
bands on both sides of the carrier
frequency within which fall the frequencies of the wave produced by the
process of modulation.
- 2. The wave components lying within such a band.
- side lobe
- See lobe.
- Of or pertaining to the stars.
- Although sidereal generally refers to the stars and tropical to the
vernal equinox, sidereal time and the sidereal day are based upon the position
of the vernal equinox relative to the meridian. The sidereal year is based
upon the stars.
- sidereal day
- The duration of one rotation of
the earth on its axis, with respect to the vernal
equinox. It is measured by successive transits of the vernal equinox over
branch of a meridian.
- Because of the precession of the equinoxes, the sidereal day thus
defined is slightly less than the period of rotation with respect to the
stars, but the difference is less than 0.01 second. The length of the mean
sidereal day is 24 hours of sidereal time or 23 hours 56 minutes 4.09054
seconds of mean solar time.
- sidereal hour angle
- (abbr SHA). Angular distance west of the vernal
equinox; the arc of the celestial
equator, or the angle at the celestial pole, between the hour circle
of the vernal equinox and the hour circle of a point on the celestial
sphere, measured westward from the hour circle of the vernal equinox
through 360 degrees.
- Angular distance east of the vernal equinox, through 24 hours, is right
- sidereal month
- The average period of revolution
of the moon with respect to the stars, a period of 27 days 7 hours 43 minutes
11.5 seconds, or approximately 27 1/3 days.
- sidereal period
- 1. The time taken by a planet or satellite to
complete one revolution
about its primary as seen
from the primary and as referred to a fixed star.
- 2. Specifically, the interval between two successive returns of an earth
satellite in orbit to the same geocentric right
- sidereal time
- Time based upon the rotation of
the earth relative to the vernal
- Sidereal time may be designated as local or Greenwich as the local or
Greenwich meridian is used as the reference. When adjusted for nutation, to
eliminate slight irregularities in the rate, it is called mean sidereal time.
- sidereal year
- The period of one apparent revolution
of the earth around the sun, with respect to the stars, averaging 365 days 6
hours 9 minutes 9.55 seconds in 1955, and increasing at the rate of 0.000095
- Because of the precession of the equinoxes this is about 20 minutes
longer than a tropical year.
- sight = celestial observation.
- sigma = standard deviation.
- 1. A visible, audible, or other, indication used to convey information.
- 2. The information to be conveyed over a communication system.
- 3. Any carrier of information; opposed to noise.
- signal strength
- In radio, a measure of the received radiofrequency power, generally
expressed in decibels relative to some standard value, normally either 1
milliwatt or that power which would have resulted at the same distance under
free-space transmission. Also called field strength.
- signal-to-noise ratio
- (abbr SNR or S/N). A ratio which measures the comprehensibility of a data
source or transmission link, usually expressed as the root-mean-square signal amplitude
divided by the root-mean-square noise amplitude.
- The higher the S/N ratio, the less the interference with reception.
- signal transmission level
- In a transmission system, the signal level, of a kind
to be specified, at a designated position in the system.
- The signal level at some specified position near the source may be
taken as the zero reference level. In an acoustic system the signal level is
often in the form of a sound pressure level; either the reference sound
pressure or the reference sound pressure level must be specified.
- signal velocity
- See velocity
of propagation, note.
- See zodiac.
- silver-cell battery
- A type of short-duration, high-power-density battery of light weight used
for single-time, high-power applications in vehicles where weight is critical.
- silver-disk pyrheliometer
- An instrument used for the measurement of direct
solar radiation. See pyrheliometer.
- It is constructed in the following manner. A silver disk located at the
lower end of a diaphragmed tube serves as the radiation receiver for a
calorimeter. Radiation falling on the silver disk is periodically intercepted
by means of a shutter located in the tube, causing temperature fluctuations of
the calorimeter which are proportional to the intensity of the radiation. The
instrument is normally used as a secondary instrument and is calibrated
against the water-flow pyrheliometer. It is used by the U.S. Weather Bureau as
a standard instrument.
- simple average
- See arithmetic
mean, sense 2.
- simple harmonic motion
- A motion such that the displacement
is a sinusoidal
function of time.
- simple harmonic quantity
- A periodic
quantity that is a sinusoidal
function of the independent
variable. Thus, γ = A sin ( ωx + φ) where y is the simple harmonic quantity;
A is the amplitude; ω is the angular frequency; x is the
independent variable; and φ is the phase of the oscillation.
- The maximum value of the simple harmonic quantity is the amplitude A;
it is sometimes called, for emphasis, the single amplitude to distinguish it
from double amplitude which for a simple harmonic quantity is the same as the
total excursion or peak-to-peak value. When a simple harmonic quantity is
expressed as a complex quantity, the term amplitude must be used with caution
in view of possible confusion with the alternate meaning of amplitude as the
angle or argument of a complex quantity.
- simple reflection = specular reflection.
- simple reflector = specular reflector.
- simple standard deviation
- See standard
- sine wave
- A wave which can be expressed as the sine of a linear function of time, or
space, or both.
- single-degree-of-freedom system
- A mechanical system for which
only one coordinate
is required to define completely the configuration of the system at any
instant. See degree of
- single-entry compressor
- A centrifugal
compressor that takes in air or fluid on only one side of the impeller, the
impeller being faced with vanes only on that side.
- single sheath
- See plasma
- single-sideband modulation
whereby the spectrum of the modulating wave is translated in frequency by
a specified amount either with or without inversion.
- single-sideband transmission
- That method of operation in which one sideband is
transmitted and the other sideband is suppressed. The carrier
wave may be either transmitted or suppressed.
- single-stage compressor
- A centrifugal
compressor having a single impeller
wheel, with vanes either on one or on both sides of the wheel; also, an axial
flow compressor with one row of rotor blades and
one row of stator blades.
Axial-flow compressors are normally multistage.
- single-stage rocket
- A rocket
vehicle provided with a single rocket propulsion system. See stage.
- 1. In the mathematical representation of fluid flow, a
hypothetical point or place at which the fluid is absorbed.
- 2. A heat
sink. See source.
- In atmospheric optics, a refraction
phenomenon, the opposite of looming, in
which an object on or slightly above the geographic horizon apparently sinks
below it. Compare inferior
- Sinking occurs whenever the rate of density decreases with height
through the atmosphere is of smaller magnitude than normal or, in extreme
cases, where the density actually increases with height.
- sintered ceramic
- A ceramic body or
coating prepared by heating a ceramic powder below its melting point but at a
sufficiently high temperature to cause interdiffusion of ions between
contacting particles and subsequent adherence at the points of contact.
- The bonding of
adjacent surfaces of particles in a mass of powders, usually metal, by
- A hollow or cavity; a recess or pocket. Specifically, sinuses: air
cavities lined by mucous membrane which communicate with the nasal cavity; the
ethmoidal, frontal, sphenoidal, and maxillary sinuses.
- sinus barotrauma = aerosinusitis.
- Having the form of a sine wave.
- 1. A dark trace oscilloscope tube. See dark trace
- 2. A display
employing an optical system with a dark trace tube.
- skimmer basin = deluge collection pond.
- The covering of a body, of whatever material, such as the covering of a
fuselage, of a wing, of a hull, of an entire aircraft, etc.; a body shell, as
of a rocket; the surface of a body.
- skin temperature
- The outer surface temperature
of a body.
- skin tracking
- The tracking of an
object by means of radar without
using a beacon or other
signal device on board the object being tracked.
- skip effect
- A phenomenon in which sound or radio
energy may be detected only at various distance intervals from the energy
source as the result of the presence of an energy reflecting or refracting
layer in the atmosphere. See radio duct.
- For long radio waves, the ionosphere acts as the reflecting layer. For
shorter wavelengths, the effect may be produced by strong superstandard
propagation in elevated layers of the troposphere. Skip effects make it
possible on occasion to detect targets at distances far greater than the
normal radio horizon, while closer targets remain undetected.
- The lower outer part of a rocket
vehicle; specifically, the half-stage of an Atlas.
- skirt fog
- The cloud of steam and water that surrounds the engines of a rocket being
launched from a wet
- skyhook balloon
- (Originally a code name for a U.S. Navy Project.) A large free balloon
having a plastic envelope, used especially for constant-level meteorological
observations at very high altitudes.
- sky light = diffuse sky radiation.
- sky radiation = diffuse sky radiation.
- sky screen
- An optical device used to detect the departure of a rocket from its
- sky wave
- In radio, radio
energy that is received after having been reflected by the ionosphere.
- slant range
- The line-of-sight
range of a radar or radio. See range.
- 1. = slave
- 2. Device that follows an order given by a master through
- slave antenna
- A directional
antenna that is positioned in azimuth and elevation by a servo system. The
information controlling the servosystem is supplied by a tracking or
- slave station
- In a hyperbolic navigation system, a station whose transmissions are
controlled by a master
station. Often shortened to slave. See hyperbolic
- Of a gyro,
the use of a torquer to
maintain the orientation of the spin axis
relative to an external reference such as a pendulum or magnetic compass.
- sleeve-dipole antenna
- A dipole
antenna surrounded in its central portion by a coaxial sleeve.
- slenderness ratio
- A dimensionless number expressing the ratio of a rocket
vehicle length to its diameter.
- To change the position of an antenna or
range gear assembly by injecting a synthetic error signal into the positioning
- 1. Of a gyro, the rotation
of the spin
axis caused by applying torque about the
axis of rotation.
- 2. In radar, changing
the scale on the display.
- A sprayable slurry
comprising a frit suspended in
a liquid carrier (sometimes also used for dip and brush coating).
- slip flow
- See rarefied
gas dynamics, note.
- slope angle
- The angle in the vertical plane between the flightpath
and the horizontal.
