Space Junk: A Risky Game of Space Invaders
Washington, Nov 16, 2010 - When, in the early hours of February 10, 2009, an American communications satellite called Iridium 33 smashed into a Russian military satellite 500 miles above Earth's surface, the experts called it an "unprecedented event". A better description might have been "an accident waiting to happen".
The space around our planet is no longer a lonely place. Vital orbits near and far from Earth's surface are shrouded in a perpetual and perilous shroud of debris and defunct satellites. In addition to thousands of large fragments, Nasa estimates there are at least half a million objects between 1cm and 10cm wide circling Earth. Even objects this small can, when hurtling at orbital velocities, cripple a satellite. And as their number grows, so does the risk of further collisions, and the release of even more shrapnel. The resulting vicious circle threatens not only the multi-billion pound satellite industry, but the safety of manned missions into space.
"The crowding in low Earth orbits is a really big issue," says Professor Martin Barstow, of the University of Leicester, "and the volume of debris will only increase unless we manage to stop it accumulating, give greater protection to satellites or clear the debris." Russia's Cosmos 2251 had been circling the planet aimlessly for 14 years, following just two years of active service after its launch in 1993. At the end of its useful life, there had been no plan to move it out of harm's way.
Fortunately, the Cosmos-Iridium smash may yet be viewed as the event that catalysed a pivotal change in attitudes to space safety: there are signs that the United States government, in particular, has accepted that things cannot go on as they are.
Of key concern are two vital areas. The first, between 200 and 1,000 miles from the planet's surface, is known as "low Earth orbit", used by the Hubble space telescope, the International Space Station and the space shuttles that restock it. The closeness to Earth makes repair missions relatively easy – but to resist gravity, objects in these orbits must travel very rapidly (approximately 17,000mph). The resulting friction against the edge of the atmosphere – and bombardment by debris – ultimately causes the devices to fail. Examining the Hubble, says Prof Barstow, "you can clearly see the severe damage that tiny objects have caused. Even dust particles travelling at very high velocities can enter and knock out a satellite if they hit the wrong part."
Because of the speed at which these satellites travel, it is hard to bounce communications signals off them, or use them to observe specific events, such as weather patterns. This is where geostationary satellites come in. Once in orbit, at approximately 22,000 miles from the planet, these craft circle in perfect synchronicity with Earth, effectively resting at a fixed point in the sky. This allows them to monitor a particular area, or to be used as a way station for the phone calls, radio signals and electronic data transfers that keep the information economy ticking over.
There are two problems, however. First, the height of the orbit makes these satellites effectively impossible to repair. Second, the need to place them far enough apart to avoid harmful radio interference means that there is a limited number of "slots" available, adding to concerns about overcrowding. There are more than 200 dead satellites in geostationary orbit, and the International Association for the Advancement of Space Safety (IAASS) has warned that this could increase fivefold within 10 years.
The growing importance of this problem was recognised in June, with the publication of the US's National Space Policy – a statement of intent that commits it to working with other nations to keep space safe and sustainable.
In particular, the document commits the US to "pursue research and development of technologies and techniques… to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment". Tommaso Sgobba, president of the IAASS, describes this as "a major development". "Finally," he says, "the US has realised that things could not go on as they were."
Professor Richard Crowther of the UK Space Agency, who advises the Government, agrees. "Underlying the new policy," he says, "is an acceptance by the US that it cannot continue to exploit space in isolation. Following the recent Cosmos-Iridium crash, there was a recognition that to manage the growing collision hazard in space, the US needed to share more information with other space-faring nations."
Such sharing of "space situational awareness data" would, says Dr Thomas Kelso of the Center for Space Standards & Innovation in Colorado, significantly reduce the number of false alarms, and allow some satellites to be steered out of the way. The importance of this was underlined last year when a speedy warning from the US allowed a Nigerian satellite to avoid colliding with another object. The American declaration also addressed the growing presence of commercial operators, and the need for them to make data about their orbital fleets available.
Some experts, including Prof Barstow, suggest this reflects a cash-strapped Nasa's intention to concentrate on blue-sky projects rather than commercial operations, which it thinks should be funded by corporate beneficiaries.
The private sector, in the form of the Space Data Association, is putting into place voluntary measures to exchange orbit data, and avoid collisions. And the UN has also become involved, with the formation of a committee headed by Dr Peter Martinez of the University of Cape Town in South Africa. His working group on the long-term sustainability of outer space, which is due to report in 2014, will look at the benefits of sharing information in several spheres, including space weather, such as sudden flare-ups in the solar wind. "We shouldn't underestimate this," he says, "There have been spacecraft lost due to space weather events."
Human safety is not being forgotten, either. With Richard Branson's Virgin preparing to send tourists into space – and another 26 companies around the globe developing services or vehicles for recreational space travel – experts, including Prof Crowther, are quietly pressing for new standards on vehicle design, take-off equipment and passenger conduct. Ideally, this would be along the lines of the rules in place for the civil aviation industry, although Prof Crowther says he "would not expect international laws to be forthcoming in the near term". Instead, he sees guidelines gradually gaining acceptance and eventually hardening into international agreements.
The Chinese, he thinks, can also be brought on board, especially if they are seeking to make diplomatic amends after a controversial episode in 2007. That saw them use a dead orbital satellite as target practice for an anti-satellite weapons system – releasing yet more debris into space.
• If debris does strike a manned craft, the results could be catastrophic. However, an Anglo-Italian firm is developing an emergency space parachute that can protect astronauts from the colossal heat as they re-enter Earth's atmosphere at 18,000 miles an hour.
The Spacecrew Emergency Module will enable individuals to escape a doomed spacecraft before it incinerates on re-entry. The inflatable device would be stored in a backpack, before – with the flick of a switch – enveloping the astronaut in a heat-proof silicon cone that would protect him as he hurtles into the atmosphere (where, in addition to the gravitational stresses, the surrounding air would heat up by thousands of degrees).
Once its wearer was safely through the atmosphere – a hair-raising, 30-minute descent – the device would turn into an ordinary parachute, landing safely on the ground. Aero Sekur engineers hope that the device will be on sale within 10 years.
• If a satellite loses power, or is about to collide with another object, is there anything we can do if communications are lost? Not at the moment – but scientists at the German Aerospace Centre are designing robots that will be launched and controlled from Earth, docking with failing satellites to refuel, steer and repair them. The robots will also be able to push defunct craft into more distant "graveyard" orbits.
A more ambitious version of the project aims to build robots that can catch malfunctioning or decaying satellites as they tumble through the skies from low Earth orbits, pushing them into the oceans to avoid damage and loss of life on land.
Original article found here.