How does Lunar Oxygen Propellant (LUNOX) used for Beamed Energy Propulsion (BEP) enable reduced cost of lunar exploration over full lunar surface?
The Apollo mission emphasized lunar material return and short duration exploration with limited science investigation and experiments. The current NASA Constellation lunar program envisions extended duration of science and engineering investigation following Apollo methodology. Advanced propulsion (cryogenic replaces hypergolic) and separate launch for crew and spacecraft are departures from the Apollo scenario. Beyond, it is expected that an exploration program might emerge which is similar to the international program of Antarctic exploration.
Exploration and scientific investigation of Antarctica provides a template for future lunar activities. The major obstacle at this time is the high cost of transport to and from the lunar surface. In situ production can address many issues of survival (food and shelter) on the lunar surface and thereby lower earth-to-moon transportation costs. Oxygen is a major constituent of lunar soil and can be processed into usable monopropellant to greatly lower the cost of return to earth.
Comparing to earth, beamed-propelled launches will be much easier to conduct from lunar surface, because there will be no air drag, no turbulence, no atmospheric scattering, no need for high delta V. This, of course, follows from the absence of atmosphere on the moon and small lunar gravity (six times smaller than ours). Hydrogen, the most efficient propellant and available everywhere on Earth can be developed only from water-rich poles of the moon. As a result, our exploration of the moon will be limited mostly to those regions. Unlike hydrogen, LUNOX can be mined everywhere and by means of beamed-energy propulsion provide earthbound transport. Therefore, LUNOX allows expansion of explored areas of the moon to non-polar regions!
Oxygen as BEP propellant will have better storage capacity than hydrogen, but it has lower exhaust velocities. At temperatures 4,000K LUNOX will provide 3000 m/sec exhaust velocity. This corresponds to specific impulse typical for chemical rocket propulsion (300 sec). At such temperatures hydrogen exhaust velocities will be 4 times higher.
As beamed power at fixed thrust is proportional to exhaust velocity, the power needed at burnout is reduced by a factor of four for oxygen compared to hydrogen.
Lower lunar gravity (comparing to earth) also means lower thrust which reduces power requirements. At lunar gravity = one-sixth earth gravity the indicated power reduction is 4 X 6= 24 for lunar beamed energy using LUNOX vs. hydrogen heated by earth-based beamed energy. This reduction is even better considering drag and atmospheric attenuation penalties for earth-based beamed-energy launches.
It is easy to show that for moon-based launches to low lunar orbit the initial mass of LUNOX propellant will be approximately equal to the payload mass. This makes feasible to use Lunar Shuttle Vehicle (LSV), which will be carrying return payload from lunar surface to Apollo-type command module, orbiting the moon.
Use of LSV makes unnecessary lunar landing (and take-off) of the Lunar Excursion Module. This will reduce initial launch mass two times for lunar mission from Earth. If LSV could provide on-orbit refueling to Earth return Command Module, then the launch mass could be reduced threefold.
To summarize: Given lunar infrastructure supporting Antarctica-style exploration (fixed-base, year round deployment) with in situ resource development, LUNOX is a plentiful by-product which can be used for Beamed Energy Propulsion (BEP). BEP is favored over chemical heating due to high cost of transporting/producing fuel at the lunar site. Source power now is in 100KW to 2MW range approaching 1 mm wavelength, already capable of lunar point-to-point experiment or small payload to low lunar orbit.
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