Docking Chaser and Target: Why it is a historic milestone

Imagine aligning/joining objects while moving at a mind-boggling speed of “roughly 28,800 km/h” on land, let alone in harsh, extreme environments of space. 

This is basically what the Indian Space Research Organisation (ISRO) achieved on Thursday when it successfully docked two fast-moving satellites—Chaser and Target—launched under its space-docking experiment, SpaDeX.

The docking made India the fourth country in the world (after the United States, Russia and China) to have this capability.

On Friday, China congratulated ISRO for the success in space.

ISRO on December 30 had launched two spacecraft — SDX01 (Chaser) and SDX02 (Target) — in a low-earth circular orbit and later set them apart at a distance of around 20 km in space.

Mastering the capability of docking is crucial for India’s future in space explorations like setting up a space station and landing an astronaut on the moon.

It enhances capabilities for long-duration space travel, a reason why there is so much more to the major scientific feat on Thursday.

It also enables India to participate in collaborative projects with other countries.

Docking—what does it mean?

Docking is a word largely used in shipping. If a ship docks, it sails into a port and stops at the dock.

In terms of space, it means sending modules separately and joining the separate free-flying, fast-moving man-made objects there.

The technology is essential when multiple rocket launches are required to achieve common mission objectives and requires extreme precision and calibration. 

Bringing together two spacecraft travelling at a speed of thousands of kilometres per hour and then joining them together securely is no ordinary feat.

In the near-earth orbit, SDX01 and SDX02 are moving at a speed of roughly 28,800 km/h, as per scientists.

Understanding SpaDex and difficulties  

SpaDeX or Space Docking Experiment is the twin satellite mission developed by ISRO to mature technologies related to orbital rendezvous, docking, human spaceflight, in-space satellite servicing and operations requiring proximity in space.

Chaser and Target were launched as co-passengers aboard a dedicated Polar Satellite Launch Vehicle on December 30, 2024.

The successful docking on January 16 came after a couple of unsuccessful attempts.  

A day ahead of the docking planned on January 9, ISRO initiated the drift on Chaser to move closer to Target from 500 m to 225 m. 

The operation was postponed as the drift was found to be more than expected.

Then on January 12, the two satellites were brought as close as 3 metres from each other, but then moved away following signal issues.

Experts say the “drift anomaly” which delayed the docking may have been due to “some issue with on-board sensors on Chaser and Target. However, ISRO scientists demonstrated their capability by rectifying it. Manual manoeuvring was also done remotely for the docking to happen.

Meanwhile, the use of Bhartiya Docking System (BDS), indigenous technology developed and patented by ISRO, made it even more special. 

Earlier, unsuccessful attempts were made to import docking technology from abroad.

The next step—the future

In-space docking capability is the basic requirement for the future of ambitious missions like Chandrayaan-4, Gaganyaan and setting up of the Bhartiya Antriksh Station, say experts.

There is a long way to go and next ISRO would have to demonstrate capability of transferring energy—another important step for space  missions.

Gaganyaan is a crewed orbital spacecraft intended to be the formative spacecraft of the Indian Human Spaceflight Programme. 

Chandrayaan-4 is a planned lunar sample return mission and the fourth iteration in its Chandrayaan lunar exploration programme.

Bharatiya Antariksha Station is a planned modular space station.

They will all be equipped with rendezvous and docking capabilities.

Experts say the next focus should or would be to carry on more docking and undocking experiments and gain capability in transferring men, energy and material from one spacecraft to another.

The capability is critical for setting up a space station and launching lunar and manned space missions.