Cavea-B is a mixture of ammonium nitrate dissolved in white fuming nitric acid researched during the 1960s by teams associated with NASA [1] as an alternative to the more commonly used hydrazinemonopropellant for use in spacecraft's attitude control and thruster systems. It was derived from an earlier, similar formulation which came to be called Cavea-A, which showed less promise.
Once ignited it is highly energetic, achieving temperatures up to 5000° and thus a specific impulse of around 280[2] seconds. Cavea-B is considerably denser, more stable[3] and less toxic[4] than hydrazine, and offers a much superior performance than that of other relatively safe monopropellants such as cold thrusters, although its use is slightly more complicated as the mechanism for ignition involves mixing it with another fuel, such as UDMH, with which it is hypergolic, to get the ignition reaction started. By comparison regular hydrazine simply commences it's violent decomposition into water and oxygen on contact with a catalyst bed or mesh of a metal such as iridium[5].
At the time it was considered beneficial to find a monopropellant whose decomposition was more energetic, and thus provided more thrust per unit mass, than the traditionally used hydrazine. This would mean that reaction control systems and thrusters for orbital maneuvers on satellites and other spacecraft could be made lighter principally by reducing the amount of reaction mass needed. This would permit, for the same amount of propellant, longer times of operation times on low earth orbit and for spacecraft intended to work on higher orbits, that a certain payload could be carried into those higher orbits by lighter and therefore cheaper to launch spacecraft. Ultimately, however, Cavea-B and other high energy monopropellants were not adopted by NASA or other actors in the spacecraft industry, and hydrazine continues to be the most commonly utilized monopropellant in spacecraft as of 2019.
