If a nuclear device were to unexpectedly detonate anywhere on Earth, the ensuing effort to attribute the weapon to its maker probably would be led by aircraft rapidly collecting radioactive particles for forensic analysis.
Relatively inexpensive unmanned aerial vehicles (UAVs) — equipped with radiation sensors and specialized debris-samplers — could fly right down the throat of telltale radiation over a broad range of altitudes without exposing a human crew to hazards.
This capability is far from fiction. In late September, a Sandia-developed airborne particulate-collection system demonstrated its capabilities in the blue skies above an Air Force base in Grand Forks, N.D. Dubbed “Harvester” for obvious reasons, the system “tasted” the atmosphere by using two particulate sampling pods to gather information. A third pod would provide directional guidance for a real event by following the trail of gamma radiation.
The three pods, with additional hardware, software, and ground-control equipment, are expected take their place on aircraft in the Air Force’s investigatory arsenal by 2014.
When they do so, they will have traversed the infamous technological “Valley of Death,” in which many promising R&D ideas die before reaching production.
The successful Grand Forks demonstration was part of a formal Department of Defense (DoD) Joint Capability Technology Demonstration (JCTD) that mated the Harvester modular pods to the long wings of a Department of Homeland Security Customs and Border Protection-provided MQ-9 Reaper UAV. (The Reaper is a more powerful cousin of the better-known Predator.)
While the recent tests did not include any radioisotope releases, the pods were able to collect and identify naturally occurring radioisotopes of lead and bismuth produced from the radioactive decay of atmospheric radon. In addition, radioactive beryllium-7 produced from cosmic ray spallation of naturally occurring carbon-14 also showed up on the filters after the flight, providing a uniform measure for debris distribution.
The modular pods eliminate the need for costly, permanent aircraft modifications that would limit the number of aircraft platforms on which Harvester can be flown.
“There’s a high likelihood the Air Force will make Harvester operational in 2014 to augment its current manned aircraft collection capability,” says project lead Joe Sanders (5943). “For maximum responsiveness, we continually engaged with the Air Force to address its technological and operational needs throughout the project.”
The Harvester’s Directional Gamma Radiation Sensor (DGRS) helps guide the aircraft toward the radioactive plume using four large sodium iodide radiation detectors and a complex processing algorithm. The pilot, located far away in a UAV ground control station, is informed by the Harvester equipment operator to fly toward the plume’s “hot spot.”
“The operator will see a vector that shows peak plume intensity up and to the right, let’s say,” says Joe. “It’s the equivalent of a guide saying, ‘You’re getting warmer.’”
Air passes through the samplers, each about the size of a small snowmobile, as the Reaper cruises at 200 mph. This rams particles into filter paper like light hitting a photographic plate, causing the particles to get stuck in the filter fibers. A separate radiation sensor analyzes the filter in realtime to estimate the type and quantity of radioactive particles collected. More extensive examination of the filters occurs after the aircraft has landed.
Because gas analysis can complement particle analysis, Sandia is developing a third type of pod called the Whole Air Sampling Pod (WASP) to demonstrate the feasibility of collecting multiple, large-volume air samples that can be analyzed for radioactive gases. Radioxenons (radioisotopes of the noble gas xenon), if detected, can provide a tell-tale indication of a nuclear detonation.
“While not small, the 9-foot-long, 650-pound WASP is designed to be compatible with an MQ-9 Reaper UAV,” says Joe. “WASP has not yet been flight-tested, but has performed well in the laboratory, and the DoD’s interest in modular gas sampling is growing. We look forward to demonstrating the WASP technology and expect that it will also cross the Valley of Death.”
Sandia developed Harvester with support from the Albuquerque office of National Technical Systems, an engineering firm. The National Nuclear Security Administration’s Office of Nonproliferation Research and Development funded the early R&D phase. The Defense Threat Reduction Agency and the Office of the Secretary of Defense’s Acquisition, Technology and Logistics Rapid Fielding Office as part of the JCTD funded the later development and qualification phase.