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

Subject: Science and Technology

Section: Space

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.

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.
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 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.

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 kilometres.

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.

What is Space Junk?

Space junk or debris consist of spent rocket stages, dead satellites, fragments of space objects and debris resulting from Anti-satellite (ASAT) System (ASAT).
Hurtling at an average speed of 27,000 kmph in Low Eart Orbit (LEO), these objects pose a very real threat as collisions involving even centimetre-sized fragments can be lethal to satellites.
This free floating space debris is a potential hazard for operational satellites and colliding with them can leave the satellites dysfunctional.
This is referred to as Kessler Syndrome, named after National Aeronautics and Space Administration (NASA) scientist Donald Kessler in 1978.
It says if there is too much space junk in orbit, it could result in a chain reaction where more and more objects will collide and create new space junk in the process, to the point where Earth’s orbit becomes unusable – a Domino Effect.

What is the NETRA Project?

‘Project NETRA’ is an early warning system in space to detect debris and other hazards to Indian satellites.
Once operational, it will give India its own capability in Space Situational Awareness (SSA) like the other space powers
It is implemented by ISRO