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AEROSPACE
NASA MARSHALL SPACE FLIGHT CENTER, HUNTSVILLE, ALABAMA
“ Since the temperature varies with time as
the soil heats, temperature-dependent soil
dielectric properties can be incorporated
into the model along with temperaturedependent
thermal conductivity of the soil.
Whatever the properties of the lunar soil
might be, we can simply put them into
COMSOL and do a calculation.”
is the total cost of the rocket, rocket hardware,
engines, and propellant. And since
water is one of the resources that will
have to be resupplied to a manned lunar
outpost, water would be part of the total
cost of the payload taken to the Moon.
While water and oxygen can be recycled
on a manned lunar outpost, no process
is 100% efficient. Dr. Ethridge cited estimates
indicating that one ton of water
and one ton of oxygen per year would be
required for the early stages of a manned
outpost. This fact alone makes it necessary
that a water extraction process will
be developed for use at an outpost. And
once the water is extracted, oxygen can be
obtained from the water by electrolysis.
“We are looking at the process of extracting
the water from the soil. Water is water.
Run it through a purification system and
you could drink it. We will extract water
[and then] electrolysis can be used to split
the water into hydrogen and oxygen.”
The Extraction Process
As a principal investigator examining
the Use of Microwaves for the Extraction
of Volatiles From Lunar Soil, Dr. Ethridge
asserts that microwave processing
to extract water has unique advantages
over other processes. “Because of the high
vacuum, the thermal conductivity of lunar
soil is very low. The Apollo astronauts
measured the thermal conductivity and it
is comparable to aerogel, a super thermal
insulator.” Additionally, microwave energy
is advantageous because it heats from the
inside out. This means that the
excavation of lunar soil could be
unnecessary, thereby minimizing
Moon dust and the negative
aspect of perhaps having
to strip-mine the Moon. Simply
put, using microwaves could
greatly reduce the complexity,
additional infrastructure,
resources, and power requirements
of other processes. This
is why Dr. Ethridge is currently
developing microwave extraction
technology for operation on
the Moon.
The basic components of the
microwave extraction system
include a microwave source,
waveguides to deliver the energy
to the soil, and a cold trap
to capture the water vapor (Figure
2). First, the microwave energy
penetrates and heats the
soil and, since ice is relatively
transparent to microwave energy,
heat is transferred from
the soil particles to the water ice
condensed onto the surface of
the soil. On the Moon, water ice
transforms directly to water vapor
by sublimation. Once in the
cold trap, the water vapor will
transform back to ice. In addition
to the system components,
a power source and a rover to
transport the extraction system
will be necessary.
Figure 2. Demonstration hardware to test the beaming of microwave
energy down into lunar soil simulant (in the box) with
the microwave hardware mounted on a mobile platform. Initial
test of the coupling of microwave energy into the simulant.
Copyright Notice: The material described in this article is declared a work of the U.S. Government
and is not subject to copyright protection in the United States.
COMSOL NEWS 2010 //
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