Humans leave their mark in space

The little-known problem of space debris threatens to make useful orbits impractical if current space exploitation practices do not change soon. Heiner Klinkrad, Head of the ESOC(1) Space Debris Office, takes stock after a Chinese ballistic missile was used to destroy the decommissioned Feng-Yun 1C weather satellite on 11 January 2007, creating at least 1 600 new pieces of space junk.

© CNES/David Ducros © CNES/David Ducros

“This is the most important incident ever, in terms of the number of pieces of debris created,” comments Heiner Klinkrad. “The pieces identified so far have increased the catalogue of space debris built up over 15 years by 15%,” he adds. “Although space missions can still be conducted safely today, American studies show that, even if we were to stop all space activities, the space debris population would grow at certain altitudes and the risk of collision would increase.”

Collisions and explosions

There are a number of different causes of space debris. Some are caused by accidental collisions, the most famous of which was undoubtedly that of the French satellite Cerise. “Ten years after the upper stage of the Ariane rocket was blown up, one of its fragments struck the French satellite in 1996,” explains Heiner Klinkrad, adding that two further collisions have been observed since then.

Some collisions are deliberate, such as the one which the Chinese caused in January 2007.

But, the most common cause of space junk is explosions. “Around 200 have been recorded since space exploration began. However, it has become a much more common occurrence in recent years. The former average of four to five explosions a year has now doubled. These accidents are caused by launchers that have been cast adrift after they have sent satellites into orbit, or by old spacecraft whose residual fuel has blown up.”

Dodging missiles

There are an estimated 18 000 large fragments that are observable from the ground, each measuring more than 10 cm; 11 500 of these are catalogued. ESOC, based in Germany, routinely stages manoeuvres to avoid these large articles of debris. But there is no way of dodging the 550 000 or so pieces between 1 and 10 cm which cannot be pinpointed. As they travel at speeds of up to 70 000 km per hour, they are capable of doing considerable damage.

ESA research is also progressing to model the path of space debris and to design advanced protection systems, in particular by impact studies on objects that have fallen back to Earth.

Changing practices

Even though such avoidance and protection measures reduce the risks caused by human activity, current practices must change if we are to reduce the increasing quantity of debris caused by chain reactions. “First we should avoid releasing objects into space unless this is necessary to the success of the mission, such as ejecting optical lenses after use. We must prevent explosions by venting or depleting the satellite’s fuel and pressurant, and by passivating the spacecraft as soon as the mission and its disposal phase has been completed. Lastly, the most effective way to reduce debris is to deorbit objects from useful orbits such as geostationary orbit, where there is fierce competition for scarce slots. At an altitude of 36 000 km, satellites on geostationary orbit cannot be brought back into the Earth’s atmosphere because they would be destroyed by overheating. When such geostationary satellites are decommissioned they are therefore shunted onto what is known as a ‘graveyard’ orbit, 300 km higher than geostationary orbit. However, low earthorbiting satellites may be allowed to disintegrate upon re-entry into the Earth’s atmosphere,” explains Heiner Klinkrad.

International efforts have now led to the adoption by 67 countries of the principles laid down by the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). However, there is still no agreement that is binding on the signatories and, according to Heiner Klinkrad, “If we do not change our ways fast, in 50 years’ time there could be more accidental collisions than explosions. International legislation in this field would help to prevent such a scenario.”

(1) European Space Operations Centre of the European Space Agency (ESA)