The kinetic power of a ship pushed by a relativistic particle stream is approximately P = F c, where F is the thrust (force, in Newtons) and c is the speed of light. If the mass of the ship plus its fuel is m and the acceleration is a then we simply have F = m a, which is familiar to students of Newtonian physics.
The relation P = F c occurs in the limit of highly relativistic exit velocities for the thrust stream, in which case the kinetic energy per particle is very much greater than the rest-mass energy of the particle (μ c², where μ is the particle mass). Otherwise, the general power/thrust equation is P = c ( q² c² + F² )1/2, where q is the mass efflux of the thrust stream (e.g. measured in kg / s).
For many classes of starships, we can calculate the engine power needed to accelerate the ship's mass at hundreds or thousands of G [as observed in the movies]. If the engines and their power feeds are efficient then the ship's maximum reactor output must be slightly greater than the maximum engine power. In comparison, the energy requirements for some kinds of weapons usage (eg. destroying asteroids) have proven to be very minimal lower limits (at least for starfighters; warships have more efficient guns).
During a hot pursuit, a starship may devote most of its reactor power to engines. During a standing battle where the relative accelerations are much less than thousands of G, a much greater share of reactor power may be devoted to weapons. During normal cruising, the reactor output may be reduced by orders of magnitude, although it probably isn't possible to completely turn off a large hypermatter reactor (like that of a star destroyer).
The idle power of a starship's engines (i.e. when the thrust streams are effectively halted) can be estimated from the power of the thermal glow visible through the engine aperture (of area A). If σ is the Stefan-Boltzmann constant and T is the effective temperature of the radiating surface, then the radiated power is P = A σ T4. For example, if a star destroyer has three online engines in which the glowing surfaces have 100m diameters, and where the glow is yellow (temperature ~ 5000K), the ship must have an idle engine power of at least 8 x 1011 W.
In normal sunlit conditions the stream of relativistic ions ejected from an ion-drive thruster is invisible to the naked eye. However the particle streams inevitably feel the drag of tenuous interplanetary and interstellar gas over astronomical distances. Like the linear beam of plasma from a micro-quasar, the thrust streams will at some point lose their energy to friction and entrainment of the surrounding gas, lose their linear collimation and stagnate. The ship's wake may include astronomically observable streaks and plumes of radio emitting plasma, and a local disturbance of the solar wind of any nearby star. The extent of these features depends on the power of the ship.
The yields of a weapon in STAR WARS can be estimated from the measurable effects of a single shot hitting a target of estimable size and composition. The vaporisation of a solid body implies the delivery of a minimum amount of energy (e.g. calorimetry of vaporised asteroids). The expansion of fireballs may provide another kind of estimate. The sustainable firepower of the weapon may be estimated from the energy of typical shots and the rate of fire. These kinds of estimates are, necessarily, lower limits because it is hard to know whether the gun is firing at its maximum capacity.
When we're unable to measure the yield of a particular type of weapon, we may safely guess that it is similar to the output of other weapons of the same physical type and similar volume. For well-measured energy weapons ranging from blaster rifles to the prime weapon of the Death Star, there is an approximate power-law correlation between the weapon's volume and its maximum shot energy. Following this trend, for example, a SPHA-T artillery piece could fire blasts comparable to the heavy turbolaser turrets on a star destroyer (a necessity when several guns overcome the shields of a Trade Federation core ship).
However size is not the only important factor limiting firepower. Heavy guns benefit from dedicated capacitors to collect energy from a ship's main reactor and store it for an intense discharge. The SPHA-T gun lacks a continuous feed to a ship's reactor, and therefore it inevitably exhausts itself long before a comparable ship-mounted gun would. The prime weapons of a well-designed warship are optimally designed so that their power feeds can fully exploit the main reactor. When the captain directs full power to recharging the main guns, the maximum sustainable firepower must be comparable to the reactor's total output. However the total firepower of secondary weapons, such as anti-fighter screening guns, may be a more limited fraction of the reactor output.