- The back-and-forth movement of a liquid fuel in
its tank, creating problems of stability and control in the vehicle.
- slow ion = large ion.
- A unit of mass; the mass of
a free body which if acted upon by a force of 1 pound would experience an
acceleration of 1 foot per square second; thus approximately 32.16 pounds.
- A suspension
of fine solid particles in a liquid.
- slurry fuel
- A fuel
consisting of a suspension of fine solid particles in a liquid.
- small calorie (abbr cal)
- See calorie.
- small circle
- The intersection of a sphere and a plane which does not pass through the
center of the sphere, as a parallel of
- small ion
- An atmospheric ion, apparently a
singly charged atmospheric molecule (or, rarely, an atom) about which a few
other neutral molecules are held by the electrical attraction of the central
ionized molecule. Estimates of the number of satellite molecules range as high
as 12. Also called light ion, fast ion.
- Small ions may disappear either by direct recombination with oppositely
charged small ions or by combination with neutral Aitken nuclei to form new
large ions, or by combination with large ions of opposite sign. The small ion,
collectively, is the principal agent of atmospheric conduction.
- small perturbation
- A disturbance imposed on a system in steady state, with amplitude assumed
small, i.e., the square of the amplitude is negligible in comparison with the
amplitude, and the derivatives of the perturbation are assumed to be of the
same order of magnitude as the perturbation. See perturbation,
of small perturbations.
- Snell law
- See refraction,
- Snort track
- A rail track on which a supersonic
rocket sled is driven, located at the Naval Ordnance Test Station.
- snow = grass.
- A device used to increase the stiffness of an elastic system, usually by a
large factor, whenever the displacement
becomes larger than a specified amount.
- (From sound fixing and ranging). A system of navigation providing hyperbolic
lines of position determined by shore listening stations which receive
sound signals produced by depth charges dropped at sea and exploding in a
sound channel which is at a considerable depth in most areas.
- This system is used in Project Mercury for locating spacecraft down at
- softening range
- An arbitrarily defined temperature range below the crystal melting point
where a ceramic becomes
soft and noticeably viscous; a softening range rather than a sharp melting
point occurs in ceramics containing a glass base.
- soft landing
- The act of landing on the surface of a planet without
damage to any portion of the vehicle or payload except possibly the landing
- soft radiation
- Radiation absorbable by an absorber equivalent to 10 centimeters of lead
- Radiation which can penetrate more than 10 centimeters of lead is
termed hard radiation.
- 1. Of or pertaining to the sun or caused by the sun, as solar
radiation, solar atmospheric tide.
- 2. Relative to the sun as a datum or reference , as solar
- solar activity
- Any type of variation in the appearance or energy output of the sun. See
faculae, flare, flocculi, granules, prominence,
- solar air mass
- The optical air mass penetrated by light from the sun for any given
position of the sun in the sky.
- solar antapex
- See solar
- solar apex
- The point on the celestial
sphere toward which the sun is traveling. Also called apex of the sun's
- The solar apex is at approximately right ascension 270 degrees
declination 34 degrees N. The point diametrically opposite the solar apex on
the celestial sphere is the solar antapex, right ascension 90 degrees
declination 34 degrees S.
- solar atmospheric tide
- An atmospheric
tide due to the thermal or gravitational action of the sun.
- Six and eight hour components of small amplitude have been observed.
They are primarily thermal in origin. The 12-hour component has by many times
the greatest amplitude of any atmospheric tidal component, about 1.5 millibars
at the equator and 0.5 millibar in middle latitudes. This relatively large
amplitude is often explained as a resonance effect. The 24-component is a
thermal tide with great local variability.
- solar cell
- A photovoltaic
cell that converts sunlight into electrical energy.
- solar constant
- The rate at which solar
radiation is received outside the earth's atmosphere on a surface normal
to the incident radiation and at the earth's mean distance from the sun.
- Measurements of solar radiation at the earth's surface by the
Smithsonian Institution for several decades give a best value for the solar
constant of 1.934 calories per square centimeter per minute. Measurements from
rockets of the intensity of the ultraviolet end of the spectrum have corrected
this value to 2.00 calories per square centimeter per minute with a probable
error of +/- 2 percent.
- solar corona
- See corona.
- solar corpuscular rays
radiation supposedly originating in the sun. See corpuscular
- solar cosmic rays
rays supposedly originating in the sun.
- solar cycle
- The periodic increase and decrease in the number of sunspots. The
cycle has a period of about 11 years.
- solar day
- 1. The duration of one rotation of
the earth on its axis, with respect to the sun.
- This may be either a mean solar day, or an apparent solar day, as the
reference is the mean or apparent sun, respectively.
- 2. The duration of one rotation of
the sun on its axis.
- solar eclipse
- The obscuration of the light of the sun by the moon.
- A solar eclipse is partial if the sun is partly obscured, total if the
entire surface is obscured, or annular if a thin ring of the sun's surface
appears around the obscuring body.
- solar flare
- See flare.
- 1. = pyranometer.
- 2. Specifically, a pyranometer consisting of a Moll
thermopile covered by a bell glass.
- solar parallax
- The angle at the sun subtended by the equatorial diameter of the earth.
- The adopted value of the solar parallax in the system of astronomical
constants is 8.80 seconds of arc.
- solar prominence = prominence.
- solar protons
- Protons emitted by the sun, especially during solar flares.
- solar radiation
- The total electromagnetic
radiation emitted by the sun. See insolation,
solar radiation, diffuse
sky radiation, global
- To a first approximation, the sun radiates as a black body at a
temperature of about 5700 degrees K; hence about 99.9 percent of its energy
output falls within the wavelength interval from 0.15 micron to 4.0 microns,
with peak intensity near 0.47 micron. About one-half of the total energy in
the solar beam is contained within the visible spectrum from 0.4 to 0.7
micron, and most of the other half lies in the near infrared, a small
additional portion lying in the ultraviolet.
- solar-radiation observation
- An evaluation of the radiation from the sun that reaches the observation
point. The observing instrument is usually a pyrheliometer
- Two types of such observation are taken. The more common consists of
measurements of the radiation reaching a horizontal surface, consisting of
both radiation from the sun (direct solar radiation) and that reaching the
instrument indirectly by scattering in the atmosphere (diffuse sky radiation).
The other type of observation involves the use of an equatorial mount that
keeps the instrument pointed directly at the sun at all times. The sensitive
surface of the instrument is normal to the path of the radiation and is
shielded from indirect radiation from the sky.
- solar radio burst
- A sudden increase in the flux from the sun
- solar radio waves
- Radiation at radio
frequencies originating in the sun or its corona.
- solar simulator
- A device which produces thermal energy, equivalent in intensity and
spectral distribution to that from the sun, used in testing materials and
- solar system
- The sun and other celestial bodies within its gravitational influence,
including planets, asteroids, satellites,
- solar tide
- See solar
- solar time
- Time based
upon the rotation of
the earth relative to the sun.
- Solar time may be designated as mean or astronomical if the mean sun is
the reference, or apparent if the apparent sun is the reference. The
difference between mean and apparent time is called equation of time. Solar
time may be further designated according to the reference meridian, either the
local or Greenwich meridian or additionally in the case of mean time, a
designated zone meridian. Standard or daylight-saving are variations of zone
time. Time may also be designated according to the timepiece, as chronometer
time or watch time, the time indicated by these instruments.
- solar wind
- Streams of plasma flowing
approximately radially outward from the sun.
- solar year = tropical year.
- A tube formed in space by the intersection of unit-interval isotimic
surfaces of two scalar quantities.
- Solenoids formed by the intersection of surfaces of equal pressure and
density are frequently referred to in meteorology. A barotropic atmosphere
implies the absence of solenoids of this type, since surfaces of equal
pressure and density coincide.
- solid angle (symbol ω)
- A portion of the whole of space about a given point, bounded by a conical
surface with its vertex at that point and measured by the area cut by the
bounding surface from the surface of a sphere of unit radius centered at that
point. See steradian.
- solid propellant
- Specifically, a rocket
propellant in solid form, usually containing both fuel and oxidizer
combined or mixed, and formed into a monolithic (not powered or granulated) grain.
- solid-propellant engine = solid-propellant rocket engine.
- solid-propellant rocket engine
- A rocket
engine fueled with a solid
propellant. Such motors consist essentially of a combustion
chamber containing the propellant, and a nozzle for the
exhaust jet, although they often contain other components, as grids, liners,
- solid rocket
- A rocket that uses a solid
- solid rocket fuel
- A solid
- solid rotation
- The rotation of a
system as though is were a solid or rigid body rotating about a fixed axis,
all points within the body having the same angular
- solid-state devices
- Devices which utilize the electric, magnetic, and photic properties of
solid materials, e.g., binary magnetic cores, transistors, etc.
- 1. One of the two points of the ecliptic
farthest from the celestial
equator; one of the two points on the celestial
sphere occupied by the sun at maximum declination.
- That in the northern hemisphere is called the summer solstice and that
in the southern hemisphere the winter solstice. Also called solstitial point.
- 2. That instant at which the sun reaches one of the solstices, about June
21 (summer solstice) or December 22 (winter solstice).
- solstitial colure
- That great
circle of the celestial
sphere through the celestial
poles and the solstices.
- solstitial point = solstice.
- (From sound, navigation, and ranging.) A method or system, analogous to radar used under
water, in which high-frequency sound waves
are emitted so as to be reflected back from objects, and used to detect the
objects of interest. Called asdic by the British.
- sonar capsule
- A device designed to reflect high-frequency sound
waves. See sonar.
- The sonar capsule, if attached to a reentry body, may be used to locate
the reentry body in case of a water landing.
