Spring cleaning in space

Space is long overdue for a spring clean suggests a NASA-sponsored report which revealed the amount of space junk orbiting the Earth has reached tipping point – but what solutions are there?

When a satellite fails, it doesn’t get recovered and brought back down to Earth, nor do the jettisoned boosters used to propel space shuttles into orbit – instead they continue to circle the Earth, reaching speeds of up to 17,500 miles an hour.

Objects can stay in this low-Earth orbit for hundreds of years. As we send up more satellites and rockets to probe the world in which we live, we’re only increasing the likelihood of some of these objects colliding.

Space junk includes old boosters, failed and decommissioned satellites, and clouds of miniscule fragments like flecks of paint. There are 22,000 pieces of junk large enough to track from the ground, but there are thousands of smaller objects that could still cause serious damage to operational satellites – and the International Space Station.

Current capabilities mean space junk can only be tracked down to a certain size – anything smaller than 10cm is very difficult to track reliably with today’s technology. But that doesn’t mean collisions – and debris – can be stopped.

Two of the largest debris-generating events occurred in 2007 and 2009, and more than doubled the amount of catalogued debris fragments. In 2007, China blew the decommissioned weather satellite Fengyun-1C into 150,000 pieces larger than 1cm as part of an anti-satellite weapon test – this debris accounts for approximately 20% of all tracked space junk. Two years later, a defunct Russian satellite – Kosmos-2251 – smashed into the 12 year-old operational US communications satellite Iridium 33 creating thousands of tiny pieces of debris.

All geostationary satellites are required to remove themselves to a graveyard orbit at the end of their life – thus reducing the amount of time they spend in low-Earth orbit and the chances of a collision. Over time, this debris will be pulled into the Earth’s atmosphere and destroyed upon re-entry, like the Upper Atmosphere Research Satellite (UARS) – a defunct geostationary satellite which made an uncontrolled return to Earth in September 2011. A month later, a second satellite belonging to Germany – the Roentgen Satellite or ROSAT – plunged back to Earth.

But while some of this space junk is returning to Earth, more debris is being created than is destroyed. A new NASA-sponsored report by the National Research Council calls for international regulations to limit the junk and for more research into removing it.

The report – Limiting Future Collision Risk to Spacecraft: An Assessment of NASA Meteorid and Orbital Debris Programs – suggests space junk could cause fatal leaks in spaceships and destroy valuable satellites. A statement from the Research Council said computer models show the amount of orbital rubbish “has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures.”

[caption id="attachment_26194" align="alignleft" width="200" caption="An impact crater on one of the windows of the Space Shuttle Challenger following a collision with a micrometeoroid – thought to be a fleck of paint – during STS-7"][/caption]

This scenario has been dubbed the Kessler Syndrome after Donald Kessler, the NASA scientist who first proposed the situation in 1978.

Kessler, the retired head of NASA’s Orbital Debris Program Office, who also led this research said: “Even if we add nothing else to orbit, the amount of debris could continue to increase as a result of random collisions between fairly large objects. You’d generate debris faster than the natural decay process could return it.”

“We’ve lost control of the environment,” said Kessler. “Space is becoming essential to our current civilisation. If for any reason we weren’t able to use satellites as easily as we do today, there would be a reduction in the standard of living.”¹

The report – issued in September 2011 – examined NASA’s efforts to understand the meteoroid and orbital debris environment, focussing on the measures the agency has or has not taken to mitigate the risks.

It made recommendations to provide a basis for prioritising efforts and allocating funds to the agency’s numerous maturing meteoroid and orbital debris (MMOD) programs. Although NASA has had an official orbital debris program in place since 1979, there has been little funding for clean-up initiatives, and nearly all programs have a single member of staff.

However, the report’s recommendations aren’t without problems – only 30% of the debris can be attributed to the US, and many countries are still very protective of their technology. According to the international legal principle, no nation may salvage other nation’s space objects – so there’s only some much NASA can do. NASA must collaborate with commercial, national and international agencies to develop information about the costs of debris avoidance, mitigation, surveillance and response.

