In big breakthrough, Isro docks 2 SpaDeX satellites for 2nd time

BENGALURU: Isro successfully managed to dock the two Space Docking Experiment (SpaDeX) satellites — chaser and target — for the second time late Sunday, an accomplishment that would give the space agency data to further better its technology in the future.
V Narayanan, chairman, Isro, told TOI: “This is a significant achievement and further activities are being planned now.” Stating that the docking operation was “smooth” he said his team managed to do it as if it were “child’s play”.
Late Monday, Isro said that a day after the second docking was accomplished at 8.20pm Sunday, it also completed the power transfer.
“...Subsequently, power transfer from SpadeX satellite-2 to satellite-1 as well as vice versa was also exercised and accomplished on April 21. The experiment involved operating a heater element in one of the satellites through power from the other satellite. The duration of power transfer was approximately 4 minutes and the performance of the satellites was as expected,” Isro said.

In the second docking attempt, the docking was completed with full autonomy from an inter-satellite distance of 15m till docking, whereas in the first docking attempt, an additional hold point was manually exercised at an inter-satellite distance of 3m.
“The second docking experiment was preceded by detailed ground simulations and on-orbit trials incorporating the experience gained from first docking & undocking experiments, thereby providing immense confidence for the second docking demonstration,” Isro said.
It added that the demonstration of the fully autonomous second docking along with power transfer marks the completion of an important milestone in the SpaDeX mission.
Earlier in the day, Union minister Jitendra Singh had said more experiments are planned “in the next two weeks”.
The PSLV-C60, carrying the two SpaDeX satellites was launched on Dec 30, 2024. Thereafter, the satellites were successfully docked for the first time on Jan 16 at 6.20am, and the successfully undocked on March 13, 2025, at 9.20am.
According to sources, the second docking was carried out “more precisely than the first attempt”. “These are important lessons,” one of them said.
Between the undocking on March 13 and the second docking operation Sunday, Isro had carried out a “rolling” or “rotating” experiment — in the last week of March, which was first reported by TOI. At the time, Narayanan, while confirming the success of the operation, had said that more docking experiments were in store.
The TOI had reported soon after the first docking operation that Isro would attempt more docking experiments using the same satellites. In late March, Narayanan had reiterated that and told TOI: “...The satellites have a lot of propellant… I have only told [the teams] one thing, please do everything [on] simulation on ground [first]. Let us be very careful. Let us not make any mistakes as a wealth of data can be generated [through various experiments].”
The rolling experiment, which was likened to the Chandrayaan-3 “hop” experiment the space agency conducted on Moon in terms of learning it provides for future missions, helped Isro validate multiple softwares, ground station control and more.
Isro’s first docking on Jan 16 was only the first step towards Isro mastering the rendezvous and docking technology critical for several future missions, including the Chandrayaan-4 sample return mission to the Moon and human spaceflight missions part of the extended Gaganyaan programme.
And, the second docking is another step. Isro would still need to dock in various conditions, some of which will be attempted as part of the current mission. The space agency is expected to conduct more docking as part of SpaDeX