Uncontrolled re-entry of satellites

More than 140 experts and dignitaries have signed an open letter published by the Outer Space Institute (OSI) calling for both national and multilateral efforts to restrict uncontrolled re-entries. The Outer Space Institute is a trans-disciplinary international institute dedicated to space studies. 

Details –

• The Outer Space Institute (OSI) has published the International Open Letter on Reducing Risks from Uncontrolled Re-entries of Rocket Bodies.
• The Open Letter calls on governments to negotiate a multilateral agreement requiring controlled re-entries.
• It also wants Nations to demonstrate leadership by immediately and unilaterally committing to national controlled re-entry regimes.
• The letter states that the conservative estimates place the casualty risk from uncontrolled rocket body re-entries as being on the order of 10% in the next decade.
  • The U.S. Orbital Debris Mitigation Standard Practices (ODMSP) require all launches to keep the chance of a casualty from a re-entering body to be below 0.01%.
• It also emphasises that countries in the Global South’ face a “disproportionately higher” risk of casualties.

Background –

• Rockets have multiple stages. Once a stage has increased the rocket’s altitude and velocity by a certain amount, the rocket sheds it.
• Some rockets jettison (throw away) all their larger stages before reaching the destination orbit; a smaller engine then moves the payload to its final orbit.
• Others carry the payload to the orbit, then perform a deorbit manoeuvre to begin their descent.
• In both cases, rocket stages come back down — in controlled or uncontrolled ways.

Uncontrolled re-entry –

• In an uncontrolled re-entry, the rocket stage simply falls. Ground stations usually lose control on such rockets.
• Its path down is determined by its shape, angle of descent, air currents and other characteristics. It will also disintegrate as it falls.
• As the smaller pieces fan out, the potential radius of impact will increase on the ground.
• Some pieces burn up entirely while others don’t. But because of the speed at which they’re travelling, debris can be deadly.
• Most rocket parts have landed in oceans principally because earth’s surface has more water than land. But many have dropped on land as well.

Recent examples of uncontrolled re-entry –

• Parts of a Russian rocket in 2018 and China’s Long March 5B rockets in 2020 and 2022 striking parts of Indonesia, Peru, India and Ivory Coast, among others.
• In October 2022, ISRO’s RISAT-2 satellite made an uncontrolled re-entry in the Indian Ocean near Jakarta.
• Parts of a SpaceX Falcon 9 that fell down in Indonesia in 2016 included two refrigerator-sized fuel tanks.

Associated dangers –

• Any kind of re-entry will inevitably damage some ecosystem and there is also an associated risk of human causalities on the ground as well.
  • A 2021 report of the International Space Safety Foundation said, an impact anywhere on an airliner with debris of mass above 300 grams would produce a catastrophic failure, meaning all people on board would be killed.
• If re-entering stages still hold fuel, atmospheric and terrestrial chemical contamination is another risk.

International Regulations –

• There is no international binding agreement to ensure rocket stages always perform controlled re-entries nor on the technologies with which to do so.
  • These technologies include wing-like attachments, de-orbiting brakes, extra fuel on the re-entering body, and design changes that minimise debris formation.
• The Liability Convention 1972 requires countries to pay for damages, not prevent them.