Gazing up into the sky on a clear night, the heavens can appear as pristine as a mountain stream. But in truth, at least in Earth's vicinity, the trash factor in space may be more akin to what is found in New York City's East River. The region known as low Earth orbit (extending from 160 to 2,000 kilometers above Earth's surface), which is where many satellites spend their lives and "afterlives," has a litter problem caused by decades of neglect, and it's one that currently lacks an expedient solution.

The number of man-made objects drifting aimlessly in orbit has grown steadily for years thanks to rocket launches that deposit spent boosters in space as well as satellite retirements, after which the defunct craft are left to roam the skies like orbital tumbleweeds. But more violent incidents of late have raised the stakes.

As of July, when NASA's Orbital Debris Program Office published its most recent quarterly newsletter, roughly 15,000 pieces of space junk were being tracked in orbit by military monitors. (That catalogue only includes debris 10 centimeters or larger—roughly softball-size and up.) More than 2,500 of those fragments originated from a 2007 Chinese missile test in which a satellite was deliberately destroyed; another 1,100 stem from an accidental collision in February between a defunct Russian satellite and a functional communications satellite owned by a U.S. firm.

With thousands of pieces of tracked debris and countless smaller chunks posing a hazard that operational satellites and even manned missions sometimes have to dodge, it is only a matter of time before somebody—be it a lone government agency or a consortium of the concerned—takes charge of the cleanup.

Such a space-based "Superfund" effort may now be in the works: The U.S. military's Defense Advanced Research Projects Agency (DARPA) posted a notice last week soliciting ideas on how to shrink the growing debris cloud in Earth orbit. The solicitation is merely a first step that promises no funding or commitment from the government, but several contractors have shown interest in contributing to a solution.

DARPA's information request calls for concepts "on the full spectrum of potential solutions, from quickly clearing a congested region in space of all types of debris to strategically removing large objects across a range of altitudes to manage the overall growth rate of debris."

Among the firms that have signed on so far to the solicitation as "interested vendors" are Boeing and Emergent Space Technologies in Greenbelt, Md. Both declined to discuss what strategies they would be suggesting. A spokesperson with Boeing's Phantom Works, home to the company's Advanced Network and Space Systems unit, said Monday that he had not yet received confirmation that his division was prepared to discuss the effort.

George Davis, president of Emergent, says his company had been considering the debris problem for some time. "Our role is likely to be one of support to a prime contractor in the areas of mission design and analysis, guidance, navigation and control, and ground systems integration," Davis says. He added that Emergent had some novel ideas for debris-mitigation missions but would not divulge any specifics.

DARPA's point person for the orbital debris inquiry, Tactical Technology Office program manager Wade Pulliam, said Tuesday morning he had not yet been given approval to discuss his agency's role publicly. A DARPA spokesperson explained that the agency needed more time to gather information before granting interviews.

More details—and possibly a formal funding opportunity—could be forthcoming after October 30, the deadline for informational submissions to DARPA.