Page:Advanced Automation for Space Missions.djvu/165

 4A.2 Propellants

There are two most promising propellant options for lunar-LEO transport systems. The first is an oxy-hydrogen combination using lunar-derived oxygen and hydrogen imported from Earth. The second option again requires native lunar oxygen as the oxidant but combines terrestrial-imported hydrogen with silicon purified on the Moon to produce a more powerful silane rocket fuel.

(a) Lunar oxygen, terrestrial hydrogen propellant option

The relevant chemical propellant combustion reaction is:


 * 2H2 + O2 → 2H2O

The molecular weight of H2 is 2 and of O2 is 32, so:


 * BH = MH2</SUB>/(M<SUB>H<SUB>2</SUB></SUB> + M<SUB>O<SUB>2</SUB></SUB>) = 1/9

The achievable specific impulse of LOX - LH<SUB>2</SUB> is about 450 sec, using heat of formation data from Weast (1978) and assuming 75% thermal efficiency. This yields an exhaust velocity of 4.41 km/sec.

(b) Lunar oxygen, Earth/lunar silane propellant option

The silane produced on the Moon is assumed here for simplicity to be entirely SiH<SUB>4</SUB>. The propellant chemical reaction is:


 * SiH<SUB>4</SUB> + 2O<SUB>2</SUB> → SiO<SUB>2</SUB> + 2H<SUB>2</SUB>O

The molecular weight of SiH<SUB>4</SUB> is 32, so B<SUB>H</SUB> = 1/24. The achievable vacuum specific impulse is within the range 328-378 sec (Lunar and Planetary Institute, 1980). Assuming the middle of the range, I<SUB>sp</SUB> = 353 and C = 3.46 km/sec.

4A.3 References

Lunar and Planetary Institute: Extraterrestrial Materials Processing and Construction, Final Report NSR 09-051-001 Mod #24, Houston, Texas, 1980.

Weast, Robert C., ed.: Handbook of Chemistry and Physics, CRC Press, West Palm Beach, Florida, 1978. Fifty-ninth Edition.