The purpose of the Oxygen Production Demonstration Plant (O2 plant) is to test in-situ one or two process(es) of oxygen production from lunar minerals in order to prove the possibility of large-scale production for a manned base (fuel and life support). Several processes are under study, and some of them are currently adapted for lunar environment [Gibson & all]. However, there exists no plan yet for a small, automated demonstration plant which could be the payload of a small lander. Therefore, considerable work remains to be done to design this device. The following figures are only a first rough estimation based on laboratory experiments. Accurate figures would required a complete design.
The processes considered here are based on the reduction of ilmenite at high temperature. Ilmenite (FeTiO3) is a common mineral in the lunar soil, and is the most likely source of lunar oxygen [Allen & all]. Other potential feedstocks are volcanic glass and basalt. The ilmenite can be reduced either by hydrogen [Gibson & all] or by carbon [Ramohalli & all]. The respective reactions are :
Since we got relatively few information on the carbon process, figures are given only for a H2-type plant. The reasons for the selection of ilmenite reduction can be found in the WORLD-M proposal. Other processes may be contemplate.
In case the rover would suffer a failure, a backup system should be on board the lander, like a simple drill to collect at least one sample.
Beneficiation itself consists in increasing the proportion of ilmenite in the feedstock. The ilmenite reduction with H2 required 30 to 60 % ilmenite in he feedstock [Mason]. Processes involve both magnetic and electrostatic separation (ilmenite has medium magnetic and conductor characteristics). An electrostatic device has been tested on true lunar soil with field strength up to 5 kV/cm2 [Agosto], but with ambiguous results [Taylor].
In the Williams' experiment, the vessel was a 2 cm*11 cm stainless steel cylinder electrically heated, which lead to 1475 W of electrical power. Of course, it will be far more interesting to use directly the solar energy. With a solar flux of 1358 W/m2, however, a direct heating is not possible : the temperature of a material with solar absorptivity a and infrared emissivity e is given by :
Where G is the solar flux and s is the Stefan-Boltzmann constant, 5.67*10-8 W.m-2.K-4
For T = 1300 K, G required is 10 to 40 times the one available on the Moon. The upper value gives us, for a cylindrical mirror, a focal length of 1 m for a width of 20 cm [Wieder]. The mirror and the furnace must be installed on the top of the lander, and a tracking device should be used.
The cooler used air circulation, and the electrolysis cell had a consumption of 677 W. This is definitely not suitable for the test plant. It would be interesting anyway to test an electrolysis device on the Moon, since it will probably be used on a large scale plant. I propose two alternatives:
|Item||Mass (kg)||Power (W)|
|Vessel + mirror||5 (?)||Solar|
|Electrolysis Cell||5||<400 (?)|
|Rover + support||14||autonomous (?)|
|Misceallenous (H2 tank, etc)||10 (?)||-|
We do not include the possibility of having two processes running on the lander, which may share some element like the mirror (the carbon reduction process requires the same temperature) [Ramohalli]. Since there will be several experiments on different samples, all the elements must be reusable. Especially, the vessel should be emptied after each experiment and the tubing purged.
|Input Groups||Variables||Output Groups|
|Landing site||Mission Planning|
|Operation during lunar day||Mission Planning|
|Propulsion||Minimising site pollution||Propulsion, Structure, NGC|
|Keeping plant almost horizontal after landing||Structure, NGC|
|Structures||Max. mass and volume|
|Power||Max. Power available|
|Isolation of "hot" elements like furnace, cell, mirror, vapour produced.||Thermal|
|Vibrations (screening, etc.)||Structure|
|Tracking device for the mirror||Structure, Power, Computer|
|Sensors data||Computer, Com.|
|Rover||Structure, Power, Computer, Comm., Sensors|
Allen C.C., Bond G.G., McKay D.S. : "Lunar Oxygen Production : a maturing technology" in Engineering, Consruction and Operations in Space IV, American Society of Civil Engineering, 1994
Annarella & all,"Water and Oxygen Resources : a Lunar Discovery Mission", Universty of Texas, Fall 1994
Donitz W., Erdle E., Striecher R. : "High Temperature Electrochimical Technology for Hydrogen Production and Power Generation": in Electrochemical Hydrogen Technologies, Hartmut Wendt, Elsevier, New-York, 1990
Fernini I., Burns J. O. Taylor, G.J., and all : "Dispersal of Gases Generated Near a Lunar Outpost" in Journal of Spacecrafts & Rockets, Vol. 27, No. 5, Sept-Oct. 1990.
Gibson M. A., Knudsen C.W., Brueneman D.J., Kanamori H. : "Kinetic Interpretation of First Reactivity Experiments on Lunar Basalt Samples" in Engineering, Construction and Operations in Space IV (American Society of Civil Engineering, 1994)
Larson W.J., Wertz J.R. : Space Mission Analysis and Design, Microcosm, inc.,Torrance, CA, 1992
Mason W.L., "On the Beneficiation and Comminution of Lunar Regolith and Beneficiation and Comminution Circuit for the Production of Lunar Liquid Oxygen in Enginnering", Construction and Operation in Space III, American Society of Civil Engineering, 1992
MFEX: Microrover Flight Experiment Control Subsystem home page in http://robotics.jpl.nasa.gov/tasks/mfex /homepage.html, 1995
Ramohalli K. and all : "A Robotic Common Lunar Lander Concept in Support of the Space Exploration Initiative" in Space Exploration, Science and Technologies Research, The American Society of Mechanical Engineers, 1992
Taylor L.A., McKay : "Beneficiationof Lunar Rocks and Regolith : Concepts and Difficulties" in Enginnering, Construction and Operation in Space III, American Society of Civil Engineering, 1992
Wieder S. : An Introduction to Solar Energy for Scientists and Engineers, John Wiley & Sons, Inc., 1982.
Williams R.J. : "Oxygen Extraction from Lunar Materials : an Experimental Test of an Ilmenite Reduction Process" in Lunar Bases and Space Activities of the 21st Century, Lunar and Planetary Institute, 1985
CSR/TSGC Team Web