The first thing I need to determine is how much oxygen will be lost through the exposed Lunar regolith and mega-regolith. We need to be able to keep it to some acceptable minimum otherwise SPORE just won’t work.
There are some major challenges though:
- The Lunar regolith is poorly defined. Only 382 kilograms of Lunar material, from 9 different sites, have been returned to the Earth for study (1, pg 5). And not all of that material has been exhaustively studied. Additionally, only 24 core samples, taken from a maximum depth of 292 cm, have been returned (1, pg 9). Individual samples may be well defined but the overall regolith is not.
- The Lunar regolith is highly variable in density, porosity, particle distribution, and every other parameter. It’s a complex mix of mineral fragments, breccias, crystalline rock fragments, agglutinates, and glass (1, pg 475). There is no “typical” sample of Lunar regolith. The regolith has been shattered, scattered, and fused repeatedly by impacts for eons. The result is a highly heterogeneous mixture that greatly varies between sample sites and between samples within the same site.
- The Lunar mega-regolith is largely undefined. None of the Apollo core samples were long enough to reach the mega-regolith so we have no physical samples from this region. We have some ideas on what it might be like but little real data.
- Ideally, SPORE will be usable on Mars, asteroids, other moons, and nearly anywhere else we want to start a Homestead. Sure, each environment will be different so we’ll need to adapt SPORE to fit those particular conditions. But the overall concept should work nearly everywhere.
The solution to these challenges is to focus on the design and implementation of the SPORE system, not on making it work under an artificially constrained set of parameters (such as a particular regolith sample). A clever design is the key to making SPORE practical.
As a bonus, data from this experiment could also be useful if we tried to dome and pressurize a Lunar crater. I’m not sure WHY anyone would want to do that when subterranean settlements offer more advantages and fewer disadvantages. But we should keep out options open.
- How much pressurized air will pass through a given volume of simulated regolith, with pre-determined densities and porosities, over a specific amount of time?
- How much gas will pass into the regolith before the exposed SPORE section can be sealed?
- Does the regolith reach equilibrium?
Since there’s no “typical” regolith sample, I don’t see the point in trying to simulate the regolith. Plus, regolith simulants are not cheap. For this experiment, I’m going to “simulate” a few key regolith parameters using common terrestrial materials.
We know next to nothing about the Lunar mega-regolith. And what little we do know comes from remote sensing and modeling. So I’m going to need an Earth analog to do this part of the experiment.
Air pressure and composition
Since this is the first experiment, I’m going to use pressurized air instead of pressurized oxygen. This will reduce the cost and complexity of the experiment. It will also be less hazardous.
Conducting this experiment in a vacuum (to simulate the Lunar environment) would be extremely expensive. Instead, I’m going to simulate the pressure difference between the Lunar surface (assuming that the voids in the regolith are also a vacuum) and the inside of the SPORE area by increasing the internal pressure by the same amount. I’ll run tests with the following range of pressures.
- Minimum test pressure = 127 kPa
- 101.325 kPa + 25 kPa +0.675 kPa (to round up) = 127 kPa
- The NASA minimum partial pressure for 100% oxygen is 24.82 kPa (4)
- The Armstrong limit is 6.3 kPa. Building in an extra 19.375 kPa will allow for unexpected pressure drops.
- ½ Standard Lunar Homestead Atmosphere (SLHA) = 137 kPa
- 101.325 kPa + 35.055 kPa + 0.62 kPa (to round up) = 172 kPa
- 1 Standard Lunar Homestead Atmosphere (SLHA) test pressure = 172 kPa
- 101.325 kPa + 70.11 kPa + 0.565 kPa (to round up) = 172 kPa
- 1 Standard Atmosphere test pressure = 202.65 kPa
- 101.325 kPa + 101.325 kPa + 0.35 kPa (to round up) = 203 kPa
The maximum dimensions of the experiment are 180 cm long by 70 cm wide by 230 cm tall. That’s so it can fit through the door to the balcony where it will be stored (part of the fun of doing research while living in a small apartment). The entire experiment will be enclosed in plywood to protect it from the elements (outside storage).
Probably a pressure gauge inside the SPORE unit to measure the pressure loss.
- Lunar Sourcebook (www.lpi.usra.edu/publications/books/lunar_sourcebook)
- Center for Lunar and Asteroid Surface Science – Planetary Simulant Database (sciences.ucf.edu/class/planetary-simulant-database/)
- Permeability of JSC-1A: A lunar soil simulant (www.sciencedirect.com/science/article/pii/S0019103510004835)
- Man-Systems Integration Standards – Natural and Induced Environments (msis.jsc.nasa.gov/sections/section05.htm#_5.1_ATMOSPHERE)