Lunar resources

There are basically four potential lunar resources:

• Silicates in regolith containing typically >40% oxygen.

• Regolith containing FeO for hydrogen reduction. FeO content may vary from 5% to 14% leading to recoverable oxygen content in the 1-3% range.

• Imbedded atoms in regolith from solar wind (typically, parts per million).

• Water ice in regolith pores in permanently shadowed craters near the poles (unknown percentage, but possibly a few percent in some locations).

5.2.4 Lunar ISRU processing 5.2.4.1 Oxygen from FeO in regolith

Hydrogen reduction of FeO in regolith is being developed by JSC as a means of extracting oxygen from regolith. Hydrogen reduction of regolith depends on the reaction of hydrogen with the FeO in the regolith to produce iron and oxygen. The remainder of the regolith does not enter into the reaction. The water (steam) produced in the reactor (at ^ 1,300 K) is electrolyzed and the oxygen is saved while the hydrogen is recirculated. Some make-up hydrogen is needed, as the process is not 100% efficient. It is not clear how the regolith is fed into and withdrawn from the reactor. It is also not clear how one prevents "gunking up'' within the reactor. Some heat recuperation can be accomplished by using heat from steam and perhaps spent regolith to pre-heat incoming regolith, but that will add considerable complexity and, for solid-solid heat transfer, introduce potential failure modes due to "gunking up.''

The expected FeO content of two sources of regolith is summarized in Table 5.2.

The energy requirement to process X kg of regolith is the energy to heat the regolith from 200 K to 1,300 K. JSC hopes that the system can recuperate 50% of heat from spent regolith in solid-solid heat exchangers—heat losses were estimated at 10%. This would imply (if taken at face value) that the heat requirement is:

Heat = (X kg)(0.00023 kWh/kg-K)( 1,100 K)(0.5 + 0.1) = (0.152X) kWh

Power requirements to heat regolith to extract oxygen by hydrogen reduction based on the above formula are given in Tables 5.3 and 5.4, assuming that solar power is used and that the duty cycle for the process is 40% (3,500 hours of processing per year). These power requirements are only for the reactor and do not include power requirements for excavation, hauling, liquefaction, and cryogenics. If some sort of

Table 5.2. FeO content of two sources of regolith.

Location % FeO in regolith

Mare 14

Highlands 5

mT of regolith needed to generate 1 mT of oxygen

32 90

Table 5.3. Projected power requirement to extract oxygen from Mare regolith assuming 50% heat recovery.

Annual oxygen production rate (mT) ^

1

10

50

100

Annual regolith rate (mT)

34

336

1,681

3,361

1,000s of kWh

5.1

51

255

510

Hours

3,500

3,500

3,500

3,500

kW to heat regolith

1.44

14.4

72

144

Table 5.4. Projected power requirement to extract oxygen from highlands regolith assuming 50% heat recovery.

Annual oxygen production rate (mT) ^

1

10

50

100

Annual regolith rate (mT)

96

947

4737

9472

1,000s of kWh

14

143

719

1437

Hours

9864

9864

9864

9864

kW to heat regolith

4.1

40.6

202.9

405.8

magnetic or other pre-processing can be used to beneficiate the regolith, power requirements might be reduced.

Alternatively, if such heat recuperation is not feasible, the power requirement would roughly double.

The technical feasibility of this process has yet to be demonstrated. The overall process includes systems for excavation of regolith, hauling regolith to the reactor, oxygen extraction in the reactor, and storage of the oxygen in a cryogenic storage system. The following aspects are not known:

• cost to develop and validate this technology;

• requirement for human oversight and control of the process;

• degree of autonomy that can be achieved.

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