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.
Cascading
problem
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."
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.
advertisement
