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International Space Station incident highlights Pave PAWS mission

The Pave PAWS at the 6th Space Warning Squadron, Cape Cod, Mass., is an Air Force Radar system designed to guard North America against sea-launched and intercontinental ballistic missiles.

The Pave PAWS at the 6th Space Warning Squadron, Cape Cod, Mass., is an Air Force Radar system designed to guard North America against sea-launched and intercontinental ballistic missiles.

6th Space Warning Squadron

6th Space Warning Squadron

FALMOUTH, Mass. -- An incident occurred far out in space on April 5 that put the job done daily by those serving at the Pave PAWS installation on Cape Cod into clearer perspective.

Space is not empty, and even the smallest object floating there can cause problems.

In April, a six-inch piece of debris came near to colliding with NASA's International Space Station, threatening the safety of the three-man crew aboard, a type of event that was neither unique nor unprecedented.

By the end of the day on Tuesday, however, it was determined that the floating bit of "space junk" would miss the station, and that the space station's crew, who had been preparing to retreat into the Russian Soyuz capsule that serves as the station's "lifeboat," would be able to remain in place.

In order to make that determination, however, the 6th Space Warning Squadron, which operates the Pave PAWS installation on the Massachusetts Military Reservation, along with its counterparts at a small number of similar installations, played a part in tracking the converging objects.

All of the data gathered on the Massachusetts Military Reservation by the Pave PAWS installation--along with information from California, Alaska, North Dakota, Greenland, and the United Kingdom--is sent to the Joint Space Operations Center at Vandenberg Air Force Base in California.

The job of that center is to act as the brain for Pave PAWS' eyes, said Lieutenant Colonel Shawn A. Smith, commander of the 6th Space Warning Squadron at Cape Cod Air Force Station.

Lt. Col. Smith said the tasking orders for the Cape Cod Air Force Station's radar come from Vandenberg, and the data it gathers is correlated and analyzed there. The center, he said, is headed by Lieutenant General Susan J. Helms, a former astronaut who once served aboard the International Space Station.

When asked about the capacity for damage of the small object that came near to, but missed, the space station this week, Lt. Col. Smith explained that there are some 500,000 bits of debris in the Earth's orbit that are smaller than a centimeter. He said that even those tiny objects can do damage.

The US space shuttle, he said, used to travel nose-first, like an airplane. However, small objects would hit its windshield. One tiny bit penetrated halfway into that windscreen. Had the tiny object penetrated the windshield completely, there could have been a disaster when the shuttle re-entered Earth's atmosphere. After that incident, the decision was made to begin orbiting the shuttle tail-first.

In addition to serving on the International Space Station, Lt. Gen. Helms also made five trips on the space shuttle. That would likely make her very sensitive to one mission of her center's Situational Awareness Operations Cell: maintaining a "space catalog" of all Earth-orbiting debris.

The primary mission of the Pave PAWS installation on Cape Cod is to detect any intercontinental ballistic missiles or sea-launched ballistic missiles fired from submarines in the Atlantic Ocean and give warning to US and allied decision-makers. Its secondary mission, however, is to help maintain that catalog.

Pave PAWS tracks every orbiting item within its range, from known objects such as the space station to any new objects. It also tracks any changes in the orbits of all such objects.

There are now more than 22,000 objects in the space catalog, not to mention the aforementioned half a million or so bits that are a centimeter or less in diameter. Pave PAWS cannot track all of them, just that portion of the cataloged objects within reach of its array.

The "Pave" in Pave PAWS is a program name for electronics systems. PAWS stands for Phased Array Warning System. Unlike conventional radar, Pave PAWS is steered electronically.

Some 3,600 active sensors are coordinated by computer. The computer feeds directions to the sensors, or antenna units, allowing them to track many objects almost simultaneously and changing the focus in milliseconds.

The main Pave PAWS building is shaped somewhat like a pyramid. It has a triangular base and two array faces. Those faces are tilted so that the radar can scan almost straight above. Its "radar beams" reach about 3,000 nautical miles in every direction, including up, in a 240-degree sweep, projecting out across the Atlantic and protecting the entire East Coast.

At its most extreme range, it can detect objects the size of a small automobile. Closer in, it can "see" much smaller objects.

Cape Cod's is the first Pave PAWS in the US. It was activated in October of 1979, predating by decades the event that created the bit of debris that caused this week's concern.

That six-inch piece of debris was the result of a 2007 test that China made of its anti-satellite capabilities. In January of that year, in order to test those capabilities, China blew up its own, defunct meteorological satellite.

That test left more than 2,300 large pieces of orbital debris that the US Air Force's space command then began tracking. There were also "tens of thousands" of smaller pieces of debris resulting from the event, Lieutenant General William L. Shelton said at the time. Lt. Gen. Shelton is now General Shelton, and the commander of Air Force Space Command. At the time of China's test, he held the Vandenberg position that Lt. Gen. Helms now holds.

When testifying at a budget hearing in 2008, then-Lt. Gen. Shelton called China's test "irresponsible" and said that the debris would be in orbit for decades, slowly decaying due to natural forces. The debris, he said, would remain a hazard to manned and unmanned spaceflight in low Earth orbit or transiting low Earth orbit on the way to higher orbits.

China's test, he said, showed the potential vulnerability of the country's space assets.

It also demonstrated, he said, the need for increased "space situational awareness."

Space Command needed "to not only know what objects are in space and where," but also to "understand the purpose of these objects, their capabilities, and their owners' intent." Now, in a time of war, that need to know is even more vital. Military commanders on the ground rely heavily on satellite communications and global positioning systems, and anything that threatens that capability, even a bit of space junk, threatens their efforts.

Pave PAWS helps fulfill its portion of that mission. The radar acts similarly to a bat, Lt. Col. Smith said, sending out a signal that bounces back when it hits an object, allowing those interpreting the signal to know where something is, what its size might be, and any changes in its orbit.

*Article courtesy of Falmouth Publishing

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