COLORADO SPRINGS — The Defense Advanced Research Projects Agency and NASA are investigating whether it will be possible to send humans into space to repair or refurbish satellites.

Roger Hall, deputy director of DARPA's tactical technology office, said the two agencies are in the preliminary stages of investigating what technologies would be needed to prove out the concept.

Further, the spacecraft DARPA wants to repair are in geo-synchronous orbit. They are deployed some 24,000 miles above the earth.

He provided few details here at the National Space Symposium, but did show an artist's concept that portrayed an astronaut in a hard casing rather than the traditional space suit currently used during space walks. The "suit" had robotic arms.

DARPA is also tackling another challenging problem — cleaning up space debris that may potentially collide with spacecraft. The Air Force is currently tracking about 20,000 objects — basketball sized or larger — that orbit the earth. They include everything from dead satellites to debris leftover from the Chinese anti-satellite test in 2007 and the 2009 collision of a defunct Russian Cosmos satellite with an Iridium communications satellite.

There are perhaps hundreds of thousands of smaller debris that pose a threat to manned and unmanned space systems.

The Air Force is expected to launch the space situational awareness satellite later this year, which will use optical sensors to find and track space debris. But even if this system does track an object that may collide with a satellite, often there is little that humans can do "but sit back and watch," said one speaker.

DARPA wants to find a way to remove these objects, Hall said.