SPORE Pressure Experiment 1

The first thing I need to determine is how much oxygen will be lost through the exposed Lunar regolith and mega-regolith in the SPORE unit. 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.
  • Any simulant I made or bought would, at best, only simulate a couple of parameters from a particular sample.  There is no way to adequately simulate the vacuum or gravity or all of the physical properties of in-situ Lunar regolith. So these experiments will be rather limited.

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.

The data from this, and other, experiments might have limited value for building actual SPORE prototypes. However, the data could be useful for creating a “Proof of Concept” paper (or two). I won’t know until I try.

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 our options open.

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. Sounds like more experiments are needed. 🙂

 

Experiment questions

  • How much pressurized air will pass through a given volume of simulated regolith, with pre-determined densities and porosities, over a specific period of time?
  • How much gas will pass into the regolith before the exposed SPORE section can be sealed?
  • Does the regolith reach gas equilibrium or saturation?

 

Experiment design

Simulated regolith

For this experiment I’m not going to use “official” Lunar regolith simulants. They’re expensive, hard to find, an not really close to Lunar regolith. Instead, I’m going to “simulate” a few key regolith parameters using common terrestrial materials.

For SPORE Pressure Experiment 1, the following materials will be used (this list isn’t finished yet):

  • TBD

Mega-regolith simulant

We know next to nothing about the Lunar mega-regolith. And what little we do know comes from remote sensing and modeling.

For SPORE Pressure Experiment 1, the following materials will be used (this list isn’t finished yet):

  • TBD

Air pressure, composition, temperature, and humidity

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 might use a vacuum pump for experiment 2.

I’ll run tests with the following range of pressures:

  • Minimum test pressure = 127 kPa
    • 101.325 kPa (one Earth atmosphere) + 25 kPa (NASA minimum) +0.675 kPa (to round up) = 127 kPa
    • The NASA minimum partial pressure for 100% oxygen is 24.82 kPa (4)
      • Keeping the SPORE atmosphere within the breathable range increases safety.
    • 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 (one Earth atmosphere) + 35.055 kPa (1/2 SLHA) + 0.62 kPa (to round up) = 137 kPa
  • 1 Standard Lunar Homestead Atmosphere (SLHA) test pressure = 172 kPa
    • 101.325 kPa (one Earth atmosphere) + 70.11 kPa (1 SLHA) + 0.565 kPa (to round up) = 172 kPa
  • 1 Standard Atmosphere test pressure = 203 kPa
    • 101.325 kPa (one Earth atmosphere) + 101.325 kPa (one Earth atmosphere) + 0.35 kPa (to round up) = 203 kPa (total for experiment)
  • 2 Standard Atmosphere test pressure (overpressure) = 304 kPa
    • 101.325 kPa (one Earth atmosphere) + 202.65 kPa (two Earth atmospheres) + 0.025 kPa (to round up) = 304 kPa (total for experiment)

For this first experiment, I’m not going to control for temperature or humidity. I’ll document these values though.

Experiment container

The maximum dimensions of the experiment are 210 cm long by 70 cm wide by 230 cm high. 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).

The pressurized container holding the regolith will have the following dimensions:

  • Height = 50 cm
  • Width = 50 cm
  • Length = 200 cm
    • 15 cm for the simulated SPORE section
      • This section needs enough volume so I’ll  have time to correctly set the oxygen flow rate from the pressure tank.
      • I also want enough volume so I can extrapolate the data for a full scale SPORE unit.
      • This section should be small enough that the target pressure can be quickly reached at the start of the experiment.
    • 180 cm for the simulated Lunar regolith or mega-regolith section
      • Experiments will be run using 90 cm and 180 cm of simulant. That way I can see if doubling the thickness makes a measurable difference.
      • I would like to make it an even 200 cm but storage constraints make that impossible.
    • 5 cm for the simulated vacuum section
      • This section is open to the atmosphere and is not under pressure.

I haven’t determined how the simulant will be secured or what material the container will be made of.

Instrumentation

Required:

  • Two pressure gauges inside the SPORE unit to measure the pressure on both sides of the simulant.
  • One pressure gauge at the pressure tank
  • Two thermometers
  • Two hygrometers (measures relative humidity)

Experiment structure

Concept 1

SPORE Pressure Experiment 1 concept 1

Concept 1A

SPORE Pressure Experiment 1 concept 1A

Simulated regolith parameters

 

Simulated mega-regolith parameters

  • For this experiment I’ll just run some simulated basalt regolith with the following parameters to very roughly simulate the mega-regolith.
  • Sample MR1
    • Bulk density = 3010 kg/m3
    • Porosity = 10%
    • Simulate the lowest density with the highest porosity for the mare
  • Sample MR2
    • Bulk density = 3270 kg/m3
    • Porosity = 2%
    • Simulate the highest density with the lowest porosity for the mare
  • Sample MR3
    • Bulk density = 3140 kg/m3
    • Porosity = 7%
    • Simulate the average density with the average porosity for the mare
  • Sample MR4
    • Bulk density = 2200 kg/m3
    • Porosity = 21%
    • Simulate the highest density with the lowest porosity for the highland
  • Sample MR5
    • Bulk density = 2600 kg/m3
    • Porosity = 4%
    • Simulate the highest density with the lowest porosity for the highland
  • Sample MR6
    • Bulk density = 2400 kg/m3
    • Porosity = 12%
    • Simulate the average density with the average porosity for the mare
  • The mega-regolith will not be realistically tested in this experiment.
  • The mega-regolith consists of particles (rocks, ejecta, breccia, etc.) that are too large for this experiment.
  • The upper layers of the mega-regolith should contain a large proportion of regolith mixed with larger particles. This experiment can test the pressure loss through the regolith component of the mega-regolith.
  • This actually makes sense because the pressure loss THROUGH the larger particles themselves should be minimal. It’s the loss through the stuff between the rocks that could be significant.
  • The deeper Homesteaders go into the mega-regolith, the less regolith they should find. This may help with the SPORE pressure loss. They may also encounter increased fractures and voids which could make the pressure loss worse. We just won’t know until we’re actually doing it.

Experiment protocols

  1. The experiment will be set up and unpressurized.
  2. The clock will start and the SPORE section will be brought up to the target pressure as quickly as possible.
  3. Additional pressurized air will be added to the SPORE section to maintain the target pressure.
  4. The experiment will continue until a known amount of air (TBD) has been released into the SPORE section.
  5. The clock will stop.
  6. Calculate the volume of air lost (fixed) over time (variable).
  7. Extrapolate that value for a hypothetical full-scale SPORE unit.

 

Resources

  1. Lunar Sourcebook (www.lpi.usra.edu/publications/books/lunar_sourcebook)
  2. Center for Lunar and Asteroid Surface Science – Planetary Simulant Database (sciences.ucf.edu/class/planetary-simulant-database/)
  3. Permeability of JSC-1A: A lunar soil simulant (www.sciencedirect.com/science/article/pii/S0019103510004835)
  4. Man-Systems Integration Standards – Natural and Induced Environments (msis.jsc.nasa.gov/sections/section05.htm#_5.1_ATMOSPHERE)
  5. Lunar Regolith Simulant Materials: Recommendations for Standardization, Production, and Usage (ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060051776.pdf)
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