India’s space programme is all set to achieve another milestone with the Space Docking Experiment (SpaDeX) on December 30 at the Satish Dhawan Space Centre in Andhra Pradesh’s Sriharikota.
ISRO will attempt the docking and undocking of two satellites in orbit, a feat mastered only by Russia, the United States and China.
This is the 62nd Polar Satellite Launch Vehicle (PSLV) mission.
This landmark mission, described as a “bold step” by ISRO Chairman Dr S Somanath, will use Indigenous technology.
“When you have multiple objects in space that need to be brought together for a specific purpose, a mechanism called docking is required. Docking is the process by which two space objects come together and connect. For example, on the International Space Station, crew modules dock at the station, equalise pressure, and transfer people,” Dr Somanath said.
This capability is central to future ambitions, including India’s Bharatiya Antariksha Station (a proposed Indian space station), human spaceflight programmes and lunar sample return missions such as Chandrayaan-4.
During docking, there is a “target” object and a “chaser” object. The chaser follows the target, comes into proximity, and establishes a connection.
“In the SpaDeX, we aim to replicate the technology needed for this process. First, there’s a mechanism to capture the object, pull it closer, and rigidise the connection. Second, sensors identify the target and the chaser and coordinate their movements to ensure precise, controlled docking without causing damage,” Dr Somanath said.
The SpaDeX mission will rely entirely on ‘swadeshi’ or Indigenous technology.
ISRO has even patented its unique docking mechanism, a scaled-down version designed to fit the current mission’s objectives.
SpaDeX will launch two small satellites aboard a PSLV rocket weighing 229 tons. These satellites will autonomously execute docking and undocking manoeuvres at an altitude of 475 kilometres.
India will be the fourth country, after Russia, the US, and China, to attempt this challenging process in low-Earth orbit.
“Docking and undocking capabilities place India in an elite group of spacefaring nations. This experiment lays the groundwork for proximity operations like satellite repair, refuelling, debris removal, and more. SpaDex is an exciting step forward for ISRO, showcasing the team's perseverance and expertise in pushing technological boundaries,” he added.
The SpaDeX mission is a stepping stone for Chandrayaan-4, but more advanced tests will be required.
The current mission focuses on circular orbits, whereas lunar docking will occur in elliptical orbits under different conditions. The lessons from SpaDeX will also feed into India's long-term goals of creating a self-sustaining space ecosystem, including human space exploration.
The ISRO chief also explained the challenges of achieving such precision in the vacuum of space: “On Earth, we don’t have a zero-gravity environment to replicate the conditions of space, making ground testing extraordinarily difficult. This required us to develop innovative hardware and robotic test setups.”
With the SpaDeX mission, India aims to join the exclusive club of nations capable of space docking. “The success of this mission will position India as a major spacefaring nation, not just in launching satellites but in conducting complex space operations,” Dr Somanath remarked.
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