Isro successfully launches SpaDeX mission for novel docking of 2 satellites in space

Indian Space Research Organisation (Isro) in its year-end mission, on 30 December 2024, carried out a rare docking mission involving the spent fourth stage of its Polar Satellite Launch Vehicle (PSLV) and two satellites.

The PSLV-C60 rocket carrying the two satellites of 220 kg each lifted off from the first launchpad of the Satish Dhavan Space Port at Sriharikota just past 10 pm (IST). They were placed in a 475-km circular orbit some 15 minutes later. The first satellite separated 15.1 minutes after lift off, and the other at 15.2 minutes.

The historic feat, named `Space Docking Experiment’ (SpaDeX), will see the two satellites, designated 'Chaser' and 'Target', merging to form a single entity in space, in a technology demonstration of what is termed `Bharatiya Docking System’.

The mission will be using an indigenous programme called `Bharatiya Docking System,’ to dock together the two satellites speeding at 28,800 km/hour in the near vacuum space by reducing their velocities to 0.036 km/hour and then carefully manoeuvring them to unite.

In the SpaDeX mission, Spacecraft A carries a high resolution camera, while Spacecraft B has miniature multispectral payload and a radiation monitor payload. These payloads would provide high resolution images, natural resource monitoring, vegetation studies among others.

The experimental module, called PS4-Orbital Experiment Module (POEM-4) makes use of the spent fourth stage of the Polar Synchronous Launch Vehicle (PSLV) to carry out certain in-orbit microgravity experiments for an extended duration of up to three months. This would otherwise end up as space debris immediately after injecting the primary payloads of the mission. 

PSLV-C60 SpaDeX mission is the fourth POEM mission (POEM-4) in the series. 

The POEM mission carries a total of 24 payloads, of which 14 are from ISRO/DOS centres and 10 payloads from various non-government entities, including academia and start-ups that have been received through IN-SPACe.

The SpaDeX mission has about 66 days to complete the experiment, although it may take only a day or two for Isro to complete the docking. For the docking demonstration, Isro will utilise the precision of the PSLV vehicle and thrusters of the spacecraft to control the relative velocities of the two satellites. Docking will be attempted at the end of this drift arrest manoeuvre, when the target and the chaser will be in the same orbit.

For the docking of the two satellites, Isro will be using a novel indigenous autonomous rendezvous and docking strategy. The mission uses power transmission technology and inter-satellite communication link, with inbuilt intelligence to know the states of the other spacecraft, as also a GNSS-based Novel Relative Orbit Determination and Propagation (RODP) processor to determine the relative position and velocity of the other spacecraft.

A successful docking of the two satellites is important for India’s future space programmes, including Gaganyaan and Chandrayaan-4 as also the proposed Bharat space station. It is also crucial for manned space missions in future.