A vessel designed for space combat must have highly efficient power network feeding its main guns. Notice that the “dagger”-style Imperial warships have a power trunk running along the longitudinal axis of the ship, and thick power conduits leading into each heavy turret. In contrast, a Trade Federation core ship (not to be confused with the conjugated battleship) is much less effective at channelling reactor power to recharge its guns, which are relatively minor weapons bolted on as after-market modifications. The converted Trade Federation ships are good for shielding self-defence, but weren't designed with efficient internal power-tree structures to feed weapons systems from the central reactor.
The process of ray shielding involves the reflection, diffusion or absorption and transfer of harmful energies. However the firepower that the shield disposes can be far greater than the power that the shield generator draws from the ship's reactor. A mirror consumes no power when it reflects a ray of light. An initially concentrated light beam may diffuse in an opaque fog, without the fog requiring power input — this is an example of passive scattering. Analogously, the perfect deflection or splintering of incoming blaster fire may require little or no energy consumption.
Splintering events are analogous to particle decay tracks photographed in the bubble chambers of old-fashioned particle physics experiments. The incident beam splits into daughter beams in a way that (generally) conserves the total momentum and energy. The daughter rays may decay further. The decay probability per unit length along a ray must depend on the energy density ratio between the beam and the ambient shield. If the decay rate is high enough, the recursive splintering cascade reduces the initially coherent beam into a diffuse ball of energy. When the decay rate is low, the shot passes through the shield volume with minimal (if any) splintering events.
Incoming firepower that is absorbed by the shield system must ultimately be re-radiated as waste heat of some kind. If starships are to avoid being melted by energy thermalised by their shields during enemy barrages, then they need two things: internal heat sinks with enormous heat capacities, and an efficient means of eventually removing the heat accumulated in these sinks. In effect, this aspect of the shield system acts like a refrigerator heat-pump, which consumes some power in order to transport and expunge a much larger amount of heat energy.
The mechanism to expunge waste heat might consist of warm radiators surfaces exposed to space, giving off thermal photons (in other words, “blackbody radiation”). However photonic radiators have the inevitable disadvantage that a fraction of the emissions falls upon adjacent areas of the ship's own hull. Self-heating might indirectly limit the effectiveness of shielding systems. Furthermore, few observed ships have hulls that are as black as an efficient radiator must be, and the absence of visible thermal glow implies temperatures no more than a few hundred K. A device that emits neutrinos as carriers of heat energy would be a better possibility. Neutrinos interact with atomic matter negligibly, and can shine freely through everything except perhaps the most exotic constituents of the ship. Neutrino emission is significant in some natural objects, e.g. harmlessly carrying away half the energy released in a supernova explosion. A starship with an extensive and effective shield system with heat sinks linked to neutrino radiators might be able to endure firepower far greater than the vessel's own maximum reactor output.
|equivalent annihilation rate|
P / c² (kg /s)
|typical adult human body||1.0||× 102||1.1||× 10-15|
|residential home, mean daily electrical usage||~1.0||× 103||~1.1||× 10-14|
|typical hair-dryer||1.5||× 103||1.6||× 10-14|
|typical car engine, highway cruising||2.0||× 104||2.2||× 10-13|
|typical car engine, maximum power||1.2||× 105||1.3||× 10-12|
|Senator Greyshade's hotrod airspeeder||3.0||× 107||3.3||× 10-10|
|cruise ship Titanic at max thrust||3.7||× 107||4.1||× 10-10|
|Su-27 jet at max thrust||5.1||× 107||5.6||× 10-10|
|Ohio-class ballistic missile submarine core S8G||2.0||× 108||2.2||× 10-9|
|civilian nuclear power core (on Earth)||~1.0||× 109||~1.1||× 10-8|
|space shuttle's solid rocket boosters in takeoff||1.1||× 1010||1.2||× 10-7|
|electrical consumption of USA in 2001||4.1||× 1011||4.6||× 10-6|
|star destroyer engines running idle||8||× 1011||9||× 10-6|
|insolation of Earth's surface||1.7||× 1017||1.9||× 100|
|Naboo senatorial barge maximum reactor output||3||× 1018||3||× 101|
|Naboo yacht maximum reactor output||7||× 1018||8||× 101|
|BDZ melting to 1m depth in 1 hour||5||× 1020||6||× 103|
|thermal radiation from Earth's surface, if it were cooling from T=3000K||2.4||× 1021||2.6||× 104|