- A unit of loudness. A
simple tone of frequency 1000 cycles per second, 40 decibels above a
produces a loudness of 1 sone.
- The loudness of any sound that is judged by the listener to be n times
that of the 1-sone tone is n sones. A millisone is equal to 0.001 sone. The
loudness scale is a relation between loudness and level above threshold for a
particular listener. In presenting data relating loudness in sones to sound
pressure level, or in averaging the loudness scales of several listeners, the
thresholds (measured or assumed) should be specified.
- 1. In aerodynamics, of or pertaining to the speed of sound; that which
moves at acoustic
velocity as in sonic flow ; designed to operate or perform at the
speed of sound, as in sonic leading edge.
- 2. Of or pertaining to sound, as in sonic amplifier.
- In sense 2, acoustic is preferred to sonic.
- sonic agglomeration
- The union of small particles suspended in a fluid medium into larger
aggregates by the action of sound
- sonic barrier
- A popular term for the large increase in drag that acts
upon an aircraft approaching acoustic
velocity; the point at which the speed of sound is attained and existing
subsonic and supersonic flow theories are rather indefinite. Also called
- sonic boom
- A noise caused by a shock wave
that emanates from an aircraft or other object traveling at or above sonic velocity .
- A shock wave is a pressure disturbance and is received by the ear as a
noise or clap.
- sonic delay line = acoustic delay line.
- sonic drilling
- The process of cutting or shaping materials with an abrasive slurry driven by
a reciprocating tool attached to an electromechanical
operating at ultrasonic
- sonic frequency = audiofrequency.
- The technology of sound in
processing and analysis. Sonics includes the use of sound in any
- sonic soldering
- The method of joining metals by metallic bonding alloys through the use of
mechanical vibrations to break up the surface oxides.
- sonic speed
velocity; by extension, the speed of a body traveling at a Mach number
- sonic wave = sound wave.
- Complex and intricate; making use of advanced art; requiring special
skills to operate.
- To take up gas by sorption.
- Gas taken up by a sorbent.
- The material which takes up gas by sorption.
- The taking up of gas by absorption,
or any combination of these process. See absorption.
- 1. An oscillation
in pressure, stress, particle displacement, particle velocity, etc., in a
medium with internal forces (e.g., elastic, viscous), or the superposition of
such propagated oscillations.
- 2. A sensation evoked by the oscillation described above in the human ear.
- In case of possible confusion, the term sound wave or elastic wave may
be used for concept 1 and the term sound sensation for concept 2. Not all
sound wave can evoke an auditory sensation, e.g., ultrasound. The medium in
which the sound exists is often indicated by an appropriate adjective, e.g.,
airborne, water borne, structure borne.
- sound absorption
- Sound absorption
is the change of sound
energy into some other form, usually heat, in passing through a medium
oron striking a surface.
- sound barrier = sonic barrier.
- sound energy
- The energy which sound waves
contribute to a particular medium.
- sound energy density
- At a point in a sound
field, the sound
energy contained in a given infinitesimal part of the medium divided by
the volume of that part of the medium.
- The terms instantaneous energy density, maximum energy density, and
peak energy density have meanings analogous to the related terms used for
sound pressure. In speaking of average energy density in general, it is
necessary to distinguish between the space average (at a given instant) and
the time average (at a given point).
- sound energy flux
- The average rate of flow of sound
energy for one period through any specified area.
- In a medium of density ρ for a plane or spherical free wave having a
velocity of propagation c, the sound energy flux through the area S
corresponding to an effective sound pressure p is J = ( p2S / ρc ) cos θ
where θ = the angle between the direction of propagation
of the sound and the normal to the area S.
- sound energy flux density = sound intensity.
- sound field
- A region containing sound
waves. See near field, far field.
- 1. In geophysics,
any penetration of the natural environment for scientific observation.
- 2. In meteorology, same as upper
air observation. However, a common connotation is that of a single
- 3. = air
- sounding rocket
- A rocket
that carries aloft equipment for making observations of or from the upper
atmosphere. See air
sounding. Compare probe, sense 3.
- Usually a sounding rocket has a near vertical trajectory.
- sound intensity
- In a specified direction at a point, the average rate of sound
energy transmitted in the specified direction through a unit area normal
to this direction at the point considered. Also called sound energy flux
density, sound power density.
- sound level
- Specifically, a weighted sound
pressure level, obtained by the use of metering characteristics and the
weightings A, B, or C specified in American Standard Publication Z24.3-1944:
Sound Level Meters for Measurement of Noise and Other Sounds. The
weighting employed pressure is 0.0002 microbar.
- A suitable method of stating the weighting is, for example, The A-sound
level was 43 decibels.
- sound power
- Of a source, the total sound
energy radiated by the source per unit of time.
- sound power density = sound intensity.
- sound pressure
- At a point, the total instantaneous pressure at that point in the presence
of a sound
wave minus the static
pressure at that point. See effective
- sound pressure level
- In decibels, 20 times the logarithm to the base 10 of the ratio of the sound
pressure to the reference pressure. The reference pressure must be
- The following reference pressures are in common use: (a) 2 X 10E-4
microbar, (b) 1 microbar. Reference pressure (a) is in general use for
measurements concerned with hearing and with sound in air and liquids, whereas
(b) has gained widespread acceptance for calibration of transducers and
various kinds of sound measurements in liquids. Unless otherwise explicitly
stated, it is to be understood that the sound pressure is the effective
(root-mean-square) sound pressure. It is to be noted that in many sound fields
the sound pressure ratios are not the square roots of the corresponding power
- sound probe
- A device that responds to some characteristic of an acoustic
wave (e.g., sound pressure, particle velocity) and that can be used to
explore and determine this characteristic in a sound field
without appreciably altering that field.
- sound wave
- A mechanical disturbance advancing with infinite velocity through an
elastic medium and consisting of longitudinal displacements of the medium,
i.e., consisting of compressional and rarefactional displacements parallel to
the direction of advance of the disturbance; a longitudinal wave. Sound waves
are small-amplitude adiabatic
oscillations. The wave equation governing the motion of sound waves has the
2 = (1/c2)(2/t2)
where 2 is the Laplace operator,
is the velocity potential, c is the speed
of sound, and t is the time; the density variations and velocities are
small. As so defined, this includes waves outside the frequency limits of
human hearing, which limits customarily define sound. Also called acoustic
wave, sonic wave. See ultrasonic,
- Gases, liquids, and solids transmit sound waves, and the propagation
velocity is characteristic of the nature and physical state of each of these
media. In those cases where a steadily vibrating sound generator acts as a
source of waves, one may speak of a uniform wave train; but in other cases
(explosions, lightning discharges) a violent initial disturbance sends out a
principal wave, followed by waves of more or less rapidly diminishing
- 1. The location or device from which energy emanates as a sound source,
heat source , etc.
- 2. Specifically, in the mathematical representation of fluid flow, a
hypothetical point or place from which fluid emanates.
- The strength of a source; the rate of mass flow of unit density across
a curve enclosing the source is given by Q = 2π r vr
where r is the distance from the source and vr is the radial speed.
- 3. Specifically, the device which supplies signal
power to a transducer.
- southbound node = descending node.
- South Tropical Disturbance
- An elongated dark band in the cloud surface of Jupiter at about the
latitude of the Great Red
Spot. It was first seen in 1901 as a dark spot which then spread rapidly.
It has at times exceeded 180 degrees of longitude in length and, like the Red
Spot, appears and disappears intermittently.
- SP (abbr) = solid propellant.
- 1. Specifically, the part of the universe lying outside the limits of the
- 2. More generally, the volume in which all celestial bodies, including the
- space-air vehicle
- A vehicle operable either within or above the sensible
atmosphere. Also called aerospace vehicle.
- space biology = bioastronautics.
- space capsule
- A container used for carrying out an experiment or operation in space.
- A capsule is usually assumed to carry an organism or equipment.
- space charge
- 1. The electric charge carried by a cloud or stream of electrons or
ions in a
vacuum or a region of low gas pressure when the charge is sufficient to
produce local changes in the potential distribution.
- 2. The net electric charge within a given volume.
- space coordinates
- A three-dimensional system of Cartesian
coordinates by which a point is located by three magnitudes
indicating distance from three planes which intersect at a point.
- Devices, manned and unmanned, which are designed to be placed into an orbit about the
earth or into a trajectory
to another celestial
- From 1957 through 1962 spacecraft were designated by the year and a
Greek letter assigned in the order of launching, as 1958α for the first satellite of 1958. When more than
one object was put in orbit by a single launch vehicle, each object was
numbered, as 1961o2. (Space probes were not included in this system until
1960). Beginning January 1, 1963, arabic numerals supplanted Greek letters in
the scientific designations of all spacecraft with a lifetime of more than 90
minutes. Thus, the first satellite launched in 1963 was 1963-1, the last was
1963-55. When more than one component is put in orbit, alphabetical suffixes
are added to the designations, as 1963-4A. The letter A usually designates the
component carrying the principle scientific payload; B, C, etc., are used as
needed for any subsidiary payloads and then for inert components in order of
maximum brightness. The designation system was promulgated formally in the
COSPAR Guide to Rocket and Satellite Information and Data Exchange. The Guide
has been published in full in COSPAR Information Bulletin No. 9, July 1962,
and in IGY Bulletin No. 61, July 1962. Table XIV
is a listing of scientific satellites and space
probes launched through 1964 and is reprinted from the IG Bulletin
(International Geophysics Bulletin) published by the National Academy of
- space equivalent
- A condition within the earth's atmosphere that is virtually identical, in
terms of a particular function, with a condition in outer space.
- For example, at 50,000 feet, the drop in air pressure and the scarcity
of oxygen creates a condition, so far as respiration is concerned, that is
equivalent to a condition in outer space where no appreciable oxygen is
present; thus, a physiological space equivalent is present in the atmosphere.
