Many of the things we take for granted in the modern world rely heavily on satellites in space. James Blake from the Astronomy and Astrophysics Group explores the growing need to safeguard these satellites against the hazards they face on a daily basis.
Not everything we can see in the night sky is natural. Indeed, most aspects of what we would consider a modern way of life are dependent upon satellites that have been built by humans and launched into orbit around the Earth.
A world without satellites is a difficult one to imagine for anyone born in the last half-Century. If satellites vanished overnight, we would wake up to find that the TV had stopped working. On the radio, anything beyond the local news would be inaccessible. The loss of accurate timings provided by Global Positioning System (GPS) satellites would result in immeasurable disruption. Over time, networks would become out of sync, causing the internet to slow to a standstill. Cloud servers would begin to fail, and any service requiring computerised transmission would gradually break down. This would lead to power cuts, sporadic water shortages, and chaos across the transport networks as signalling systems stall. A loss of satellite communications would eventually cause mobile phone services to fail, and flights would be grounded all over the world. Weather systems would become far less predictable, posing a threat to shipping networks and slowing trade. Interruptions to the running of businesses would cause the global economy to suffer. Given the politically fragile world we live in, a lack of fast communication would heighten tensions on a global scale. Put simply, a hypothetical world we wouldn't want to inhabit.
The debris problem
Fortunately, this is an extremely unlikely scenario, especially happening all at once. Threats to satellite safety do exist, however, and it’s important that we tackle them as early as possible before they spiral out of our control. Perhaps the greatest danger satellites face has arisen for a very familiar reason: a failure to clean up after ourselves.
Consider a racetrack, with the competitors looping round, lap after lap. If left unpoliced, the race may turn ugly with nobody there to prevent the drivers jostling for the lead. Sooner rather than later a crash will take place, littering the track with debris and causing a hazard for the other drivers. What if the race was forced to continue despite the risk imposed by the debris? In that case, the debris would likely cause another crash, creating more debris, which would in turn cause more crashes, and so on. This runaway process of objects colliding and creating debris in the context of space was first proposed by NASA Scientist Don Kessler in 1978 and has since become known as the Kessler Syndrome.
The situation is even more challenging in space. Satellite operators (the ‘drivers’) don’t have a comprehensive view of what lies ahead. To borrow further from our Formula One analogy, imagine that it’s raining during the race and the drivers can’t clearly see all of the debris that’s waiting to puncture their tyre or spin them off-course. In space, debris can be extremely dangerous even if it’s small. In low Earth orbit (altitudes less than 2000 km, where most of the debris resides), a piece of debris can be moving several kilometres per second. At these immense speeds, even centimetre-sized objects have enough energy to take out an operational satellite. The problem is that these tiny satellite killers are really far away, so are very hard to detect, and even harder to track and monitor. What’s more, we can’t simply press ‘stop’ and sweep up the debris like we would in a race, as the technology required to make this feasible in space needs a lot more work.
10,000 satellites and more to come
Sputnik 1 was the first satellite to be launched into space, orbiting for nearly 3 months before falling back into the Earth’s atmosphere.
The first satellite to blast off into space was Sputnik 1 in 1957 and since then, nearly 10000 satellites have followed. Not all of these satellites remain in space; at the lower altitudes, there is still enough resistance from the atmosphere to slowly bring a satellite back to Earth, in much the same way as an aeroplane would plummet if its engines were switched off. The Space Surveillance Network, which is made up of over 30 ground-based radars and optical telescopes, alongside six satellites in orbit, tracks and maintains a catalogue of around 23,000 objects. Owing to the difficulties in detecting these objects, this number pales in comparison to the true population of debris. Recent models have predicted that nearly one million objects larger than one centimetre are in orbit around the Earth, so we have a very long way to go!
How can we fix this problem?
The short answer is that we need to change. Continuing to do things as we have done for the past six decades will ultimately render certain parts of space unusable, which is something we really want to avoid in order to ensure that future generations can benefit from them.
The long answer is more complicated.
Policy is the first hurdle. We need to recognise that this is a global issue that requires cooperation across the board for all to prosper, and policies need to reflect this both at national and international levels. Who is responsible for a collision and the debris it generates? Who should clean up the mess? How do we make this fair to ensure that any space-faring nation can benefit from space, regardless of how developed they are? Operators need incentives and, more importantly, deterrents to encourage sustainable practices both during and after the active lifetime of their satellite.
Every satellite is future debris
It is important to remember that every satellite will eventually become debris when its mission reaches an end, it runs out of fuel or becomes damaged in some way.
Beyond this, we need to better monitor the environment to gain a clearer picture of what’s out there. Operators need to be warned as far in advance as possible to make sure they can carry out manoeuvres and avoid debris that’s on a collision course with their satellite. Accurate, real-time monitoring will become essential as companies like SpaceX are set to add thousands of new satellites in proposed constellations over the coming decade.
In the long term, testing is underway for a variety of concepts designed to actively remove debris from space. The RemoveDebris mission that was launched in 2018 captured planted pieces of debris with a net and a harpoon. AstroScale plan to take this a step further by using a magnetic docking system to retrieve a ‘lost’ target as part of their upcoming ELSA-d mission. Despite the very promising start, these technologies are still in their early stages of development, and it will be a long time until they can play a significant role in cleaning up the space environment.
Next time you’re checking your messages, or perhaps flying somewhere exotic, spare a thought for those working tirelessly to protect the satellites we’ve become so reliant on as a society. Much more needs to be done to ensure our use of space is sustainable, and this will be a job for many future generations to come.
9 July 2020
The Astronomy and Astrophysics group at Warwick is interested in a huge range of scales across the Universe: planetary systems, how they form, live and die; stars, stellar binaries and and the exotic physical processes that they allow us to explore; as well as the transient events which mark the end of stellar lifetimes and the galaxies stars inhabit across the Universe. The group started in September 2003 and is both an observational and theoretical group. The group makes use of a wide range of ground-based telescopes, such as ESO's Very Large Telescope (VLT) in Chile and the Isaac Newton Group of telescopes (ING) in the Canary Islands, or the Atacama Large Millimetre Array (ALMA), as well as space telescopes such as NASA's Chandra and ESA's XMM-Newton X-ray observatories and the Hubble Space Telescope. The Warwick astro group partners in the four large spectroscopic surveys (DESI, SDSS-V, WEAVE, and 4MOST) that will start operations throughout 2020-2021.
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