UNCONTROLLED RE-ENTRIES OF SATELLITES
1. Context
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 phenomenon of rocket parts falling back to earth in an unguided fashion once their missions are complete.
2. Key points
- The Soviet Union launched the first artificial satellite in 1957.
- Today, there are more than 6, 000 satellites in orbit, most of them in low-earth (100-2, 000 km) and geostationary (35, 786 km) orbits, placed there in more than 5, 000 launches.
- The number of rocket launches has been surging with the advent of reusable rocket stages.
3. Stages in the 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 and then perform a deorbit manoeuvre to begin their descent.
- In both cases, rocket stages come back down in controlled or uncontrolled ways.
4. About Uncontrolled re-entry
- 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.
- 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.
- Because of the speed at which they are travelling, debris can be deadly.
| A 2021 report from the International Space Safety Foundation said, "an impact anywhere on an airliner with the debris of mass above 300 grams would produce a catastrophic failure, meaning all people on board would be killed". |
- Most rocket parts have landed in oceans principally because the earth's surface has more water than land. But many have dropped on land as well.
5. Falling off Rockets
- The examples of 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 the Ivory Coast, among others.
- Many news reports have focused on Chinese transgressions of late, but historically, the U.S. has been the worst offender.
- Parts of a Space X Falcon 9 that fell in Indonesia in 2016 included two "refrigerator-sized fuel tanks".
- If re-entering stages still hold fuel, atmospheric and terrestrial chemical contamination is another risk.
5.1 RISAT-2
- 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 a month beforehand.
- It plotted its predicted paths using models in-house.
- The RISAT-2 eventually fell into the Indian Ocean on October 30.
6. Scientists' concerns
Conservative estimates place the casualty risk from uncontrolled rocket body re-entries as being on the order of 10 per cent in the next decade and that countries in the "Global South" face a "disproportionately higher" risk of casualties.
7. ODMSP
- 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 per cent.
- 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.
8. Liability Convention 1972
- 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.
- These technologies include wing-like attachments, de-orbiting brakes and extra fuel on the re-entering body and design changes that minimise debris formation.
9. The Wayforward
- Any kind of re-entry will inevitably damage some ecosystems, it recommends that bodies aim for an ocean to avoid human casualties.
- The future solutions be extended to re-entering satellites as well.
- Advances in electronics and fabrication have made way for smaller satellites, which are easier to build and launch in large numbers.
- These satellites experience more atmospheric drag than if they had been bigger, but they are also likelier to burn up during re-entry.
For Prelims & Mains
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For Prelims: Outer Space Institute (OSI), International Space Safety Foundation, China's Long March 5B rocket, Space X Falcon 9, RISAT-2, ISRO, NASA, Orbital Debris Mitigation Standard Practices (ODMSP), Liability Convention 1972
For Mains:
1. What are the different stages of a rocket launch? How do uncontrolled re-entries of rockets into the earth's orbit cause damage? (250 Words)
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Source: The Hindu
