Sounding rockets are a sort of ballistic missile able to boost payloads of a few hundred kilograms to altitudes of 250-750 km, with almost vertical ascent and descent trajectories.
Originally conceived to sound the physical properties of the upper atmosphere, hence the name 'sounding' rockets, their use has been extended to provide 'weightlessness' conditions for experimental research in space physical and life sciences.
Those conditions are met during the freefall phase of the payload once the rocket motors have exhausted their thrust and have dropped. The freefall ends with the deployment of the parachute that lowers the payload to the ground with appropriate impact speeds (of about 8 m/s).
The duration of weightlessness, in the range from 6 to 13 minutes, is determined by the apogee reached by the rocket.
Since 1982, ESA has used sounding rockets as carriers for its microgravity research programmes. Two different rocket configurations, MASER/TEXUS and MAXUS, are currently in use and their main features are given below.
Esrange, in northern Sweden, is the launch site where all sounding rockets for ESA’s microgravity research programme are launched from.
Performance and dimensions
|- Mass||285 kg||260 kg||485 kg|
|- Diameter||0.43 m||0.43 m||0.64 m|
|- Length||3.3 m||3.3 m||3.5 m|
|Apogee||250 km||250 km||750 km|
|Residual acceleration||≤10-4 g||≤10-4 g||≤10-4 g|
|Microgravity duration||6 min||6 min||13 min|
The sounding rocket modular concept
Sounding rocket experiments are accommodated in circular and stackable decks with useful diameters of 40 cm or 60 cm for MASER/TEXUS and MAXUS, respectively. These decks are eventually installed into cylindrical structures and attached by means of elastic dampers that reduce the impact of launch vibrations. The resulting assembly that includes power batteries, control electronics, data interfaces and service accesses constitutes an experiment module. The external structures can be hermetically sealed when the need arises for a pressurised environment.
Modules can be stacked on top of each other up to a maximum length limited by stability conditions. Besides the experiment modules other functional modules complement each sounding rocket mission, such as the service module for telemetries and telecommands as well for the rocket attitude control, the video module to relay multiple video channels to the receiving ground stations, the recovery system that commands the deployment of the parachute packet in the nosecone of the rockets, and the separation module needed to detach from the payload stack when the rocket motors are at the end of their thrust.
Most of the functional modules are reused from one flight to the next after some appropriate refurbishment and upgrade, as needed. The experiment modules can be re-used as well, whenever the experiments need several runs in microgravity either with new samples or with different boundary conditions, parameters, and experiment protocol. This combination of standard and modular blocks gives the Sounding Rocket programmes both a strong reliability asset and a unique flexibility facet.
Data transmission and ground control
Each experiment module is connected to the telemetry system hosted in the service module that, during flight, transmits the data to the ground at appropriate resolution and rate. Both housekeeping and scientific data are relayed, the latter including sequences of video images. Data is recorded onboard and on ground according to the required parameters of speed and accuracy.
The availability of real-time data allows the experimenters to follow the course of their experiments. If required by the experiment protocol or by contingency reasons, the process can be directed from the ground in response to the actual behaviour of the system being investigated; an uplink channel enables the transmission of telecommands in those cases. The number and nature of telemetries and telecommands are jointly pre-defined as part of the experiment module design and development.
During the launch phase, the experiment payloads experience both random vibration and linear accelerations; the latter reach a peak of about 12g and last for about 45 s in total, which is the time needed for the complete burn of both stages of the motor.
After burnout and separation of the motor from the experiment payloads the Attitude Control System reduces the Payload motions in order to obtain the minimum residual acceleration; at that point the microgravity phase starts and the experiments may be performed.
During launch the experiment modules may be operational in order to maintain certain conditions, such as a given temperature in a furnace, but have to be mechanically resilient to the launch vibrations and accelerations.
The experiment modules are recovered after landing and transported via helicopter back to the launch site; the scientific samples are then returned within few hours to the scientists.
The launch preparation campaign is performed at the Esrange premises, where state-of-the-art facilities are available for use by the scientific teams. The laboratories include clean benches, laminar flow benches, microscopes, centrifuges, autoclaves and incubators, to enable the investigators to perform the final flight preparation of their samples in the week before the launch.
The launch preparation activities allow for a late access to the experiment modules; such late access activities may include activities such as the insertion of biological samples prepared shortly before launch, or the activation of an experiment. Such late access activities may be performed up to 30 minutes before the scheduled launch time.
Last update: 9 November 2010