An illustration showing a satellite breaking up in orbit creating space debris. Credit: European Space Agency/ CC BY SA 3.0 IGO

As part of India's plan to ensure debris-free space missions by 2030, space agency ISRO recently lowered a spent rocket from an astronomy mission that burnt up on re-entry into Earth's atmosphere with practically no orbital debris.

ISRO’s XPoSat mission, launched in January 2024, wound up on 21 March as the rocket plunged into the North Pacific Ocean without leaving a trail of junk in space.

Space debris is any non-functional object humans leave in space. It can come from rocket-launching material and defunct satellites or from metal, screws, paint flakes, and other smaller items.

Beginning 2025, ISRO plans to include the debris-free approach for each mission. This would include carefully selecting clean orbits, budgeting for fuel to dispose of rockets after the mission and efficiently controlling trajectories as they re-enter the Earth's atmosphere.

The European Space Agency estimates that more than 1 million pieces of orbital debris a cm or larger, and more than 30,000 pieces bigger than 10 cm, litter the low-Earth orbit (upto 2000 km above the Earth's surface).

These hurtle past the Earth at nearly 10 km per second — almost seven times faster than a bullet — and risk colliding with communication, monitoring, and astronomy satellites. “Even a single paint flake at that speed can damage or destroy a satellite,” says Anirudh Sharma, co-founder and CEO of Digantara, a Bengaluru-based space-technology startup.

Explosions in orbit, triggered by residual energy stored in fuel and batteries aboard spacecraft and rockets, are a significant source of debris.

Spacecraft hit with debris can explode into thousands of shards and cascade the danger multiple times. Anti-satellite missile tests that destroy satellites create such space debris. Increasing government and private space traffic is pushing up the combined mass and area taken up by space trash.

Current attempts to minimise debris formation and prevent crashes revolve around re-entry burn up exercises for spent spacecraft and debris avoidance manoeuvres for satellite launches.

Rocket emissions and debris from spacecraft falling out of orbit affect global atmospheric chemistry1. A recent study2 discovered metals from spacecraft re-entry in aerosol particles in the stratosphere. Such remnants, which orbit the Earth above the ozone layer, can trigger chemical reactions that deplete the layer and affect atmospheric chemistry, cloud formation, and even the climate.

“We are practically using Earth’s atmosphere as a waste bin,” says Leonard Schulz at Technische Universität Braunschweig, Germany.

Efforts to control space junk

India's Debris Free Space Missions initiative to start in 2025 aligns with global and national efforts underway to regulate space debris creation and disposal.

Voluntary advice, such as the Space Debris Mitigation Guidelines of the United Nations Committee on the Peaceful Uses of Outer Space, work to limit the long-term presence of spacecraft and launch vehicles in low Earth orbit after missions end. The European Space Agency (ESA) updates regulations on design, operation, and decommissioning of missions, furthering its commitment to the Zero Debris Charter.

But there is no standard legal framework to regulate space traffic and mitigate space debris. International cooperation complexities, divergent national policies, enforcement challenges, and security concerns create hurdles to setting up a global law.

An international coalition is also needed to maintain a record of tracked debris, says Sanat K. Biswas, an Assistant Professor at the Indraprastha Institute of Information Technology, Delhi (IIIT-Delhi). Countries, including the United States, China, and Russia, track them individually. Researchers rely on North American Aerospace Defense Command data to spot debris and issue alerts to satellites.

The European Union Space Surveillance and Tracking (EU SST) is trying to create a new catalogue which can run in parallel, says Harleen Kaur Mann, doctoral candidate and Astrodynamics and Space Surveillance and Tracking specialist at Brunswick, Germany.

ISRO’s NEtwork for space object TRacking and Analysis (NETRA) project is also geared towards space situational awareness, including debris mitigation and remediation.

Checking debris to reduce collision risk

While launching satellites, ISRO considers known debris, including residues of old satellites like Cosmos 2251, and adjusts the launch time to avoid the junk. For this reason, the lift-off for Chandrayaan-3, India’s mission that landed on the Moon, was delayed by 4 seconds.

All space agencies, including the International Space Station, execute technological manoeuvres to prevent satellites from hitting junk. The number of such operations is on the rise, with the ISRO reporting 23 such manoeuvres in 2023, from just three in 2015.

The satellites use propulsion systems to avoid collisions, but the manoeuvres require agility and precision. “The satellites have only a few seconds,” says Sharma. Satellites also have a shielding mechanism to protect themselves from small debris. But, small satellites often do not have such systems, and more satellite agencies are making them mandatory, he says.

One way to reduce the risk of future impacts with space litter is to burn up spent satellites and rockets in the atmosphere. So, space agencies discharge residual batteries, remove unused fuels from the rockets, and then re-enter them into the atmosphere, where they naturally burn up. “If they are kept in orbit, they might explode,” says K. Sivan, former ISRO chief.

Re-entry calculations are done to maximize the chances of the final fall over oceans but mishaps do occur. In March 2024, a battery pack released from the International Space Station struck through a home in Florida, in the United States. NASA said a piece of the hardware, which should have burnt up, survived re-entry into the Earth's atmosphere.