PASADENA, Calif. — The U.S. Defense Advanced Research Projects Agency (DARPA) and NASA are preparing to co-host an international conference this year focused on ridding space of manmade debris endangering spacecraft orbiting the Earth.

Wade Pulliam, a DARPA program manager helping organize the conference, said the Dec. 8-10 gathering will be the first conference “solely dedicated to addressing the issues and challenges involved with removing manmade orbital debris from Earth orbit.”

In advance of the conference, DARPA is asking all comers to send in ideas for clearing away manmade space debris ranging in size from as small as a millimeter to as large as spent rocket bodies and defunct satellites. A formal request for information was issued Sept. 17 with responses due Oct. 30.

Speaking at the American Institute of Aeronautics and Astronautics’ Space 2009 conference here the same day DARPA put out the call for ideas, Pulliam and other orbital debris experts said the challenges associated with removal are both technical and political.

But unless action is taken to rid Earth orbit of some of its space junk, the risk of losing satellites and other spacecraft to in-orbit collisions will continue to grow.

Adding to the problem is the proliferation of tiny satellites, such as cubesats.

“These little satellites, while they are neat, while they are cheap, while they do great stuff … they are increasing orbital debris — and it’s uncontrolled orbital debris,” said John Lyver, an orbital debris expert in NASA’s Office of Safety and Mission Assurance in Washington.

Joseph Rouge, director of the Pentagon’s National Security Space Office, said a debate is under way as to when the point will be reached that there are so many collisions between space junk that incidents grow exponentially — a phenomenon referred to as collisional cascading.

“Some in my office say that the crossing point was 10 years ago … others say it’s 20 years away,” Rouge said during a space debris panel discussion here. “I think the real key is we need to do something about it or we’re going to be in real trouble.”

Heiner Klinkrad, head of the European Space Agency’s Space Debris Office in Darmstadt, Germany, said collisional cascading — where one collision has the potential to produce many others — is unavoidable at this point.

“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,” he said. “This is even so if we stop all launching activities right now … once that [cascading] process has started there is no way of controlling it again.”

Klinkrad said space debris remediation will be a technically demanding and expensive undertaking but such costs must be viewed in relation to the value of space assets.

Various orbital debris removal ideas have been championed over the years, such as shooting debris with lasers, snagging space junk with foam spheres or nets, and retrieving spent spacecraft with space tugs.

Pulliam said the solutions must be innovative and inexpensive if they are to stand a chance of being embraced.

William Ailor, principal director of the Aerospace Corp.’s Center for Orbital Reentry and Debris Studies in El Segundo, Calif., said orbital debris mitigation presents a commercial opportunity for enterprising firms offering satellite repositioning or debris removal services.

But as Rouge and others pointed out, differentiating between a debris removal system and an anti-satellite capability could be a thorny issue.

As Ailor put it: “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.”

Klinkrad agreed. “I guess the debris removal system has the potential to be an anti-satellite [system] if you don’t ask the owner if he wants the spacecraft to be removed,” he said.

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...