SpaDEX: All you need to know about ISRO’s groundbreaking space docking mission

India is set to take a major leap in its space programme with the launch of the Space Docking Experiment (SpaDEX) on December 30, 2024. The Indian Space Research Organisation (ISRO) will deploy this mission using the Polar Satellite Launch Vehicle (PSLV-C60), which is scheduled to lift off at 21:58 IST from the Satish Dhawan Space Centre in Sriharikota.

This mission is a significant milestone for ISRO, as it will demonstrate in-space docking capabilities, a critical technology for future space endeavours. The primary aim is to develop and test the systems required for the rendezvous, docking, and undocking of two spacecraft.

Mission Overview and Objectives

SpaDEX will involve the launch of two identical satellites, the Chaser (SDX01) and the Target (SDX02), each weighing approximately 220 kg. These satellites will be placed in a 470 km low-Earth circular orbit with a 55° inclination. The mission's objectives are:

• Demonstrating precision manoeuvres to rendezvous and dock the satellites.
• Validating the transfer of electrical power between docked spacecraft.
• Operating payloads post-undocking, with a mission life of up to two years.

ISRO stated that the PSLV-C60 vehicle has been fully integrated and moved to the First Launch Pad for final checks ahead of the mission.

A Step Towards India's Space Station

“The SpaDEX mission is crucial for India's ambitions in space exploration,” said an ISRO official. “It positions India to become the fourth country globally to achieve advanced docking technology.”

This capability is essential for missions requiring multiple launches to achieve common objectives, such as satellite servicing, formation flying, and assembly of complex structures like the proposed Bharatiya Antariksh Station (BAS).

Innovative Use of PSLV's Fourth Stage

In addition to its docking objectives, the mission will utilise the PSLV's spent fourth stage, named POEM-4 (PSLV Orbital Experimental Module), as a platform for microgravity experiments. A total of 24 payloads, contributed by academic institutions and startups, will be carried on board.

Mission Concept and Execution

The Chaser and Target will be deployed independently but simultaneously into orbit. The PSLV’s precision will ensure a small initial relative velocity between the satellites. Using onboard propulsion, the Target will gradually create an inter-satellite separation of 10-20 km, known as the Far Rendezvous phase.

The Chaser will then approach the Target in stages, reducing the distance progressively to 5 km, 1.5 km, 500 m, 225 m, 15 m, and finally 3 m, where docking will occur. Once docked, the mission will demonstrate power transfer between the spacecraft before undocking them for payload operations.

Why SpaDEX Matters

The SpaDEX mission is not just a technological demonstration; it is a stepping stone for ISRO’s larger goals. The ability to dock spacecraft is crucial for ambitious projects like lunar sample-return missions, interplanetary exploration, and building a sustained human presence in space.

India aims to join an elite group of nations—currently the US, Russia, and China—that have mastered in-space docking technology. This mission underscores ISRO’s commitment to developing cost-effective yet highly advanced space capabilities.

With the countdown underway, SpaDEX is poised to showcase India's growing expertise in space exploration. The mission promises to unlock new avenues for research and collaboration, solidifying India’s role as a key player in the global space community.