Nearly two months after the Indian Space Research Organisation (ISRO) successfully demonstrated its docking capability, it disengaged and undocked the two satellites, SDX01 and SDX02, at 9.20 am Thursday. This capability is essential for future ISRO missions such as exploring the Moon, human spaceflight, and building its own space station. The two satellites, SDX01 (Chaser) and SDX02 (Target), are now moving around independently in orbit. For the undocking process, the SDX02 arm connecting the two satellites was extended, the capture levers released, and then the two satellites were given the command to separate. With this manoeuvre, ISRO successfully demonstrated critical capabilities like rendezvous, docking and undocking, making India the fourth country after the United States, Russia and China to possess such capability. Asked why the manoeuvre was carried out nearly two months after docking, ISRO officials said: “This is the first time we are attempting these capabilities, we did not want to go wrong at all. We were studying everything before carrying out the undocking manoeuvre.” The space agency may carry out further docking and undocking experiments to improve precision. In a statement, ISRO said: “Exhaustive ground simulations and analysis were the cornerstone of achieving the undocking in the first attempt itself. Various tests replicating in-orbit conditions were meticulously planned and carried out in preparation for the earliest opportunity for undocking operations.” The window for carrying out the undocking manoeuvre was between March 10 and 25. The Space Docking Experiment (SpaDeX) mission saw two small 220-kg satellites being brought together in the same orbit, then progressively brought near each other, before finally being joined early January 16. ISRO also demonstrated power sharing and the capability to give command to both the satellites as a single composite. The capability is essential for several large, complex missions that ISRO has planned. For Chandrayaan-4, the next lunar mission which will bring back samples from the surface of the Moon, ISRO will need to carry out two dockings – one in the Moon orbit and one in the Earth orbit. After landing on the Moon and collecting the samples, the ascender module will fly back to the transfer module waiting in the lunar orbit. The transfer module will carry the samples back to the Earth orbit where it will meet the separately launched re-entry module capable of withstanding the heat of re-entry into the Earth’s atmosphere. The Bharatiya Antariksha Station, which the space agency plans to build by 2035, will comprise five modules that will be launched separately and joined in space to create the space station. The International Space Station also utilises the same mechanism to transport astronauts as well as supplies. Importantly, ISRO developed its own Bharatiya Docking System for the experiment. It is on the lines of the International Docking System Standard used by spacecraft going to the International Space Station. The system is androgynous – 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 has two.
