Historical perspective - Viking Mars Lander propulsion

Abstract

Developed for the Viking mission to Mars in 1975-76, the Viking Lander Capsule terminal descent monopropellant hydrazine rocket engine assemblies represented unique technology for an unusual mission. Intended solely for the purpose of landing an unmanned spacecraft on Mars in support of scientific exploration of the planet, the design and construction of the engines was so optimized for the mission that it is literally unusuable for any other application. It was required that the engine have twice the thrust of the largest monopropellant hydrazine engine ever developed, but weigh considerably less. It had to have 18 nozzles, the capability of 10:1 throttling, a new catalyst, be totally sealed until fired, employ no organic unsealed materials, be 100% germ free, utilize a new propellant, and start at a temperature more than 45°F below the propellant's freezing point. The schedule was short and inviolate. The contract was firm-fixed price. After 30 months, the flight engines were delivered, capable of a mission firing time of 45 seconds. They encompassed technology advances that were the foundation for longer life, lower cost monopropellant hydrazine thrusters and gas generators now in use with operational lifetimes that are longer by 3-4 orders of magnitude.