- space medicine
- A branch of aerospace
medicine concerned specifically with the health of persons who make, or
expect to make, flights into space beyond the sensible
- space modulation
- The combining of signals outside of an electronic device or conductor to
form a signal of desired characteristics. See modulation.
- space motion
- Motion of a celestial
body through space.
- That component perpendicular to the line of sight is termed proper
motion and that component in the direction of the line of sight, radial
- space polar coordinates
- A system of coordinates by which a point on the surface of a sphere is
located in three dimensions by (a) its distance from a fixed point at the
center, called the pole; (b) the colatitude or angle between the polar axis (a
reference line through the pole) and the radius vector (a straight line
connecting the pole and the point); and (c) the longitude or angle between a
reference plane through the polar axis and a plane through the radius vector
and polar axis. See polar
- space probe
- See probe,
note, and spacecraft,
note and Table XIV.
- space reddening
- The observed reddening, or absorption of shorter wavelengths,
of the light from distant celestial
bodies due to scattering
by small particles in interstellar space. Compare red shift.
- space simulator
- 1. Any device used to simulate one or more parameters of the space environment
used for testing space systems or components.
- 2. Specifically, a closed chamber capable of approximately the vacuum and
normal environments of space.
- space suit
- A pressure
suit for wear in space or at very low ambient pressures within the
atmosphere, designed to permit the wearer to leave the protection of a pressurized
- 1. The dimension of a craft measured between lateral extremities; the
measure of this dimension.
- 2. Specifically, the dimension of an airfoil from
tip to tip measured in a straight line.
- Span is not usually applied to vertical airfoils.
- spark discharge
- That type of gaseous
electrical discharge in which the charge transfer occurs intermittently
along a relatively constricted path of high ion density, resulting in high luminosity.
It is of short duration and to be contrasted with the nonluminous point
discharge, with the diffuse corona
discharge, and also with the continuous arc
- The exact meaning to be attached to the term spark discharge varies
somewhat in the literature. It is frequently applied to just the transient
phase of the establishment of any arc discharge. A lightning discharge is a
large-scale spark discharge, though its very length introduces certain details
not found in laboratory short-spark processes.
- spark spectrum
- The spectrum of an
ion. The degree
of ionization, or order of the spectrum, is indicated by a Roman numeral
following the symbol for the element. The first spark spectrum is indicated by
II, the second by III, and so on. Thus Fe IV indicates the spectrum of an iron
atom which has lost three electrons. See arc
- Pertaining to space.
- A combining form meaning space.
- special perturbations
- A method of orbit
determination by numerical integration which takes into account the perturbing
forces which are causing the orbit to depart from the orbit as calculated by
- A modifier generally implying per unit mass.
- specific heat
- The ratio of the heat absorbed (or
released) by unit mass of a system to the corresponding temperature
rise (or fall). If this ratio varies with temperature, it must be defined as a
differential quotient dQ/dT, where dQ is the infinitesimal
increment of heat per unit mass and dT is the infinitesimal increment
- For gases the thermodynamic process must be specified; two specific
heats are defined, one being the specific heat in a constant-pressure process
cp = (dQ / dT)pand the other, the specific heat in a
constant-volume process cv = (dQ / dT)v
In a perfect gas these are, by definition,
constants with respect to temperature, and the difference of the specific heat
at constant pressure and the specific heat at constant volume is equal to the
gas constant: R = cp - cv
- specific humidity
- In a system of moist air, the (dimensionless) ratio of the mass of water vapor
to the total mass of the system. The specific humidity may be approximated by
ratio for many purposes: q = w /(1 + w ) where q
is the specific humidity and w is the mixing ratio. See absolute
humidity, dew point.
- specific impulse (symbol Isp)
- A performance parameter of a rocket
propellant, expressed in seconds, equal to the thrust F
in pounds divided by the weight flow rate in pounds per second:
Isp = F /
- Specific impulse is also equivalent to the effective exhaust velocity
divided by the gravitational acceleration.
- specific power
- The energy delivered
per pound of fuel in a reactor or in a
radioisotope power source.
- specific propellant consumption
- The reciprocal of the specific
impulse, i.e., the required propellant
flow to produce one pound of thrust in an equivalent rocket.
- specific speed
- Of a pump, a parameter used to predict pump performance.
- specific thrust = specific impulse.
- specific volume (symbol v )
- Volume per unit mass of a substance. The reciprocal of density.
- Plural of spectrum.
- 1. Of or pertaining to a spectrum.
- 2. Referring to thermal radiation properties, for ratios such as emittance, reflectance,
at a specified wavelength; for powers, such as emissive
power, within a narrow wavelength band centered on a specified wavelength.
- spectral absorptance
- See absorptance,
- spectral emissivity
- See emissivity,
- spectral function
- The Fourier representation of a given function; that is, the Fourier
transform if the given function is aperiodic or the set of coefficients of
series if the given function is periodic. Also called spectrum. See
- spectral line
- A bright, or dark, line found in the spectrum of
some radiant source. See absorption
- Bright lines indicate emission, dark lines indicate absorption.
- See spectroscope.
- See spectroheliograph.
- An instrument for taking photographs (spectroheliograms) of the image of
the sun monochromatic
light. The wavelength of light chosen for this purpose corresponds to one of
lines, usually the light of hydrogen or ionized calcium. A similar
instrument used for visual, instead of photographic, observations in a
- See spectroheliograph,
- A photometer
which measures the intensity of
radiation as a function of the frequency (or
wavelength) of the radiation. Also called spectroradiometer. See Dobson
- In one design, radiation enters the spectrophotometer through a slit
and is dispersed by means of a prism. A bolometer having a fixed aperture
scans the dispersed radiation so that the intensity over a narrow wave band is
obtained as a function of frequency.
- An instrument which measures the spectral distribution of the intensity of
solar radiation. See pyrheliometer,
- An apparatus to effect dispersion
of radiation and visual display of the spectrum
- A spectroscope with a photographic recording device is called a
- spectroscopic binaries
- See binary
- 1. In physics, any series of energies arranged according to wavelength
- 2. The series of images produced when a beam of radiant
energy is subject to dispersion.
- 3. Short for electromagnetic
spectrum or for any part of it used for a specific purpose as the radio
spectrum (10 kilocycles to 300,000 megacycles).
- 4. In mathematics, = function.
- 5. In acoustics, the distribution of effective sound
pressures or intensities measured as a function of frequency in specified
- specular reflection
in which the reflected radiation is not diffused; reflection as from a mirror.
Also called regular reflection, simple reflection. Compare diffuse
- The angle between the normal to the surface and the incident beam is
equal to the angle between the normal to the surface and the reflected beam.
Any surface irregularities on a specular reflector must be small compared to
the wavelength of the incident radiation.
- specular reflector
- Any surface exhibiting specular
reflection. Also called regular reflector, simple reflector.
- specular transmission density
- See photographic
transmission density, note.
- Rate of motion.
- Rate of motion in a straight line is called linear speed, whereas
change of direction per unit time is called angular speed. Speed and velocity
are often used interchangeably although some authorities maintain that
velocity should be used only for the vector quantity.
- speed of light (symbol c )
- The speed of propagation of electromagnetic
radiation through a perfect vacuum; a universal dimensional constant equal
to 299,792.5 +/- 0.4 kilometers per second. Also called velocity
- speed of relative movement
- Also called relative speed. See relative
- speed of sound (symbol cs)
- The speed of propagation of sound waves. In the atmosphere
cs = [γ (R*/M0)TM]1/2 where γ
is the ratio of specific heat of air at constant
pressure to that a constant volume, R* is the universal gas constant,
M0 is the mean molecular weight of air at sea
level, and TM is the molecular scale temperature.
- At sea level in the standard atmosphere, the speed of sound is 340.294
meters per second (1116.45 feet per second). The concept of the speed of sound
in the atmosphere loses its applicability at about 90 kilometers where the
mean of free path of air molecules approaches the wavelengths of sound waves.
- sphere of influence
- The surface in space about a planet where the
ratio of the force with which the sun perturbs the motion of a particle about
the planet, to the force of attraction of the planet equals the ratio of the
force with which the planet perturbs the motion of a particle about the sun,
to the force of attraction of the sun on the particle.
- The volume inside this surface defines the region where the attracting
body exerts the primary influence on a particle.
- sphere of position
- See line of
- spherical angle
- The angle between two intersecting great
- spherical coordinates
- 1. A system of coordinates
defining a point on a sphere or spheroid by its angular distances from a primary
great circle and from a reference secondary great circle, as latitude and
longitude. See celestial
- 2. = space
- spherical excess
- The amount by which the sum of the three angles of a spherical
triangle exceeds 180 degrees.
- spherical stratification
- See horizontal
- spherical system
- A trajectory
measuring system, whose locus of the measured range is a sphere with the
ground equipment at the center.
- A unique point in space is determined by the intersection of three or
more spheres. The term spherical system has been applied to systems using
three or more slant
ranges to determine space position.
- spherical triangle
- A closed figure having arcs of three great
circles as sides.
- spherical wave
- A wave whose phase front
surfaces are spheres. Such waves propagate from a point source.
- Variant spelling of sferics.
- An ellipsoid; a
figure resembling a sphere. Also called ellipsoid or ellipsoid of
revolution from the fact that it can be formed by revolving an ellipse
about one of its axes. If the shorter axis is used as the axis of revolution,
an oblate spheroid results, and if the longer axis is used, a prolate spheroid
results. The earth is approximately an oblate spheroid.
- spheroidal excess
- The amount by which the sum of the three angles of a triangle on the
surface of a spheroid
exceeds 180 degrees.
