Uncontrolled re-entries of satellites
26-08-2023
12:07 PM
1 min read
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.
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.