The Space Docking Experiment (SPADEX) mission, which will dock two payload satellites in its final phase, will lay the foundation for India’s ambition of having its own space centre orbiting the planet. The mission was launched on 30 December 2024, and the final phase, which is the docking, will take place within days. If successful India will be the fourth country to have space docking technology after America, Russia and China. ISRO, the Indian Space Research Organisation in recent years established itself as the leading space research organisation in the world and it holds the ambition to have its own space station in the lower Earth orbit similar to the ISS (International Space Station). This SPADEX mission which will execute the docking experiment will be the first step towards that dream.
Space Docking and its Significance:
As a species the more we progress the more we explore outer space. Traditional space missions comprise the launch of machinery from Earth into space for various purposes. However, the complexity of modern missions requires multipurpose megastructures operating in the earth’s orbit which can be used for stationing, refuelling and repairing. The International Space Station (ISS) is an example of such a megastructure. The ISS is the largest space station ever constructed with the joint effort of the space agencies of America, Russia, Canada, Europe and Japan. Constructed in 12 years from 1998 to 2010, the space station cost $150 Billion to make.
It was impossible to launch a megastructure into the space from Earth. So, it was manufactured and launched in parts onto the earth orbit and was assembled there. For the assembling of the modules, a crucial technology was developed and used which was ‘space docking’. Space docking is the process where to vehicle joined while floating in the space. A successful docking results in the joining of two modules and synchronisation of their velocity, path of orbit and functions. The technology was developed by NASA- the American Space Agency and ROSCOSMOS- the Russian Space Agency. Later China on its own developed this technology for their planned space station and now India is on its way to executing it.
India’s SPADEX Mission:
The Space Docking Experiment or SpaDeX is the ISRO’s mission to develop and demonstrate the rendezvous, docking, and undocking of two small spacecraft in a low-Earth circular orbit. The mission was launched from Satish Dhawan Space Centre (SDSC) at Srihari Kota using the indigenously developed PSLV-C60 rocket.
Objective and Ambitions:
This success of the mission will lay the foundation for India’s most ambitious mission of the development of its own space station; the Bharat Antariksh Station (BAS). The main objective of this mission is to demonstrate the docking and undocking of the two satellite modules carrying payloads. Apart from that its secondary objectives include the demonstration of the transfer of electric power between the docked spacecraft which is essential for future applications such as in-space robotics. The mission will also execute the compositing of spacecraft control and payload operations after undocking. The spacecrafts used in this mission were designed and manufactured by the UR Rao Satellite Centre (URSC) with the support of other ISRO centres. In its orbital phase, they will be controlled from ISTRAC using ISRO ground stations and other externally hired ground stations. The organisation indigenously developed all the machinery and technologies for this mission which will manage specific aspects of the mission. They are:
- A Docking and Undocking mechanism,
- A suite of four rendezvous and docking sensors,
- Power transfer technology,
- Indigenous novel autonomous rendezvous and docking strategy,
- Inter-satellite communication link (ISL) for autonomous communication between spacecraft, incorporated with inbuilt intelligence to know the states of the other spacecraft,
- GNSS-based Novel Relative Orbit Determination and Propagation (RODP) processor to determine the relative position and velocity of the other spacecraft,
- Simulation test beds for both hardware and software design validation and testing.
SPADEX Mission Progress
The launch vehicle carried two spacecraft each weighing about 220 kg. Both the spacecraft are launched, independently and simultaneously by the PSLV, into a 470 km circular orbit at 55° inclination. One spacecraft SDX01 is the Chaser and the other SDX02 is the Target. The demonstrated precision of the PSLV vehicle was utilized to create a small relative velocity between the Target and the Chaser. This incremental velocity allowed the Target spacecraft to build a 10-20 km inter-satellite separation with respect to the Chaser within a day. At this point, the relative velocity between the spacecraft was gradually reduced using the propulsion system of the Target spacecraft and pushed the mission into the final stage where the docking will be executed.
As per the mission planning, the Chaser will approach the Target with progressively reduced inter-satellite distances of 5 km, 1.5 km, 500 m, 225 m, 15 m, and 3 m, ultimately leading to the docking of the two spacecraft. After successful docking and rigidization, electrical power transfer between the two satellites will be demonstrated before the undocking and separation of the two satellites to start the operation of their respective payloads for the expected mission life of up to two years.
On the 8th of January, while initiating manoeuvring for the modules to reduce the inter-satellite distance from 500m to 225m the drift was found to be more than calculated. Thus, the docking was postponed and since then the ground station has been working to reestablish the planned docking route. The official handle of ISRO on the 10th has notified that the modules were at a 1.5 km distance and the drift to reduce it to 500m will be complete on the 11th. The docking is expected to take place in the coming days.
Impact of the ISRO’s SPADEX Mission
The most important impact of this mission’s success is that India will attain the technology to build its own space station in Earth’s orbit. The station will act as a hub for resting and preparation for distance space travel and a repairing and refuelling hub for its spacecraft. By mastering the docking technologies, ISRO is set to enhance its operational flexibility and also expand its mission horizons. The ‘dockings’ will also contribute to future ISRO missions like Chandrayan-4 which will bring lunar samples to Earth and Gaganyan which is the organisation’s first manned space mission. The PSLV rocket used in this mission is the first launch vehicle of India which is integrated into the fourth stage which is vital for India’s future lunar and interplanetary missions.
And it again put India into the exclusive league of nations capable of mastering space docking. This feat will inspire thousands to further work in the field of space research for the betterment of the country.