ISRO to launch SPADEX for catching satellites in space with robotic arms

India is set to take a huge step toward a debris-free space with plans to launch at least two key missions — SPADEX and ISRO Servicer Mission next month. These missions aim to dock, refuel, repair, relocate, deorbit, and extend the life of satellites that have reached the end of their operational lifespan.

Indian Space Research Organization (ISRO) chairman S Somanath on Oct 25 said that the space agency will launch the Space Docking Experiment (SPADEX) mission in November this year. This mission will test low-impact cooperative docking technology, allowing communication between satellites. After this, a propulsive device can be attached to deorbit satellites safely.

Additionally, the agency will test the ISRO Servicer Mission, which will use a tethered debris capture technique where a robotic arm on the upper stage will grab a satellite in motion. This mission will demonstrate capabilities in on-orbit servicing, life extension, and inspection.

Speaking at the Chanakya Defence Dialogue 2024 on 'Space Situational Awareness - Monitoring and Protecting National Interests,' Somanath said, "Many of these problems — space debris management — don’t yet have a cost-effective solution, but that doesn’t mean we will shy away from developing new technologies.”

Tethered space debris capture

Tethered space debris capture is a proposed method for removing space debris using a long, strong tether (rope-like) attached to a satellite.

The tether is deployed to capture a piece of debris, and then the combined mass of the satellite and debris is de-orbited, causing both to burn up in the Earth's atmosphere, Manish Purohit, a former ISRO scientist and founder of Nimbus Education was quoted as saying.

In one aspect of its mission, the ISRO Servicer Mission will operate on the PS4 Orbital Platform and perform several on-orbit operations while tethered to it, he said.

Recently, ISRO has published two patents related to spacecraft capturing mechanisms for on-orbit satellite servicing, he added.
According to Purohit, the technology has several challenges to overcome:

Precise targeting: Accurately targeting and capturing small pieces of debris is challenging due to their high speed and unpredictable orbits.

Tether deployment and control: Deploying and controlling a long tether in space is complex and requires precise engineering. The initial phase of extending the tether is critical. Any irregularities, such as snags or vibrations, can lead to system instability. Additionally, maintaining optimal tension in the tether is essential. Too much tension can damage it, while too little can cause slack, leading to oscillations and entanglement.

De-orbiting: Safely and efficiently de-orbiting the captured debris poses a significant challenge.

Severity of space debris threat

Space debris includes everything from inactive satellites to errant fragments of broken equipment. At present, around 18,897 pieces of trackable space junk orbit Earth, according to Jonathan McDowell, a Harvard astronomer.

Recently, a Chinese rocket collided with debris, adding significantly to the junk cloud.

National Aeronautics and Space Administration (NASA) reported that earlier events, including the 2007 destruction of China’s Fengyun-1C satellite and a 2009 U.S.-Russian collision, added nearly 70 % more debris. In 2021, a Russian anti-satellite missile test created 1,500 new fragments, some of which have since decayed.
Anti-satellite tests by the US in 2008 and India in 2019 also contributed to the growing clutter.

India’s zero-debris space missions by 2030

India aims to achieve space missions with 'zero debris' by 2030 with its Debris Free Space Missions (DFSM) initiative. Starting in 2025, all Indian space missions, whether governmental or private, will adopt a “zero debris” approach.

Earlier this year, ISRO successfully re-entered a spent rocket from the XPoSat mission, which fell in the Pacific Ocean. ISRO also lowered the orbit of PSLV-37’s spent upper stage, ensuring it re-entered Earth’s atmosphere on Oct 6.

The space agency is now exploring mid-orbit debris capture technology, advancing India's sustainable space exploration.