BENGALURU: As the Indian Space Research Organisation (ISRO) successfully docked two low-orbit satellites — SDX-01 and SDX-02 (Target and Chaser) -- as part of the Space Docking Experiment (SpaDeX) on Monday morning, scientists said there is no time to relax as challenges are still on.
The scientists are now monitoring the transfer of energy from one satellite to the other. “This work is more crucial than docking and undocking. The success and progress of transfer of energy, which is also one of the parts of the experimental mission, will decide the future course of action of ISRO’s missions,” ISRO sources said.
“The exercise of switching off the energy of one satellite and using solar energy to transfer power to the other satellite and vice-versa is being done. A continuous supply of power and then a sudden stop and its impact also needs to be studied. There is no time limit for the experiments as the two satellites can live for 10-15 years. There is abundant solar energy and sufficient fuel in the satellites for docking and undocking. However, efforts are being made to ensure there are no errors,” the sources said.
ISRO Chairman N Narayanan said that while docking and undocking did not happen in the first attempt during the first trials, it was a success in the first attempt in the second trial.
“Work on transfer of energy from one satellite to the other started from Monday morning. The next undocking will not happen immediately. We will wait for some time before working on the next course,” he said and added that with 50% fuel capacity available, all caution is being exercised.
ISRO sources said the SpaDeX mission and now the exercise of transfer of energy is more crucial and difficult because the spacecraft are small. “These are 220kg, low-orbit satellites and are not easy to handle.
The management has been given full freedom to work with the spacecraft and take time in completing all mission exercises through controlled and uncontrolled panels,” the sources said. ISRO launched the mission in December 2024 with SDX-01 and SDX-02 on PSLV-C-60 into the 470 km circular orbit at 55 degree inclination with a time difference of 66 days. The first docking was on January 16, 2025 and they were undocked on March 13, 2025.
ISRO on Monday shared that the second docking experiment too was a success and it happened at 8.20pm on April 20. ISRO also completed the power transfer from SDX-02 to SDX-01 satellite as well as vice-versa 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 four minutes and the performance of the satellites was as expected.The scientists added that in the second attempt, the docking was completed with full autonomy from an inter-satellite distance of 15 metres till docking, whereas in the first docking attempt, an additional hold point was manually exercised at an inter-satellite distance of 3 metres.