In the early 1970s, NASA engineer Dale Reed was investigating methods for sampling the atmosphere at very high altitudes, up to 21 kilometers (70,000 feet). NASA's studies into supersonic transport jets had led to questions about their possible impact on the upper atmosphere, and Reed designed a series of "Mini-Sniffer" drones to take air samples at high altitudes. Three Mini-Sniffers were built by NASA Dryden Flight Research Center, and were flown from 1975 through 1982.