- Bright spikes extending into the chromosphere
of the sun from below.
- They are several hundred miles in diameter and extend outward 5000 to
10,000 miles. Spicules have a lifetime of several minutes and may be related
- spin = angular momentum (in atomic and nuclear physics).
- spin axis
- The axis of rotation of the rotor of a gyro.
- spineward acceleration
- See physiological
- Rotating part of a radar antenna used to
impact any subsidiary motion in addition to the primary slewing of the beam.
- spin rocket
- A small rocket that
imparts spin to a larger rocket
vehicle or spacecraft.
- spin stabilization
- Directional stability of a spacecraft obtained by the action of gyroscopic
forces which result from spinning the body about its axis of symmetry.
- spin table
- A flat round platform on which human and animal subjects can be placed in
various positions and rapidly rotated, much as on a phonograph record, in
order to simulate and study the effects of prolonged tumbling at high rates.
- Complex types of tumbling can be simulated by mounting the spin table
on the arm of a centrifuge.
- spiral layer = Ekman layer.
- spiral scanning
- Scanning in
which the direction of maximum radiation describes a portion of a spiral. The
always in one direction.
- A plate, series of plates, comb, tube, bar, or other device that projects
into the airstream
about a body to break up or spoil the smoothness of the flow, especially
such a device that projects from the upper surface of an airfoil, giving an
increased drag and a decreased lift. Compare deflector,
- Spoilers are normally movable and consist of two basic types: the flap
spoiler, which is hinged along one edge and lies flush with the airfoil or
body when not in use, and the retractable spoiler, which retracts edgewise
into the body.
- spontaneous emission
- The decay of an atom or ion in an excited energy state Ej to a lower state Ei
without the influence of any external
perturbation. This process results in the emission of a photon of energy
hv = Ej - Eiwhere h is the Planck constant and v
is the frequency.
- spontaneous-ignition temperature
- In testing fuels, the lowest temperature of a plate or other solid surface
adequate to cause ignition in air of a fuel upon the surface.
- sporadic D
- See ionosphere.
- sporadic E
- See ionosphere.
- sporadic meteor
- A meteor
which is not associated with one of the regularly recurring meteor
showers or streams.
- The reproductive element of the lower forms of living organism, usually
- spray electrification = Lenard effect.
- spray region = fringe region.
- spread reflection
- Reflection from a rough surface with large irregularities. Also called
- spurious disk
- The round image of perceptible diameter of a star as seen through a
telescope, due to diffraction
of light in the telescope.
- spurious emission = spurious
- spurious radiation
- 1. Any undesired emission from
a radio transmitter.
- 2. Any electromagnetic
radiation from a radio receiver. Also
- spurious response
from a receiver due
to a signal or signals having frequencies other than that to which the
receiver is tuned.
- spurious transmitter output
- Any part of the radio
frequency output of a transmitter which is not a component of the
theoretical output as
determined by the type of modulation and specified bandwidth limitations.
- spurious tube counts
- In radiation-counter tubes, counts other
counts and those caused directly by the radiation to be measured.
- Spurious counts are caused by failure of the quenching process,
electrical leakage, and the like. Spurious counts may seriously affect
measurement of background counts.
- Dislocation of surface atoms of a material from bombardment by high-energy
- square wave
- 1. An oscillation,
the amplitude of which shows periodic discontinuities between two values,
remaining constant between jumps.
- 2. Specifically, in radar a pulse initiated
by a rapid rise to peak power, maintained at a constant peak power over the
finite pulse length, and terminated by rapid decrease from peak power.
- 1. Any of various small explosive devices.
- 2. An explosive device used in the ignition of a
Usually called an igniter.
- A squib -operated switched.
- Random firing, intentional or otherwise, of a transponder
transmitter in the absence of interrogation.
- SSB (abbr) = single sideband.
- SS loran
- Sky-wave synchronized loran, or loran
in which the sky wave
rather than the ground wave from the master controls
the slave. SS
loran is used with unusually long baselines.
- 1. The property of a body, as an aircraft or rocket, to maintain its
attitude or to resist displacement, and, if displaced, to develop forces and
moments tending to restore the original condition.
- 2. Of a fuel, the capability of a fuel to retain its
characteristics in an adverse environment,
e.g. extreme temperature.
- stability augmentation system
- An auxiliary system to the basic manual vehicle
control system whereby response of the control surfaces to inputs by the
pilot can be adjusted to give a preselected vehicle response by selection of
certain fixed gains in a standard feedback loop
on control-surface output.
- stabilized data
- Radar data
output corrected for tilt or roll of an unstabilized radar antenna, such
as shipboard installations, etc.
- stable platforms
- A gyroscopic
device so designed as to maintain a plane of reference in space regardless of
the movement of the vehicle carrying the stable platform.
- An instrument for determining the distance to an object of know dimension
by measuring the angle subtended at the observer by the object. The instrument
is graduated directly in distance.
- Pertaining to a navigational fix which involves
a measure of distance.
- 1. A self-propelled separable element of a rocket
vehicle. See multistage
- 2. A step or process through which a fluid passes,
especially in compression or expansion.
- 3. A set of stator blades
and a set of rotor blades in
an axial-flow compressor or in a turbine; an impeller
wheel in a radial-flow compressor. See multistage
compressor, single-stage turbine.
- A liquid-propellant
rocket of which only part of the propulsion unit falls away from the rocket
vehicle during flight, as in the case of booster
rockets falling away to leave the sustainer
engine to consume remaining fuel.
- The process or operation during the flight of a rocket
vehicle whereby a full stage or half
stage is disengaged from the remaining body and made free to decelerate or be
propelled along its own flightpath. See separation.
- stagnation point
- A point in a field of flow about a body
where the fluid particles
have zero velocity with respect to the body.
- stagnation pressure
- 1. The pressure at a stagnation
- 2. In compressible flow, the pressure exhibited by a moving gas or liquid
brought to zero velocity by an isentropic process.
- 3. = total
- 4. = impact
- Because of the lack of a standard meaning, stagnation pressure should
be defined when it is used.
- stagnation region
- Specifically, the region at the front of a body moving through a fluid
where the fluid has negligible relative velocity.
- 1. An exact value, or a concept, that has been established by authority or
agreement, to serve as a model or rule in the measurement of a quantity or in
the establishment of a practice or procedure.
- 2. A document that establishes engineering and technical limitations and
applications for items, materials, processes, methods, design, or engineering
- standard artillery atmosphere
- A set of values describing atmospheric conditions on which ballistic
computations are based: namely, no wind, a surface temperature of 15 degrees
C, a surface pressure of 1000 millibars, a surface relative humidity of 78
percent, and a lapse rate which yields a prescribed density-altitude relation.
- standard artillery zone
- A vertical subdivision of the standard
artillery atmosphere. It may be considered a layer of air of prescribed
thickness and density.
- standard atmosphere
- 1. A hypothetical vertical distribution of atmospheric temperature,
pressure, and density which, by international agreement, is taken to be
representative of the atmosphere
(see Table XV ) for purposes of pressure altimeter
calibrations, aircraft performance calculations, aircraft and rocket design,
ballistic tables, etc. The air is assumed to be devoid of dust, moisture, and
water vapor and to obey the perfect gas law and the hydrostatic equation (the
air is static with respect to the earth).
- Standard atmospheres, sense 1, which have been used are: (a) The NACA
standard atmosphere, also called U.S. standard atmosphere, prepared in 1925,
which was supplanted by (b) The ICAO standard atmosphere, adopted in 1952,
which was extended to greater altitudes by (c) The ARDC model atmosphere,
1956, and (d) The U.S. extension to the ICAO standard atmosphere, adopted in
1956, which has been revised by (e) The ARDC model atmosphere, 1959, which
incorporated some satellite data which has been supplanted by (f) The U.S.
Standard Atmosphere-1962. (See Table XV ).
- 2. (abbr atm). A standard unit of atmospheric
pressure, defined as that pressure exerted by a 760-millimeter column of
mercury at standard gravity (980.665 centimeters per second per second) at
temperature 0 degrees C.
- 1 standard atmosphere = 760 millimeters of mercury; = 29.9213 inches of
mercury; = 1013.250 millibars.
- standard conditions = standard temperature and pressure.
- standard deviation (symbol σ)
- A measure of the dispersion
of data points around their mean value. It is the positive square root of the
mean of the squares of the deviation from the arithmetic mean of the population:
where m is arithmetic mean; d is
deviation from the arithmetic mean; and n is number of points.
- standard-deviation estimate
- See standard
- standard error of estimate (symbol S)
- A measure of the dispersion
(scatter) of data points with respect to a curve
of regression. S is the positive square root of the arithmetic
mean of the squares of the deviations from a curve of regression:
where d is deviation from R ; R
is curve of regression; and n is number of points.
- S is a measure of the variation to be expected in making predictions
from the regression equation.
- standard gravity
- See gravity.
- 1. The act or process of reducing something to, or comparing it with, a standard.
- 2. A measure of uniformity.
- 3. A special case of calibration
whereby a known input is applied to a device or system for the purpose of
verifying the output or adjusting the output to a desired level or scale
- Applied to transducers,
indicates adjustments of the output to a standard value within specified
limits of error.
- standardize = normalize.
- standard pressure
- 1. In meteorology, usually a pressure of 1000 millibars, but other
pressures may be used as standard for specific purposes.
- 2. In physics, a pressure of 1 standard
- standard propagation
- The propagation
energy over a smooth spherical earth of uniform dielectric constant and
conductivity under conditions of standard refraction
in the atmosphere, i.e., an atmosphere in which the index of refraction
decreases uniformly with height at a rate of 12 N-units per 1000 feet. See superstandard
- Standard propagation results in a ray curvature due to refection which
has a value approximately one-fourth that of the earth's curvature, giving a
radio horizon which is about 15 percent greater than the distance to the
geometrical horizon. This is equivalent to straight-line propagation over a
fictitious earth whose radius is four-thirds the radius of the actual earth.
