On January 16, the Indian Space Research Organisation (ISRO) successfully performed space docking, which involves connecting two moving satellites in space.
Two small satellites, each weighing 220 kg, were brought within 3 metres of each other in orbit. Their extended rings were connected, retracted, and locked together.
ISRO also showed that the two satellites could be controlled as a single unit after docking. This achievement makes India the fourth country, after the United States, Russia, and China, to achieve this capability.
India’s SpaDeX Mission: Key Details
The SpaDeX mission used two satellites:
- Chaser (SDX01): The active satellite that moved and docked with the Target.
- Target (SDX02): The passive satellite equipped with a docking mechanism for the Chaser.
Both satellites were launched on December 30, 2024. After several maneuvers, the Chaser successfully docked with the Target on January 16, 2025.
What Is “Docking” And Why Is It Important?
Docking is the process of bringing two fast-moving spacecraft to the same orbit, moving them closer manually or automatically, and finally connecting them.
This skill is essential for missions involving large spacecraft that cannot be launched with a single rocket.
It is also crucial for assembling space stations by joining separate modules in orbit and for transporting crew and supplies to these stations.
The Docking Process: Step-by-Step
- Approach: The Chaser slowly moved closer to the Target in controlled stages.
- Alignment: Advanced sensors helped the Chaser align accurately with the Target’s docking port.
- Capture: The docking systems on both satellites made contact and started the connection.
- Secure: The mechanisms retracted, pulling the satellites together and locking them securely.
Key Sensors: Critical Tools for Docking
- Laser Range Finder: Measured the exact distance between the satellites.
- Rendezvous Sensor: Tracked the Target’s position and speed.
- Proximity and Docking Sensor: Provided essential data for the final approach and docking.
When Was The First Docking In Space Achieved?
United States
In 1966, NASA’s Gemini VIII became the first spacecraft to dock with the target vehicle Agena. This was a crewed mission commanded by Neil Armstrong, who later became the first person to walk on the Moon in 1969. The success of docking was a critical step in achieving the goal of sending humans to the Moon.
Soviet Union
In 1967, the Soviet Union demonstrated the first uncrewed, automated docking between Kosmos 186 and Kosmos 188 spacecraft. Unlike the US mission, this docking did not require astronauts to steer the spacecraft.
China
China achieved docking capability in 2011 when the unmanned Shenzhou 8 spacecraft docked with the Tiangong 1 space laboratory. In 2012, China successfully completed its first crewed docking when astronauts manually connected the Shenzhou 9 spacecraft to the same space laboratory.
Why Has India Conducted Its Docking Mission Now?
Enabling Larger Spacecraft
Docking allows separate components to be launched individually and assembled in space to form a larger module. This makes it possible to plan missions with spacecraft too heavy for existing rockets. For example, the Chandrayaan-4 lunar sample return mission is designed to rely on this capability.
Advancing Space Goals
ISRO aims to establish a space station by 2035 and send humans to the Moon by 2040. These ambitious goals require key technologies, including docking and a new heavy-lift launch vehicle capable of carrying up to 30 tonnes to low Earth orbit.
Building the Bharatiya Antariksh Station
India’s planned space station, the Bharatiya Antariksh Station, will consist of five modules assembled in orbit. The first robotic module is expected to launch in 2028, making docking a crucial skill for this project.
Preparing for Chandrayaan-4
Docking is essential for Chandrayaan-4, a lunar mission aimed at collecting and returning samples from the Moon. This mission involves launching five modules in two phases.
- First Launch: Four modules, including a propulsion module, will travel to lunar orbit. The lander and ascender modules will then collect samples from the surface.
- Second Launch: The ascender module will dock with the transfer module in lunar orbit. This transfer module will bring the samples back to Earth orbit, where it will dock with a re-entry module designed to withstand Earth’s atmosphere.
Testing for Future Missions
ISRO conducted a “hop experiment” during Chandrayaan-3 to prepare for these advanced missions. A future human Moon mission is expected to follow a similar docking-based approach.
What Is The Bharatiya Docking System?
Docking Mechanism
The Bharatiya Docking System uses an androgynous design, meaning the docking systems on both satellites are identical. While it is similar to the International Docking System Standard (IDSS) used for the International Space Station, it is simpler, using two motors instead of the 24 motors in IDSS.
Advanced Sensors
The system relies on several advanced sensors, including:
- Laser Range Finder: Measures the exact distance between the satellites.
- Rendezvous Sensor: Tracks the position and speed of the target satellite.
- Proximity and Docking Sensor: Provides critical data during the final approach and docking.
Navigation Processor
A new processor, based on satellite navigation systems, calculates the relative position and speed of the spacecraft. This technology is a step toward fully autonomous docking systems that won’t rely on satellite-based navigation data for future missions.