Why in news? More than 140 experts and dignitaries have signed an open letter published by the Outer Space Institute (OSI) for both national and multilateral efforts to restrict uncontrolled re-entries to earth

Highlights

What is an uncontrolled re-entry?

• The rocket stage simply falls and path down is determined by its shape, angle of descent, air currents and other characteristics.
• It will disintegrate as it falls and the smaller pieces fan out, the potential radius of impact will increase on the ground.
• Some pieces burn up entirely while others don’t increasing the impact on an airliner with debris of mass above 300 grams would kill all people on board
• 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.

Why are scientists worried about the re-entries?

• Re-entering stages still hold fuel, atmospheric and terrestrial chemical contamination is another risk.

Ex: Parts of a SpaceX Falcon 9 that fell down in Indonesia in 2016 included two “refrigerator-sized fuel tanks”

• The casualty risk from uncontrolled rocket body re-entries as being on the order of 10% in the next decade and that countries in the ‘Global South’ face a “disproportionately higher” risk of casualties.
• 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.

What can make minimum damage?

• While the Outer Space Institute admits that any kind of re-entry will inevitably damage some ecosystem, it recommends that bodies aim for an ocean in order to avoid human casualties.
• 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.

Successful Model

• 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.