SRE-1 was designed to demonstrate the capability to recover an orbiting space capsule, and the technology of an orbiting platform for performing experiments in microgravity conditions. It was also intended to test reusable Thermal Protection System, navigation, guidance and control, hypersonic aero-thermodynamics, management of communication blackout, deceleration and flotation system and recovery operations. The information obtained from this technology and experiment is being applied to the design of India's Gaganyaan crewed orbital capsule.
Design
SRE-1 is a 555 kg capsule. It comprises aero-thermo structure, internal structure, Mission Management Unit, Altitude sensors and Inertial measurement unit, S-band transponder with unique belt array antenna embedded to ATS, power and electronics packages to support deceleration and flotation system. It also houses two microgravity payloads. It has a sphere-cone-flare configuration with a spherical nose of about 0.5 m radius, base diameter of 2 m and 1.6 m height. The parachute, pyro devices, avionics packages of triggering unit and sequencer, telemetry and tracking system and sensors for measurement of system performance parameters are placed inside the SRE-1 capsule. Parachutes for SRE capsule were provided by ADRDE. To withstand the heat of re-entry, the cone-shaped SRE-1 has a Thermal protection systemcomposed of 264 silica tiles of 14 different types over conical surface, and an ablative nose cap of carbon-phenolic composite. ISRO is also working on technology to manufacture carbon-carbon composite TPS, which, along with the silica tiles tested with the SRE-1, could find use in future reusable spacecraft such as ISRO's planned Reusable Launch Vehicle.
Re-entry
SRE-1 was traveling around the earth in a circular polar orbit at an altitude of 637 kilometers. In preparation for its reentry, SRE-1 was put into an elliptical orbit with a perigee of 485 kilometers and an apogee of 639 kilometers by issuing commands from the spacecraft control centre of ISTRAC at Bangalore on January 19, 2007. The critical de-boost operations were executed from SCC, Bangalore supported by a network of ground stations at Bangalore, Lucknow, Sriharikota, Mauritius, Biak in Indonesia, Saskatoon in Canada, Svalbard in Norway besides shipborne and airborne terminals. On January 22, 2007, the re-orientation of SRE-1 capsule for de-boost operations commenced at 08:42 am IST. The de-boost started at 09:00 am with the firing of on-board rocket motors and the operations were completed at 09:10 am. At 09:17 am, SRE-1 capsule was reoriented for its re-entry into the dense atmosphere. The capsule made its re-entry at 09:37 am at an altitude of 100 kilometers with a velocity of 8 km/s. During its reentry, the capsule was protected from the intense heat by carbon phenolic ablative material and silica tiles on its outer surface. By the time SRE-1 descended to an altitude of 5 km, aerodynamic braking had considerably reduced its velocity to 101 m/s. Pilot and drogue parachute deployments helped in further reducing its velocity to 47 m/s.
Splashdown and recovery
The main parachute was deployed at about 2 km altitude. SRE-1 splashed down in the Bay of Bengal with a velocity of 12 m/s at 09:46 am IST. The flotation system, which was immediately triggered, kept the capsule afloat. Recovery operations were supported and carried out by the Indian Coast Guard and Indian Navy using ships, aircraft and helicopters.
Experiments and results
During its stay in orbit, the following two experiments on board SRE-1 were successfully conducted under microgravity conditions.
The second experiment, jointly designed by National Metallurgical Laboratory, Jamshedpur and ISRO Satellite Centre Bangalore, studied the synthesis of nano-crystals under microgravity conditions. This was an experiment in designing biomaterials that better replicate natural biological products. The experimental results have yet to be analysed.
Performance of Silica TPS tiles in conical region of capsule was satisfactory and tile surfaces were found intact with some minor handling related damage during recovery operations. The spacecraft remained afloat for approximately 2 hours in seawater before recovery, causing minor cracks and seawater deposits on tile surfaces.
