A discarded part of a rocket – whose origins are debated – collided with the moon in March. It represents the growing problem of space debris: human-made objects orbiting the Earth that no longer serve a function. Objects range from whole spacecrafts to tools dropped by astronauts, to paint flecks. The European Space Agency estimates there are 36,500 pieces of space junk over ten centimetres currently orbiting the Earth, and more than 13 million pieces over one millimetre.
Apart from extending pollution to outside of our atmosphere, space debris is dangerous. It can damage operational satellites which we rely on for telecommunications and meteorology. The International Space Station must constantly monitor for potential collisions in case avoidance manoeuvres are needed. This is currently necessary about once a year. If avoiding the debris is impossible, the crew move into the spacecraft used for transport to Earth, in case the debris causes critical damage, and they need to escape.
The majority of debris orbits within 2000 km of Earth, with the highest concentration 750-1000 km away. If debris comes through the atmosphere it usually burns, so it does not pose a risk to people on the ground. However, above 800 km the debris will remain in orbit for centuries, and above 1000km over a thousand years, keeping it in the orbits we use for satellites. Even if launches stop, debris will increase from collisions of existing satellites. For example, this April an object from a 2007 satellite space tug broke into 16 pieces, exploding due to the propellant it still contained and creating more debris in orbit.
If the problem continues some scientists are afraid of Kessler Syndrome, where a series of collisions will lead to the Earth orbit becoming unusable. Regulations and enforcement to prevent discarding defunct material is challenging between public and private space missions on an international scale. However, commitments are growing and recognising this concern, members of the G7 last year committed to use space safely and sustainably. Many companies are working on new launches, but this time with a focus on sustainability. While most strategies are focused on reduction and prevention of future debris, research is ongoing to find methods to remove existing debris.
A company called Astroscale plan to launch a ‘space junk servicer’ test in 2024, with €14.8 million in funding from the European Space Agency and the UK Space Agency. Unfortunately, their demonstration mission in March last year to capture a simulated piece of space junk was not completed due to ‘anomalous spacecraft conditions’. Their research is ongoing, and many other organisations are investigating other methods for debris capture.
However, the problem is also growing in other directions. With a new picture from NASA’s Perseverance robot spotting a piece of shiny silver material, our pollution has now extended to Mars. The material is thought to be from a thermal blanket discarded when the craft arrived in February. The robot is on a mission to find signs of ancient life on Mars in its Jezero crater, which could theoretically have supported microbial life when it was filled with water over 3.5 billion years ago. The litter should not interfere with the mission, as everything was sterilised before going, but deliberately discarded parts like this are common from the missions we send out into space.
Between space debris and littering new planets, pollution beyond Earth is a growing issue. But it is encouraging to see increasing commitments to future reductions and exciting projects to recapture space debris, so our future can focus on sustainability as well as exploration.