BENGALURU: The Indian Space Research Organisation (ISRO) on Thursday recorded its first successful undocking as part of the Space Docking Experiment (SpaDeX) mission. The two light weight satellites, SDX-01 (the chaser) and SDX-02 (target) successfully separated almost a month-and-a-half after it was supposed to be achieved.
With this success, ISRO is now bracing for its future missions — Chandrayaan-4, Bhartiya Antriksh Mission, the manned space mission Gaganyaan, and Man on Moon mission. Most of these would require the docking and undocking procedures in which one satellite or spacecraft attaches or detaches from the other.
SDX-01 and SDX-02 had autonomously docked on January 16, nine days after the initial plan of docking on January 7. Subsequently, the undocking of these satellites — which was planned to happen by January-end or February first week — got delayed due to technical issues.
Although the successful undocking happened at around 9.20 am, ISRO announced on social media platform ‘X’ only at 12.21 pm, after assessing all the parameters.
The two satellites had remained docked since January 16. ISRO scientists had then said the power generation in the two spacecraft was not matching the requirements and the composite control of both was taking time, due to which undocking could not be done earlier.
ISRO resolved these issues when the two satellites remained docked all these days, and all required exercises were completed, including power transfer technology, inter-satellite communication and transfer of energy. The information obtained from each of the autonomous satellites were successfully relayed to the other before undocking the two satellites on Thursday morning when the energy availability was in full capacity, the scientists said.
Another ISRO scientist, who did not prefer to be named, said there were certain technical issues that were being analysed when they remained docked, so they were in a better position to do the next docking smoothly. “Since there were issues in the angling and during the docking earlier, we wanted to be sure this time.
This is the reason why we did not try to undock earlier. As in the future we will be sending a 9,200 kg satellite on the Chandrayaan-4 mission, we want to be sure that there will be no errors then.” he said.
ISRO Chairman V Narayanan explained to The New Indian Express that the delayed undocking was also due to the fact that they get 15 days’ time once in two months (March 10-March 25) to do the docking/ undocking procedures.
“While there were some issues during docking, we were cautious before undocking the two satellites, and it was done successfully in the first attempt. The next docking is planned after a month (in April),” he said.
ISRO scientists explained that the undocking of SDX-01 from SDX-02 took place in the 460km circular orbit at a 45 degree inclination. The two satellites are now orbiting independently and are in good condition. Images from both the satellites are being taken and relayed.
While assessing the satellites, the days between March 10 and 25, 2025 were found ideal for undocking and it was done on March 13, 2025. The operations were monitored from their ground stations in Bengaluru, Lucknow and Mauritius.
Narayanan said independent operations of the two satellites will be studied. Functions of their sensors, lens, cameras, propulsion systems and other components are being analysed. “We have sufficient propellant to undertake more docking and undocking experiments,” he added.