Long March 5B

The Chinese launch vehicle - Long March 5B has been in the news over the past week. The rocket was launched at the end of last month to carry the living quarters of China's independent space station into orbit.

While the launch of the rocket was controlled, its fall back to earth was not. The concern was that, with uncontrolled descent, it might land on a populated area.

As I write this on Sunday afternoon, it has been reported that the rocket has crashed down near the Maldives, in the Indian Ocean, though there were tracking predictions that it could come down on Australia or New Zealand.

From a skeptical perspective, it's interesting to consider the concerns expressed about this, and the attention that it has captured.

As most of the world is uninhabited (with much of the population being clumped into dense spots) the chances of it hitting an inhabited area are extremely low. The lifetime odds of a single person being hit by space debris are more than a billion to one.

However, the law of large numbers kicks in, and while the chance of being hit by falling space debris is very low, it has happened. Lottie Williams, of Tulsa Oklahoma was walking through a park at 4am back in 1997 when she was hit by a piece of a falling Delta II rocket!

Of more concern about space debris is the large number of small pieces of space junk in low earth orbit that could cause catastrophic damage to satellites or to rockets being launched into space. NASA has estimated there's in excess of 23,000 untracked objects that have the potential to wreak havoc. It's counter-intuitive but even a tiny piece of metal, because of the energy it has due to the speed at which it's orbiting, is capable of causing a lot of damage.

At present there's over 3,000 satellites in orbit but that number is set to increase immensely with the launch of systems such as Starlink which plans to put 12,000 satellites into orbit. What will be the fate of all these satellites at the end of their lives? And what happens if a piece of space debris hits an existing satellite setting off a “chain reaction”? This is the space debris we should really be worried about!