Explained: How success of SpaDeX mission is key for ISRO's ambitious space programmes

The Space Docking Experiment (SpaDeX), a pioneer mission by the Indian Space Research Organisation (ISRO), is designed to demonstrate autonomous spacecraft docking in orbit. This mission involves two satellites—SDX-01 (the Chaser) and SDX-02 (the Target)—which successfully docked on January 16. The docking was originally planned for January 7 but faced a nine-day delay before it was successfully completed. The mission, launched on December 30 last year aboard PSLV-C60 from Sriharikota, aims to test key docking and undocking technologies crucial for India's future space station and interplanetary missions.

Following the successful docking, the next step in the mission was to undock the two spacecraft around the end of January or the first week of February. However, technical challenges have now delayed the undocking process. ISRO is yet to provide specific details about the nature of these issues. Speaking about the mission status on January 29, the ISRO chairman pointed out, “We have loaded five kg of propellant on both the satellites. The propellant is needed for docking and undocking exercises. Currently, we have 60 to 70 per cent of the propellant remaining in the spacecraft. There are going to be a lot of experiments in the docking, undocking and power connection exercises, and it is not a one-time exercise.” This suggests that while the undocking is facing hurdles, ISRO has sufficient propellant for multiple attempts and related experiments.

Undocking refers to the separation of two spacecraft after docking. “Although SpaDeX is a test mission, undocking is a critical step for future real-world space missions. A failure to undock in an operational mission could jeopardize mission objectives, making this an essential part of the experiment. ISRO planned to demonstrate electrical power transfer between SDX-01 and SDX-02 before initiating the undocking process. This capability is important for future missions, where spacecraft may need to share power while in orbit,” explained space expert Girish Linganna. 

However, the undocking process has run into difficulties, reportedly due to power generation issues in both SDX-01 and SDX-02. “The power generated is not meeting the required levels, making it harder to execute planned operations. Additionally, coordinated control of both spacecraft is taking longer than expected, further delaying the separation process,” added Linganna. 

Since docking on January 16, SDX-01 and SDX-02 have been testing several cutting-edge technologies for space docking and undocking including four rendezvous and docking sensors, infrared sensors, Lidar sensors, optical cameras, radar sensors, power transfer technology, navigation based on Global Navigation Satellite System (GNSS) etc. 

As per the SpaDeX mission plan, once docking was completed, the next step was to demonstrate power transfer between SDX-01 and SDX-02 before undocking. After separation, both spacecraft were expected to operate independently for up to two years to conduct scientific experiments. “Due to technical difficulties preventing undocking, these planned experiments could now face delays or even be compromised. If SDX-01 and SDX-02 remain docked longer than planned, they may not be able to fully utilize their payloads for Earth imaging, natural resource monitoring, radiation data collection and other research activities,” remarked Linganna. 

ISRO engineers are actively working to resolve the issue as undocking is a key part of testing autonomous space operations. These operations are essential for future missions, including India’s upcoming space station, satellite servicing missions, and interplanetary exploration.