What's up in space?

Air Force Space Command’s Space Fence likely to be the largest phased array radar ever built

A decade ago, the military minds at the Air Force Space Command would have said space situational awareness (SSA) was just a basic space surveillance network on the ground. They tracked objects in space and populated a catalog with that data, which they updated regularly.

That environment has changed dramatically. Space is congested, it is contested, and it is competitive.

Rather than taking a reactive posture to events in space, AFSPC must be proactive in its strategies and actions to know when new objects show up in space, which countries own them and what their intent might be. Answering those questions could have immediate applicability to the nation’s present and future military actions.

“All your space-based capabilities that are relied on to execute missions in theater have to be protected and understood,” said Col. Stephen Butler, command lead for SSA and command and control at the Directorate of Requirements at Headquarters AFSPC at Peterson Air Force Base, Colo. “We have capabilities that are space-based that could be jeopardized as threats change. That is what SSA is all about because we need to stay ahead of those. If we don’t, then our eyes and ears will go away, which will have a direct impact on the theaters in terms of providing comms; missile warning;" and position, navigation and timing information.

AFSPC has identified four pillars of SSA: intelligence characterization, data integration and exploitation, threat warning, and attack reporting, Butler said. To address those pillars, AFSPC has three major SSA hardware programs: the Space Based Space Surveillance (SBSS) space vehicle, Space Fence and Space Surveillance Telescope (SST).

When operational, the SBSS spacecraft would detect objects in deep space, particularly those in geosynchronous orbit, such as telecommunications satellites and missile warning systems. Boeing and Ball Aerospace have already built the spacecraft, which is waiting for Orbital Sciences to prove that it has fixed a problem that led to the failure of the spacecraft's Taurus rocket. The Taurus shares components with the Minotaur IV rocket that will launch the SBSS satellite. The new launch date is slated for this summer.

The second program is Space Fence. Geared toward detecting small satellites and debris in low-Earth orbit, Space Fence will consist of a trio of S-band ground-based radar systems. In mid-2009, Lockheed Martin, Northrop Grumman and Raytheon each received $30 million contracts from the Electronic Systems Center at Hanscom Air Force Base, Mass., for concept development.

The third project is SST, a joint effort between AFSPC and the Defense Advanced Research Projects Agency. It is a ground-based 3.5-meter optical system designed to search for and identify small objects in geosynchronous orbit. The agencies are building SST in Socorro, N.M, south of Albuquerque. They expect to open the telescope system's dome for the first time in January 2011.

The space-based and ground-based SSA systems have their pros and cons, Butler said. For example, SBSS offers a resilient space-based capability that weather cannot affect. It doesn’t have foreign basing issues. And it provides more timely revisit rates for high-interest objects at geosynchronous orbit. The con is that a space-based piece is expensive.

Conversely, the Space Fence would scour the low-Earth orbit, while SST searches the geosynchronous orbit belt to identify new objects.

The AFSPC's most challenging SSA activity is searching for smaller objects in higher orbits, Butler said.

“Smaller spacecraft don’t need a big booster to get into orbit, which makes it easier for more people to do and increases the number of things that we have to track, identify and understand,” Butler said. The smaller things are harder to track and identify. When you talk SSA, you have to understand what are the capabilities of each object, what is its mission and what is its intent.”

Putting up a Fence

SSA is all about protecting assets owned by the United States or its allies. Those assets have become much less secure since the Chinese government tested anti-satellite measures in 2007 and an Iridium satellite and Russian satellite accidentally collided in 2009.

“The realities of today make the development of SSA systems like Space Fence necessary so we are able to see what’s up there, understand it and be assured that we are doing what we need to do to protect our assets,” said Linda Haines, a retired Air Force colonel and now Space Fence program manager.

Unlike other ground-based radar systems that track specific objects in the sky, Space Fence would throw radar signals into space on a fixed plane and then notes any object that cuts through that plane. The system would relay that information to a command-and-control center, and experts can decide whether to more closely track an object.

“I would say, almost by design, we are not stressing the state of the art with this system,” Haines said. “However, given the volume and the size of this radar — Space Fence is likely going to be the largest phased array radar ever built…up to two football fields large. We’re talking about thousands and thousands of transmit-and-receive elements and potentially from 10,000 to 120,000 digital channels.

“Going up to that kind of volume means that we can actually harness commercial technology from things like cell phones, which actually is a good thing because the environment that we’re in with Iraq and Afghanistan and the priorities of the Obama administration means that there is obviously not a limitless DOD budget,” Haines added.

The Space Fence is in the concept development phase. “The only thing we’re taking delivery of during this stage is data,” Haines said. “To date, we’ve gotten 10,000 pages of data from the three contractors.”

For the remainder of 2010, the contractors will conduct modeling and simulation to prove that the program is achievable and affordable. Another competitive contract will follow in 2011 when the contractors will begin prototype demonstration of an operational radar and major components. They will need to demonstrate technical readiness at TRL Level 6 maturity of their design solutions showing that it has been tested in a relative environment. An eventual selection of a single contractor is scheduled for mid-2012.

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