The US military plans to boost the number of satellites it routinely monitors for the risk of a smash-up with orbiting debris. The move could prevent future accidents like the recent collision between a US communications satellite and a defunct Russian probe.

The US Air Force has catalogued more than 19,000 pieces of space debris larger than 10 centimetres across, General Robert Kehler, Commander of Air Force Space Command, told reporters on Tuesday at the National Space Symposium in Colorado Springs, Colorado.

But despite the extensive catalogue, the military does not have the ability to calculate the risk this space junk poses to every operational satellite. "We keep that catalogue up to date, but we do not watch everything for collision purposes all the time," Kehler said.

"We're limited by computing and we're limited by analytical wherewithal, both of which we are now going to increase in the near-term so that we can expand the population of satellites that we can perform routine collision avoidance assessments on," he added.

Near-complete survey

The exact number of satellites the Air Force will aim to routinely screen for the risk of collision is unclear. "We want to stay away from numbers and specifics right now," Andy Roake, a spokesperson for Air Force Space Command, told New Scientist.

But another official has put the target at 800 manoeuvrable satellites by 1 October, Reuters reported on Monday. There are no details yet on how the effort would be funded or how much it might cost, Reuters said, quoting an Air Force official.

That would put the Air Force close to a complete survey of the risk to space probes. Some 900 operational satellites currently orbit the Earth, according to data compiled by the Union of Concerned Scientists.

'Right direction'

"It's absolutely a step in the right direction," says Brian Weeden, a technical consultant for the Secure World Foundation and a former orbital analyst at the US Strategic Command's Joint Space Operations Center.

The exact number of satellites that the Air Force currently monitors for the risk of collision on a daily basis was not immediately available.

But Weeden says the number may be close to 330, according to his notes from a speech given by Lieutenant General Larry James at a conference on space traffic management held last week at Intelsat Headquarters in Washington, DC. That number is up from 140 satellites routinely tracked before February's collision between an Iridium communications satellite and a defunct Russian Cosmos satellite.

The right data

Boosting the number of satellites that are routinely watched may reduce the chance of collisions, but only if satellite operators are notified and given the information they need to determine whether to move the satellite, Weeden says.

"A lot remains to be seen about how it comes out," Weeden told New Scientist. "If they're just providing warnings, that's not as good as if they're proving warning and the data to allow operators to make good decisions."

Key details about the plan, such as how the data would be shared with the satellite community, are still being hammered out, according to Reuters.

Collisions warnings have not always proved useful. At a June 2007 forum, John Campbell, Iridium's executive vice president for government programmes, said the firm was getting an average of 400 warnings per week that a piece of debris might come within 5 kilometres of one of its satellites.

"Even if we had a report of an impending direct collision, the error would be such that we might manoeuvre into a collision as well as move away from one," Campbell said at the time.