WASHINGTON — The heads of the U.S. and Australian defense departments on Nov. 8 signed a pact in Melbourne to cooperate on space situational awareness activities, which may include placing U.S. radars in Australia to track satellites and debris in low Earth orbit.

U.S. Secretary of Defense Robert Gates and Australian Minister of Defence Stephen Smith signed a statement of principles that says the two governments will “work together in the spirit of cooperation on the space situational awareness partnership for the mutual benefit of our countries’ national security.” The document was posted on the Australian Ministry of Defence website.

(Read more on space situational awareness at www.onorbitwatch.com, a community site of Space News and AGI).

The United States operates a worldwide network of ground radars and optical telescopes for tracking objects in space, though its ability to track objects orbiting over the Southern hemisphere is quite limited. The primary U.S. system for tracking objects in low Earth orbit is the Air Force Space Surveillance System — known as the Space Fence — which  comprises three Very High Frequency radar transmission sites and six receive sites spread across the southern United States.

The Air Force since 2006 has been studying options for replacing the Space Fence with a system capable of tracking a greater number of smaller objects in low and medium Earth orbit. In June 2009, the service awarded $30 million contracts to Lockheed Martin Corp., Raytheon Co. and Northrop Grumman Corp. to conduct trade studies and prototyping for a new Space Fence. The Air Force stopped funding Northrop Grumman’s contract in February, and Lockheed Martin and Raytheon recently completed their respective system design reviews and have submitted cost estimates for building the new system.

On Oct. 20, the Air Force issued a request for proposals for the next phase of the program, for which it will issue up to two 18-month contracts worth $107 million each to continue Space Fence development through preliminary design review. When this phase is complete in 2012, the service plans to choose one prime contractor to build the system. The entire system is expected to cost more than $3.5 billion to complete, according to an Oct. 27 Air Force press release.

In the past few years, the lower orbits around Earth have become much more congested as the number of spacefaring nations has increased. And events like the 2009 collision of an Iridium communications satellite with a Russian satellite have left thousands of pieces of junk in orbit. The changing environment has driven the Air Force to accelerate its plans to ensure the new Space Fence achieves initial operation capability by September 2015, said Scott Spence, Raytheon’s Space Fence program manager.

The Air Force wants the new system to increase the number of objects the Space Fence can track in low Earth orbit by tenfold, from around 20,000 objects today to upwards of 200,000 objects in the future, Spence said in a Nov. 8 interview.

Current plans for the new Space Fence call for the deployment of two or three radar sites that both transmit and receive signals, said John Morse, Lockheed Martin’s Space Fence program director. Whereas the current Space Fence is located entirely inside the continental United States, it is likely that the next-generation system will be located entirely outside of the continental United States, though no firm plans have been announced, Morse said in a Nov. 9 interview.

“The Air Force went through a rigorous analysis of alternatives with regard to [where the sites should be placed],” Morse said. “They’ve looked at combinations of sites in a variety of places. They’re really trying to get coverage in the southern hemisphere.”

In addition to Australia, the Pentagon is considering placement of sites on the Kwajalein Atoll in the Pacific Ocean and Ascension Island in the Atlantic Ocean, Air Force spokesman Charles Paone said.

The Nov. 8 accord states, “Australia and the United States will investigate the potential for jointly establishing and operating space situational awareness facilities in Australia to support the United States space surveillance network and to support the development of Australia’s space situational awareness and mission assurance capability.”

In a Nov. 8 press conference in Melbourne, Gates said further discussions with Australia about the placement of Space Fence radar sites are expected to begin in January.