Mounting Space Debris Poses Danger
From spent rocket stages and old satellites to lens caps, bolts, and chips of paint, it’s all up there drifting around in outer space.
And since it travels at speeds as high as 28,000 kilometres per hour, this space debris poses a significant threat to spacecraft.
However, getting rid of it is no simple task. It will need more money, better engineering designs, and international cooperation to solve the growing problem of Earth-orbiting debris, experts say.
“Impact by an object larger than 10 centimetres will destroy your spacecraft totally and release a big cloud of fragments which will also deteriorate the environment at that altitude,” said Dr. Heiner Klinkrad, Head of the European Space Agency’s (ESA) Space Debris Office at the European Space Operations Centre in Darmstadt, Germany.
Meanwhile, debris as small as 1 millimetre can cause damage and even disable part of a spacecraft depending on where it hits, he said.
Since launching the first spacecraft, Sputnik I, in 1957, humans have put some 6,000 satellites into orbit serving civil, commercial, and military applications. Today, we rely on about 800 active satellites for numerous everyday activities including communications, travel, trade, earth observations, weather monitoring, and news and entertainment.
But space missions have produced huge amounts of debris that can stay in orbit for decades or longer.
The U.S. Space Surveillance Network (SSN) regularly tracks about 13,000 catalogued objects 10 centimetres or larger. Operational spacecraft comprise only 6 per cent. The rest are debris that includes retired spacecraft, rocket bodies, and mission-related items released during operations.
About 50 per cent are fragments resulting from the breakup of over 200 of these manmade objects. Meanwhile, radar and telescopes show numerous other smaller debris particles that are not routinely tracked.
“It is estimated that there are over 300,000 objects measuring between 1 and 10 cm in diameter, and billions smaller,” according to Space Security 2008, an annual Canadian report produced by a group of governmental, non-governmental, and academic organizations.
The Inter-Agency Space Debris Coordination Committee (IADC), a group of 11 space-faring nations composed of about 100 top-ranking scientists, warns that the problem affects spacecraft, crew safety on manned missions, as well as people on the ground.
“As the population of debris continues to grow, the probability of collisions that could lead to potential damage will consequently increase. In addition, there is also the risk of damage on the ground, if debris survives Earth’s atmospheric re-entry.”
Space-faring Nations Must ‘Avoid Intentional Destruction’
Of the over 200 breakups, most were explosions, but there were also three accidental and two intentional collisions. The good news is that the three accidents only created one to four new pieces of tracked fragments each.
The U.S. shot down the failed USA-193 satellite in February this year to prevent its toxic fuel from endangering people in case it fell in a populated area. It was at a fairly low altitude and all the catalogued debris had re-entered the atmosphere, said Mr. Klinkrad.
However, China’s anti-satellite (ASAT) test against its aging Fengyun-1C weather satellite in January 2007 was a different story. According to NASA’s Orbital Debris Program, by January 2008 the SSN had catalogued 2,317 fragments and was still identifying more.
The program estimates that the test created at least 150,000 fragments one centimetre and larger.
What makes matters worse is that the debris is in the middle of the most crowded region in space — between 800 and 1,000 kilometres in the low Earth orbit (LEO) regime.
Project Ploughshares’ Jessica West, managing editor for the space security 2008 report, said the growing debris problem “is more to do with…reckless activity, the purposeful destruction of objects in space” than with day-to-day space activities.
However, 2007 also saw a successful landmark: the adoption of debris mitigation guidelines by the United Nations, based on content developed by the IADC.
One of the guidelines requests space-faring countries to “avoid intentional destruction and other harmful activities,” Ms. West said.
In addition, “nationally many of the big space-faring countries also have stringent rules placed on their companies and civil space agencies.”
SSI’s Space Security 2008 report says the Chinese ASAT test created the “largest manmade debris field in history.”
Prevention and Mitigation
The simplest measure is to design spacecraft to reduce the number of mission-related objects released into space during operations, said Mr. Klinkrad.
And protective shields can improve spacecraft survivability against debris impact, such as those used by the International Space Station (ISS) and the Canadian Radarsat.
The Canadian Space Agency (CSA) is working with universities and industries to study how hyper-velocity debris propagates through spacecraft and to devise more robust spacecraft designs.
Dr. Darius Nikanpour, Manager of Space Technologies – Materials and Thermal Group, said CSA is also developing self-healing materials for spacecraft.
If a spacecraft fails or when it reaches end of life, another guideline is to prevent accidental explosions via “passivation” measures that remove all remaining stored energy onboard including fuel, pressure build-up, and battery charge.
Noting that as the number and mass of orbital debris increase, most new debris will likely come from collisions, the guidelines stipulate limiting this risk by using space surveillance data to adjust launch time or manoeuvre spacecraft out of harm’s way.
Such a manoeuvre took place on August 27 when ESA’s Jules Verne Automated Transfer Vehicle was used to move the ISS out of the way to avoid collision with a piece of debris.
The guidelines also stipulate that spacecraft and rocket stages be removed from their orbit when their mission ends, said Mr. Klinkrad.
Those at high altitudes in the geostationary ring (approximately 36,000 kilometres above Earth) should have enough remaining fuel to propel them to a “graveyard orbit” about 300 kilometres higher where they cannot perturb functional satellites lower down, he said.
And those in the low Earth orbit (LEO) region (below 2,000 kilometres) should be taken down by natural forces or active measures within 25 years.
A related technology direction at CSA is “demise technology that breaks up the satellite so it ensures that there are no parts left which could survive the re-entry and land on populated areas,” said Mr. Nikanpour. For example, “novel reactive materials” are being studied that will start a reaction in the heat of re-entry to ensure a tank disintegrates.
Call for an International Treaty
Recent NASA analysis has indicated that in the crowded LEO region, even applying all of these measures will still not be enough.
NASA suggests the need to actively remove debris. Although the technology exists, such as using a tether to swing an orbital stage back into the atmosphere or mounting and igniting a solid rocket motor on an orbital stage to de-orbit it, the costs remain prohibitive.
“It’s much less expensive to plan your mission beforehand to be removed from orbit after it ends rather than do that retroactively,” said Mr. Klinkrad.
This requires goodwill, more financial investment, and extra design efforts, he said.
Prof. Ram Jakhu at the McGill University Institute of Air and Space Law in Montreal emphasized that the mitigation guidelines are voluntary and not legally binding under international law. Therefore, “they are not sufficient in my view. Much more needs to be done.”
“International cooperation is indispensible” to stop intentional debris creation, mitigate and reduce debris, and regulate the problem, said Mr. Jakhu, who is also the research director for Space Security 2008.
He called for greater technological research and better information sharing among countries. “This kind of research should form a basis for negotiations for international treaties which mitigate space debris and also to a degree ban the creation of debris,” he said.
Mr. Jakhu and Mr. Klinkrad are both presenting this week at an international conference on space safety in Rome, Italy.