BENGALURU: ISRO’s ambitious Space Docking Experiment (SpaDeX) mission is set to perform a historic rendezvous and docking maneuver on January 7. The mission will involve two satellites executing a meticulously planned orbital “dance” before attempting to dock with one another.
Here’s how the operation will unfold:
The launch will initiate a small velocity difference between the two satellites. At a rate of 10 m/s, this differential will cause the satellites to drift apart by approximately 20 km, starting as early as the evening of December 31. Once this separation is achieved, ISRO will begin adjusting their relative positions.
“We’ll activate the onboard propulsion systems on one of the satellites to control the drift and maintain a 20 km distance between the two,” explained M. Sankaran, Director of ISRO’s UR Rao Satellite Centre (URSC). This marks the beginning of a highly intricate sequence of events.
The two satellites will then orbit in tandem, moving at the same speed and along the same trajectory. A four-day waiting period is built into the timeline to ensure optimal solar orientation, which is critical for generating the necessary power during the docking process.
“At this stage, we will begin closing the gap between the two satellites, reducing the distance from 20 km to 5 km, then to 1.5 km, and so on. When the separation reaches 5 km, we will activate the inter-satellite radio frequency (RF) link, allowing the satellites to communicate and exchange data such as position and orientation,” Sankaran explained. This exchange will help assess the software’s performance and refine the docking strategy.
Several new sensors developed by ISRO’s Laboratory for Electro-Optics Systems (LEOS) in Bengaluru will be tested to evaluate their readiness for initiating the docking sequence. Once the distance between the satellites reduces to 1.5 km, three distinct guidance algorithms will take over to ensure a precise approach.
The docking process itself is likened to a “hugging” action. “The final approach will require great delicacy. The chaser satellite will move towards the target satellite at a constant speed of just 10 mm/s. Upon contact, the latches will release, and clamps on both sides will engage to secure the satellites,” Sankaran detailed.
Once the satellites are locked together, a ring extended from the chaser satellite will retract, pulling the target satellite towards the chaser. At this point, the two satellites will become a single, unified system.
Following the successful docking, the satellites will demonstrate power transfer capabilities. Electricity will flow from one satellite to the other to power a heater, verifying that the connection is stable. The combined unit will then be controlled by the control system of one satellite, marking a crucial milestone for future space station operations, including India’s planned Bharati Antriksh station.
The SpaDeX mission represents a major leap in ISRO’s journey from concept to execution. “This idea, initially conceived as a thought experiment in 1989, was once considered unnecessary. But through persistence, we managed to realize it. The project was formally approved in 2016, and after years of development, we’re now on the verge of making it a reality,” Sankaran reflected.
The mission has required extensive preparation and rigorous testing. ISRO developed multiple testbeds to validate the docking mechanisms, sensors, and overall sequence. “This is the result of a collective effort from numerous ISRO centers and industry partners,” Sankaran noted.
A successful docking will not only mark a significant milestone in India’s space capabilities but will also position the country as one of the few nations capable of performing in-orbit spacecraft docking. This technology is essential for future space station missions and satellite servicing, bringing India closer to joining an elite group of space-faring nations.
