Chinese rocket debris falls into the sea again — why does this happen?

Subject: Science and Technology

Context-

On Nov. 4, large fragments of China’s Long March 5B rocket plunged uncontrolled into the south-central Pacific Ocean.
The fragments were stages of the rocket used to deliver the third and final module of the Tiangong space station.

How big the debris are:

One of the pieces was left over from the core stage of the rocket that was about 30 metres long and weighed between 17 and 23 tonnes.

How dangerous it can be-

Spain’s air navigation authority shut down parts of its airspace for about 40 minutes in view of “the uncontrolled entry of remains from the Chinese space object CZ-5B in a descending orbit crossing our national territory”.
The rocket stage did not by design have a system to ensure it fell in a designated place on Earth.

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 manoeuvre is required for a steered, controlled return using engine burn.
Without a de-orbit manoeuvre, the orbital core stage makes an uncontrolled fall.

Earlier instances-

It was the fourth time something like this had happened with a Chinese rocket.
In May 2020, during the rocket’s first deployment, fragments landed in Ivory Coast, causing some damage to buildings; debris from the second and third flights had plunged into the Indian Ocean and near the Philippines respectively.
A rocket of the same design is expected to be used again in 2023.

China’s stand on this-

It says that the reentry of the last stage of a rocket is an international practice”, and that the Long March 5B rockets are “designed with special technology; most of the components will burn up and be destroyed during the reentry process, and the probability of causing harm to aviation activities and on the ground is extremely low”.

Are there laws regulating space junk?

Yes.

The Space Liability Convention of 1972.

It 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.

Cases of settlements

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 erstwhile Soviet Union and Canada over the 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.

Long March 5-

Long March 5 or Changzheng 5 (CZ-5), also by its nickname “Pang-Wu”( “Fat-Five”), is a Chinese heavy-lift launch vehicle developed by the China Academy of Launch Vehicle Technology (CALT).
It is the first Chinese launch vehicle designed to use exclusively non-hypergolic liquid propellants.
It is the fifth iteration of the Long March rocket family.
There are currently two CZ-5 variants:CZ-5 and CZ-5B (also called Long March 5B).
The maximum payload capacities are approximately 25,000 kg (55,000 lb) to low Earth orbit (for CZ-5B) and approximately 14,000 kg (31,000 lb) to geostationary transfer orbit (for CZ-5).
As of 2021, a 3-core human-rated variant, referred to as CZ-5G, designed for manned moon missions, is under development; this variant will be capable of launching a crewed spacecraft into lunar orbit.
China currently relies on the Long March 5B to carry its heaviest payloads to space.
The rocket has a big central booster and four smaller boosters on the side, which drop off sometime after lift-off.
The core booster stage, however, goes to orbit.

Tiangong Space Station-

The Tiangong space station is a Chinese space station being built in low Earth orbit between 340 and 450 kilometres above the earth.
It is part of China’s Manned Space Program and is the country’s first long-term space station.
China is going to operationalize its new Tiangong multi-module space station for at least ten years.
China launched an unmanned module named “Tianhe”, or “Harmony of the Heavens” for its permanent space station in 2021.
Recently in Sept 2022, China launched another unmanned module names “Wentien”, or “Heavenly Palace”.