- standard refraction
- The refraction which would occur in an idealized atmosphere in which the
index of refraction decreases uniformly with height at the rate of 39 X 10E-6
per kilometer. See standard
- Standard refraction may be included in ground-wave calculations by use
of an effective earth radius of 8.5 X 10E6 meters, or four-thirds the
geometrical radius of the earth.
- standard temperature
- 1. A temperature
that depends upon some characteristic of some substance, such as the melting,
boiling, or freezing point, that is used as a reference standard of
- 2. In physics, usually the ice point (0 degrees C); less frequently, the
temperature of maximum water density (4 degrees C).
- 3. In meteorology, this has no generally accepted meaning, except that it
may refer to the temperature at zero altitude in the standard atmosphere (15
- standard temperature and pressure
- (abbr STP). Usually a temperature of 0 degrees C but also used to
designate a temperature of 15 degrees C and 1 standard
atmosphere (see standard
- standard time
- See time.
- standard value of gravity
- See acceleration
- standing wave
- A periodic wave having a
fixed distribution in space which is the result of interference
of progressive waves of the same frequency and kind. Such waves are
characterized by the existence of nodes or partial
nodes and antinodes
that are fixed in space.
- stand talker
- A person on a static test stand
responsible for coordinating and timing the preparations for a static
- Stanton number
- (symbol NSt). A number expressing the ratio of the heat
transmission perpendicular and parallel to the flow direction, defined as h/cp
where h is the heat transfer
coefficient, cp is the specific heat, ρ is the density,
and v is the flow velocity.
- 1. A self-luminous celestial body exclusive of nebulas, comets, and
meteors; any one of the suns seen in the heavens. Distinguished from planets or
that shine by reflected light. See navigational
stars, table VII.
- 2. Any luminous body seen in the heavens.
- The star (sense 1) of our solar system is the sun. In sense 2, star
sometimes excludes the sun, the moon, and manmade satellites from the
- star catalogue
- A listing of stars giving positions for a specified mean equinox and
equator. Stars are often identified by catalogue numbers.
- star classification
- Stars are classified by their spectra, designated by letters, sometimes
with numerical subdivisions, as the sun is a G1-type star. The seven main
types with their principal spectral characteristics are, in order of
O - He II absorption;
B - He I absorption;
A - H absorption;
F - Ca II absorption;
G - strong metallic lines;
K -bands developing;
M - very red.
Also, the letters, P, W, Q, R, N, and S are used to designate comparatively
rare types of stars which do not fall into the main series.
- star cluster
- A group of stars physically
close together in space.
- star grain = star perforated grain.
- Stark effect
- The broadening or splitting of a spectral
line observed when a luminous gas is acted upon by a strong electric
- star perforated grain
- A hollow rocket propellant grain with the
cross section of the hole having a multipointed shape.
- starting pressure
- In rocketry, the minimum chamber
pressure required to establish shock-free flow in the exit plane of a
- star tracker
- A telescopic instrument on a rocket or other
flight borne vehicle that locks onto a celestial
body and gives guidance
reference to the vehicle during flight. See celestial
- state of the art
- The level to which technology and science have at any designated cutoff
time been developed in a given industry or group of industries.
- state parameter = thermodynamic function of state.
- state variable
- Any independent variable in a problem which must be specified to define a
condition of state, as for example a component of position.
- 1. Involving no variation with time.
- 2. Involving no movement, as in static test.
- 3. Any radio interference
detectable as noise in the
audio stage of a receiver.
- static conversion
conversion in which no moving parts or equipment are utilized.
- static firing
- The firing of a rocket
engine in a hold-down position to measure thrust and
accomplish other tests.
- static pressure (symbol p)
- 1. The pressure with
respect to a stationary surface tangent to the mass-flow velocity vector.
- 2. The pressure with respect to a surface at rest in relation to the
- static test
- An instance of static
- static testing
- The testing of a rocket or other
device in a stationary or hold-down position, either to verify structural
design criteria, structural integrity, and the effects of limit loads or to
measure the thrust of a
- A location where measurements are made, e.g., along an airfoil in a wind tunnel
- stationary orbit
- An orbit
in which the satellite
revolves about the primary at the
angular rate at which the primary rotates on its axis. From the primary, the
satellite thus appears to be stationary over a point on the primary.
- A stationary orbit with respect to the earth is commonly called a
- stationary wave
- A standing
wave in which the net energy flux is zero at
- Stationary waves can only be approximated in practice.
- station constants
- In tracking and
constants usually associated with instrumentation sites, e.g., survey
coordinates, zeroing correction, etc.
- station error
- In geodesy and surveying, the difference, usually negligible, between the
latitudes, due to local gravitational anomalies.
- station keeping
- The sequence of maneuvers that maintains a vehicle in a predetermined orbit.
- station pressure
- The atmospheric
pressure computed for the level of the station elevation.
- This may or may not be the same as either the climatological station
pressure or the actual pressure, the difference being attributable to the
difference in reference elevations. Station pressure usually is the base value
from which sea-level pressure and altimeter setting are determined.
- In machinery, a part or assembly that remains stationary with respect to a
rotating or moving part or assembly such as the field frame of an electric
motor or generator, or the stationary casing and blades surrounding an
axial-flow-compressor rotor or turbine wheel; a stator blade.
- statute mile
- 5280 feet = 1.6093 kilometers =
mile. Also called land mile.
- steady flight
- steady flow
- A flow
whose velocity vector components at any point in the fluid do not vary
with time. See streamline
- steady state
- 1. The condition of a substance or system whose local physical and
chemical properties do not vary with time.
- 2. Specifically, the stable operating condition of a reactor in
which the neutron inventory remains constant; that is, the effective
multiplication factor ke is equal to 1.
- steady-state problem
- See initial-value
- steady-state vibration
- A condition that exists in a system if the
velocity of each particle is a continuing periodic
- steerable antenna
- A directional
antenna whose major lobe can be readily shifted in direction.
- steering function
- An empirical relation based on the relative
distance and velocity of the target, used in guidance of
rockets and spacecraft.
- Stefan-Boltzmann constant
- (symbol σ). A universal constant of proportionality
between the radiant emittance of a black body
and the fourth power of the body's absolute
temperature; 5.6697 X 10E-5 erg centimeter squared second degrees KE4.
- Stefan-Boltzmann law
- One of the radiation
laws which states that the amount of energy radiated per unit time from a
unit surface area of an ideal black body
is proportional to the fourth power of the absolute
temperature of the black body. The law is written: E = σT4where E is the emittance of the black
body; σ is the Stefan-Boltzmann constant; and T
is the absolute temperature of the black body. Also called Stefan law.
- This law was established experimentally by Stefan and was given
theoretical support by thermodynamic reasoning due to Boltzmann. This law may
be deduced by integrating Planck law
over the entire frequency spectrum.
- Stefan law = Stefan-Boltzmann law.
- Of or pertaining to stars.
- stellarator machine
- An experimental thermonuclear
device where containment in a magnetic
field is achieved by closing the field upon itself and thus allowing the
particles to perform endless spiral motion.
- stellar classification
- See star
- stellar inertial guidance
- The guidance of a flight-borne vehicle by a combination of celestial and
guidance; the equipment which accomplishes the guidance.
- stellar magnitude = magnitude.
- stellar map matching
- A process during the flight of a vehicle by
which a chart of the stars set into the guidance
system is automatically matched with the position of the stars observed
through telescopes so as to give guidance to the vehicle. See map-matching
- stellar parallax = heliocentric parallax.
- stellar scintillation = astronomical scintillation.
- St. Elmo's fire = corona discharge.
- step rocket = multistage rocket.
- The unit solid angle which cuts unit area from the surface of a sphere of
unit radius centered at the vertex of the solid angle. There are 4 steradians in a sphere.
- Chemistry dealing with the arrangement of atoms and molecules in three
- sternumward acceleration
- See physiological
- stiction = static friction.
- The ratio of change of force (or torque) to the corresponding change in
translational (or rotational) displacement of an elastic element.
- A unit of luminance (or
brightness) equal to 1 international
candle per square centimeter. Compare apostilb.
- 1. = excitation.
- 2. = measurand.
- Stirling cycle
- A theoretical heat engine
cycle in which heat is added at constant volume, followed by isothermal
expansion with heat addition. The heat is then rejected at constant volume,
followed by isothermal compression with heat rejection.
- If a regenerator is used so that heat rejected during the
constant-volume process is recovered during heat addition at constant volume,
efficiency of the Stirling cycle is the same as for the Carnot
cycle, with less compressive work needed.
- Conjectural; in statistical analysis, = random.
- stochastic process
- An ordered set of observations in one or more dimensions, each being
considered as a sample of one item from a probability
- Of a mixture of chemicals, having the exact proportions required for
complete chemical combination, applied especially to combustible mixtures used
- An atmospheric
refraction phenomenon, a mirage; a special case of sinking in
which the curvature of light rays due to atmospheric refraction decreases with
elevation so that the visual image of a distant object is foreshortened in the
- The opposite of stooping is towering.
- stopping point
- The end of the highly luminous path of a visual meteor. Also
- Of a liquid; subject to being placed and kept in a tank without benefit of
special measures for temperature or pressure control, as in storable
- 1. The act of storing information.
- 2. Any device in which information can be stored. Also called a memory
- 3. In a computer, a
section used primarily for storing information. Such a section is sometimes
called a memory or a store.
