Integrated Cryogenic Fluid Study for Life Support Systems on the Moon
Research Associate: C. Andrew Harner
Principal Investigator: David Plachta
The first leg of the Constellation program involves sending humans back to the moon and setting up a Lunar Outpost. While on the moon, oxygen and other fluids will be necessary for survival. Oxygen will be used in the Environmental Control and Life Support System (ECLSS), Extra-Vehicular Activities (EVA), the power system, and Lunar Rovers. Other gasses such as hydrogen or methane could be used as propellants. A trade study is necessary to find the most efficient and effective way to transfer and store the necessary fluids to the moon to conserve mass and volume, while not significantly complicating systems. The systems proposed to be studied will involve cryogenic and non-cryogenic storage of fluids.
Gasses dispersed for human use on the moon have certain requirements. The most important is non-propulsion oxygen. The Exploration Life Support (ELS) Lunar Reference Mission Document states that there will be 300 EVAs in each 180 day mission. For these missions, two oxygen tanks are required, one primary maintained at 3000 psi and weighing 1.6 lbs, and one secondary maintained at 3000 psi and weight 2.6 lbs. These will be refilled for each mission, and if there are no emergencies only the primary needs refilling. Also, oxygen will be used to purge the Extravehicular Mobility Unit (EMU) of carbon dioxide. This tank will be at a lower pressure and requires 1.0 lb of fluid. Mission types include sortie, super-sortie, and outpost and will be located at polar and low latitude regions of the lunar surface. Oxygen will also be needed to support life within part of the ECLSS. Since regenerative fuel cells will be used hydrogen and oxygen will be needed to generate power. Power through fuel cells and oxygen may also need to be provided to the Lunar Rover. Further, if ISRU (In-Situ Resource Utilization) occurs, storage of discovered gasses will be required. Propellant in the form of hydrogen and methane may also need to be stored.
Many storage systems have been conceptualized for non-propulsion oxygen. A baseline technology is to transport all non-propulsion fluids needed in high pressure storage tanks. This is the simplest plan as the gasses would only need to be transferred between tanks at regulated pressures to be usable. Other technologies involve more complex systems, some utilizing cryogenics. These are listed below.
- Deliver of cryogenic oxygen in storage tanks followed by vaporization.
- Scavenging and vaporization of liquid oxygen left over in Lander fuel tank.
- Water Electrolysis to get hydrogen and oxygen followed by a multi-stage compressor.
- High-pressure Oxygen Generation Assembly (HPOGA).
- Water Electrolyzer combining power, ECLSS, and EMU needs.
Each method’s feasibility and benefits will be studied. The cryogenic tools necessary will be traded and an optimum method is desired.
My Role as a Research Assistant
I will be working to compare all the proposed methods for acquiring the amount of gaseous oxygen at the desired pressures. Many factors will be taken into account including the mass, volume and power required for fluid storage. Major differences between cryogenic and non-cryogenic storage will be studied. I will be working with software analysis tools to quantify tank masses as well as other quantities. The Cryogenic Analysis Tool (CAT), a spreadsheet-based tool, will be improved to better understand the technologies needed for the cryogenic storage. Visual Basic will be used write modules for the tool’s sections. Parametric studies will be applied to current major research including subcritical oxygen storage for EMU, EVA, and ECLSS as well as hydrogen and methane propellants, and fluids used in power generation. The goal of the study is to simplify the life-support oxygen storage systems. This involves minimizing mass and volume of necessary storage tanks and possible integration of fluids for the various systems. The advantage of using cryogens will be especially examined.
The final outcomes of this research will include an updated, more streamlined CAT for updated lunar architectures and combined systems concepts. Trade studies will be constructed for the decision process between each system. Plots of mass/power/volume vs. time and other parameters comparing cryogenic and non-cryogenic will be constructed. Marginally helpful (gray) areas and areas where cryogenics are clearly better will be identified within the data. Combined cryogenic storage facilities will be investigated and traded. Master Equipment Lists (MEL) of gaseous and liquid oxygen systems will be constructed. Further necessary advances in both cryogenic and non-cryogenic technologies will be suggested.