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.

Objectives

• to explore the surroundings of the lander with a teleoperated rover, then collect various samples of lunar soil and bring them back to the lander
• on board the lander, to treat the samples to obtain a suitable feedstock for the plant
• to process the feedstock to obtain O2 (or if power is limited, only an intermediate product, such as H2O or CO2)
• to measure with sensors the efficiency of the process(es) (weight of O2 produced/weight of the sample), and draw conclusions on the overall process by comparing the results with the ones obtained in laboratory.
• if possible, to monitor the behaviour of the components of the plant, and check their resistivity to the lunar environment.

Design

Collecting the samples.

• mass : 9 Kg + 5 Kg for support equipment
• power : 0.2 m2 of solar cells + D-cell batteries

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.

Sizing and beneficiation

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].

Process

1. the sample is put in a vessel heated up to 1000 C, under a flow of H2, then a reaction occurs :
   FeTiO3 + H2 ---> Fe + TiO2 + H2O

   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 :

   T^4 = G*a/e*s [Larson]

   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.

   he output of the vessel contains both H2 and H2O : water must be collected and electrolyzed, providing there is enough power available. Williams used a cooler to condense the water, a drier to absorb it produced and measure the quantity, then electrolyzed it.

   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:

   1. stock the water vapour produced by the reaction in a tank, then measure the quantity.
   2. design a test electrolysis cell, using a vapour phase electrolysis concept. This operation is described in [Donitz]. It works with vapour a 1000 C, which is the exhaust temperature from the vessel, and requires half less power than a liquid phase electrolysis.

Measurement

Integration

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.

Interfaces

1. landing site: Although regolith and then ilmenite are common on the surface of the Moon, it will be more reliable to select a landing site suitable for a human occupation (not in the Highlands, for example).

2. operation during lunar day An experiment on a sample may take a couple of hours, and we want to repeat it as many time as possible. The only limit seems to be the lunar night : the plant may not survive. Therefore, landing should occur as soon as possible in the lunar day.

3. minimising site pollution There has been some concern on the possibility of a pollution of the site during the landing. Most of the propulsion systems exhaust contain some oxygen-based product. But according to [Fernini], the most susceptible species to be adsorbed is H2O, which is immediately released in the lunar atmosphere. However, we still don't know the thermal impact of the exhaust gas on the soil composition. It would be safe to design a landing sequence with the main engine cut off 10 m above the ground.

References

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