- The physical means of storing information may be electrostatic,
ferroelectric, magnetic, acoustic, optical, chemical, electronic, electrical,
mechanical, etc., in nature.
- storage capacity
- The amount of information,
usually expressed in bits (i.e., the
log2 of the number of distinguishable states in which
the storage can exist), that can be retained in storage. Also
called memory capacity.
- 1. To retain information in a device from which it can later be withdrawn.
- 2. To introduce information into such a device.
- 3. A container, rocket, bomb, or vehicle carried externally in a craft.
- straddle carrier
- A ground vehicle that carries its load suspended between its wheels.
- The deformation produced by a stress divided
by the original dimension.
- strain gage
- An instrument used to measure the strain or
distortion in a member or test specimen (such as a structural part) subjected
to a force.
- See atmospheric
- stratosphere radiation
- Any infrared
radiation involved in the complex infrared exchange continually proceeding
within the stratosphere.
- A group of meteoroids
with nearly identical orbits, also called meteor stream.
- A line whose tangent at any point in a fluid is parallel
to the instantaneous velocity vector of the fluid at that point. The
differential equations of the streamlines may be written dr X v = 0, where dr is an element of the
streamline and v is the velocity vector; or in Cartesian coordinates, dx
/ u = dy /v = dz /w, where u, v, w, are the fluid velocities
along the orthogonal X, Y, Z axes, respectively.
- In steady-state flow the streamlines coincide with the trajectories of
the fluid particles; otherwise, the streamline pattern changes with time. See
streamline. Compare trajectory.
- streamline flow = laminar flow.
- 1. The force per unit
area of a body that tends to produce a deformation.
- 2. The effect of a physiological, psychological, or mental load on a
biological organism which causes fatigue and tends to degrade proficiency.
- stress concentration
- In structures, a localized area of high stress. See stress
- stress cycle
- A variation of stress with
time, repeated periodically and identically. See fatigue.
- stress raisers
- Changes in contour or discontinuities in a structure that cause local
increases in stress.
- stress ratio
- The ratio of the minimum stress to the
maximum stress occurring in one stress
- stress tensor
- The complete set of stress
components in a solid or fluid medium, which are written as a tensor τij. It has nine components, one for each of the
coordinate faces of an imaginary element upon which the stress acts ( j
= x, y, z ) and for each direction in which the stress is directed
( i = x, y, z ).
- By definition, an inviscid fluid is one in which the six tangential
stresses (i +/- j) are zero, and the three normal stresses (i =
j) are equal to the negative of the pressure.
- An action whereby the time for completing an action, especially a
contract, is extended beyond the time originally programmed or contracted for.
- strewn field
- See tektite.
- A slender, lightweight, lengthwise fill-in structural member in a rocket
body, or the like, serving to reinforce and give shape to the skin.
- Strouhal number (symbol NStr)
- A nondimensional number occurring in the study of periodic or
quasiperiodic variations in the wake of objects immersed in a fluid stream: NStr = nl / u where n is a frequency; l is a
representative length, and u is a representative velocity of the
- structural weight = construction weight.
- An assembly that
is a component part of a larger assembly.
- subastral point = substellar point.
- subatomic particle
- Any particle of
less than atomic mass, e.g., the electron, proton, and neutron, also called
- Subatomic particles are classified by relative mass into four groups:
leptons, mesons, nucleons, and hyperons, from lowest to highest masses,
- subaudio frequency
- A frequency
below the audiofrequency
range, below about 15 cycles per second.
- A carrier which
is applied as a modulating
wave to modulate another carrier or an intermediate subcarrier.
- subcarrier oscillator
- In a telemetry
system, the oscillator
which is directly modulated by the measurand or
by the equivalent of the measurand in terms of changes in the transfer
elements of a transducer.
- In a telemetry
system, the route required to convey the magnitude of
a single subcommutated measurand.
- In telemetry, commutation
of additional channels with
output applied to individual channels of the primary commutator.
- Subcommutation is called synchronous if its rate is a submultiple of
that of the primary commutator. Unique identification must be provided for the
subcommutation frame pulse.
- In telemetry, a complete sequence of frames during
which all subchannels of a specific channel are
- A condition in which the acceleration
acting on a body is less than normal gravity,
between 0 and 1 g.
- A sinusoidal
quantity having a frequency
that is an integral submultiple of the fundamental
frequency of a periodic
quantity to which it is related.
- The transmission of a substance directly from the solid state to the vapor
state, or vice versa, without passing through the intermediate liquid state.
- subliming ablator
- An ablation
material characterized by sublimation
of the material at the heated surface.
- sublunar point
- The geographical
position of the moon; that point on the earth at which the moon is in the
zenith at a
- subpermanent magnetism = permanent magnetism.
- The expression subpermanent magnetism is sometimes used because of the
slow dissipation of such magnetism, but the expression permanent magnetism is
- Less-than-normal refraction,
particularly as related to atmospheric
- Greater-than-normal refraction is called super refraction.
- A set of instructions necessary to direct a computer to carry out a
well-defined mathematical or logical operation; a submit of a routine,
usually coded in such a manner that it can be treated as a black box by
the routine using it.
- subsatellite point
- Intersection of the local vertical
passing through a satellite in
orbit with the earth's surface.
- subsolar point
- The geographical
position of the sun; that point on the earth at which the sun is in the zenith at a
- In aerodynamics, of or pertaining to, or dealing with speeds less than acoustic
velocity as in subsonic aerodynamics.
- subsonic flow
- Flow of a fluid, as air
over an airfoil, at speeds less than acoustic
- Aerodynamic problems of subsonic flow are treated with the assumption
that air acts as an incompressible fluid.
- substandard propagation
- The propagation
of radio energy under conditions of substandard refraction in the atmosphere,
that is, refraction by an atmosphere or section of the atmosphere in which the
of refraction decreases with height at a rate of less than 12 N-units per
1000 feet. See standard
- Substandard propagation produces a less-than-normal downward bending or
even an upward bending of radio waves as they travel through the atmosphere,
giving closer radio horizons and decreased radar and radio coverage. It
results primarily when propagation takes place through a layer in which
moisture remains constant or increases with height.
- substandard refraction
- Also called subrefraction. See substandard
- substantial derivative = individual derivative.
- substellar point
- The geographical
position of a star; that point on the earth at which the star is in the zenith at a
specified time. Also called subastral point.
- Loosely and nontechnically, the very high troposphere.
- To be opposite, as an arc of a circle subtends an angle at the center
of the circle , the angle being formed by the radii joining the ends of
the arc with the center.
- sudden-commencement magnetic storm
- A magnetic storm characterized by a world-wide sudden commencement which
takes place in a matter of minutes and shows no recurrence after 27 days, the
period of rotation of the sun.
- sudden ionospheric disturbance
- (abbr SID). A complex combination of sudden changes in the condition of
and the effects of these changes.
- The following are the most important effects accompanying a sudden
ionospheric disturbance: (a) radio fadeout, a condition in which there is a
marked and abrupt increase in absorption in the D-region for high frequency
radio waves (2 to 3 megacycles) and a consequent loss of long-distance radio
reception in this range of frequencies; (b) magnetic crotchet, a sudden change
in the earth's magnetic field due to an increase in the conductivity of the
lower ionosphere, the change being in the nature of an augmentation of the
normal quiet-day magnetic change; (c) sudden enhancements of long-wave
atmospherics recorded in the frequency range between 10 and 100 kilocycles due
to the improved reflectivity at oblique incidence of the D-region for such
low-frequency radio waves; (d) sudden phase anomalies of discrete
low-frequency radio waves (10 to 100 kilocycles) due to descent of the
D-layer; and (e) sudden field-strength anomalies of distant low-frequency
radio signals (10 to 100 kilocycles) due to interference between the
groundwave and the skywave. A sudden ionospheric disturbance usually occurs a
few minutes after a solar flare and is noted only on the sunlit side of the
earth. The return of the ionosphere to its normal condition following a
pronounced sudden ionospheric disturbance usually takes from half an hour to an
hour, sometimes longer.
- summer solstice
- 1. That point on the ecliptic
occupied by the sun at maximum northerly declination. Sometimes called June
solstice, first point of Cancer.
- 2. That instant at which the sun reaches the point of maximum northerly declination,
about June 21.
- The star at the center of the solar
system, around which the planets, planetoids, and comets revolve. It is a
- The sun visible in the sky is called apparent or true sun. A fictitious
sun conceived to move eastward along the celestial equator at a rate that
provides a uniform measure of time equal to the average apparent time is
called mean sun; a fictitious sun conceived to move eastward along the
ecliptic at the average rate of the apparent sun is called dynamical mean sun.
- The crossing of the visible horizon by the
limb of the ascending sun.
- The crossing of the visible horizon by the
limb of the descending sun.
- A relatively dark area on the surface of the sun consisting of a dark
central umbra surrounded by a penumbra which is intermediate in brightness
between the umbra and the surrounding photosphere.
- Sunspots usually occur in pairs with opposite magnetic polarities. They
have a lifetime ranging from a few days to several months. Their occurrence
exhibits approximately an 11-year period (the sunspot
- sunspot cycle
- A cycle with an average length of 11.1 years but varying between about 7
and 17 years in the number and area of sunspots, as
given by the relative
sunspot number. This number rises from a minimum of 0 to 10 to a maximum
of 50 to 140 about 4 years later, and then declines more slowly.
- An approximate 11-year cycle has been found or suggested in
geomagnetism, frequency of aurora, and other ionospheric characteristics. The
u-index of geomagnetic intensity variation shows one of the strongest known
correlations to solar activity. Eleven-year cycles have been suggested for
various tropospheric phenomena, but none of these has been substantiated.
- sunspot number
- See relative
- sunspot relative number = relative sunspot number.
