NASA Mini-Sniffer

The NASA Mini-Sniffers were a series of unmanned aerial vehicles designed to sample the air at high altitude to support various scientific studies.

[1] 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.

Instead of gasoline, Reed planned to use hydrazine, or N2H4, which breaks down spontaneously when run across a catalyst, generating hot gas (ammonia, hydrogen and nitrogen) to drive the engine.

Hydrazine is a corrosive, toxic, and unstable propellant, but its ability to "burn" without oxygen makes it useful for spacecraft thrusters and for such high-altitude engine applications.