How airborne detectives collect evidence from a cloud of atomic debris.
- By James Schultz
- Air & Space magazine, July 2000
(Page 3 of 5)
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.”