Air Force to build Space Fence to track orbital junk

Space can be a crowded place. That is especially true for the mid- and low-orbit regions around the Earth where operational spacecraft share space with thousands of bits of debris ranging in size from paint chips to decommissioned satellites.

The Air Force has been tracking spacecraft for decades, but its current generation of ground-based radars can’t track smaller pieces of space junk — objects that are only a few inches in diameter.

That’s the goal of the Space Fence program: track the cloud of small and potentially deadly bits of orbital litter. Higher fidelity is necessary because the debris cloud is constantly growing, said Douglas Burgess, senior manager of space situational awareness programs at Raytheon, one of three companies that have submitted designs for the program. But the debris is not tracked very well or routinely. “The future is about seeing smaller objects at higher altitudes more often,” Burgess said.


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More accurate debris tracking increases the safety of space missions because it allows ground controllers to plan orbits around space junk or move spacecraft out of the way when debris drifts too close. Knowing when to move spacecraft is also important because it helps conserve fuel used for maneuvering, he said.

Space Fence is a ground-based phased array radar operating in the S band, which is capable of detecting smaller objects at greater distances and through weather such as rain. The shorter wavelength of the S band will be an improvement over the current system, known as the very-high-frequency fence, which has been in service since the early 1960s and uses longer wavelength radars.

When Space Fence is operational, it will allow ground controllers to see as many as 100,000 objects, a big jump from the 20,000 objects currently tracked. The new radar will also use state-of-the-art algorithms to better track objects, Burgess said.

Raytheon is working with the Air Force to reduce the risk in the technology used to develop such a large phased array radar. But the company has years of experience developing phased array radar systems and understands how data is used in the space industry, Burgess said.

Raytheon, Lockheed Martin and Northrop Grumman have all submitted designs for Space Fence. A preliminary design review of the program is scheduled in 2012, after which the Air Force will award a contract to one of the competing firms.

Initial operating capability is slated for 2015 when the first sensor will be operational. Before going operational, Burgess said the program will test a prototype radar to mitigate technical risks and demonstrate that the design works and is economical to produce.

When Space Fence is complete, it will use as many as three radars located on or near the equator in Australia, the Marshall Islands and Ascension Island. The radars will be large phased array structures, similar to the systems used to track ballistic missile launches. The VHF fence system’s radars are based in the continental United States.


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