But This Is Not Your Grandpa's Zeppelin

A giant, unmanned airship capable of hovering at about 70,000 feet promises to give future warfighters an unprecedented eye on the battlefield.

The Defense Advanced Research Projects Agency's Integrated Sensor is Structure program, ISIS for short, will provide a detailed, real-time picture of all movement on or above the battlefield, explained program manager Timothy Clark.

As envisioned, the ISIS airship will be able to follow troop movements - friendly as well as enemy - up to 180 miles away, and track the most advanced cruise missiles from about 370 miles away.

It also will be able to watch ground targets through heavily forested areas, a capability not possible without the huge ultra-high-frequency antenna ISIS will provide.

Operating outside of controlled air space and out of the range of most surface-to-air missiles, Clark said, the system will bring a capability not possible with satellites: the ability to maintain watch over a huge, fixed position without blinking.

The American Forces Press Service reports ISIS is expected to have a 10-year lifespan, although engineers estimate it could last even longer. When it's no longer needed in one location, it can be moved to watch another. "We should be able to get it to anywhere the services would need it in about 10 days," Clark said.

Since the program's inception in 2004, its focus has been on developing technologies needed to create extremely large, super-sensitive, but also super-lightweight phased-array radar antennas. That's been accomplished, Clark said, with 6,000 square meters of X-band and UHF antenna condensed onto a 40-by-46-meter cylinder - about the size of a 15-story apartment building. Meanwhile, the antenna's weight has been cut 90 percent, from 20 kilograms per meter to about 2.

Powering the system so it can stay aloft was another challenge. Batteries were too heavy, so engineers tried something else. They opted to use solar rays during the daylight hours and to electrolyze water, storing the hydrogen and oxygen separately so they could be run through a hydrogen fuel cell at night. "Then we collect the water and run it again," Clark said. "It's a fully regenerative system."

The next step is to incorporate these technologies into the hull of a non-rigid, pressurized airship. A demonstration program already is under way to see how this will work, Clark said.

Large pieces of the system are being put together at various locations around the country, and if all goes as planned, they'll be put together in a Lockheed-Martin hangar in Akron, Ohio. Flight tests are expected to begin in late fall 2012, likely in the Florida Keys. Initially, DARPA will conduct 90 days of tests worldwide against air, ground and surface targets at known positions and sizes to ensure the radar is operating properly.

From there, the Air Force will take over the program, conducting its own additional testing before taking the ISIS operational.

FMI: www.darpa.mil