NASA Mini-Sniffer
NASA high-altitude air-sampling drones using hydrazine engine.
In the early 1970s, NASA engineer Dale Reed sought ways to collect air samples at extreme altitudes, up to 21 kilometers, to study the potential effects of supersonic transport jets on the upper atmosphere. He designed a family of unmanned aircraft called the Mini-Sniffers, which NASA also considered for sampling the Martian atmosphere. Three versions were built and flown by the Dryden Flight Research Center between 1975 and 1982.
The first, Mini-Sniffer I, had a 5.5-meter wingspan, wingtip tailfins, and canards on the nose. Powered by a gasoline piston engine, it completed a dozen low-altitude test flights to prove the design. It was then modified into Mini-Sniffer II by removing the canards and wingtip fins, adding tail booms, and extending the wings to 6.7 meters. Still using gasoline, it made 21 flights, reaching a maximum altitude of 6,100 meters.
To reach 70,000 feet, Reed planned an unusual engine that burned hydrazine. At that height, the air is too thin for a normal gasoline engine. Hydrazine breaks down spontaneously over a catalyst, producing hot gases—ammonia, hydrogen, and nitrogen—to drive the engine. Though corrosive, toxic, and unstable, hydrazine works without oxygen, making it suitable for spacecraft thrusters and high-altitude aircraft.
Mini-Sniffer III was a new build, similar to the second version but with a longer fuselage and the hydrazine engine. A catalytic gas generator, converted from a spacecraft thruster, decomposed the hydrazine, and the hot gas drove a piston engine producing 11.2 kilowatts. That engine turned a propeller and an electric alternator through a 2:1 reduction drive, with a special poppet valve regulating gas flow into the cylinder. It was designed to carry an 11.3-kilogram payload to 70,000 feet or higher, but made only a single flight to 6,100 meters. Fuel leaks made it hazardous, NASA lost interest, and the high-altitude UAV concept was shelved until the later ERAST Program revived it.
- Number built
- 3
- First flight
- 1975
- Last flight
- 1982
- Builder
- NASA Dryden Flight Research Center
- Mini-sniffer i wingspan
- 5.5 meters (18 feet)
- Mini-sniffer ii wingspan
- 6.7 meters (22 feet)
- Mini-sniffer iii payload capacity
- 11.3 kilograms (25 pounds)
Lore & Background
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. NASA also considered them for planetary atmospheric sampling flights over Mars.
The initial 'Mini-Sniffer I' had a wingspan of 5.5 meters (18 feet), tailfins on the wingtips, and canards on the nose. It used a gasoline-powered piston engine and performed a dozen low-altitude flights to validate the design. The Mini-Sniffer I was then modified into the 'Mini-Sniffer II' by removing the canards and the wingtip tailfins, then adding tail booms and extending the wings, giving it a wingspan of 6.7 meters (22 feet). It was still powered by a gasoline engine, and made 21 flights to a maximum altitude of 6,100 meters (20,000 feet).
To get to much higher altitudes, Reed planned to use an unusual engine that burned hydrazine. 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. 'Mini-Sniffer III' was a new build aircraft, similar to Mini-Sniffer II but with a longer fuselage and the hydrazine engine. Hydrazine was decomposed in a catalytic gas generator, made from a converted spacecraft thruster. Hot gas drove the piston engine with 11.2 kW of power. The engine drove an electric alternator and a propeller through a 2:1 reduction drive. The flow of hot gas into the cylinder was regulated by a special poppet valve. It was designed to carry an 11.3 kilogram (25 pound) payload to 70,000 ft or higher. However, the Mini-Sniffer III only made a single flight to 6,100 meters (20,000 feet), and was not flown again because fuel leaks made it hazardous to handle.
Reader's Guide
The Mini-Sniffer series represents an early NASA effort to develop a high-altitude unmanned aerial vehicle for atmospheric sampling, driven by concerns about the impact of supersonic transport jets on the upper atmosphere. The program demonstrated incremental design evolution from the gasoline-powered Mini-Sniffer I and II to the hydrazine-powered Mini-Sniffer III, which was intended to reach 70,000 feet. The use of hydrazine as a monopropellant for a piston engine was an innovative solution to the problem of thin air at high altitudes, but the Mini-Sniffer III's single flight and subsequent grounding due to hazardous fuel leaks ended the program. NASA lost interest in the idea, and the concept of a high-altitude UAV was abandoned until later when the NASA ERAST Program resurrected the idea. The Mini-Sniffers thus serve as a precursor to later high-altitude long-endurance UAVs, highlighting both the technical challenges and the early recognition of the need for such platforms in atmospheric science.
Did You Know?
- The Mini-Sniffer III used a hydrazine engine that decomposed the fuel in a catalytic gas generator made from a converted spacecraft thruster.
- NASA considered the Mini-Sniffers for planetary atmospheric sampling flights over Mars.
- The Mini-Sniffer I had tailfins on the wingtips and canards on the nose.
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