How Isro pulled off ‘historic’ feat of docking two satellites

In a historic moment, the Indian Space Research Organisation (Isro) Thursday (January 16) successfully docked its Space Docking Experiment (SpaDeX) satellites in space. The Indian space agency shared the update on X, saying spacecraft docking was “successfully completed”.

“Let’s walk through the SpaDeX docking process: Manoeuvre from 15m [metre] to 3m hold point completed. Docking initiated with precision, leading to successful spacecraft capture. Retraction completed smoothly, followed by rigidisation for stability. Docking successfully completed,” Isro tweeted.

SpaDeX Docking Update:

🌟Docking Success

Spacecraft docking successfully completed! A historic moment.

Let’s walk through the SpaDeX docking process:

Manoeuvre from 15m to 3m hold point completed. Docking initiated with precision, leading to successful spacecraft capture.…

— ISRO (@isro) January 16, 2025

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Prime Minister Narendra Modi congratulated Isro for the feat. “It is a significant stepping stone for India’s ambitious space missions in the years to come,” he wrote on X.

India has become the fourth country to have achieved an unmanned docking in space. With this, Isro has taken a giant step ahead for future space endeavours.

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Let’s take a look at how the SpaDeX mission was conducted and why it is significant.

What is docking?

Docking is a process wherein two spacecraft are brought to the same orbit to join them together.

This is needed for missions that require heavy spacecraft that may not be lifted off with a single launch vehicle, as per an Indian Express report.

Docking can be used to set up a space station as well as to carry crew and supplies to it.

Isro’s SpaDeX mission

On December 30, 2024, Isro launched the SpaDeX mission, with two small 220 kg spacecraft blasting off from the Satish Dhawan Space Center in Andhra Pradesh’s Sriharikota aboard the PSLV-C60 rocket.

The two satellites, called Target [SDX02] and Chaser [SDX01], were injected into a circular 450 km orbit. They then drifted away from each other at a distance of around 20 km in space for the docking experiment, which was initially to take place on January 7.

However, Isro announced on January 6: “The SpaDeX docking scheduled on 7th is now postponed to 9th. The docking process requires further validation through ground simulations based on an abort scenario identified today.”

On January 8, the space agency said it had “initiated the drift on the spacecraft to move closer from 500 m to 225 m”. It declared later that day that the docking had been delayed due to a technical issue.

“The drift has been arrested and spacecrafts put in a slow drift course to move closer to each other. By tomorrow, it is expected to reach initialisation conditions,” Isro said in a statement on January 9.

The Indian space agency said Sunday (January 12) that it successfully carried out a trial attempt to bring the Chaser and Target satellites three metres closer to each other. They were then moved apart to a “safe distance.” Isro described it as an “exciting handshake” of the two satellites in space.

SpaDeX Docking Update:

SpaDeX satellites holding position at 15m, capturing stunning photos and videos of each other! 🛰️🛰️

#SPADEX #ISRO pic.twitter.com/RICiEVP6qB

— ISRO (@isro) January 12, 2025

On Thursday, Isro announced that the docking process of the SpaDeX satellites was successful. In another post, it said, “Post docking, control of two satellites as a single object is successful. Undocking and power transfer checks to follow in [the] coming days.”

The space agency kickstarted the final docking manoeuvre after the two satellites were just 3 metres away from each other. As per Indian Express, the extended rings on both spacecraft would have joined, retracted and locked in place.

“Latches on both spacecraft will be released, and clamps will engage to secure a firm connection. Throughout this process, the thruster systems on both spacecraft will work in concert to maintain stability and prevent any unintended collisions. The Target satellite is equipped with a special docking mechanism that complements the Chaser’s, ensuring a secure and reliable connection,” space expert Girish Linganna told The Week previously.

Once the spacecraft are linked, they will demonstrate the transfer of electric power between them. “This capability is essential for future missions involving in-space refuelling, repairs, or the assembly of larger structures. Following the docking and power transfer demonstration, the spacecraft will undock and continue with their independent mission objectives, which include conducting scientific experiments using their onboard payloads,” Linganna added.

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Why it matters

India has joined an elite group of nations that have achieved space docking. Until now, only the United States, Russia, and China had developed and tested the docking capability.

This technology is critical for India’s future space endeavours. Isro is likely to use the docking capability for the Chandrayaan-4 mission, which will entail carrying lunar samples back to Earth.

Docking will also be needed for establishing the Bharatiya Antariksh Station, which will be built by bringing together five modules in space. The first module is expected to be launched in 2028.

It will also advance India’s ambition of sending a human to the Moon by 2040.

With inputs from agencies