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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.

The Sniffer is scrambled when any of the worldwide network of AFTAC sensors detects a nuclear blast and the Joint Chiefs of Staff at the Pentagon give the final go-ahead for flight. Data from a combination of orbiting satellites and ground and undersea sensors is funneled to AFTAC headquarters at Patrick Air Force Base in Florida. The triad works in combination, each part supporting the others. If a detonation is above ground, satellite-borne sensors can distinguish between the optical signature of conventional explosives and the flash of nuclear ordnance. Other detectors mounted on satellites discern post-detonation gamma rays at high altitudes, observe slight atomic-blast-induced fluctuations that disturb Earth’s magnetic field, and monitor chemical signatures of radioactive particles at a distance. If detonation occurs underground, sensitive seismometers track the signatures of acoustic pressure waves rippling through Earth’s crust, while underwater hydrophones can “hear” the distinctive after-blast sound that can carry for thousands of miles through the world’s oceans.

When the notice is given, aircraft maintainers in Nebraska run through the preflight checklist while the aircrews hustle from Patrick to Orlando International Airport, an hour’s drive, to catch the first available commercial flight to Omaha. Once they land, it will be another half-hour drive down the interstate to Offutt, and takeoff in the waiting WC-135.

Inside a Sniffer as it flies toward the location of a recent detonation, as more than 30 crew members may be on board, including three pilots, two navigators, one deployment commander, a mission commander (who supervises the running of the Phoenix’s atmospheric sampling gear), as many as three special equipment operators (SEOs), three atmospheric technicians, and some 18 maintainers who will work on the airplane when it sets down. Once airborne, directed by sensor data and constantly updated weather forecasts, the WC heads for the fallout plume and hours of sampling. It can fly the better part of a day before it arrives at the location of a blast and begins the methodical tracks that will take it through whatever airborne fallout awaits. Landings are required every 24 hours to allow the crew to rest and to unload samples that have to get to laboratories for fast analysis.

“Those 18- to 20-hour missions are a killer,” says Technical Sergeant Richard Bohn, an SEO. “You’re just transiting, flying along fat, dumb, and happy. It’s lots of boredom followed by lots more boredom.”

In flight, a senior SEO sits at an equipment console roughly the size of two large filing cabinets. The console is electrically connected to four externally mounted Geiger-Müller tubes that watch for the presence of gamma radiation.

The WC must remain outside national boundaries, in international airspace, a task made far easier by the latest generation of navigational aids. “We have to know our location at all times,” says Riley. “When we say we know where we are, we know where we are. We don’t want to violate anyone’s airspace.”

The Sniffer’s array of sampling apparatus includes filter assemblies, large-pizza-size disks that rotate from an interior storage mechanism into twin fairings—known as U-1 foils—mounted mid-fuselage over either wing. The assemblies, made from cotton-based filter paper with a gauze backing, trap particulates like dust, dirt, and the byproducts of fissionable material down to micrometer size and lower—mainly the debris that would linger from an above-ground nuclear test. Before opening the U-1 foil’s pneumatic clam-shell door, a console operator slides the filters one by one into position to face the onrushing airstream, as a jukebox might ready an oversized record for play if the turntable were vertical instead of horizontal.

As the foils sit in place, any particle with ionizing radiation that strikes the surface is sensed by the Geiger-Müller tubes, which send an electrical signal to the SEO’s equipment. Increasing radiation detected means that particles are building up on the foil, and that the aircraft is indeed flying through a radioactive cloud from a nuclear blast.

When such levels are detected, SEOs often direct the pilot to start a left or right orbit to remain inside the cloud. If radiation levels continue to rise, the orbit is continued while filter foils are changed, usually every hour or so. Whenever rain threatens to dilute or wash away a particulate collection, the filters are retrieved. In addition, operators must be aware of effluent from volcanic eruptions, the dust from which contains naturally occurring radioactivity that could contaminate samples.

