India's Space Prowess Soars: ISRO's SpaDeX Mission marks new era in satellite docking technology

A few days after bringing the satellites as close as 3 meters to each other, the Indian Space Research Organisation (ISRO) successfully docked the SpaDeX satellites on Thursday (16th Jan)  according to sources.

ISRO proudly announced the achievement on the social media platform X, saying: “Spacecraft docking successfully completed! A historic moment.” They explained the steps of the SpaDeX docking process as follows: 

1. The spacecraft was carefully maneuvered from 15 meters to a hold point 3 meters away.  

2. Docking was then started with precise alignment, allowing the spacecraft to connect successfully.  

3. After connection, the spacecraft smoothly retracted to ensure a firm hold.  

4. Finally, the system was locked in place to make it stable.  

This marked the successful completion of the docking process.

ISRO had earlier missed two planned docking dates, January 7 and January 9, because of technical problems. The satellites were launched by the space agency on December 30.

On January 12, ISRO announced that they had successfully conducted a trial to bring the two satellites closer. They managed to first reduce the distance to 15 meters and then further down to 3 meters.ISRO stated that the spacecraft were moved back to a safe distance, and the docking process would be carried out after further analysis of the data.

What is Docking?

Docking is the process of bringing two spacecraft, moving at high speeds, into the same orbit. Once aligned, they are carefully brought closer to each other, either manually or automatically, and then connected. This skill is essential for missions that involve large spacecraft, which cannot be launched by a single rocket due to weight limitations.

What is the reason behind India undertaking a docking mission at this time?

ISRO has big plans for the future, including building a space station by 2035 and sending humans to the moon by 2040. To achieve these goals, they are developing important technologies, like a powerful new rocket that can carry up to 30 tonnes of cargo into low Earth orbit, which is up to 2,000 km above the Earth.

These missions will need the ability to dock spacecraft in space. For instance, the Bharatiya Antariksh Station will be assembled in orbit by connecting five separate modules. The first module, which will be robotic, is planned to launch in 2028.

What is expected to take place during the docking test?

The docking test will involve a series of steps to gradually move the Chaser satellite (SDX01) closer to the Target satellite (SDX02).

The satellites will slowly move closer to each other, stopping at distances of 5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m. In the final step, the rings on both satellites will touch and connect. Once connected, the rings will be pulled back and locked securely in place.

After connecting, the satellites will share electrical power. ISRO scientists will also show how they can control both satellites as if they are one. Once this is successful, the satellites will separate and move apart. They will stay in space and carry out experiments for the next two years.

What is the design of India’s docking mechanism?

Over the years, different space agencies have used various types of docking systems, some of which can work together. Spacecraft traveling to the International Space Station use the International Docking System Standard. India, however, is using an androgynous docking system.

This means that the docking systems on both the Chaser and Target satellites are exactly the same, making them compatible with each other. It works in a way similar to the International Docking System Standard (IDSS), which is used by other space agencies. However, India’s system is simpler and uses only two motors, while the IDSS uses 24 motors to control its movements. These motors help guide and align the spacecraft during docking, so having fewer motors makes India’s system more efficient and less complex as reported by Indian Express 

The mission will use advanced sensors like the Laser Range Finder, Rendezvous Sensor, and Proximity and Docking Sensor to make accurate measurements as the two satellites move closer and connect. It will also use a new processor, similar to those in satellite navigation systems, to figure out the position and speed of the other satellite.

This is an important step toward fully automatic systems for future missions, where spacecraft will be able to dock on their own without relying on navigation data from satellites.

(The author of this article is an award-winning Science Writer and a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach Girish Linganna at: girishlinganna@gmail.com)

(Disclaimer: The views expressed above are the author's own and do not reflect those of DNA)