Mars In-Situ Oxygen Production, 18-9065Printer Friendly Version
Inclusive Dates: 07/01/99 - 12/28/00
Background - With the recent discovery of evidence of life in meteoritic rocks from Mars, there has been a renewed interest in sample return missions and eventually a manned mission to Mars. Initial plans for a mission to Mars were formulated during the Apollo program, but no serious funding was provided to implement those ambitious plans. More recently, a number of studies have rekindled interest in a Mars mission. NASA plans an extensive exploration of Mars, including manned missions, in the early 21st century. One of the main goals of NASA's Human Exploration and Development of Space (HEDS) enterprise is to establish a long-term human presence on Mars at a "reasonable" cost. To meet this objective, the launch mass of the Mars spacecraft must be significantly reduced. With current technology, the initial propellant load of the spacecraft is so large (more than 90 percent of the total launch mass) that no current launch vehicle has the lifting capacity to launch the entire mission payload with a single rocket. If the propellant for the Mars-Earth return phase of the mission were produced on Mars, the total spacecraft mass could be reduced to one-sixth of the mass of a spacecraft that initially carried all its propellant for the return trip. This spacecraft could be launched by current launch technology. The challenge is to devise a practical method of producing the needed propellants on Mars using the resources available on Mars.
Approach - The overall objective of this program is to develop and demonstrate in the laboratory a simple, reliable, low-power catalytic process for converting carbon dioxide into carbon monoxide and oxygen. The conceptual approach is based on the electro-chemical reduction of CO2 at a catalytic surface under potentiostatic conditions with selective separation of product gases. This process involves the development of an electrochemical cell (shown below) that comprises a solid electrolyte for oxygen conduction sandwiched between porous working and counter electrodes. The working electrode affects the electrochemical reaction that is facilitated by the catalytic properties of the electrode material, and by the potential applied between this electrode and a counter electrode. From an electrochemical viewpoint, the reduction of CO2 is the reverse endoenergetic reaction that occurs in a low-temperature CO/O2 fuel cell. The reverse reaction is to be exploited in the present effort through careful choice of a catalytic surface for which only a slightly cathodic potential is needed to drive the electrochemical reduction.
Accomplishments - A number of electrocatalytic materials have been synthesized, and a select few have been shown by thermal desorption and recoiling mass spectrometry (TDARMS) to be active in the heterogeneous reduction of CO2 at relatively low temperatures (ca. 150 °C). These catalysts have been combined with electrically conductive support materials to form a porous working electrode. Ceramic electrolytes have been prepared as solid wafers through a pressing and sintering process that yields an oxygen-deficient microstructure for selective conduction of oxygen ions. While preliminary testing of the wafer material showed promising results, robust wafers capable of withstanding the rigors of full-scale testing were not successfully fabricated. The materials processing methods will require further development before this technology can be brought to a fully functional level.