BENGALURU: Isro’s ambitious Space Docking Experiment (SpaDeX) mission, which is scheduled to do the docking manoeuvre on January 7, will see the two satellites perform a carefully choreographed orbital dance before attempting to dock with each other.
And here’s how:
The launch has given a small difference in velocity between the satellites. At 10m/s rate, this distance will further grow and the satellites will grow apart by about 20km, as early as by the evening of December 31.
Once the satellites reach this separation, Isro will begin controlling their relative positions.“We’ll start using the onboard propulsion systems on one of the two satellites to arrest the drift so that we maintain the 20km distance between the two satellites,” M Sankaran, director, UR Rao Satellite Centre (URSC), said, explaining the intricate sequence of events that will unfold.
And like twins, the satellites will go around in the same orbit with the same speed. The mission timeline includes a four-day waiting period to achieve optimal solar orientation, crucial for generating sufficient power during the docking procedure.
“At this point again, we’ll initiate the drift of the two satellites. So that the 20 km distance is progressively reduced to 5km, 1.5km and so on. And after we reach 5km, we’ll enable the inter-satellite radio frequency (RF) link so that the satellites talk to each other and exchange their own position, attitude, etc, which’ll enable us to evaluate the software logics,” Sankaran said.
Several new sensors developed by the Laboratory For Electro Optics Systems (LEOS) in Bengaluru will be evaluated for their fitness for initiating the docking sequence, which will start once the inter-satellite distance is reduced to 1.5km, utilising three different guidance algorithms.
The docking mechanism involves a “hugging” action. “The final approach will be particularly delicate. With a constant velocity of about 10mm/s, the chaser satellite will go and enter into the target satellite. The latches will be released and clamps on both sides will try to grab each of the satellites,” Sankaran added.
…And once they hold each other together, the ring which has been extended on the chaser satellite will be retracted so that the target satellite will be pulled towards the chaser satellite and the two will become as a single unit.
Once docked, the satellites will demonstrate power transfer capabilities, with electricity flowing from one satellite to the other to power a heater, confirming successful connection. The combined unit will then be controlled by a single satellite’s control system, demonstrating technology crucial for future space station operations, including India’s planned Bharati Antriksh station.
The SpaDeX mission represents a long journey from concept to reality. “This work, as a thought experiment, started around 1989 and at the time, nobody thought that this was required for us, but the tenacity was there. When the project was approved in 2016, we were able to realise it over several years,” Sankaran said.
The mission has required extensive preparation and testing. Isro developed several testbeds to validate the mechanism as well as the docking sequence, the sensors, etc. It has been a combined effort of so many people across Isro centres and the industry,” noted Sankaran.
The successful completion of this mission would mark a significant milestone in India’s space capabilities, particularly in developing technologies necessary for future space station operations and satellite servicing missions. The ability to dock spacecraft in orbit is a crucial capability possessed by only a few space-faring nations, and India is now on the cusp of joining this elite group.
