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Bomb Squad

How airborne detectives collect evidence from a cloud of atomic debris.

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Navigator Jimmie Riley fondly remembers a mission when he could smell popcorn all the way to the cockpit. More frequently, there are the aromas of fresh-baked pizza and the unmistakable scents of TV dinners, baking slow and steady, the old-fashioned way. You got a stove, you use it, Riley says—even if you’re 30,000 feet up and especially when you’ve been flying 15 hours straight. Long missions are the standard for Riley and his many crewmates. He navigates one of the last remaining WC-135s equipped for Constant Phoenix, the nation’s only airborne program to detect nuclear fallout. It’s a mission that takes Riley all over the world to retrieve evidence from the area of a nuclear explosion.

In early May 1998, the WC-135s were only days away from administrative death. Escalating maintenance and repair costs for the aging aircraft (today, two survivors of a sampling fleet that in its heyday numbered more than six dozen) had convinced the Phoenix program’s managers at the Air Force Technical Applications Center just south of Cocoa Beach, Florida, to ground the 135s while the center developed a modular system of sensors that could be plugged in and flown on any cargo-type aircraft. AFTAC operates the U.S. Atomic Energy Detection System, a global network of nuclear blast detectors that includes, in addition to the aircraft, seismometers, undersea listening devices, and satellite-mounted optical sensors calibrated to detect the flash of an above-ground atomic explosion. There hasn’t been an above-ground test since 1980, when China detonated two bombs in the atmosphere.

“By 1997, the debate was: Should we continue to fund this aircraft, which needed major maintenance, or not fund it and take the risk that it wouldn’t be needed?” says David O’Brien, AFTAC chief scientist. “The decision was made not to fund the maintenance…. We thought we could live with a gap.”

The answer seemed clear. In addition to waiting for enhanced grab-and-go airborne sampling equipment, policymakers put their money on pending advances in remote sensing technology, hoping that the Phoenix aircraft, sometimes called “Sniffers,” would enjoy a quiet retirement—an approach that appeared to be the best option given a tight budget.

The equation suddenly changed over two weeks in May 1998. In rapid succession, India and Pakistan set off nuclear explosions in underground test chambers. “At the 11th hour and 59th minute something happened,” O’Brien says. “If India and Pakistan hadn’t occurred, that aircraft would be retired and sitting in the desert outside Tucson, Arizona.”

The two main benefits of airborne sampling—mobility and pinpoint retrieval of debris—kept the Sniffer in business. “If you have a ground sampler at a forward location, you’ll collect effluent if the wind is kind to you,” O’Brien says. “We have sensors around the world to detect the blast. We do air mass projections and put the plane where there is radioactive xenon [the telltale sign of a nuclear blast], which has a short decay life.”

Xenon radionuclides exist in minute parts-per-trillion concentrations after a blast, and can be detected only by sampling. Seismic or space-based detection can determine only that a test has taken place and cannot provide detailed information about the weapon’s technology. Airborne sampling is actually the retrieval of microscopic pieces of the bomb itself, which are subjected to radiochemistry to analyze the materials used. “There’s nothing [else that] can do what that aircraft does,” says Lieutenant Colonel Steven Nachtwey, 45th Reconnaissance Squadron commander. “[Constant Phoenix] is an extremely valuable program that provides hard evidence to decision-makers.”

In addition to improving its airborne capability through Sniffer upgrades, AFTAC is developing an enhanced network of automated, ground-based samplers that will collect and analyze air in place and send the results over high-speed, secure networks. But such devices, no matter how sophisticated or robust, are vulnerable. Friendly governments can fall, replaced by hostile ones. Sabotage occurs. Accidents happen. By the time the air mass reaches samplers on the ground, traces of xenon could already have disappeared. What guarantees against such failures is redundancy, in a geopolitical environment that remains unpredictable, even with the much touted safety that the end of the cold war was supposed to bring. The key to detection remains flexibility.

“You have a finite number of assets. You have to deploy them prudently as events occur,” says Cargill Hall, chief historian in the National Reconnaissance Office in Chantilly, Virginia. “What Constant Phoenix provides is definite confirmation of an above-ground test, or a leak from underground testing. Sniffer aircraft are a vital element of any strategic reconnaissance program.”

On a blustery January day this year, a WC-135 sat on the ramp at Offutt Air Force Base in Nebraska, bright afternoon sun playing over its fresh coat of white and blue paint. (Even though AFTAC oversees the Constant Phoenix mission, the Air Force’s Air Combat Command at Offutt has operational responsibility for the WC-135 airframe.) Riley, a captain in the 45th Reconnaissance Squadron, shepherded visitors through a quick tour of the aircraft, which had just returned from an exhaustive, months-long refurbishing in Greenville, Texas. For the 39-year-old airplane, it was not just a minor facelift. The WC was stripped down to skin and struts and put back together, panel by panel, rivet by rivet. Wiring by the mile was checked or replaced and some key avionics systems upgraded: There’s a new digital altimeter and souped-up navigation system with enhanced Global Positioning System capability. Outside, Air Force maintainers braved wind chills in the teens as they checked engines and landing gear, while inside, a cockpit electronics check was in progress. Sound-deadening carpet arrived for reinstallation. This WC, once ready for retirement, was again ready for the call.

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