NASA Procedural Requirement 8020.12C entitled “Planetary Protection Provisions for Robotic Extraterrestrial Missions” states that the source-specific encapsulated microbial density for encapsulated organisms (div(0)) in nonmetallic materials ranges from 1-30 spores/cm3. The standard laboratory procedure, NASA Standard Procedures for the Microbial Examination of Space Hardware, NHB 5340.1B, does not provide any direction into the methodologies to understand the bioburden within such a fluid as CFC-11 (Freon). This general specification value for the Freon would be applicable to the Freon charged within the Mars Science Laboratory’s (MSL’s) Heat Rejection System. Due to the large volume required to fill this system, MSL could not afford to conservatively allocate 55.8% of the total spore budget of the entire laboratory system (rover, descent stage, cruise stage, and aeroshell) of 5.00 × 105 spores at launch.
A novel filtration approach was developed to analyze the Freon employing a 50 kDa molecular weight cutoff (MCO) filter, followed by 0.22-μm pore-size filter to establish a calculated microbial bioburden.
Filtration of microorganisms from liquid matrices is a standard laboratory approach. Due to the volatility of Freon, a standard vacuum filtration unit would not suffice because of the lack of a cold trap on the vacuum unit. A more economical approach had to be devised. The two-pronged concentration approach is advantageous due to the fact that it initially concentrates the Freon from liters to milliliters where it can then be feasibility filtered and microbes extracted from the filter. This is a technology improvement over prior art as it defines the specific parameters to concentrate microbial organisms from a low-boiling-point fluid such as Freon.
This work relates to the current MSL mission but also has implications for future NASA missions that will utilize the same or similar heat rejection fluids. If the same lot of material is utilized on a future mission, then the experimentally derived value can be directly used based on this study (MSL-heritage). If a new lot or similar material composition is used in a future mission, then this technology can be employed or modified accordingly to accommodate such a fluid. This technology development will allow for a heritage-based starting point for fluids on other missions in which a calculated microbial bioburden is necessary.
This work was done by James N. Benardini, Robert C. Koukol, Gayane A. Kazarians, and Fabian Morales of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48303