E
Approaches to Bioburden Reduction for Lander Missions to Mars

TABLE E.1 Approaches to Bioburden Reduction for Lander Missions to Mars

Mission

Type

Year

Viking Pre-Sterilization

Viking Post-Sterilization

Other Approaches

Viking Landers

Life-Detection Instruments

COSPAR Category IVb

1975-1976

Assembly was done in class-100,000 clean rooms.a Thousands of microbial assays were conducted during assembly, which established an average spore burden per square meter of less than 300. The total burden on the lander surface (i.e., the exposed exterior and those parts of the interior communicating directly with the exterior) was less than 300,000.

Bacillus subtilis, the spore-forming microbe, was used as an indicator organism in the microbiological assays because of its resistance to heat, desiccation, and radiation.

After assembly in clean rooms and application of microbial assays, the landers were sealed in bioshields. Bioburden was further reduced through dry heating at humidity of 1.3 mg/l. A minimum temperature of 111.7°C was maintained for 30 h and much of the lander was subjected to higher temperature over a longer time period.

The efficacy of the sterilization procedure was estimated indirectly on the basis of the known heat-survival characteristics of B. subtilis and was credited with reducing the lander’s bioburden by a factor of 104.b

 



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Preventing the Forward Contamination of Mars E Approaches to Bioburden Reduction for Lander Missions to Mars TABLE E.1 Approaches to Bioburden Reduction for Lander Missions to Mars Mission Type Year Viking Pre-Sterilization Viking Post-Sterilization Other Approaches Viking Landers Life-Detection Instruments COSPAR Category IVb 1975-1976 Assembly was done in class-100,000 clean rooms.a Thousands of microbial assays were conducted during assembly, which established an average spore burden per square meter of less than 300. The total burden on the lander surface (i.e., the exposed exterior and those parts of the interior communicating directly with the exterior) was less than 300,000. Bacillus subtilis, the spore-forming microbe, was used as an indicator organism in the microbiological assays because of its resistance to heat, desiccation, and radiation. After assembly in clean rooms and application of microbial assays, the landers were sealed in bioshields. Bioburden was further reduced through dry heating at humidity of 1.3 mg/l. A minimum temperature of 111.7°C was maintained for 30 h and much of the lander was subjected to higher temperature over a longer time period. The efficacy of the sterilization procedure was estimated indirectly on the basis of the known heat-survival characteristics of B. subtilis and was credited with reducing the lander’s bioburden by a factor of 104.b  

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Preventing the Forward Contamination of Mars Mission Type Year Viking Pre-Sterilization Viking Post-Sterilization Other Approaches Mars Pathfinder Lander/ Rover No LifeDetection Instruments COSPAR Category IVa 1996 Assembly was done in class-100,000 clean rooms. All exposed surfaces were cleaned by alcohol wiping or dry heat, except that Sojourner rover was precision cleaned by Freon vapor degassing. Pre- and post-process microbial burden tests were performed for components that had not maintained humidity controls during heating. During early assembly, test, and launch operations at JPL, flight hardware was periodically cleaned by alcohol wiping. Final aerobic spore density and total burden were calculated at 14.9 spores m–2 and 2.9 × 10 4 spores, respectively.c N/A At Kennedy Space Center, SAEF-2 clean-room and strict personnel garment requirements were used; ground-support equipment and nonflight equipment were alcohol wiped. Beagle 2 Lander/ Rover Life-Detection Instruments COSPAR Category IVa+ 2003 The probe was assembled aseptically in a class-100 clean room. Some components were sterilized with dry heat. Gamma irradiation, gas plasma, and alcohol wipes were used to sterilize technologies that were susceptible to heat. The assembly facilities were monitored at Viking levels for microbial presence, and assays were conducted based on NASA protocols.d The completed probe was sealed in a front and back shield and bioseal and protected from recontamination by a HEPA filter. The probe was fitted with the Mars Express spacecraft in Toulouse, France, at a class-100,000 clean room and assembled and integrated with the launch vehicle in Baikonaur, also in a class-100,000 clean room. The external area of the Beagle was cleaned at each location.d Established policies and procedures for planetary protection were followed in the assembly facility, including training, apparel, monitoring of people and material flow into assembly area, cleaning, cleaning of hardware, and sterilization.

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Preventing the Forward Contamination of Mars Mission Type Year Viking Pre-Sterilization Viking Post-Sterilization Other Approaches MER Landers/ Rovers No Life-Detection Instruments COSPAR Category IVa 2004 The hardware design was compatible with swab assays and alcohol wipe cleaning. Hardware that could not tolerate alcohol (honeycomb structures, airbags, parachutes, solar arrays) was sterilized using dry heat. Heating was done at 110°C for 50 h and 125°C for 5 h for some components. Tubing elements were precision cleaned with an acid wash, Freon degreasing, and other cleaning methods. Enclosed electronic components were isolated from the Mars environment by high-efficiency particulate air (HEPA) filters. The spacecraft was assembled in a class-100,000 clean room. Hardware that was dry heat sterilized was double bagged for protection. Elements that were not cleaned were covered.e N/A Early planning allowed for more extensive use of dry heat. aClass-100,000 clean rooms: rooms with air quality control to a maximum of 100,000 particles of 0.5 µm in diameter per cubic foot of air. bNRC, Preventing the Forward Contamination of Europa, National Academy Press, Washington, D.C., 2000, p. 5. cJack Barengoltz. Microbial cleanliness of the Mars Pathfinder spacecraft. Pp. 242-248 in Proceedings of 43rd Annual Technical Meeting Contamination Control. Institute of Environmental Sciences, 1997. dAndrew Spry, Open University, presentation to the NRC Committee on Preventing the Forward Contamination of Mars, February 27, 2004. eLaura Newlin, Planetary Protection Lead for the MER Missions, Jet Propulsion Laboratory, discussion with the NRC Committee on Preventing the Forward Contamination of Mars, February 26, 2004; “Mars Exploration Rover Spacecraft Undergo Biological Testing and Cleaning Prior to June Launches,” KSC Release No. 37-03, May 23, 2003, NASA John F. Kennedy Space Center.