The Sniffer also carries 40-pound air collection spheres, and handling them is the hardest and potentially the most dangerous part of the mission. Run off a quartet of compressors, the spheres collect and confine air that could contain trace signs of underground nuclear tests. “Unless someone violates the old [test ban] treaties, you won’t get solid debris,” says AFTAC’s O’Brien. “If you get debris at all, it’s probably in gaseous form.”

Since there are only four compressors but as many as 44 spheres on a given flight, the stainless steel containers have to be regularly swapped out. Once unbolted from a compressor, an air-containing sphere is stored on a nearby rack, while an empty one is attached to the compressor line, a process known as “throwing spheres.” Sometimes when the ride gets bumpy, that is exactly what happens. “I hit the ceiling once with two spheres in my hand,” Bohn says. “I thought, We hit an air pocket. Then I thought, This is not a good thing. When we bottomed out, I was on the floor.” Fortunately for Bohn, no permanent damage was done.

Depending on takeoff and estimated arrival time, technicians, SEOs, and maintainers catch some shut eye, bunking down wherever there’s space. Bunk beds are aft, and there’s that padded carpet—for insulation and noise abatement—for those who prefer to stretch out on the floor. Because of prevailing global air circulation, the WC often finds itself 20 degrees north or south of the equator, usually flying at relatively low altitudes to enable effective sampling. That often makes for a bumpy, hot ride. “Often you’ll be flying through clouds at 3,000 feet,” says Phoenix co-pilot Marc Lynch. “It’s an uneasy feeling when you can’t see the ground,” navigator Jimmie Riley says. “Tension definitely increases. You can hit some rough weather and get boxed in. You look for where the hard [thunderstorm] cells are and try to avoid them.”

Because air sampling compressors run constantly and throw off heat, temperatures inside the fuselage can blossom to equatorial levels, despite the best efforts of the aircraft’s air conditioning system. To provide temporary relief, WC pilots will often “cold soak” the aircraft by climbing up to 30,000 feet, with heaters off and crew bundled up, and direct the outside subfreezing air inside. Then it’s back down to altitude, and to business.

Once collected, air and filter samples are stored. After the WC lands—almost always at a military base—technicians, SEOs, and maintainers pitch in to off-load the samples and put them into another transport, which will fly them Stateside. “You’ve got a very perishable commodity,” says Doris Bruner, chief of the AFTAC atmospheric test branch. “Those little radioisotopes can decay quickly. You try to get into position as quickly as you can for collection and then back to the laboratory for analysis.”

Bohn, a 10-year Constant Phoenix veteran, says that once a bomb goes off somewhere on the globe, crew members can forget any scheduled weekend getaways, chores, or time with the family. For Bohn, a fervid Florida volleyballer, it might be a long time before he’s back on the beach. “It seems like [missions] usually happen on Friday afternoons before a holiday or a three-day weekend,” he says. “But as soon as the balloon goes up, we’re gone. In 30 minutes my bag is packed and I’m ready. I keep a bag for summer and I keep a bag for winter. If there’s a possibility that we’ll be seeing both hot and cold weather, I bring both.”

“It tightens everybody up when you get the call,” says Lynch. “You sit back and think What are we going to fly into? The Phoenix missions are long and they’re sudden. You go and for the next week you’re going to live in that airplane.”

The Sniffer is continuing work begun on September 16, 1947, when then General Dwight Eisenhower assigned the Air Force the responsibility for detection of atomic explosions worldwide. By the close of 1948, 55 filter-equipped RB-29 Air Weather Service aircraft were flying frequent sampling missions from Guam to the North Pole. A year later, on September 3, 1949, an RB-29 flying between Alaska and Japan detected what the entire fleet had been searching for: debris suspected to be from a Soviet atomic test. Confirmation came with 92 flights that collected 500 air samples in a two-week period. In a national radio address on September 23, President Harry Truman announced that the United States was no longer the planet’s sole possessor of nuclear weapons.

