Uncontrolled Reentries 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.
Stages of Rocket launch
- 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 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.
What is uncontrolled reentry of Satellites
- It is the phenomenon of rocket parts falling back to earth in unguided fashion once their missions are complete.
- In an uncontrolled re-entry, the rocket stage simply falls.
- Its path down is determined by its shape, angle of descent, air currents and other characteristics.
- It will also disintegrate as it falls.
- 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.
Concerns about Reentry
- Conservative estimates place the casualty risk from uncontrolled rocket body re-entries as being on the order of 10% in the next decade
- Countries in the ‘Global South’ face a “disproportionately higher” risk of casualties.
- If re-entering stages still hold fuel, atmospheric and terrestrial chemical contamination is another risk.
- There is no international binding agreement to ensure rocket stages always perform controlled re-entries nor on the technologies with which to do so. The Liability Convention 1972 requires countries to pay for damages, not prevent them
- 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%. But the U.S. Air Force and NASA have waived this requirement on multiple occasions.
- A July 2022 study by researchers in Canada found that this threshold, which some other countries have also adopted, is “arbitrary and makes little sense in an era when new technologies and mission profiles enable controlled re-entries,” and because many places have become more densely populated.
Examples of such Reentry
- 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.
- Parts of a SpaceX Falcon 9 that fell down in Indonesia in 2016 included two “refrigerator-sized fuel tanks
How to minimise damage
- Bodies aim for an ocean in order to avoid human casualties.
- Future solutions to be extended to re-entering satellites as well.
Reentry of India’s RISAT satellite
- India’s 300-kg RISAT-2 satellite re-entered earth’s atmosphere in October after 13 years in low-earth orbit.
- The ISRO tracked it with its system for safe and sustainable space operations management from a month beforehand.
- It plotted its predicted paths using models in-house.
- The RISAT-2 eventually fell into the Indian Ocean on October 30.
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