Each dot represents a bit of known space junk that's at least 4 inches (10 cm) in low-Earth orbit, where the space station and shuttles roam. In total, some 19,000 manmade objects this size or bigger orbit Earth as of July 2009; most are in low-Earth orbit. Countless smaller objects are also circling the planet.
Credit: NASA/Orbital Debris Program Office.
There are serious challenges ahead in mitigating space clutter now orbiting the Earth, problems that are exacerbated by the rise of small satellite launchings as well as using debris removal techniques that mimic anti-satellite systems.
Experts focused on the escalating menace of orbiting litter during ?Green Space: Addressing Space Debris - End of Life Operations,? a recent session at the Space 2009 Conference and Exposition in Pasadena, Calif., staged by the American Institute of Aeronautics and Astronautics.
Recent maneuvers by both the space shuttle and the International Space Station to avoid speeding space junk have helped flag the issue. So too has the February 11 collision between Russia?s defunct Cosmos 2251 satellite and a U.S. commercial Iridium spacecraft ? purportedly the first time two intact spacecraft have accidentally rammed into each other.
Moreover, China?s anti-satellite test in January 2007 peppered low Earth orbit with thousands of fragments that continue to plague the safety of healthy spacecraft operated by multiple nations.
Over 20,000 objects are being tracked at present, noted William Ailor, Principal Director of The Aerospace Corporation?s Center for Orbital Reentry and Debris Studies in El Segundo, California. ?A large majority of those are in low Earth orbit,? he said, consisting of dead satellites, spent rocket bodies, as well as large debris fragments from collisions and explosions.
Ailor said that untracked objects ? greater than one centimeter in size ? are estimated to range between 200,000 and 600,000 bits of flotsam, such as slag from solid rocket motors, liquid metal droplets from nuclear reactors, as well as items like lens covers that are shed during operations.
These objects, most of which flitter through low Earth orbit, are of a size that could take out a satellite, Ailor added, or could reduce the performance of orbiting assets.
One newcomer to the dilemma is the proliferation of tiny satellites, dubbed cubesats, ?making the orbital debris environment worse,? said John Lyver, Manager of the NASA Orbital Debris Program, Office of Safety and Mission Assurance at NASA Headquarters in Washington, D.C.
?These little satellites, while they are neat, while they are cheap, while they do great stuff?yes, they are increasing orbital debris and its uncontrolled orbital debris,? Lyver pointed out.
Active discussion is underway as to when the point will be reached when there are so many collisions between space junk that it grows exponentially.
?That debate is going on right now,? said chair of the session, Joseph Rouge, Director of the Pentagon?s National Security Space Office, Washington, D.C.
?Some in my office say that crossing point was 10 years ago?others say it?s 20 years away,? Rouge said. ?I think the real key is we need to do something about it or we?re going to be in trouble.?
Collisional cascading will start in low Earth orbit within a few decades, explained Heiner Klinkrad, head of the European Space Agency/European Space Operations Center?s Space Debris Office in Darmstadt, Germany.
?When we do long-term projections of the space debris environment, it turns out that space debris mitigation measures will delay, but not prevent, collisional cascading from happening in the low Earth orbit regime,? Klinkrad advised. ?This is even so if we stop all launching activities right now,? he added, and ?once that [cascading] process has started there is no way of controlling it again.?
Klinkrad said that the application of mitigation measures is a necessary but insufficient step to control the space debris environment. Additionally, space debris remediation will be a technically demanding and expensive undertaking, he said, but such costs must be viewed in relation to the value of space assets.
?Debris removal is part of a whole suite of solutions,? said Wade Pulliam, Program Manager for the Defense Advanced Research Projects Agency (DARPA) in Arlington, Virginia. That solution set, he said, includes satellite situational awareness, avoidance maneuvers, as well as removal of end-of-life satellites.
?I think [debris] removal is important and critical in the future?and it?s also a technically difficult problem,? Pulliam said. There are different solutions for different regimes at different particle sizes, he explained, so grappling with small particles in low Earth orbit in not the same as dealing with large derelict satellites in geosynchronous orbit.
Wanted: common formats and protocols
?Space is getting crowded,? especially in the geosynchronous satellite belt, said Joseph Chan, Senior Manager, Flight Dynamics for Intelsat in Washington, D.C. There?s definite need for better communication between satellite operators, he said, and for all to make use of common formats and protocols to better compute close approaches between spacecraft.
At the moment, ?our most comprehensive source? for knowing the whereabouts of space objects, Chan said, is a computer-generated two-line element set of orbital information such as those provided by the U.S. North American Aerospace Defense Command and used by NASA. But there are ?large uncertainties? in this kind of data, and there?s need to improve the way to detect close-approaches and monitor conjunctions of objects, he said.
?We don?t have a warp drive like on Star Trek,? Chan advised. ?We would like to detect close approaches a few days in advance.?
Debris removal or ASAT system?
DARPA?s Pulliam said that international participation is extremely important in debris removal. But first and foremost, ?we need to find innovative solutions that are as inexpensive as possible,? he said.
?In the end?I think economics are going to drive us,? Pulliam said.
Over the years, various orbital debris removal ideas have been championed: from debris-blasting laser systems, use of large junk-snagging foam spheres or nets, even space tugs.
Pulliam said that DARPA is engaged in assessing the orbital debris dilemma, eying a range of prospective ideas to deal with the issue.
?DARPA has initiated a study to examine the problem, survey possible solutions, and determine if emerging technologies and concepts can be combined to provide an economical solution to this problem,? Pulliam told SPACE.com.
To this end, DARPA and NASA are co-hosting an international conference on orbital debris removal in the Washington, D.C. area December 8-10, Pulliam explained.
?This first of its kind conference is solely dedicated to addressing the issues and challenges involved with removing manmade orbital debris from Earth orbit,? Pulliam said.
Ailor of The Aerospace Corporation said there?s potential for a commercial debris removal service. There might be a business case for an enterprising firm to make money on satellite repositioning or removing debris, he said.
However, Rouge of the National Security Space Office underscored the thorny issue of differentiating between a space debris removal system and an anti-satellite capability.
?The idea that a debris removal system is operated by one country?goes up and removes something that is owned by another?that?s going to be a touchy issue,? Ailor said.
ESA?s Klinkrad concluded: ?I guess the debris removal system has the potential to be an anti-satellite if you don?t ask the owner if he wants the spacecraft to be removed.?
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Leonard David has been reporting on the space industry for more than four decades. He is past editor-in-chief of the National Space Society's Ad Astra and Space World magazines and has written for SPACE.com since 1999.