- sun's way
- The path of the solar
system through space. See solar apex.
- sun tracker
- A species of star
tracker designed to lock onto the sun to afford guidance to a
rocket or other flight-borne object. See star
- superadiabatic lapse rate
- An environmental lapse rate
greater than the dry-adiabatic
lapse rate, such that potential temperature decreases with height.
- An alloy developed for very high temperature service where relatively high
stresses (tensile, thermal, vibratory, and shock) are encountered and where
oxidation resistance is frequently required.
by connection of single data input source to equally spaced contacts of the commutator
- Corresponding crosspatching is required at the decommutator.
- super high frequency (abbr SHF).
- See frequency
- superior conjunction
- The conjunction of a planet and the sun when the sun is between the earth
and the other planet.
- superior mirage
- A spurious image of an object formed above its true position by abnormal
refraction conditions; opposite to an inferior
mirage. Compare towering, looming, inferior
- Superior mirages occur when the temperature lapse rate near the earth's
surface is less than its normal value or, especially, when the temperature
actually increases with height. Under these conditions the velocity of light
increases upward in such a way that light rays are bent downward as they
propagate through the layer in quasi-horizontal directions. The downward
curvature gives the impression that the position of the object viewed is well
above its true position in space. The object also appears inverted. Complex
combination of superior and inferior mirages may occur with unusual density
- superior planets
- The planets with orbits larger
than that of the earth: Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
- superior transit = upper transit.
- superpressure balloon
- See constant-level
- superrefraction = superstandard refraction.
- Of or pertaining to, or dealing with, speeds greater than the acoustic
velocity. Compare with ultrasonic.
- supersonic compressor
- A compressor
in which a supersonic
velocity is imparted to the fluid relative to the rotor blades, the
blades, or to both the rotor and stator blades, producing oblique shock waves
over the blades to obtain a high pressure rise.
- supersonic diffuser
- A diffuser
designed to reduce the velocity and increase the pressure of fluid moving at
- supersonic flow
- In aerodynamics, flow of a fluid over a body
at speeds greater than the acoustic
velocity and in which the shock waves
start at the surface of the body. Compare hypersonic
- supersonic nozzle
- A converging-diverging nozzle designed
to accelerate a fluid to supersonic
- Specifically, the study of aerodynamics
speeds. See hypersonics.
- superstandard propagation
- The propagation
of radio waves under conditions of superstandard refraction (superrefraction)
in the atmosphere, that is, refraction
by an atmosphere or section of the atmosphere in which the index
of refraction decreases with height at a rate of greater than 12 N-units
per 1000 feet. See standard
- Superstandard propagation produces a greater-than-normal downward
bending of radio waves as they travel through the atmosphere, giving extended
radio horizons and increased radar coverage. It results primarily from
propagation through layers near the earth's surface in which the moisture
lapse rate is greater than normal, or the temperature lapse rate less than
normal, or both. A condition in which warn dry air moves out over a cool water
surface is an example of superrefraction. A layer in which the downward
bending is greater than the curvature of the earth is called a radio duct.
Frequently, the general term, anomalous propagation, is used for superstandard
- superstandard refraction
by an atmosphere or section of the atmosphere in which the index
of refraction decreases with height at a rate greater than 12 N-units per
1000 feet. Also called superrefraction.
- An angle equal to 180 degrees minus a given angle. Thus 110 degrees is the
supplement of 70 degrees and the two are said to be supplementary. See
- supplementary angles
- Two angles whose sum is 180 degrees.
- support equipment
- See ground
- 1. A two-dimensional extent; the outside or superficies of any body;
especially, the surface of the earth, either land or water, used in
combinations as surface-to-air, etc.
- 2. A wing, rudder, propeller blade, vane, hydrofoil, or the like - applied
in this sense to the entire structure or body.
- surface boundary layer
- That thin layer of air adjacent to the earth's surface, extending up to
the so-called anamometer level (the base of the Ekman layer). Within
this layer the wind distribution is determined largely by the vertical
temperature gradient and the nature and contours of the underlying surface;
shearing stresses are approximate constant. Also called surface layer,
friction layer, atmospheric boundary layer, ground layer. See logarithmic
velocity profile, planetary
boundary layer, free
- surface duct
- An atmospheric
duct for which the lower boundary is the surface of the earth.
- surface layer = surface boundary layer.
- surface of position
- A surface on some point of which a craft is located. See line of
- A transient rise in power, pressure, etc., such as a brief rise in the
discharge pressure of a rotary compressor.
- The process of determining accurately the position, extent, contour, etc.,
of an area, usually for the purpose of preparing a chart.
- suspended phase
- See suspension.
- In physical chemistry, a system composed
of one substance (suspended phase, suspensoid) dispersed throughout another
substance (suspending phase) in a moderately finely divided state, but not so
finely divided as to acquire the stability of a colloidal
- Given sufficient time, a suspension will, be definition, separate
itself by gravitational action into two visibly distinct portions, whereas a
colloidal system, by definition, is stable. Dust in the atmosphere is an
example of a suspension of a solid in a gas.
- See suspension.
- Anything that acts to sustain an action or movement already begun;
specifically, a sustainer
- sustainer engine
- A rocket
engine that maintains the velocity of a rocket vehicle once it has
achieved its programmed velocity by use of booster or
- This term is applied, for example, to the remaining engine of the Atlas
after the two booster engines have been jettisoned. The term is also applied
to a rocket engine used on an orbital flider to provide the small amount of
thrust now and then required to compensate for the drag imparted by air
particles in the upper atmosphere.
- sweat cooling = transpiration cooling.
- The motion of the visible dot across the face of a cathode-ray
tube, as a result of deflections of the electron
- A linear time-base sweep has a constant sweep speed before retrace. An
expanded time-base sweep is produced if the sweep speeds is increased during a
selected part of the cycle; a delayed time-base sweep if the start of the
sweep is delayed, usually to provide an expanded scale for a particular part.
A sweep intended primarily for measurement of range may be called a range
sweep. See trace.
- swing-around trajectory
- A planetary round trip trajectory
which requires no propulsion at the destination planet, but uses the planet's
field to effect the necessary orbit change to return to earth.
- A cyclotron in
which the frequency of the electric field is frequency
modulated to permit the acceleration of particles to relativistic
energies. Also called FM cyclotron.
- The relationship between two or more periodic
quantities of the same frequency
when the phase
difference between them is zero or constant at a predetermined value.
- Coincident in time, phase, rate, etc.
- synchronous computer
- A computer in
which the starting time of every ordinary operational cycle is controlled by
which occur at regular intervals. Contrast with asynchronous
- synchronous satellite
- An equatorial west-to-east satellite
orbiting the earth at an altitude of approximately 35,900 kilometers at which
altitude it makes one revolution
in 24 hours, synchronous with the earth's rotation.
- A device for accelerating particles,
ordinarily electrons, in
a circular orbit in an increasing magnetic
field by means of an alternating electric
field applied in synchronism with the orbital motion.
- synergic ascent
- The ascent of a rocket vehicle along a synergic
- synergic curve
- A curve plotted for the ascent of a rocket
vehicle calculated to give the vehicle an optimum economy in fuel with an
- This curve, plotted to minimize air resistance, starts off vertically,
but bends towards the horizontal between 20 and 60 miles altitude to minimize
the thrust required for vertical ascent.
- synodical month
- The average period of revolution
of the moon about the earth with respect to the sun, a period of 29 days 12
hours 44 minutes 2.8 seconds.
- This is sometimes called the month of the phases, since it extends from
new moon to the next new moon. Also called lunation.
- synodic period
- The interval of time between and planetary
configuration of a celestial
body, with respect to the sun, and the next successive same configuration
of that body, as from inferior
conjunction to inferior conjunction.
- synodic satellite
- A hypothetical earth satellite,
situated 0.84 of the distance to the moon on a line joining the centers of the
earth and moon and having the same period of revolution
as the moon.
- Pertaining to or affording an overall view.
- In meteorology, this term refers to meteorological data obtained
simultaneously over a wide area for the purpose of presenting a comprehensive
and nearly instantaneous picture of the state of the atmosphere. Thus, to a
meteorologist, synoptic takes on the additional connotation of simultaneity.
- synoptic correlation = Eulerian correlation.
- synoptic meteorology
- The study and analysis of weather information gathered at the same time.
- The situation of two or more oscillating circuits
having the same resonance
- 1. Any organized arrangement in which each component part acts, reacts, or
interacts in accordance with an overall design inherent in the arrangement.
- 2. Specifically, a major component of a given vehicle such as
a propulsion system or a guidance system. Usually called a
major system to distinguish it from the systems subordinate or
auxiliary to it.
- The system of sense 1 may become organized by a process of evolution,
as in the solar system, or by deliberate action imposed by the designer, as in
a missile system or an electrical system. In sense 2, the system embraces all
its own subsystems including checkout equipment, servicing equipment, and
associated technicians and attendants. When the term is preceded by such
designating nouns as propulsion or guidance, it clearly refers to a major
component of the missile. Without the designating noun, the term may become
ambiguous. When modified by the word major, however, it loses its ambiguity
and refers to a major component of the missile.
- systematic error
- An error
that is always a function of the magnitude of
- When the error is constant it is called a bias error. Systematic errors
are often caused by false elements in an instrument. An example is an
eccentrically mounted azimuth circle or an azimuth circle with graduation
- system of astronomical constants
- An interrelated group of values constituting a model of the earth and the
motions which together with the theory of celestial
mechanics serves for the calculations of ephemerides.
constants, note and tables II and III.
- A point of the orbit or a planet
or satellite at which it is in conjunction
- The term is used chiefly in connection with the moon, when it refers to
the points occupied by the moon at new and full phase.