ISRO likely to attempt undocking of satellites today; will conduct docking experiment again

On January 16, India became the fourth country in the world — after the United States, Russia and China — to successfully dock two satellites in space. Isro had to postpone the docking experiment at least twice — on January 7 to carry out more simulations on the ground and on January 9 when the satellites drifted more than expected during one of the manoeuvres.

Docking is a process by which two fast-moving satellites or spacecrafts are brought together and joined in orbit. It is essential for missions that require big payloads that cannot be carried to the orbit in a single launch.

During the feat, two small 220-kg satellites were brought within a distance of 3 metres of each other in orbit, their extended rings were joined with each other, retracted, and locked in space. The space agency also demonstrated sending commands to both the satellites as one composite spacecraft.

Afterwards, the satellites were moved away to a safe distance before the space agency brought them to a distance of 3 metres of each other on January 12. At this point, the on-board cameras could clearly see the two satellites. The docking, however, was not attempted and the satellites were moved back. The space agency then studied the data and re-attempted docking later.

India required docking capability for its planned Chandrayaan-4 missions that will bring back lunar samples, its own Bharatiya Antariksh Station, and a mission to take an Indian to the Moon by 2040. Take for example, the Bharatiya Antariksh Station, which is planned to be constructed by bringing together five modules, the first of which is scheduled to be launched in 2028.

The Chandrayaan-4 mission will also see samples being brought from the Moon in a transfer module which will dock with the re-entry module waiting for it in Earth orbit. The re-entry module would be designed to withstand the heat when the spacecraft enters Earth’s atmosphere.

Significantly, the mission has utilised an indigenous Bharatiya Docking System. The docking mechanism being used by India is on the lines of the International Docking System Standard used by spacecrafts going to the International Space Station. The system is androgynous — meaning the systems on both the Chaser and Target satellites are identical. However, instead of the 24 motors used in the International Docking System Standard, the ISRO system had two.