Uncontrolled re-entries of satellites

What’s in today’s article?

• Uncontrolled re-entry of rockets
• News Summary

Why in News?

• 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 transdisciplinary international institute dedicated to space studies.
• Among others, the letter is addressed to S. Somanath, chairman of the Indian Space Research Organisation (ISRO).

Background: different stages of rockets

• 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.

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What is 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.

What are the associated dangers with uncontrolled re-entry of rockets?

• 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.

What are the international regulations on uncontrolled re-entry of rockets?

• 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.

News Summary

• 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 emphasizes that countries in the Global South’ face a “disproportionately higher” risk of casualties.

Q1) What is the re-entry speed of a space shuttle?

As a spacecraft re-enters the earth’s atmosphere, it is traveling very much faster than the speed of sound. The aircraft is said to be hypersonic. Typical low earth orbit re-entry speeds are near 17,500 mph and the Mach number M is nearly twenty five, M < 25.

Q2) What is the re-entry corridor?

The re-entry corridor is a narrow region in space that a re-entering vehicle must fly through. If the vehicle strays above the corridor, it may skip out. If it strays below the corridor, it may burn up.

Source: The uncontrolled re-entries of satellites