Millions of pieces of space debris are orbiting Earth dating back to Sputnik-1 in 1957. Could we use fishing nets, harpoons and sails to reel them in?
Almost 5,000 launches since the beginning of the space age have left orbits littered
with defunct satellites, parts of rockets, fuel tanks, tools lost
by astronauts and other fragments which threaten to damage and destroy active spacecraft.
As more satellites are launched every year, collisions are becoming increasingly likely. In Low Earth Orbit (LEO) objects move at around 7.5 km/s (the equivalent of travelling from Guildford to London in six seconds). This speed means that if two objects collide they will create thousands of other pieces of debris, as happened with the 2009 collision
between the Russian Kosmos 2251 and US Iridium 33 satellites. SSTL encountered the problem first hand when a piece of debris from an Ariane rocket severed the gravity gradient boom of the Cerise mission
just one year after its 1995 launch– this was the first verified case of two objects colliding in space.
Scientists worry that this could result in a cascade of collisions known as the Kessler Syndrome
, where the amount of debris increases exponentially, with the potential to seriously impede opportunities for new missions and degrading, or eventually, stopping the vital services satellites provide.
Space debris mitigation measures are gradually being defined and brought into action by national and international space agencies around the World. Best practice dictates that satellites should have some ability to manoeuvre into a re-entry trajectory at end of life to burn up in the Earth’s atmosphere within 25 years. SSTL attempts to comply with these guidelines for all of its missions, ensuring that where spacecraft with propulsion are launched, sufficient fuel is retained until the end of the mission so that it can be removed from ‘busy’ orbits, lessening the chances of a future collision.
However, not all missions manage to adhere to these mitigation guidelines. The 8-tonne Envisat satellite, for example, lost contact
with ground controllers last year and is now stuck in an orbit that is estimated to take 150 years to re-enter the atmosphere. Until it re-enters, this object and others like it will pose a large and on-going risk to other satellites and the services that they deliver.
It is clear that as well as mitigation, active removal of large debris objects from orbit is also necessary to control the space debris problem. Currently, the best estimates suggest we need to remove between 5-10 objects from the busiest orbits every year to stabilise the number of objects orbiting the Earth, and avoid the onset of a Kessler Syndrome scenario.
Developing de-orbit technologies has never been more urgent and the race is on to find a suitable solution to the space debris problem. SSTL is currently working on a satellite design that carries a net based capture system to catch debris and tow it down into the Earth’s atmosphere where it will burn up and be destroyed. This is a simple system that hopefully won’t have to be tailored to each individual item of space debris, making it cost-effective over the long term. It’s not the only debris removal project that takes inspiration from fishing– Astrium is working on a project to harpoon threatening debris
from close range and pull it downwards to burn up in the atmosphere using a propulsion system.
A team at the Surrey Space Centre (SSC), meanwhile, has a range of projects looking at de-orbiting solutions using a more passive approach, though still with inspiration from the maritime domain. Among these is Cubesail
– a project that will use a deployable sail to drag a Cubesat back into the Earth’s atmosphere for burn-up. Cubesail is a demonstration of a system that will be applicable to larger satellites and other objects in the future. Other projects that the SSC are working on involve innovative inflatable structures and new Electric Propulsion technology to address the challenge. Cranfield University has also created a de-orbit sail that will be tested on the UK’s space technology demonstration mission TechDemoSat-1
which is due to launch later this year. These are just a few of the many ideas being developed for space debris removal that range from using lasers to gently ‘nudge’ debris into new orbits, to robotic arms and even grasping ‘tentacles’.
There is no quick and easy solution to space debris but it is a problem that needs to be addressed if we are to protect our valuable resources in space. Cooperation of the entire global space community is the only way that we can make progress in preventing collisions. And the longer we wait, the more likely it is that we run the risk of a cascading Kessler Syndrome.