By July 1950, equipment aboard Constant Phoenix aircraft was capable of collecting air samples at altitudes ranging from 1,000 to 30,000 feet and quickly returning them to ground-based laboratories for analysis. By 1953, monitoring techniques improved with the addition of compressors and spherical containers that could hold more sampled air under higher pressure. A decade later, just prior to the signing of the Limited Test Ban Treaty, sampling reached its peak, as 77 airplanes—including B-52s and U-2s—regularly scrambled from nine airfields, covering roughly two-thirds of Northern Hemisphere airspace. By December 1965, WC-135s had taken the stage as the newest addition to the Constant Phoenix fleet. These were the aircraft flying in 1995 when both France and China conducted underground tests. Even when a nation admits to testing a nuclear device, the aircraft are sent  to search for possible leaks of radioactive debris.

For crew members used to the cramped confines of earlier aircraft, the WC’s 136-foot-long, 12-foot-wide size was a relief, with plenty of walk-around space and legroom to spare. Inside, improvements to air-sampling equipment made it easier to collect evidence of fallout and to preserve it for laboratory analysis. The aircraft could operate for longer periods of time; extended-range versions capable of being refueled in flight appeared in 1968. Sampling missions were routinely conducted over the poles, the Far East, the Indian Ocean, the Bay of Bengal, and the Mediterranean Sea, as well as off the coasts of South America and Africa.

Phoenix equipment on board the WC-135 seems straight from the 1960s: consoles made of painted steel with analog gauges and dials. In fact, concedes Doris Bruner, Constant Phoenix equipment has changed very little since then: “There have not been a lot of technology improvements. We’re working at the limits of detection.”

But when the new gear for the Constant Phoenix program is completed, it will grab the first available seat. No longer will Constant Phoenix be “tail designation specific,” limited to flying on a single airplane. In a sense, the program will eventually return to its glory days, when dozens of aircraft were involved in sampling missions. To boost portability, the sampling system will be plug-and-play, with simple on/off switches and direct electrical connections to onboard power supplies. To avoid cutting holes in airframes, engineers at AFTAC are considering modified aircraft doors. Particulate collectors could be affixed to the doors, which could then be installed on the aircraft selected for the next mission. Although in theory the system could be put on several different kinds of aircraft, managers are now eyeing the current fleet of KC-135s and C-135s, as well as the two WC-135s also used. “We want to get away from the concept of one, two, or three airplanes,” says O’Brien. “We want to be able to pick up the phone and fly a mission right away. Whatever [aircraft] is ready, we load our equipment and off we go.”

The current WC-135 Sniffer aircraft are, despite advanced age, sturdy and reliable, but they require constant vigilance nevertheless. Concerns about encroaching on foreign airspace mandate flights over water, requiring the 45th Reconnaissance Squadron to adhere to an aggressive program to control corrosion. Every day technicians inspect all parts of the aircraft, including engines, hydraulic systems, and control surfaces, to catch corrosion in the earliest stages. The sampling technology may not have changed much since the 1960s, but with upgrades to the airframe, the WC-135 has actually become more reliable. “Thanks to its advanced avionics and improved technology, it’s doing its job better than ever,” says Technical Sergeant Frank Morales, a maintainer who has worked on the WC since 1986. “It’s amazing this 135 has gone through the transitions it has.” Morales reports that, with the exception of certain stretches of old and brittle wiring and the occasional hydraulic leak that occurs as seals stiffen in cold weather, there is no single WC-135 component that requires repeated monitoring and replacement.

Despite the Sniffer’s hardiness, money is what lifts its wings. The Constant Phoenix annual operating budget stands at $2.3 million, a pittance compared to expected and enormously expensive upgrades. So budget planners don’t see a realistic prospect of continuing the program as is. “The big rock in the road is the $29 million that we’ll need to re-engine the WC in 2003,” says Charles McBrearty, AFTAC director of materials technology. “There won’t be buckets of money rolling in. That’s why we’re planning now.”

Constant Phoenix was a creature of the cold war, born and bred because of superpower rivalries and threats to political stability. Ironically, the unpredictability of the post-cold-war world may be what ensures its survival.

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