The Indian Space Research Organisation (ISRO) has undertaken an exciting mission called the Space Docking Experiment (SpaDeX). This mission is designed to test and showcase India's ability to dock and undock two small satellites in space.
Docking is a complex process where two spacecraft connect while orbiting the Earth. This achievement is a huge milestone for India, placing it among a select group of nations capable of performing in-space docking. The mission involves two small satellites, each weighing about 220 kilograms, which will be launched on a PSLV-C60 rocket from the Satish Dhawan Space Centre in Sriharikota on December 30 at 9.58pm.
One of the key goals of this mission is to demonstrate the transfer of electric power between the docked satellites, a critical feature for future space operations like robotic missions and building India's planned space station, the Bharatiya Antariksh Station (BAS). When comparing SpaDeX to similar missions by other space agencies, there are several similarities and differences as many space technology experts point out.
“NASA, the space agency of the United States, has been a leader in docking technology. Its Gemini programme in the 1960s was the first to successfully dock two spacecraft in orbit, paving the way for future missions to the Moon, such as the Apollo programme. NASA continues to use docking technology today with the International Space Station (ISS), where spacecraft regularly dock to deliver astronauts and supplies," says space expert Girish Linganna.
"Russia, through its space agency ROSCOSMOS, also has a long history of expertise in docking. Its Soyuz spacecraft has been a reliable transport vehicle for astronauts to the ISS for decades. A notable achievement was the Apollo-Soyuz test project in 1975, the first international space mission, where a Soyuz spacecraft docked with an American Apollo spacecraft, showcasing advanced docking technology and international collaboration,” added Linganna.
He further explains that China has also made significant progress in docking technology. Through its Tiangong programme, China launched space laboratories like Tiangong-1 and Tiangong-2 to test docking systems. In 2011, the Shenzhou VIII spacecraft successfully docked with Tiangong-1, marking a major step forward for China's space programme. The operational Tiangong space station now features multiple docking ports for various spacecraft, both crewed and uncrewed.
“Europe, through the European Space Agency (ESA), has contributed to docking advancements with its Automated Transfer Vehicle (ATV). The ATV was an uncrewed spacecraft that docked with the ISS to deliver supplies and even helped adjust the station's orbit. These missions demonstrated Europe's ability to perform autonomous docking, which is important for future deep space missions,” added Linganna.
Although the ESA's ATV missions were successful, their main purpose was delivering cargo and helping maintain the space station. They were not designed for missions involving astronauts. As a result, ESA is usually not considered among the countries with the ability to independently dock crewed spacecraft.
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ISRO's SpaDeX mission, while similar in objective, stands out for being a cost-effective technology demonstration. By developing its own docking systems and technology, ISRO is positioning itself as a major player in global space exploration. The success of SpaDeX will not only enhance India's capabilities but also pave the way for ambitious future missions, such as returning samples from the Moon and building a space station. This mission is a bold step forward for India in establishing itself as a leader in space technology, showcasing the nation’s growing expertise and ambition in space exploration.
SpaDex introduces two advanced satellites, SDX01 (Chaser) and SDX02 (Target), weighing 300kg and 350kg, respectively. These satellites, deployed into a 470km orbit, carry entirely homegrown docking systems designed by ISRO. Beyond demonstrating basic docking, the mission includes autonomous manoeuvres like rendezvous, undocking, and post-docking operations, signalling India’s readiness for more sophisticated space endeavours.
“India’s docking system employs a compact, streamlined design with a 450mm interface. Incorporating features like advanced LiDAR for precise measurements, indigenous sensors for navigation, and a soft-capture mechanism, the system reflects a hybrid approach. This unique configuration blends simplicity with cutting-edge technology, optimizing reliability while adhering to international compatibility standards. At the same time, this mission exemplifies ISRO’s hallmark efficiency, completing this ambitious project on a remarkably economical budget of Rs 375 crore. Strategic decisions, including indigenous development, innovative designs, and efficient resource allocation, have kept costs significantly lower than international counterparts. This achievement underscores India’s ability to deliver high-quality results without excessive expenditure,” remarked Srimathy Kesan, founder and CEO of Space Kidz India.
It is expected that this mission is poised to propel India’s space programme toward transformative goals. Autonomous docking technology is pivotal for initiatives like the Gaganyaan human spaceflight programme, facilitating crew transfers, modular construction, and emergency rescues. Additionally, it is integral to the planned Bharatiya Antariksh Station, supporting assembly and resupply operations. Beyond human spaceflight, SpaDEX opens avenues for orbital servicing, enabling maintenance, repairs, refuelling, and debris management.
