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Bomb Squad

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

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(Continued from page 1)

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.”

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