The largest-ever gathering of experts on the subject recently met in Darmstadt, Germany at the Sixth European Conference on Space Debris, under the auspices of the European Space Agency. MOD DCB examines the problem of space junk, the challenge it presents and the solutions proposed.

According to the European Space Agency (ESA), the time has come to remove space debris from the Earth’s orbit. The largest-ever gathering of experts on the subject met in Darmstadt, Germany on 22-25 April 2013 at the ESA-hosted Sixth European Conference on Space Debris to discuss the issue. Their verdict? Governments and the aerospace industry need to take space debris seriously, because the problem isn’t getting better: it’s getting worse.

Space debris, or junk, in near-Earth orbit is an ongoing problem – experts estimate there are over 170 million pieces of such debris orbiting the Earth, including some 29,000 objects larger than ten centimetres in diameter. Worryingly, only 17,000 of these objects are currently being tracked.

At average speeds of 15,500 mph, all of these objects are a potential hazard to the immensely valuable satellite infrastructure currently circling the planet.

The debris cluttering the orbital paths of operational spacecraft ranges from old rocket bodies and disused satellites to fragments resulting from disintegration, erosion and collisions. Since trajectories overlap, debris may collide with spacecraft and cause damage. There have been few costly collisions in Earth orbit to date but collisions are expected to rise.

One of the most notable incidents was in 2009 when an Iridium Satellite LLC communications satellite was destroyed in a collision with the defunct Soviet Kosmos 2251 satellite. The clash produced two large clouds of debris consisting of over 2000 pieces and resulted in limited disruption to Iridium’s mobile voice and data communications service. In this one instance, two large orbiting objects became 2000 small orbiting fragments of debris,

A recent almost disastrous near-miss occurred when NASA’s $690 million Fermi Gamma-ray Space Telescope narrowly avoided a direct hit with the defunct 1.5-ton Russian reconnaissance satellite Kosmos 1805 in April 2012.

Satellites are relied on worldwide for communications, navigation, observation, weather, broadcast and climate-monitoring operations and provide constant benefits to industry, citizens and economies. They are also expensive to replace – the replacement cost for the approximately 1000 active satellites in orbit today is estimated to be around €100 billion.

The European Space Agency says society would be severely affected if satellites were to be regularly damaged in orbit. This danger will only grow more real as the problem worsens.

In 2006, a NASA computer simulation exercise suggested that even if no new satellite launches took place, the amount of space junk will sustain until about 2055, when it will begin to increase of its own accord. This scenario of ‘collisional cascading’ was proposed by Donald J Kessler in 1978 and is known as the Kessler Effect. Other predictions have the Kessler Effect occurring much sooner. Richard Crowther of the UK’s Defence Evaluation and Research Agency believes it will begin by 2015 at the latest.

What practical steps can be taken to deal with this problem?

Experts at the recent ESA conference agreed that the current levels of space debris mean that the active removal of debris from orbit is essential, with research and development urgently required for pilot ‘cleaning’ missions. ESA said that five to ten large objects need to be collected from space every year to help reduce smashes and the risk of fragments being sprayed into space causing even more damage. It also said there is an urgent need to fly satellites in the future without creating new debris.

Heiner Klinkrad, Head of ESA’s Space Debris Office, 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.”

A number of long-standing space debris-related research activities are being reinforced by the Agency. This includes improving understanding of the debris environment and its evolution using novel, sensitive measurements and improved modelling of debris sources.

ESA’s new Clean Space initiative includes maturing technology to approach, capture and de-orbit targets, and a mission is already under study. Clean Space will also develop techniques to mitigate the problem, such as passive and active de-orbiting devices and the means to ‘passivate’ retiring satellites. The Darmstadt event saw many examples of technologies that could be used to do achieve this.

In one of the more imagination-catching solutions, EOS Space Systems told the conference that its laser systems could help move space junk out of the ‘danger zone’. The company builds custom laser systems for space surveillance, optical communication, laser ranging and other applications. The option offered by EOS Space Systems is one that would see ground-based lasers sending just enough energy to push junk away from dangerous orbits.

A similar solution is on offer from British company Astrium for both the removal and surveillance of space debris. Astrium has also developed a harpoon capture system that operates by attaching a harpoon to a junk object before reeling it in and disposing of it in the Earth’s atmosphere where it would safely burn up and not create any further debris.

Another project, which has been funded by Astrium, has seen the University of Surrey develop a device called CubeSail. CubeSail is a 3kg nanosatellite fitted with a solar sail, which can attach itself to an object and use its sail to slow it down and burn it up in the atmosphere. The process has been described as a ‘satellite suicide mission’ and CubeSail is expected to be available for shifting existing debris from later in 2013.

Other options include capturing debris in a giant net in a project being developed by Star Technology and Research Inc. Their ElectroDynamic Debris Eliminator would capture orbital debris in a net and then drag it out of harm’s way. Russian company Energia announced plans in 2010 for a nuclear-powered pod that would grab disused satellites and destroy them by dropping them into the atmosphere or into the ocean. This pod is to become operational from 2023 and will have a 15-year lifespan at a cost of $1.9 billion.

The Sixth European Conference on Space Debris attracted over 350 participants worldwide representing almost all the major national space agencies, industry, governments, academia and research institutes. This serves to show that the removal of space debris is an environmental problem of global dimensions that must be assessed in an international context. The ultimate goal is to prevent Kessler’s cascade of self-sustaining collisions from setting in over the next few decades. ESA says that further to clean-up, future space missions must be sustainable, including safe disposal of objects when they are completed. Much depends on it.