Oceans

Explained: As Chinese rocket debris plunges into the ocean, the risks of space junk and its uncontrolled descent

Ending over a week of global anxiety and alarm, the debris from a large Chinese rocket – the Long March 5B – crashed to earth over the Pacific and the Indian oceans. As the 22-tonne core stage of the rocket hurtled uncontrollably back to earth, there were fears that it might hit a populated area. China, however, had dismissed these fears despite widespread criticism for rocket re-entry risks imposed by it on the world.

The Long March 5B blasted off on July 24 to deliver a laboratory module to the new Chinese space station under construction in orbit, marking the third flight of China’s most powerful rocket since its maiden launch in 2020.

What is an uncontrolled re-entry?

Generally, the core or first stage of a rocket is made up of heavy pieces that usually don’t reach orbit after liftoff, and fall back safely along a near-precise projected trajectory.

If they do enter an orbit, then a costly de-orbit maneuver is required for a steered, controlled return using engine burn. Without a de-orbit maneuver, the orbital core stage makes an uncontrolled fall.

Gigantic remnants from China’s Long March 5B rockets’ core stage are known to make such fiery, out-of-control descents back to earth. The reason is a difference in the mission sequence where the core stage reaches orbit, and then crashes back.

Most nations’ rockets, according to a report in the Guardian, separate the launcher from the payload before leaving the atmosphere. An extra engine then gives the payload a final boost. But China’s 5B series does not use a second engine and pushes right into orbit, the report points out.

In May 2020, Long March 5B debris had apparently fallen in Ivory Coast; and a year later in May 2021, remains of a Chinese rocket had dived uncontrolled into the Indian Ocean near Maldives.

Why is it difficult to track uncontrolled descents?

The variables involved make it difficult to precisely track the re-entry time and drop zone of rocket debris in uncontrolled descents. The factors that make this prediction extremely challenging include atmospheric drag, variations in solar activity, angle and rotational variation of the object among others.

A miscalculation of even a minute in re-entry time could result in the final resting place of the debris changing by hundreds of kilometers.

“It’s important for people to understand that among the 10 tough things that we do in space, debris re-entry is probably one of the toughest ones to predict,” Dr. Darren McKnight from satellite tracking company LeoLabs told Cosmos Magazine.

Are there laws regulating space junk?

The Space Liability Convention of 1972 defines responsibility in case a space object causes harm. The treaty says that “a launching State shall be absolutely liable to pay compensation for damage caused by its space objects on the surface of the earth or to aircraft, and liable for damage due to its faults in space. The Convention also provides for procedures for the settlement of claims for damages.”

However, there is no law against space junk crashing back to earth. In April this year, suspected debris from a Chinese rocket was found in two Maharashtra villages.

In 1979, the re-entry of NASA’s 76-ton Skylab had scattered debris over uninhabited parts of Australia, and the space agency was fined $400 for littering by a local government.

The only settlement using the Liability Convention was between the former Soviet Union and Canada over debris of Soviet Cosmos 954 falling in a barren region.

Canada was paid CAD 3 million in accordance with international law for cleaning up the mess.

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