Scientists from across the globe agreed at the sixth European Conference on Space Debris yesterday (25 April). that there is an urgent need to address levels of space debris, particularly in the Low Earth Orbit (LEO) to reduce the chances of future collsions.

The findings from the conference, reported to be the ‘largest ever’ held in Europe, were announced during a media briefing at the European Space Agency’s (ESA) European Space Operations Centre in Darmstadt, Germany.

Presented to ‘over 350 worldwide participants’, the conference found that ‘current levels [of space debris] mean that we must soon begin removing debris from orbit’ and urged that ‘future space missions must be sustainable’.

According to the ESA, the removal of space debris from the LEO - defined as an orbit below 2000km (1,200 miles) – ‘is an environmental problem of global dimensions’, that requires ‘urgent’ research and development.

Space debris

There are currently 20,000 pieces of space debris with a diameter of 10cm or more being monitored in orbit, though the actual amount of debris in space may be much higher, perhaps in the millions.

Over the past 20 years gains had been made in reducing space debris production from spent rocket explosions, but these advances have been negated by a destructive anti-satellite test by China on a retired weather satellite in 2007 and a collision between the Cosmos 2251 and Iridium 33 satellites in 2009.

Cost of replacing satellites could cost over €100 billion

Head of the ESA’s Space Debris Office, Heiner Klinkrad, said: “There is a wide and strong expert consensus on the pressing need to act now to begin debris removal activities.

“Our understanding of the growing space debris problem can be compared with our understanding of the need to address Earth’s changing climate some 20 years ago.”

One of the strongest areas of consensus was about the potential for economic damage resulting from an increased need to replace the defunct satellites. Indeed, not only do current satellites perform vital economic and social functions, the cost of replacing the ‘approximately 1000 active satellites in orbit today’ would stand at around €100 billion, the conference found.

Further, the ESA found that when you factor in the functions performed by satellites, ‘the impact on the overall economy of losing these satellites would be several orders of magnitude higher [than €100 billion]’ and ’society would be severely damaged’.

“While measures against further debris creation and actively deorbiting defunct satellites are technically demanding and potentially costly, there is no alternative to protect space as a valuable resource for our critical satellite infrastructure”, Klinkgrad continued.

“Their direct costs and the costs of losing them will by far exceed the cost of remedial activities.”

‘Clean Space’

As a result of these findings, the ESA has decided to reinforce ‘a number of long-standing space debris-related research activities’, including developing a greater understanding of ‘the debris environment and its evolution’.

Dubbed ‘Clean Space’, this initiative ‘includes maturing technology to approach, capture and de-orbit targets’. One line of inquiry has been set up to develop ways of ‘passively’ and ‘actively’ de-orbiting devices.

Number of ‘catastrophic collisions’ increasing

However, despite a growing awareness of the need to reduce the amount of space debris in the LEO, a report published by the Inter-Agency Space Debris Coordination Committee (IADC) found that the number of ‘catastrophic collisions’ could increase dramatically over the next 200 years, despite an assumed post-mission disposal (PMD) compliance level of 90 per cent.

The report, ‘Stability of the Future LEO Environment’, is based on six member models created by six of the world’s space agencies; the Italian Space Agency (ASI), ESA, Indian Space Research Organisation (ISRO), Japan Aerospace Exploration Agency (JAXA), National Aeronautics and Space Administration (NASA) and the UK.

According to IADC the cumulative number of catastrophic collisions – defined as those ‘characterised by an impactor kinetic energy to target mass ration of 40 joules per gram (J/g)’,– could be as many as one every five years, but no less than one every nine.

One of the reasons behind the increase in catastrophic collisions is the expected occurrence of ‘a cascade of self-sustaining collisions’, triggered by collisions which would in turn generate further space debris, thus increasing the likelihood of further collisions.

It is expected that the ‘majority of catastrophic collisions’ would occur between the altitudes of 800km and 1000km, ‘due to high concentrations of space objects’ at those levels.

As such, the report concluded that current space debris measures ‘will not be sufficient to constrain the future LEO object population’ and that ‘more aggressive measures’, such as the ‘removal of the more massive non-functional spacecraft band launch vehicle stages, should be considered and implemented’.

However some have argued that the report’s assumed PMD compliance level of 90 per cent isn’t currently being observed. Should the compliance level be lower, it is likely the collision rate will be higher.

Lecturer in Aerospace Engineering at the University of Southampton, Dr Hugh Lewis, said: "We're certainly not at 90 per cent compliance with the 25-year rule yet, and we see explosion events on average about three times a year."

The IADC is an ‘international governmental forum’ whose primary purpose is the exchange of ‘information on space debris research activities between member space agencies, to facilitate opportunities for cooperation in space debris research, to review the progress of ongoing cooperative activities, and to identify debris mitigation options.’

Read more about the Inter-Agency Space Debris Coordination Committee and read IADC’s ‘Stability of the Future LEO Environment’ report.

To find out more about efforts to clean up space debris, read Resource's feature 'Waste of space'.