What goes up doesn’t necessarily come down when it comes to manmade objects orbiting the planet.
During the last 52 years, the space-faring nations of the world have trashed the low, medium and geosynchronous orbits where their satellites operate. The Air Force is improving its ability to monitor all the active and dead satellites, spent rocket boosters, collision wreckage and debris from anti-satellite tests that threaten commercial, scientific and military satellites alike.
A new satellite dedicated to monitoring space is expected to be launched this year, and the service says it is improving its ability to predict possible accidents.
Until recently, though, little thought was given to ideas that would remove the trash itself.
But that has changed. The Defense Advanced Research Projects Agency and NASA are teaming up to find out what, if anything, can be done to clean up space.
It will be a daunting challenge, both technically and financially, experts said at the Space Symposium in Colorado Springs, Colo.
“The number of manmade objects continues to accumulate in orbit,” said Nicolas Johnson, NASA’s chief scientist for orbital debris. Of the 20,000 or so objects tracked by the Air Force, about 95 percent of them are about the size of a marble, or larger. Even something as small as one centimeter in diameter can cause a catastrophic accident, he noted. As for the unknown number of objects smaller than that size, estimates are as high as 500,000, he said.
The amount of debris could rise exponentially, Johnson and other experts have suggested. A collision creates more debris, which increases the chance for other collisions, and so on.
A case in point is the January 2009 incident where a defunct Russian Cosmos satellite slammed into an active Iridium communications satellite at a speed of about 15,000 miles per hour about 490 miles above Siberia. The accident created hundreds of objects large enough to damage other spacecraft. Johnson estimated that in the future, collisions will be the number one source of new orbital debris.
Retired Lt. Gen. Brian Arnold, vice president for space strategy at Raytheon space and airborne systems and former commander of the Air Force’s space and missile systems center, said, “Virtually every time we launch a vehicle into space, we contribute and continue to contribute to space debris. Fuel tanks, bolts, and screws come loose, paint chips come off and eventually satellites die in orbit.”
Johnson said, “The most effective means of curtailing the long-term hazard to operational space craft is to remove the large … nonfunctional spacecraft and rocket bodies which now number about 4,000.”
The Air Force is improving its ability to monitor objects in space and predict possible “conjunctions,” which is its euphemism for collisions.
Since last year, it has catalogued an additional 500 objects, pushing the number it tracks to about 20,000.
Its series of earth-based Cold War era radars and optical sensors can track items about the size of a basketball or larger. However, many of these radars were first used to track incoming missiles from the former Soviet Union and are configured for the Northern Hemisphere. There is a lack of assets in the south, Air Force officials have said.
Gen. C. Robert Kehler, Air Force Space Command commander, said the service is now able to track all “active satellites in orbit” and do conjunction analysis for each of them.
Later this year, the Air Force hopes to launch its space-based space situational awareness (SBSS) satellite. The optical sensor aboard the aircraft will be placed in low-earth orbit and be able to track new satellites as they are being placed into space, he said.
Col. James Jordan, space-based surveillance system mission director, said the satellite will be able to search for previously uncatalogued objects.
“There may be things out there that are just too small for current systems to pick up,” he told reporters. How small an object the new system will be able to detect is classified. The gimbaled camera will only be able to look up, and finding debris in low-earth orbit — roughly 100 to 1,250 miles up — will not be possible. Radars may be best suited for that range, he said.
The Air Force wants to maintain this capability beyond the life of the SBSS spacecraft, he said. There will be an open competition for a follow-on satellite later his year. And “we have done some studies that suggest having two on orbit would be a good thing to do,” he added.
The increased analysis and tracking is all very well and good, said Arnold. But when it comes to preventing two objects from striking each other, at least one of them has to be an active spacecraft with some available fuel. If not, “all we can do is sit back and watch those two systems collide because they cannot be moved,” he said.
The vast majority of space junk is small and cannot be moved under its own power, he added.
There are the beginnings of an effort to actually remove orbital trash, said Roger Hall, a DARPA project manager.
“Space situational awareness is an enabler, not a response,” he said. In December, DARPA and NASA hosted the first international conference on space debris removal. It attracted 300 participants from several nations.
DARPA also sent out a request for information from industry with an eye toward funding a program if an intriguing proposal came forth. A DARPA website devoted to the RFI showed that about 20 organizations from private industry and academia had submitted ideas.
Meanwhile, the Surrey Space Center in the United Kingdom announced in March that it was working with the European space company, Astrium, to build a three-kilogram nanosatellite, called the CubeSail. It hopes to deploy a solar sail that would connect to a piece of space debris, unfurl itself and then drag the object into the atmosphere where it would burn up.
Solar sails collect charged particles emanating from the sun to provide propulsion. The demonstration is slated for late 2011. A larger sail could be scaled upwards to take larger objects such as defunct satellites out of orbit, said a Surrey Space Center statement.
Johnson stressed that space debris is not solely a U.S. problem. It is actually a minority contributor to the collection of orbital junk, he maintained.
“Space is an international commons,” he said. Cleaning it up “will likely be an international undertaking.”