Space debris: an economic issue

On 10 February 2009, a collision occurred in low Earth orbit 800km above Siberia between one of America's 66 Iridium commercial telephone satellites and the Russian Kosmos-2251 military satellite, which had been out of service for 14 years, generating hundreds of pieces of debris at an altitude occupied by a very large number of satellites. This unprecedented satellite-to-satellite crash – all previously recorded instances had been of satellites being struck by debris – has reignited the debate on space congestion and the accumulation of debris.

What is this debris?

While it is hard to calculate accurately the number of objects in orbit above our heads, their origin and their possible impacts have been clearly identified. There are an estimated 3,000 active or inactive satellites orbiting the Earth, together with hundreds of thousands of pieces of detritus of all types. Beyond an altitude of 200km (extra-atmospheric space), there are launcher stages which have remained in orbit, satellites which have ceased to function or have reached the end of their operational life, waste from manned vessels or orbital stations, and debris resulting from fragmentation.

Inner space also abounds in objects of human origin (assembly components, jettisoned protective covers, bolts, shields, etc), which collide and in turn create large numbers of fragments. Depending on the material they are made from and their orbit, the lifespan of all of these objects can be anything from six months to several million years.

To date, about 13,000 objects, varying in size from 10cm to 30cm in low Earth orbits and up to 1m in geostationary orbit, have been officially identified and are being tracked (using ground-based radar or telescopes, or space-borne instruments). Then there would seem to be between 200,000 and 250,000 fragments smaller than 10cm, tens of millions (source: CNES) of 0.1cm–1cm diameter fragments, with micrometric objects representing a figure of about 10¹³ or 10¹⁴.

Image: Objects varying in size from 10cm to 30cm in low Earth orbits (left) and up to 1m in geostationary orbit (right). These artist's impressions are based on actual density data. The relative size of the objects in the pictures is not to scale so that they can be seen more easily.

Impact on a satellite (© CNES)

Objects such as these, even when no bigger than a millimetre, can create considerable damage owing to their extremely high orbital speeds (8–10km/s) and thus their kinetic energy. An item half a millimetre in diameter, travelling at 26,000km/h can easily pierce an astronaut's spacesuit, while a particle larger than one centimetre can disable a satellite. For example, in July 1996 a fragment of an old Ariane launcher seriously damaged the French Cerise satellite, striking it at a relative speed of 50,000km/h.

Aleksandr Serebrov, a Soviet engineer and cosmonaut, recently told Izvestia newspaper about the scare he had on board Mir: "One day, I was looking out of the station window and I saw a twisted piece of metal the size of an armchair heading straight for us. It was terrifying!" Similarly, there is a risk of larger and above all denser items passing through the atmosphere without completely disintegrating before falling back to Earth. Finally, some waste elements also arouse concern because of their radioactivity: old satellites, mostly Russian and American, contain radioactive materials which, were they to collide with other debris, could pollute inner space.

So what can be done?

Although not yet critical, the build-up of objects of human origin in orbit is beginning to pose problems, in particular with regard to the safety of current and future space missions. The scientific and space community’s concern was demonstrated at the 5th European Conference on Space Debris organised by ESA from 30 March to 2 April this year, which was attended by a number of representatives from Astrium. The issue is to limit the risks on the ground and in orbit, both by restricting the amount of debris in orbit and by protecting what is known as the zones of interest in space, such as low Earth orbits, mid-Earth orbits (20,000km altitude), geostationary orbit and geosynchronous orbits.

"As a responsible company and the leading industrial firm in the sector, we are fully aware of the situation and are clearly very concerned by the problem of space congestion and space debris,” says Robert Lainé, Astrium’s Chief Technical Officer. “We must ensure that space remains a safe place for the applications of today and tomorrow and we must make an active contribution to mitigating the amount of debris."

How can this be done?

First of all, the rules of good conduct already laid down by various space agencies (ESA, CNES, NASA, JAXA) and the Inter Agency Space Debris Coordination Committee (IADC) must be followed, as they aim to mitigate the generation of new debris in space. These rules should eventually lead to stricter legislation, both in France and at an international level, under the aegis of the UN. Preparation for this phase, however, must begin now.

‘Smart’ technologies must then be developed and used in the manufacture of satellites, launchers and space infrastructures in order to minimise the generation of debris in the operational and post-operational phases.

Finally, medium- and long-term solutions must be examined: although complex and costly, it is possible to eliminate existing debris and to repair satellites, and many ideas are currently being studied.

Astrium already applies several solutions for debris mitigation. "For telecommunications satellites in geostationary orbit,” says Astrium Satellites’ Telecoms Marketing Manager Gérard Berger, “we adhere closely to the recently tightened international regulations, along with the Code of Conduct laid down by the main European agencies. We make it a point of honour to manufacture ‘clean’ satellites, which remain intact and release no debris into space during their operational phase. They are also capable of leaving geostationary orbit when they reach the end of their life in order to make room for other operational satellites and avoid running the risk of interfering with them. Once their operational mission has been completed, they must therefore have enough propellant left to climb to 300km above geostationary orbit. There, they are rendered ‘passive’ – the various tanks are depressurised so that, in the event of the deactivated satellite being struck by a micrometeorite, there is no risk of explosion and new debris being created."

The same integrity precautions are taken for observation satellites in low Earth orbit. However, in certain cases they too have additional propellant so that they can make extremely rare avoidance manoeuvres or, more frequently, a controlled atmospheric re-entry during which they will break up (this was the case with Spot 1). Other techniques are currently being examined, such as passive aero-braking.

Image: The significant measures adopted today at Astrium to mitigate the creation of debris include: boosting the orbit of an end-of-life satellite to 300km above geostationary orbit; the use of ‘smart’ technologies to prevent satellites releasing debris into space; passivation of the energy sources on-board launch vehicles or satellites.

For space infrastructures such as the ATV and Columbus, Astrium has developed special coatings and shields to protect the astronauts’ living quarters from impacts by particles of debris and micrometeorites. Part of the ATV’s mission is to help the International Space Station (ISS) to make avoidance manoeuvres out of the path of potentially dangerous debris. At the end of its mission, the ATV is loaded with station waste and de-docks from the ISS prior to controlled disintegration by burn-up in the dense layers of the atmosphere, over the Earth's largest uninhabited area, the South Pacific.

With regard to Ariane 5, a number of specific rules recommended by the IADC Code of Conduct are applied, aiming to limit the intentional generation of debris by launch vehicles. These include the use of pyrotechnic and solid rocket systems (boosters, manoeuvring rockets) which do not generate particles larger than 1mm, and limitation of the number of debris items released during launch operations to one for a single-payload launch and two for a multiple-payload launch. Another rule aims to limit the accidental creation of debris: this involves passivation of the energy sources on-board the launch vehicle (pressurised tanks or reservoirs, batteries).

Surveillance, regulation, prevention, protection, and, tomorrow elimination: these are the watchwords for the new economic debate surrounding space debris in the coming years.

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Space debris: an economic issue