The uncontrolled re-entries of satellites

Source– The post is based on the article “The uncontrolled re-entries of satellites” published in The Hindu on 23rd December 2022.

Syllabus: GS3- Awareness in the field of space

Relevance– Issues related to safety of space assets

News– The article explains the issue of uncontrolled re-entry of satellites.

What are the stages of a rocket launch?

Today, there are more than 6,000 satellites in orbit, most of them in low-earth and geostationary orbits.

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 an 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.

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.

Some pieces burn up entirely while others don’t. But because of the speed at which they’re travelling, debris can be deadly.

Why are scientists worried about the re-entries?

Parts of a SpaceX Falcon 9 that fell down 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.

The USA, it requires 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 is arbitrary and makes little sense in an era when new technologies and mission profiles enable controlled re-entries. Many places have also become more densely populated.

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.

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. It means all people on board would be killed”.

How can the damages be minimised?

Satellite bodies should aim for an ocean in order to avoid human casualties.

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.