In Situ Resource Utilization (ISRU) is at the forefront of near-term lunar and Martian missions. While many technologies and program strategies focus in ISRU, propellant production substantially impacts the scope and duration of these missions. Through ISRU, missions can benefit from substantial mass savings, and size reduction which, in turn, result in longer durations and larger payloads. Moreover, reusable landers within situ propellant production can reduce cost and benefit critical functions such as life support, energy storage, and scientific payloads.
With the potential benefit comes certain technical challenges. While pure methane is a well-characterized propellant, impurities that may be present in in situ production can cause a variety of issues. Beginning in the manufacturing process, the presence of carbon dioxide, carbon monoxide, and water can affect the success of liquefaction processes. Carbon dioxide and water both have freezing points above the saturation temperature of methane that could cause the build up of solids in liquefaction plumbing. Moreover, carbon monoxide has a lower saturated temperature so it may either, not condense and cause gas pocket, or condense and boil off later. It may require a conditioning stage to separate carbon monoxide from methane or maintaining temperatures low enough to keep it from boiling.
In this effort GTL proposes to determine the effect of impure propellant on mission critical systems, including storage, pressurization systems, thermal management systems, and combustion instability.
Since this effort is focused towards defining standards for impure propellant properties, the commercial marketplace is small. Therefore, the direct commercialization impact is also small. However, since several current and future propulsion systems are expected to use methane fuel, the secondary impact of safely relaxing specifications is sizeable.
On the other hand, validation of GTL’s computational physics framework used in this effort supply another tangible benefit to NASA for combustion and combustion instability modeling.
Several commercial space ventures have baselined methane or natural gas fuels for propulsion systems. Characterizing the limitations of subpure propellants can have an impact of launch costs, mission scope, and logistical supply chains for these entities. Moreover, military applications could find value from in situ methane production and refinement for remote missions.