The Technology Transfer and Partnerships Office
Propellant Fuels from Mission Waste

   The high cost of re-supply from Earth demands that on-board resources be utilized to the fullest extent for exploration missions. This is particularly true in the case of life-support and propellant consumables. The ability to refuel on the lunar surface would reduce the vehicle mass during launch and create more cargo space. The production of propellant on the surface of Mars may be critical for the feasibility of round-trip human missions or robotic sample return missions. Recycling is a key technology that maximizes the available resources by converting mission waste products into useful commodities. One example of this is to convert plastic packaging, food scraps, and human waste into fuel. The process being studied thermally degrades plastic in the presence of oxygen producing CO2 and CO. The CO2 and CO gases are then reacted with hydrogen over catalyst (i.e. Sabatier reaction) producing methane (CH4), a potential propellant fuel. An end-to-end laboratory-scale system has been designed and built to produce methane from plastic, in this case polyethylene. The first generation system yields 9% CH4 by weight of plastic used.


In the case of the Moon, production of propellant is limited to the production of oxygen due to the lack of an in-situ source of carbon or hydrogen required to produce fuel. However, recent NASA missions have indicated the presence of water throughout the surface of the Moon, and the water could be used to produce H2-O2. It must be emphasized that the findings of water on the Moon are very recent and incomplete at this time and water is found at low concentrations (10 – 1,000 ppm) on the surface of the Moon. NASA's In-Situ Resource Utilization (ISRU) project has been developing various oxygen production processes to extract oxygen found in lunar soil, which is nearly 50% oxygen. In order to produce fuel on the Moon, it is required to use other resources that are made available by the presence of humans. Trash (leftover food, food wrappers, paper, etc) and human waste (fecal matter, and metabolic CO2) are a good source of carbon from which methane can be produced. Recent estimates show that the propellant required for a lunar crew ascent stage is approximately 4,000 kg of propellant (at a 3.4 O2:CH4 ratio: 3,090 kg of O2 and 910 kg of CH4). If all this propellant is produced on the surface of the Moon, it would make available 4,000 kg for payload usage, a total of 40,000 kg over a 10-year life of the lunar outpost.


Mars offers the reagents required to produce in-situ propellants: atmospheric carbon dioxide (CO2) to produce methane-oxygen (CH4-O2) with hydrogen (H2) either brought from Earth or in-situ hydrogen-oxygen from water ice on the surface of Mars. The disposal of waste in a remote outpost, lunar or Martian is also an important consideration: the shipment of such waste back to Earth as it is practiced from the International Space Station would expand precious launch volume and mass from the Moon and Mars and discarding it in the local environment is a polluting practice.


weightswaste
Elemental weights in grams for the daily packaging plastic waste, human dry solid waste,
and dry food waste attached to plastic waste for a crew of four. (Source: E. Santiago-Maldonado 2010)


production_methane_propellant
First Generation integrated system for the production of methane propellant fuel from waste plastics. (Image credit: Kennedy Space Center)

References:
Creating Methane from Plastic: Recycling at a Lunar Outpost E. Santiago-Maldonado, J. Captain, R. Devor, J. Gleaton, AIAA 2010-1551, 48th AIAA Aerospace Sciences Meeting, 4-7 January 2010, Orlando, FL.