A Milestone in Space Docking Technology

ISRO Achieves Historic SpaDeX Satellite Undocking

Following the successful docking of two satellites—SDX01 (Chaser) and SDX02 (Target)—in January 2025, ISRO has now achieved another milestone by successfully undocking the SpaDeX satellites on March 13, 2025, at 09:20 Hrs. This makes India the fourth country, after the United States, Russia, and China, to demonstrate in-space docking technology.

About the SpaDeX Mission

Utilizing two diminutive satellites—SDX01 (Chaser) and SDX02 (Target)—SpadeX is a technology demonstrator mission that is intended to demonstrate and refine in-space docking, rendezvous, and undocking capabilities. PSLV-C60 was utilized to launch the satellites.

The UR Rao Satellite Centre (URSC) in Bengaluru led the design and realization of the SpaDeX spacecraft, with support from other ISRO centers, including VSSC, LPSC, SAC, IISU, and LEOS. URSC, established in 1976, is responsible for designing, assembling, and integrating ISRO's communication, navigation, remote sensing, scientific, and small satellite missions.

Technological Innovations in SpaDeX

Docking Mechanism: A low-impact, androgynous docking system ensures smooth connection between spacecraft.

Inter-Satellite Communication Link (ISL): Enables real-time data transfer between the two spacecraft.

GNSS-Based Relative Orbit Determination: Relative Orbit GNSS ensures precise docking navigation and control.

Power Transfer Technology: This demonstrates the transfer of energy between satellites that are docked.

Autonomous Rendezvous and Docking Algorithms: Used for precise maneuvering of satellites in orbit.

Post-Docking Applications

Once the satellites docked and undocked, they continued their independent payload operations:

• High-Resolution Imaging (SDX01): Captures images for Earth observation.

• Multi-Spectral Payload (SDX02): Monitors natural resources and vegetation.

• Radiation Monitoring (SDX02): Studies space radiation for future human missions.

Undocking Success

On March 13, 2025, ISRO successfully undocked the SpaDeX satellites in their 460 km circular orbit with a 45-degree inclination. Today, spacecraft orbit independently and are healthy. This achievement marks a significant step in demonstrating all the required capabilities for rendezvous, docking, and undocking operations in a circular orbit.

The performance of the docked satellites was carefully analyzed, and the undocking operation was carried out during a feasible window from March 10, 2025, to March 25, 2025. Ground stations located in Bengaluru, Lucknow, and Mauritius monitored the entire operation.

Looking Ahead

This success in undocking was the result of exhaustive ground simulations and analysis, which were crucial to ensuring the operation could be achieved on the first attempt. ISRO plans to continue further experiments with the satellites in the coming days.

With this, ISRO has successfully demonstrated space rendezvous, docking, and post-docking control technologies. The mission proved to be a cost-effective experiment that showcased India’s technological advancements in space.