ISRO successfully docks two satellites in space, India fourth country to achieve feat after US, Russia, China

Calling it a “historic moment”, ISRO said on X: “Post docking, control of two satellites as a single object is successful. Undocking and power transfer checks to follow in coming days.”

Docking refers to joining together two or more fast-moving objects in space. Most larger space assets, particularly those that involve two-way journeys, from and to Earth, are made of several parts that are taken one at a time and integrated in space.

Space facilities like the International Space Station, as big as a typical six-bedroom house in the United States, cannot be launched into space at one go. Similarly, spacecraft taking humans to the Moon are composed of multiple components. A part of the spacecraft has to detach and land on the Moon, and then re-integrate on the return journey.

Satellites in space move at very high speeds, thousands of kilometres per hour. For docking to happen, they have to move at exactly the same speed, so that relative to each other, they are almost stationary. Docking, thus, is an extremely complicated process requiring very high precision manoeuvres. The smallest of errors can lead to complete destruction of the satellites.

This extremely delicate manoeuvre had to be put off at least twice in the last few days because the two spacecraft, which had been launched into space on December 30 last year, were not able to achieve ideal conditions for docking.

“Congratulations to our scientists at @isro and the entire space fraternity for the successful demonstration of space docking of satellites,” Prime Minister Narendra Modi said in a post on X.

“SpaDeX has accomplished the unbelievable … and it is all (using the) indigenous Bharatiya Docking System. This paves the way for smooth conduct of ambitious future missions including the Bharatiya Antriksha Station, Chandrayaan 4 and Gaganyaan,” Union Science Minister Dr Jitendra Singh said.

The SpaDeX mission consisted of two relatively small spacecraft, called Target and Chaser, each weighing about 220 kg, that were launched together into space. They were injected with slightly different force to allow them to attain a separation of about 20 km, while keeping them in the same orbit around Earth, about 470 km from the surface.

The satellites were then brought progressively closer, in stages, before being docked together on Thursday morning. The two satellites which carry several scientific payloads will eventually be undocked and fulfil their science objectives over the next two years.