|Acclamator maximum reactor output||2||× 1023||2||× 106|
|BDZ melting to 1km depth in 1 hour||5||× 1023||6||× 106|
|Trade Federation core ship maximum reactor output||3||× 1024||2||× 107|
|BDZ melting to 10km depth in 1 hour||5||× 1024||6||× 107|
|star destroyer engines at maximum thrust||~ 1025||~ 108|
|solar luminosity (G2 star)||3.8||× 1026||4.3||× 109|
|Executor engines at maximum thrust||> 1027||> 1010|
|Death Star minimum recharge rate||2.8||× 1027||3.1||× 1010|
|Death Star full recharge rate||3.9||× 1033||4.4||× 1016|
It's noteworthy that the maximum power output of a star destroyer is of a stellar magnitude. The power requirements of a ship's life-support etc are utterly insignificant compared to the power demonstrated by the weapons and propulsion systems. There are serious thermodynamic implications to using such power. If stellar-scale power were consumed and dissipated inside the ship then the waste heat would make the ship glow like a stellar object, and soon evaporate. Since an intact star destroyer does not tend to vaporise, we can infer that its most powerful components must be of a nature that dumps energy externally. Thrusters and weapons fit that description. Ion drives eject streams of charged particles at near light speeds; they inevitably carry their heat away with them. Ion cannons are somewhat similar to ion drives, but they eject plasma for destructive effect. Turbolasers and laser cannons fire concentrated beams of massless energy, which inherently carries power outwards. The beams may be non-thermal anyway. If only a tiny fraction of the reactor's maximum output were to leak into the ship's interior then the sudden, catastrophic heating could damage the reactor enough to cut the power, or (at worst) turn the entire vessel to vapour.
The largest warships and battle stations are considerably more powerful than steadily burning, main-sequence stars. This may seem surprising, but a star is actually an extremely slow producer of energy: the nuclear reaction rates at the core are just sufficient to provide pressure support against gravity. A normal star is in almost an equilibrium state, burning its fuel slowly and lasting for millions or billions of years. An artificial nuclear (or antimatter or hypermatter) reactor is designed to sustain higher reaction rates per particle, and consumes fuel rapidly for its size. For its mass, even a primitive nuclear explosive releases its energy much faster than the power generation in the core of a star. Although starships and battle stations can attain stellar power levels, their small size limits the fuel they can carry, and thus the lifetime of a ship is far less than astronomical in duration. The sun's immense mass enables it to last ten billion years or more. A star battlecruiser operating continuously at the same power may exhaust its more limited fuel within hours. Peak performance involving thousand-G accelerations and heavy fighting may last a few hours, while relatively sedate coasting (continuous accelerations of a few G) between the active episodes means that a few years elapse between refuelling stops (depending on the ship's ratio of fuel to structural mass).
The mighty warships of the Galactic Empire/Republic and its enemies (typically star destroyers or greater in scale) generate and deliver power at stellar rates. Reactor and power distribution systems are the most fundamental components of these vessels. The primary weapons, engines and other systems are designed to draw and expend the maximum output of the available reactor. Support and containment of the power systems is one of the most fundamental requirements guiding the ship's design.
The reactor is usually a spherical device. Such a shape provides a minimum surface area for its interior volume, and may be an easy way to bear the structural and force-field burden of containment. The deepest interior of the reactor is a realm of exotic physics, where phenomenal energy densities are maintained. Outer layers or subsidiary systems may involve nuclear fusion reactions but the scale of power generation requires that the core process is direct and total annihilation of mass. Possible fuels might include:
The performance of 3000G accelerations and the bombardment of habitable planets to slag implies that the mass of fuel may exceed the warship's dry mass by a considerable amount. Fuels are carried in immensely dense forms within silos or tanks of relatively small volume distributed throughout the ship, but connected intimately with the reactor. Fuel feeding rates may be as highly variable as the reactor output levels, which could be raised or lowered by orders of magnitude within minutes (judging by the known feats and performance of particular observed warships).
