Sunday Space: Why a rocket can accidentally crash into the moon

Whose rocket booster it belonged to was a bit of a mystery. When Bill Gray, who spends his time tracking objects in space, both human-made and natural, found it, it came as a bit of a surprise. Further data showed that it would crash into the moon. However, working out its orbit, as well as where it came from, is tricky.

Originally it was believed to be a booster from a SpaceX launch of a satellite. However, later data confirmed that it was not that. It was then concluded to be from a Chinese launch of a probe to the moon. While China has denied it, most are convinced it is indeed a Long March 3C rocket booster. However, no-one can 100 per cent say it was.

Objects around the Earth have a fairly defined and controlled orbit thanks to Earth's gravity. However, when you get out past the Earth, towards the moon, orbits get chaotic.

The gravitational pull of the Earth is substantially weaker, and there is also the moon who tugs on objects. To get it out that far, the rocket or satellite ends up in a long path to get to the moon - going the 384,000 kilometres to the moon versus the 200 to 500 kilometres around the Earth where most satellites are, is a big difference.

Because of all this tugging from the Earth,moon, and even the sun in various directions, objects out there are harder to predict, both where they came from and where they are going. It could have gone out into space, been pulled towards the sun, or even back towards the Earth and crashed into the atmosphere.

This time, it crashed into the moon, the first time we think something has accidentally crashed into the moon. Other objects have crashed into the moon, but on purpose (or at least aim).

In the past 50 years of lunar exploration, multiple probes and satellites going to the moon have failed and crashed on the surface. None though close to an object the size of a bus like the rocket on Friday night.

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NASA has also intentionally crashed a probe into the moon. In 2009, NASA's LCROSS crashed into the moon on purpose. By doing so, NASA was able to measure the dust and dirt that came out of the crater, an easy way to see what was underneath the surface.

This incident has also highlighted the issue around tracking objects, especially junk, in space. Spent rocket boosters, old satellites, and even a screwdriver are all up in space orbiting around. Most of these objects are not tracked. With the growing rate of junk in space, and the technology to track them, it is an area that people, especially in Australia, are rushing to solve.

By finding them, and knowing where they are going, we can hopefully prevent future collisions. Even worse, only objects near the Earth are tracked. When you get further out into space, near the moon or further, is even more of a problem.

The moon has a new crater, and it is our fault.

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