ISRO's successful docking mission sets stage for future space projects - All about SpaDex mission explained

PSLV-C60 launch carrying SpaDeX (Courtesy: ANI)

The Indian Space Research Organisation (ISRO) on Thursday successfully completed the docking process of the SpaDeX satellites. The achievement has placed India alongside the United States, Russia, and China as one of the few nations capable of this advanced space technology.

The historic moment came just days after the space agency, on January 12, brought the two spacecraft to three metres and then placed them back at a safe distance in its trial attempt to dock the satellites.

Mission so far

On Sunday, January 12, ISRO conducted a trial run, bringing two satellites —- Chaser and Target —- within three meters of each other in low Earth orbit (450 kilometers above the planet's surface). The satellites were later moved apart to a safe distance while engineers analysed the data to prepare for the final docking attempt.

These two satellites, weighing 220 kilograms each, were launched on December 30, 2024, from Sriharikota. Once deployed, they were intentionally set on separate orbits with a slight relative velocity, ensuring they drifted apart as part of the experiment’s design.

The docking attempt was initially scheduled for January 7, then moved to January 9, and now awaits a final date as ISRO refines its approach.

What is docking and why is it important?

Docking is a process where two spacecraft in orbit are brought together, aligned precisely and physically joined. Achieving this requires navigating two fast-moving objects that are traveling at thousands of kilometers per hour to the same orbit and position. Docking can be performed manually or autonomously.

Docking is a vital capability in space exploration for several reasons. It plays a key role in assembling modular space stations, such as the International Space Station (ISS), which was constructed by joining multiple modules in orbit. Beyond construction, docking supports crewed missions by enabling spacecraft to deliver astronauts, supplies, and scientific equipment to orbiting stations. It also enhances mission efficiency by allowing heavy payloads to be launched in separate components and assembled in space, overcoming the constraints of single-launch payload capacities. In these ways, docking serves as a cornerstone of modern space operations.

Space dockings by US, Russia and China

Docking dates back to the Cold War-era space race. The first successful docking was achieved by the United States in 1966 during the Gemini VIII mission. Astronauts, including Neil Armstrong, manually docked their spacecraft with the Agena target vehicle in Earth’s orbit.

The Soviet Union followed in 1967, successfully performing the first automated docking with its Kosmos 186 and Kosmos 188 spacecraft. This groundbreaking uncrewed mission demonstrated the feasibility of autonomous docking systems.

China joined the elite group in 2011 when its unmanned Shenzhou 8 spacecraft docked with the Tiangong 1 space laboratory. A year later, China achieved its first crewed docking with Shenzhou 9.

India's docking process

India's foray into docking is part of its broader vision for space exploration. ISRO has ambitious plans to establish a space station by 2035 and send humans to the moon by 2040. Docking technology is a prerequisite for these goals. India’s docking technology is a mix of global standards with homegrown innovations.

At its core is an androgynous docking system, where both the Chaser and Target satellites are equipped with identical mechanisms. Inspired by the International Docking System Standard (IDSS), India’s design stands out for its efficiency, using only two motors compared to the IDSS’s 24.

To ensure precision, the mission employs advanced sensors such as Laser Range Finders, Rendezvous Sensors and Proximity Sensors, which work in tandem to measure distances and align the satellites.

A newly developed processor, based on satellite navigation technology, calculates the spacecraft’s relative position and velocity with remarkable accuracy. Looking ahead, this mission also paves the way for fully autonomous docking systems, eliminating the need for satellite navigation data and marking a significant leap in India’s space exploration capabilities.