Report Series: Committee on Planetary Protection Planetary Protection for the Study of Lunar Volatiles (2020) / Chapter Skim
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3 Transfer of Volatiles to Lunar Polar Cold Traps by Spacecraft Exhaust
3 Transfer of Volatiles to Lunar Polar Cold Traps by Spacecraft Exhaust
Pages 19-26
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From page 19... ...
This information can be compared to a variety of possible scenarios of what is expected to be found on the PSRs, based on existing data collected by remote sensing, the LCROSS mission, current understanding of volatiles in the early solar system, and from ground truth measurements as earlier investigations at the poles are performed. Mission planners and planetary protection officials can then determine whether the level of volatile contamination expected from these missions is of concern for scientific investigations of primordial chemistry and what approaches are appropriate for its mitigation.
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From page 20... ...
cryogenic propellants for larger missions.2 Smaller landers are likely to use hypergols because of their relatively simpler engineering design. Larger robotic landers and human exploration missions are likely to use cryogenic H2-O2 and CH4-O2 combinations because of the significantly higher performance in spite of the more complicated engineering associated with these cryogenic propellants.
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From page 21... ...
Over 150 combustion products, including larger molecules, were considered in this calculation but were below the 10-10 mass fraction threshold. BOX 3.1 Brief Summary of Prem et al.
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From page 22... ...
Improving the performance of rocket engines explicitly requires the optimization of the combustion process toward complete combustion. Combustion characteristics will change as a function of propellant mixture ratio, nozzle expansion ratio, degree of propellant mixing, chamber pressure, and other parameters.
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From page 23... ...
, area of lunar cold traps (e.g., including recent discovery of "micro cold traps" extending the total area to ~40,000 km2;7 and others will alter the results. TABLE 3.3 Representative Mission Types for Missions Using Hypergolic (Smaller/Exploration Landers)
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From page 24... ...
, photolysis plays an important role, which is molecule-specific, and for water -- only up to 20 percent of the water is deposited in permanently shadowed areas. Combining the total amount of propellant burned and the mass fractions of the combustion products, the maximum average surface densities if all exhaust products were deposited at the permanently shadowed regions for a 1 metric ton hypergolic lander are as follows: < 2 × 10-9 kg/m2 of H2O < 2 × 10-13 kg/m2 NH3 < 2 × 10-17 kg/m2 HCOOH < 8 × 10-18 kg/m2 HNCO For a human-class, 100 metric ton CH4-O2 lander, the maximum average surface densities if all exhaust products were deposited at the permanently shadowed regions are as follows: < 4 × 10-7 kg/m2 H2O < 2 × 10-15 kg/m2 COOH < 5 × 10-15 kg/m2 HCOOH < 3 × 10-16 kg/m2 HCHO For a human-class, 100 metric ton H2-O2 lander, the maximum average surface densities if all exhaust products were deposited at the permanently shadowed regions are as follows: < 6 × 10-7 kg/m2 H2O < 3 × 10-8 kg/m2 H2 < 3 × 10-15 kg/m2 H < 7 × 10-16 kg/m2 OH As a comparison point, the weight percent of volatiles present in PSRs as observed in the LCROSS mission was 5.6 percent H2O, 0.32 percent NH3, and 0.16 percent CH3OH.8,9 In trying to directly compare these values with the contamination from combustion products, the collected sample characteristics must be considered.
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From page 25... ...
The molecules produced by the combustion process are also readily found in the Earth environment in which the science instruments are built, and the sampling instruments themselves may be contaminated with these molecules, inherently contributing to uncertainty in the measurements. Conclusions These estimates point to what appears to be a small level of likely contamination, but further information is required to determine whether this constitutes "harmful contamination," as required for planetary protection considerations.
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From page 26... ...
During landing, regolith will also be lofted and may cover PSRs along with volatiles coming from the rocket exhaust. While this regolith material may have implications for science investigations, it is not expected to have any biological impact on the lunar surface due to its lack of organic material.
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