Only three countries in the world – United States, Russia, and China – have the ability to carry out docking of two spacecraft or satellites in outer space. India is now on the cusp of achieving that feat as ISRO’s last mission of 2024 – named SpaDeX – lift-off from Andhra Pradesh’s Sriharikota at 2200 hrs (10 pm) IST.

SpaDex is short for Space Docking Experiment. This involves an experimental docking, subsequent interlocking and pressure checks, and undocking of two satellites. The mission is important for ISRO’s future moon missions, including Chandrayaan 4. It is also particularly important for India’s plan to set up its own space station.

In October this year, the government had announced that India will have its own Space Station called the Bharatiya Antriksh Station by 2035.

ISRO’s PSLV-C60 carrying SpaDeX and its payloads, lifts off from the first launch pad at Satish Dhawan Space Centre, in Sriharikota

So far, there are two other space stations – the International Space Station, built by the United States (NASA) and Russia (Roscosmos). The US side of the ISS is built by NASA and European Space Agency or ESA. The second space station is being built by China, and is called the Tiangong Space Station. India aims to set up the third.

Every time astronauts or cosmonauts are sent to space, especially the International Space Station, the shuttle or capsule they travel in needs to perform a docking manoeuvre. Only after the docking procedure is complete, and the two objects are securely interlocked, can the astronauts get into the pressurised cabin of the space station.

ISRO’S DOCKING EXPERIMENT EXPLAINED WITH THE HELP OF ‘INTERSTELLAR’

Docking in space is one of the most difficult and complicated procedures – the slightest of errors can lead to a catastrophe – an example of which was shown in the epic sci-fi movie Interstellar – where Cooper and the crew had to navigate a near-impossible and heart-pounding docking scenario after a minuscule error by Dr Mann sends the Endurance space station into an uncontrolled spin due to a catastrophic decompression. The scene highlights a complex docking manoeuvre.

Just like in the movie, where there was a Lander spacecraft and a Courier spacecraft, ISRO’s mission has two spaceships – the Chaser (SDX01) and the Target (SDX02), each weighing 220 kilograms. As the names suggest, the aim of the mission will be for the chaser to chase the target while both are orbiting Earth at a high speed and dock with it expeditiously.

ALL ABOUT ISRO’S SPADEX MISSION

The SpaDex mission lift-off at 2200 hrs (10 pm) IST on December 30 from the Satish Dhawan Space Centre in Sriharikota, Andhra Pradesh.

ISRO’s launch was onboard the workhorse PSLV-C60 rocket, which put the two spacecraft in low-Earth orbit, roughly 475 km above the Earth’s surface. The inclination of the two spacecraft will be at 55 degrees facing the Earth. After being deployed in a circular orbit, the two spacecraft will grow apart by around 20 kilometers over 24 hours. The scientists will first carry out several other experiments under the POEM-4 mission – a parallel mission to SpaDex (explained below).

The scientists sitting at ISRO’s mission control in Bengaluru are expected to initiate the intricate and precise docking and undocking manoeuvre in the later half of the first week of January. If successful, India will create history by becoming only the fourth nation in the world to possess such technological ability.

According to ISRO, the main objectives of the SpaDeX mission include:

• To develop and demonstrate the technology needed for rendezvous, docking, and undocking of two small spacecraft.
• The demonstration of the transfer of electric power between the docked spacecraft, which is essential for future applications such as in-space robotics.
• Composite spacecraft control, including remotely controlling it both in space and from mission control.
• Payload operations after undocking.

This mission is crucial for India’s ability to set up its own Space Station. It will also give India’s RLV or Reusable Launch Vehicle – India’s variant of NASA’s iconic space shuttle – docking capability in future.

India’s Reusable Launch Vehicle or RLV

HOW THE INTERNATIONAL SPACE STATION WAS BUILT

Among other key missions, NASA’s space shuttle was used by the United States to construct the US side of the International Space Station. Russia too used their own space shuttle to build the Russian side of the International Space Station. While NASA had a series of space shuttles, starting with Columbia and evolving into Challenger, Discovery, Atlantis, and Endeavour, Russian space agency Roscosmos named their space shuttle Buran.

NASA’s Space Shuttle (L) and Russia’s Space Shuttle (R)

Here is a insightful video of how the International Space Station – the largest man-made space object – was built by the US and Russian space shuttles using the docking mechanism and robotic arms in addition to astronauts and cosmonauts:

ISRO’S POEM-4 MISSION – AND EXPERIMENT WITH MICROGRAVITY

Besides the space docking manoeuvre, there is another key mission objective. ISRO plans to experiment with microgravity during the PSLV rocket’s fourth-stage. ISRO aims to use the spent fourth stage, which it has termed POEM-4 or PSLV Orbital Experimental Module 4, as a platform for carrying our experiments with microgravity.

According to the space agency, it provides an opportunity for the scientific community to carry out certain in-orbit microgravity experiments for an extended duration of up to three months using the POEM platform, which otherwise would end up as space debris immediately after the mission objective of injecting the primary payloads of the mission.

A total of 24 payloads are part of the POEM-4 mission, of which 14 payloads are from ISRO/DOS centres and 10 payloads are from various Non-Government Entities (NGEs) comprising Academia and Start-ups that have been received through IN-SPACe.

One of the fourteen payloads by ISRO is of a robotic arm – again a crucial element to constructing India’s own space station in future. For now the experiment will involve a robotic arm to demonstrate the capturing of tethered debris.