Preventing the Forward Contamination of Mars (2006) / Chapter Skim
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2 Policies and Practices in Planetary Protection
2 Policies and Practices in Planetary Protection
Pages 22-35
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PLANETARY PROTECTION POLICY Historical Review During the early years of the space program, forward contamination controls for missions to Mars were guided by a probabilistic approach as the framework for developing quarantine standards.1 COSPAR Resolution No. 26, which COSPAR issued at its 1964 Scientific Assembly in Florence, Italy, accepted "a sterilization level such that the probability of a single viable organism aboard any spacecraft intended for planetary landing or atmospheric penetration would be less than 1 × 104, and a probability limit for accidental planetary impact by unsterilized flyby or orbiting spacecraft of 3 × 105 or less" (COSPAR, 1964, p.
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.2 According to Hall (1968) , studies at that time indicated that accidental impacts of spacecraft on the martian surface and premature entry of orbiting vehicles into the martian atmosphere represented principal forward contamination concerns.
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Current NASA practices for estimating bioburden (be it N0 or N0R, the bioburden present after bioburden reduction measures) on spacecraft are by proxy (as measured by colony-forming units after heat shock at 80°C followed by incubation for 72 h; see Appendix C)
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.8 These are summarized in the section below titled "Implementation Requirements." NASA adopted the revised COSPAR policy for application to all solar system exploration missions beginning with the Galileo mission in 1989. In 1990, in anticipation of upcoming robotic missions to Mars, NASA requested that the NRC revisit the matter of the potential forward contamination of Mars and provide recommendations that could become the basis for updating the requirements for forward contamination controls for Mars landers.
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plus requirements pre-launch report, contamination control, Pc analysis plan, post-launch report, organics inventory microbial reduction plan, post-encounter report, (as necessary) ; microbial assay plan, end-of-mission report implementing organics inventory; procedures such as implementing procedures trajectory biasing, such as clean room, trajectory biasing, bioload reduction clean room, (as necessary)
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sensitivity of the particular biological burden levels. sterile or contained life-detection experiments, returned hardware, whichever are more stringent, Case 2: continual monitoring of project If the special region is accessed activities, or through horizontal or vertical project advanced mobility, either the entire landed studies/research the subsystems that are involved system shall be sterilized to in the acquisition, delivery, and the Viking post-sterilization If unrestricted Earth return: analysis of samples used for biological burden levels, none life detection must be sterilized to these levels, and a method of or preventing recontamination of the sterilized subsystems and the the subsystems that directly contact contamination of the material to the special region shall be sterilized be analyzed is in place.
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have been adopted for use in revisions to COSPAR's policies. In practical terms, they have been translated into forward contamination controls for NASA missions in the form of procedural requirements for actions under the control of mission designers, spacecraft and equipment builders, and planetary protection technicians.
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Based on the category assigned by NASA to a particular mission, different implementation guidelines and specific requirements outlined in the NPR apply to trajectory biasing, clean-room assembly, microbial reduction and assaying, organics inventory and archiving, and recontamination control. In addition, the NPR establishes requirements for documentation and schedules for reviews, and it provides assigned quantitative values for specifications on a wide variety of parameters.14 Specific information required in mission plans includes analysis of the probability of impact, estimates of microbial bioburden, a contamination analysis plan, microbiological assay plans, a microbial reduction plan if contemplated, and reporting plans and schedules.
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for bioburden of exposed, mated, and encapsulated materials 2b. Alternative methods for hardware Xe Must demonstrate effectiveness in reducing bioburden; decontamination approval by the planetary protection officer; no standard certification process exists for new methods Non-Nominal Impact Avoidance X Total probability of any accidental impact by hardware other than probe or lander modules must not exceed 104 Assay Methods 1.
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, microbial reduction for an entire planetary spacecraft, including entry probes and landing capsules, may be accomplished by any qualified process approved by the planetary protection officer. At present, the dry-heat cycle is considered the preferred method for conditioning spacecraft to a sterile or near-sterile condition, and it is the only NASA-certified method for bioburden reduction.16 A dry-heat cycle involves heating the entire spacecraft or particular components to specified elevated temperatures and atmospheric conditions for defined lengths of time.
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Thus, a comprehensive understanding of potential forward contamination of Mars remains elusive. Finally, in attending to the forward contamination control requirements for Category IV landers, the flight program office must provide for collection and storage of the bulk (>1 kg)
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CURRENT LIMITATIONS OF STANDARD METHODS AND IMPLEMENTING REQUIREMENTS Although COSPAR's planetary protection policies and NASA's implementation requirements have been modified over time, the standard NASA methods and practices for cleaning, sterilizing, and assaying spacecraft in preparation for launch have remained largely unchanged for nearly 3 decades. Even the 1992 NRC report on Mars forward contamination accepted the continuing use of established practices while encouraging the development and adoption of more modern molecular methods for assaying spacecraft and spacecraft assembly clean rooms (see Appendix B)
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bioburden reduction and sterilization methods; (2) assigned parameter values and specifications used in contamination control planning; (3)
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1992. Biological Contamination of Mars: Issues and Recommendations.
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