[Answered] Briefly describe the uncontrolled re-entries of satellites and highlight the threats associated with it. Also, bring out the mechanisms available to control it.

The uncontrolled re-entries of satellites are the phenomenon of rocket parts falling back to earth in unguided fashion once their missions are complete.  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.

Threats associated with the uncontrolled re-entries of satellites:

• Risk to human life: When an abandoned rocket body reenters the atmosphere, approximately 20-40% of the mass survives reentry and reaches the ground intact. This creates a risk of casualty to people on the ground, in ships and in aircraft. E.g. debris from two separate Long March launches landed in India [8].
• About 65% of low Earth orbit (LEO) launches in 2021 resulted in a rocket body being abandoned in orbit. These large space objects pose a collision risk with satellites and other debris, and some rocket bodies explode in orbit, creating significant debris.
• Any kind of re-entry will inevitably damage some ecosystems.
• If re-entering stages still hold fuel, atmospheric and terrestrial chemical contamination is another risk.

Mechanisms to control it:

• The technologies such as wing-like attachments, de-orbiting brakes, extra fuel on the re-entering body, and design changes can minimize debris formation.
• Bodies aim for an ocean in order to avoid human casualties.
• The future solutions should 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.

There is no international binding agreement to ensure rocket stages always perform controlled re-entries nor on the technologies with which to do so.  Liability Convention 1972 does not provide and solution to control re-entry, but impose penalties later on.

Other means include retro-rockets, ground-based lasers, or clean-up missions, all of which could bring down satellites at the end of their operational careers. But these alternatives have yet to be tested.