ISRO SpaDeX mission: What does docking in space mean?

With the launch of the SpaDeX Mission, India is pacing to become the fourth nation after the US, Russia, and China to master space docking. Space-docking capabilities are essential for the Indian space industry. They are a stepping stone towards future human spaceflights, the Chandrayaan-4 mission, and the building of Bharatiya Antariksh Station (BAS).

The Indian Space Research Organisation (ISRO) launched the SpaDeX mission late December 30. It is now expected to demonstrate in-space docking using two 220-kg satellites — Chaser and Target — in a low-Earth circular orbit. The docking process is likely to be attempted on January 7, Isro Chairman S Somanath said on Monday.

But what does docking mean?

Have you heard about the International Space Station (ISS)? It's like a home for humans in space. The US has launched multiple spacecraft carrying humans into space and carried out months-long missions in microgravity at the ISS while their spacecraft remained "docked" at the space station.

Two space objects coming and joining together for a purpose is called ‘docking’.

"Docking" happens when a spacecraft can manoeuvre and attach to a space station by itself. The National Aeronautics and Space Administration defines docking as “mating operations where an active vehicle flies into the mating interface under its own power”.

Meanwhile, ISRO explains that in-space docking technology is useful when multiple rockets are launched into space to achieve common mission objectives.

ISRO Chairman Somanath also explained the meaning and purpose of docking in an interview. He said, “When you have multiple objects in space, and we need to bring them together for a specific purpose, we need a mechanism called docking.”

He said docking can be done through various approaches: soft mechanisms, hard mechanisms, or pressurised compartments for human transfer (it's done for human transportation from one spacecraft to another).

"For example, on the International Space Station, when a crew module connects to the station, you equalise the pressure, and transfer people," Somanath said.

The ISRO chief further said that initially, a mechanism comes and connects, and later, a sealed connection is established. "Suppose you want to build a space station. Not everything is launched in one go. Modules go one after the other. They are connected to each other to build a long, big, complex space station," he said.

One of the objects of Isro's SpaDex mission is to demonstrate this docking process on January 7. The mission will dock two satellites in space (Chaser and Target).

What to look out for in SpaDeX mission

Somanath said that in the SpaDeX, Isro aims to replicate the technology needed for the docking process. He talked about the key things Isro is looking for in the SpaDex mission. These are:

1. Mechanism - how to connect two objects and rigidize them to make an integral body.

2. How to control it after it has become integrated.

3. How to have a set of sensors which will enable these objects in autonomous docking.

4. How to handle failures, if it fails to dock properly.

6. Disconnect the two spacecraft whenever needed.

Why is a docking system important?

India needs a docking system for its future missions. Somanath said SpaDex is important because building complex systems in space requires connections to be made.

"So how do we connect objects in space? And connections can't happen in the same way it happen on ground because they are moving at tremendously high speeds. When objects move at very high speeds, doing maneuverers requires finesse, requires good control system, good sensors, the algorithm, the software must be good. We are testing all of this in space," Somanath told India Today TV.