Imperial warships invariably have a spherical reactor, with its centre on the longitudinal axis of the ship, close to the ship's centre of mass. In some cases an armoured ventral bulb covers a part of the reactor that protrudes outside the planes of the ventral hull. This is the result of compromise: a larger reactor produces more power; an exposed reactor is more vulnerable; yet there are limited ways of fitting the reactor within the functional wedge shape of the hull. It is conceivable that a ship with an insufficient covering of dorsal terraces may show a dorsal bulbous structure covering the top side of the reactor too (although no examples have yet been catalogued).
A “power tree” or “power trunk” runs internally along the longitudinal axis of the ship. This system distributes power efficiently from the reactor to many tributary power feeds and thence to the vital components of the ship. It may also serve as the conduit for whatever fields maintain the inertial compensator effects. Consequently, it is impossible for this trunk or spine to be cut by any internal cavity. This sets a limit on the highest possible ceiling of a docking bay. In the Executor, the main ventral cavity has a thick spinal ridge along the middle; the power tree is perhaps only a few tens or hundreds of metres inside this surface.
These critical systems are as heavily armoured as possible. It is probably for this reason that the Imperator exhibits a long strip of dense armour along most of the keel line and over the ventral bulb. Docking cavities necessarily suffer lessened physical protection. This can't be helped, if the ship needs to be able to deploy fighters and shuttles, or interface with other vessels ranging up to corvette size. The Executor has more extensive, gaping hangar cavities than many warship classes, but it probably benefits from a phenomenal shield capacity compared to its mass. The communications ship at Endor [ROTJ novel, chapter 9] was destroyed after it lost its shields in a fight with a Mon Calamari cruiser, and subsequently rebel fighters and the Millennium Falcon attacked the power tree through hangar openings.
The stability of damaged warships reveals an interesting facet of reactor physics and engineering. A Death Star's damaged reactor core releases just enough heat to vaporise the superstructure, but not much more. Exploding warships (e.g. star destroyers) naturally yield just as a few times the heat necessary to obliterate the ship's own mass. In all cases, the destruction apparently disrupts whatever processes regulate the fuel supply, and annihilation can then contributes no more heat. Hypothetically, if all the fuel had been available to annihilate at once, then the nearby planet Yavin (or moon Endor) would have been blasted apart. The fact that this didn't happen hints that the conflagration is self-limiting; the majority of the fuel is lost and dispersed in some unreacted form. A spill of antimatter would be deadly to a nearby planet, and may be inconsistent with observed incidents. The expansion of an unleashed tachyonic (hypermatter) fuel cloud is an interesting topic deserving further study, but probably less inherently lethal than antimatter. A mechanism that catalyses total annihilation of conventional fuel mass may suffer the mildest of self-limiting explosions. [See the speculation on black-hole catalysed reactor in appendices below.]
Starfighters & Small Ships
It is possible that some of the smallest starship designs don't use the high-yield mass-annihilation technologies employed in warships' reactors. Many starfighters are described as having fusion power, which implies that their reactors fuse nuclei of a light element (optimally hydrogen) into heavier elements (most likely and directly helium, but possibly any nucleus up to the mass of iron). Thermal and radiant energy is derived from the small mass deficit between the products and the reactants.
The fuels of some starfighters are intriguingly described as liquid metallic substances. Sometimes they are said to be highly radioactive isotopes. If these materials are fusion reactants then they must almost certainly be hydrogen or helium in liquid-metallic form, which would require storage at stupendously high pressures and low temperatures. Alternatively, the “fuel” liquids may merely be the propellant mass that is ionised and electromagnetically accelerated out of the ion drive to provide thrust. As such they would not be the source of power within the reactor, but rather a consumable material for the thrusters. A heavy metal like mercury might be suitable for this purpose.
