Development of a Microchannel In Situ Propellant Production System

Abstract

This document was printed on recycled paper. PNNL-15456 Development of a MicrochannelIn Situ Propellant Production System Executive SummaryAn in situ propellant production plant (ISPP) on future Mars robotic missions can produce oxygen (O 2 ) and methane (CH 4 ) that can be used for propellant for the return voyage. By producing propellants from Mars' atmospheric carbon dioxide (CO 2 ) and hydrogen (H 2 ) brought from Earth, the initial mass launched in low Earth orbit can be reduced by 20 to 45%, as compared to carrying all of the propellant for a round-trip mission to Mars' surface from Earth. Furthermore, by utilizing ISPP, both robotic and manned missions to Mars can be enhanced, enabled, and extended. The propellant generated can provide fuel for hoppers and rovers for increased mobility on the surface, allow additional propellant to be created to increase the return trip payload, and provide oxygen for longer mission stays. With a durable heat source, this ISPP could also use in situ sources of hydrogen to provide a sustainable propellant supply.Pacific Northwest National Laboratory used microchannel architecture to develop a Mars-based In Situ Propellant Production (ISPP) system. This three-year research and development effort focused on process intensification and system miniaturization of two primary subsystems: a thermochemical compressor and catalytic reactors. Both of these systems were designed based on a robotic direct return mission scenario, but can be scaled up to human flight missions by simply numbering up the microchannel devices. A microchannel condenser/phase separator was developed under another NASA project. The results of this device are provided here to offer insight on performance of another necessary system component.The thermochemical collection and compression of CO 2 was developed using absorption and adsorption. Both membrane and microwicking absorbers were evaluated using 100-and 240-µm microchannels. CO 2 was absorbed from a 20%-CO 2 :80%-N 2 mixture into either a diethanolamine/water (DEA) or a DEA/PEG solution. Improved mass transfer was observed for the thinner films. Overall mass transfer coefficients were as much as 2.6 times greater than a conventional packed column for the thinnest microwick and about 7.1 times greater for the membrane system. A multichannel adsorption system was designed to meet the full-scale CO 2 collection requirements using temperature swing adsorption. Each stage is designed to achieve a 10x compression of CO 2 . A compression ratio to collect Martian atmospheric CO 2 at ~0.8 kPa and compress it to at least 100 kPa can be achieved with two adsorption stages in series. A compressor stage incorporates eight thermally coupled adsorption cells at various stages in the adsorption/desorption cycle to maximize the recuperation of thermal energy and provide a nearly continuous flow of CO 2 to the downstream reactors. Experimental work was performed in a single channel adsorber to validate this process. A temperature cycle between 12 and 77°C could be achie...

Demonstration of Critical Systems for Propellant Production on Mars for Science and Exploration Missions

“…5 The unit, pictured in Fig. 2, was designed as an integrated system incorporating micro-channels for heat exchange and meso-channels for the adsorption media, with the close contact of adsorbent and heat exchanger channels allowing for rapid thermal cycling and high CO 2 throughput per unit adsorbent and hardware volume and mass.…”

“…Flow rates were much lower than anticipated based on tests with the single sorption cell performed by Battelle. 5 In the Battelle tests, a vacuum chamber was not available, so tests were performed with CO 2 added to nitrogen at a partial pressure equal to the total pressure on Mars (approximately 1/100 th of an Earth atmosphere). The data obtained here in the Mars environment chamber can now be compared to the previous data and combined to develop improvements in the sorption pump mechanical design and adsorbent material to optimize performance at a variety of conditions.…”

Mars Surface Mobility Leading to Sustainable Exploration

“…Table IX lists the production rates for the large and small hoppers, and also shows the rate for a sample return ascent vehicle for comparison. 11 The production plant for the large hopper vehicle would be 1/10 th scale of that for a sample return mission, and would therefore be a significant risk reduction mission to demonstrate the feasibility before relying on in-situ propellants in the critical path for sample return. The initial vehicle mass, hop distances, and propellant requirements were taken from the preliminary trajectory analysis and were used for sizing the production plant.…”

“…A simplified schematic of the production plant considered in this study is shown in figure 18, taken from ref. 11. In this system, a Sabatier reactor produces methane and water from carbon dioxide and hydrogen, which is then electrolyzed to produce oxygen and hydrogen.…”

“…Preliminary work has shown the feasibility of rapid cycles on the order of 2 minutes with very efficient heat transfer from one unit to the next in an 8-unit system, resulting in little external power requirement after initial heat-up. 11 With the short cycles, the total amount of adsorbant can be significantly reduced, resulting in a very compact and lightweight unit. Tests at PNNL demonstrated a 10-times increase in pressure at a throughput of 95 g/hr for a single unit with a mass of 1.3 kg.…”