Despite detailing over 30 different findings and making 20 recommendations to NASA, the new report does not actually make any recommendations about how to clean up the field of debris.

[caption id="attachment_26195" align="alignright" width="200" caption="Image of the entry hole created on Space Shuttle Endeavour's radiator panel by the impact of unknown space debris"][/caption]

However, a Defense Advanced Research Projects Agency (DARPA) report – dubbed Catcher’s Mitt – was released early last year and did mention a few space spring cleaning options. It listed harpoons, nets, tethers and magnets, plus an umbrella-shaped device to push the debris towards Earth’s atmosphere where it would burn up on re-entry, or to push it up even higher, into a safer orbit. However, Catcher’s Mitt doesn’t actually recommend the use of any of this technology².

Kessler said he liked one company’s idea of a satellite armed with nets which can be launched at wayward junk. These nets would be fitted with an electromagnetic tether which could pull junk down to a point where it would burn up, or boost it into a safer orbit.

Other suggestions have included a grappling spacecraft that could attach rockets to larger pieces of debris and propel them towards the Earth – although this could create more debris if the grappler shreds the junk – and covering the debris in foam, causing a greater drag and speedier demise of the junk.

Among the more promising ideas is a laser broom – a ground-based laser. In the early 1990s, researchers predicted a ground-based pulsed laser could ablate or vaporise the debris and cause a rocket-like thrust to slow it down. The scheme uses photon pressure to disturb the orbit of the debris – done repeatedly, this could alter the orbit enough to reduce the risk of collisions. Although this type of system will just move debris out of the way, continued application could cause the debris to lose altitude where it could become subjected to atmospheric drag and eventually return to Earth. They suggested one laser was capable of clearing all the debris within three to five years.

In late 1990s the US Air Force were working on a laser broom design called Project Orion – it concluded that a ground-based laser was feasible and cost-effective, but an international agreement forbidding the testing of lasers in space means this technology has not progressed any further. A similar proposal sees the laser replaced with a beam of accelerated ions and may also have uses in deflecting asteroids.

Jim Hollopeter – who helped design rockets in the 1980s – realised that space would become cluttered and suggested using aging rockets loaded with water to spray orbiting junk. The extra-terrestrial shower would eventually guide junk towards the atmosphere where it would burn up on re-entry, along with the rocket.

Hollopeter said he was excited by water-basting because it was so low-tech: “This is basically the cheapest way I could come up with.”³

Other suggestions have included a remotely controlled vehicle to rendezvous with debris and capture it before returning it to a central station. The MDA Space Infrastructure Servicing Vehicle (SIS) is being developed by a Canadian aerospace firm. The SIS is due to be launched in 2015 with the aim of acting as a small-scale in-space refuelling depot for communications satellites in geosynchronous orbit. It will push dead satellites into graveyard orbits and is designed to have the potential for high leftover fuel margins so it can capture and store debris.

However, none of the clean-up technologies have been considered viable options – each would be as expensive as launching a spacecraft said NASA scientist Nicholas Johnson. Any clean up technologies will require significant research and development before being successfully implemented, and the ideas would need to be designed and tested to work under actual operating conditions.

While a spring clean is space might be necessary, it just isn’t practical – at least for the moment. Space agencies need to remove damaged satellites and spent propulsion systems, but they also need to be thinking about long-term strategies to minimise the amount of junk they add to the melee. So it looks like the only thing we can do is try to limit the amount of debris we create and keep tracking our junk.

References:

1. Space junk problem is more threatening than ever, report warns http://www.space.com/12801-space-junk-threat-orbital-debris-report.html
2. Space pollution: Junk needs clean up, scientists say http://www.huffingtonpost.com/2011/09/01/space-pollution-junk_n_945020.html
3. Cosmic Question, how to get rid of all that orbiting space junk http://online.wsj.com/article/SB123672891900989069.html

Kerry Taylor Smith Kerry is Web Editor at Laboratory News, and has a degree in Natural Sciences from the University of Bath