Many fighters demonstrate firepower much less than their engine (kinetic) power (considering their accelerations and likely estimates of ship's mass). For example a fighter that fires kiloton-scale laser cannon shots up to several times per second may actually exhibit engine power equivalent to a thousand of these shots per second. The reasons for this apparent discrepancy are due to the differences between the scales and internal structures of a tiny fighter and a flagrantly spacious naval vessel. In small-scale ships the reactors may really be inseparable from the engines, with tenuous plasma emerging from the reactor feeding into the ion drives. As such the reactor power and engine power are linked directly. However the power feeds to the weapons are indirect. They may carry lesser power fluxes than the conduits in a warship, due to inefficiencies of the compact scale. Heat dissipation is likely to be a crucial limiting factor in starfighter weaponry. Machinery and conduits that are only centimetres thick may be unable to pass power at multi-megaton-per-second rates. The tiniest inefficiencies would quickly lead to the accumulation of enough heat to melt the entire structure. The prevalence of radiators and unfolding wings in many starfighter designs demonstrates the critical importance of heat disposal. It is also possible that the energy weapons' recoil forces are a structural challenge on starfighter-scale craft (especially for guns mounted on thin wings).
Vast warships, on the other hand, distribute their energy through broad power trunks. They also have many active and passive heat-disposal systems, e.g. neutrino radiators, which may be unfeasible on fighter scales. A warship's thick cladding of exotic, thermally superconducting hull armour effectively turns the entire surface into a unitary heat sink. Such armour is equally good at dispersing internal waste heat or the heat of a turbolaser hit. Relatively heavy internal supports, both structurally and by tensor-field generators, cope with the recoil of heavier guns that compare to the ship's engine power.
Ground Vehicles & Equipment
Domestic appliances, planetary installations, ground vehicles and aircraft usually do not require power generation of the intensity and efficiency of hypermatter or antimatter annihilation. They employ a variety of simpler power technologies.
Most droids are thought to carry power cells (presumably chemical), although some may contain miniature nuclear reactors or radioisotope thermoelectric generators. Power droids must carry unusually high energy densities inside them, since one of their roles is to maintain vehicles and other heavy hardware.
The very largest ground devices may need to draw power from buried reactors that use the same technologies as the main reactors of warships or battle stations. Devices with these power requirements include strategic and global shield generators (e.g. those on Hoth, Endor, Alderaan and Coruscant), and the heaviest kinds of planetary defensive artillery (e.g. the rebel ion cannons on Hoth and Yavin 4).
Consider a hypothetical reactor containing a lattice of mini-black holes held in a constant heat-bath. In normal operation they radiate away mass-energy [by “ Hawking radiation”], which can be replenished by a continuous fuel mass injection. Such a system could in principle provide total mass annihilation without the potential hazzards of antimatter.
In a mishap, disruption of the reactor vessel starves the holes of fuel. At worst, they subsequently decay and vanish in a flash of radiation. Although this is destructive to the surrounding ship and immediate environs, this explosion is merely equivalent to the holes' present mass-energy, which is much less than the ship's fuel reserves. The reservoir fuels are dispersed in the fireball along with the ship's ordinary structure and contents.
It is not yet known whether such technologies are possible [in STAR WARS], nor whether they form part of hypermatter reactors. Nonetheless the idea is an encouraging analogy or thought-experiment, illustrating how destructive chain reactions could limit their final yields to a minority of the fuel present.
If “hypermatter” consists of intrinsically faster-than-light particles (tachyons) in some harnessed (perhaps gyrating) form then they could in principle be used as a power source. The act of accelerating a tachyon from c up to infinite speed (considering the complex, supra-light Lorentz-transformations) unleashes all of the particle's mass-energy. This is analogous to the deceleration of ordinary sub-light particles, which however have a lower energy limit mc². A tachyon accelerated to infinite speed and zero energy becomes less like matter and more effectively an omnipresent wave of zero intensity — intangible to the ordinary world. Such a process would achieve complete mass-energy conversion without needing to react this exotic fuel with any antiparticle. The power output would depend on the rate at which the “reactor” can decelerate available fuel, and not upon any reaction process.
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