SPADEX

24 payloads on the PSLV 4th stage will perform various experiments

ISRO's Space Docking Experiment (SPADEX) mission comprises two satellites weighing 220 kg each: a Chaser and a Target. One satellite will attempt to dock with the other, testing this crucial capability for ISRO's upcoming Indian Space Station and Chandrayaan-4 missions. The demonstrated precision of the PSLV vehicle will be utilized to give a small relative velocity between the Target and Chaser spacecraft at the time of separation from the launch vehicle. This incremental velocity will allow the Target spacecraft to build a 10-20 km inter-satellite separation with respect to the Chaser within a day. At this point, the relative velocity between the Target will be compensated using the propulsion system of the Target spacecraft. At the end of this drift arrest maneuver, the Target and Chaser will be in the same orbit with identical velocity but separated by about 20 km, known as Far Rendezvous. With a similar strategy of introducing and then compensating for a small relative velocity between the two spacecraft, the Chaser will approach the Target with progressively reduced inter-satellite distances of 5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m, ultimately leading to the docking of the two spacecraft. After successful docking and rigidization, electrical power transfer between the two satellites will be demonstrated before undocking and separation of the two satellites to start the operation of their respective payloads for the expected mission life of up to two years.