India Achieves Satellite Docking

January 17, 2025

Recently, the Indian Space Research Organisation (ISRO) successfully completed its first satellite docking manoeuvre, milestone in India’s space exploration efforts. This makes India the fourth country after the US, Russia, and China to achieve this capability.

What is Docking?

It is the process of joining two fast-moving spacecraft in the same orbit.
Its use cases include:
- Building space stations (joining modules in space).
- Transporting crew and supplies to space stations.

Historical Context

United States:
- First docking in 1966: NASA’s Gemini VIII docked with Agena.
- Astronauts manually controlled the spacecraft (Neil Armstrong was the commander).
USSR:
- 1967: First uncrewed automated docking (Kosmos 186 & 188).
China:
- 2011: First unmanned docking (Shenzhou 8 with Tiangong 1).
- 2012: First crewed docking (Shenzhou 9 with Tiangong 1).

ISRO’s Space Docking Experiment (SpaDeX)

The SpaDeX mission commenced on December 30, 2024. It involved two satellites, which were launched separately, joining at an altitude of approximately 475 km. The final docking commands were executed from the ISRO Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru.

Docking Process

Two 220-kg satellites – SDX01 (“Chaser”) and SDX02 (“Target”) – were brought within 3 meters of each other in orbit.
It involves several phases:
- Satellites were brought progressively closer: 5 km → 1.5 km → 500 m → 225 m → 15 m → 3 m.
- Joined at 3 meters and operated as one unit.
Their docking rings connected, retracted, and locked together.
Commands were successfully given to the satellites as a single unit.

Technical Specifications

ISRO employed a petal-based docking system, adhering to the International Docking System Standard (IDSS). This technology is crucial for future missions, ensuring compatibility with international space vehicles.

Challenges Faced

The docking process faced several delays due to the need for further validation and ground simulations. Initial attempts were aborted due to issues like drifting and accuracy. Adjustments ensured success on January 16.

India’s Docking Mission Objectives

Space Station:
- India aims to set up the Bharatiya Antariksh Station using five modules.
- First module launch is expected to take place in 2028.
Chandrayaan-4:
- Docking is essential for the Moon sample-return mission involving five key modules.
- Modules will perform complex docking maneuvers in lunar orbit.
Future Human Missions:
- Likely to follow similar docking techniques for lunar missions.