O2/CO Ignition System for Mars Sample Return Missions

Returning a geological sample from the surface of Mars will require an ascent propulsion system with a comparatively large velocity change (delta-V) capability due to the relatively deep Martian gravity well. Consequently, a significant propellant mass will be required. Bringing that mass from Earth, while technically possible, would be impractical and grossly inefficient. Manufacturing propellant from the Martian atmosphere would be far more practical. Highly efficient electrolyzers for splitting carbon dioxide into carbon monoxide (CO) and oxygen (O2) have been demonstrated. These can be run off solar power and used to generate high-pressure propellant without the need for pumps. With a theoretical vacuum specific impulse (Isp) of 324 sec (1000 psia chamber pressure, 40:1 nozzle expansion ratio), an O2/CO propulsion system would provide higher Isp than a solid rocket, and only a small fraction of the propulsion system wet mass would have to be brought from Earth. Previous testing with O2/CO propellant at NASA GRC has demonstrated that ignition of this mixture is very difficult. In that work, spark igniters were used, and every test resulted in a catastrophic detonation and damage to equipment. In this project, Ultramet will develop a high-performance ignition system for use with O2/CO propellant that is based on resistively heated silicon carbide open-cell foam. Previous testing has demonstrated that by passing an electric current through it, the foam can be heated to 1300 C in just 2 seconds. By flowing the non-hypergolic bipropellant mixture through the foam, ignition will take place in a pseudo-homogeneous manner as the gases enter the foam rather than only in the isolated vicinity of the arc in a spark igniter. This will prevent propellant accumulation in the chamber and subsequent detonation. Safe, reliable ignition of O2/CO is an enabling technology for the use of in-situ manufactured propellants on Mars.