The U.S. Air Force plans to increase the number of satellites it routinely monitors for possible collisions with orbiting debris. The move could prevent future accidents like the February 11th collision between a US Iridium communications satellite and a defunct Russian probe.

Orbit evolution of collision fragments

Step out of the way! Here's how the orbits of fragments from the February satellite collision are likely to evolve, based on models by orbital-debris specialists at NASA's Johnson Space Center.

NASA / N. Johnson

The Air Force tracks more than 19,000 pieces of space debris larger than 10 centimeters across, General C. Robert Kehler, Commander of the Air Force Space Command, told reporters on March 31st at the National Space Symposium in Colorado Springs. But despite this extensive catalog, the military does not have the ability to calculate the risk that these objects pose to every operational satellite. "We keep that catalog 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."

Near-complete survey?

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

Another official put the target at 800 maneuvrable satellites by next October, Reuters reported on March 31st. 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 live satellites. Some 900 operational satellites currently orbit Earth, according to data compiled by the Union of Concerned Scientists.

The exact number of satellites that the Air Force already 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 Lt. Gen. Larry James at a conference on space-traffic management held in late March at Intelsat headquarters in Washington, DC. That number is up from 140 that were routinely tracked before the February collision.

The Right Data

Boosting the number of satellites that are routinely watched will reduce collision chances only if satellite operators are given the information they need to determine whether to maneuver a satellite, Weeden notes. "A lot remains to be seen about how it comes out," Weeden said. "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." These procedures are still being worked out.

Collisions warnings have not always proved useful. At a June 2007 forum, John Campbell, Iridium's executive vice president for government programs, 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 maneuvre into a collision as well as move away from one," Campbell said.



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