Category

Recommendation

Report

Sterilization and Pre-sterilization

Based on the MESUR [Mars Environmental Survey, later renamed Mars Pathfinder] group’s consensus and the task group’s agreement with it, the task group makes the following recommendations for control of forward contamination, each tied to specific mission objectives.

Biological Contamination of Mars: Issues and Recommendations,

NRC, SSB, 1992, p. 7.

 

Landers carrying instrumentation for in situ investigation of extant martian life should be subject to at least Viking-level sterilization procedures. Specific methods for sterilization are to be determined. Viking technology may be adequate, but requirements will undoubtedly be driven by the nature and sensitivity of the particular experiments. The objective of this requirement is the reduction, to the greatest feasible extent, of contamination by terrestrial organic matter and/or microorganisms deposited at the landing site.

 

 

Spacecraft (including orbiters) without biological experiments should be subject to at least Viking-level presterilization procedures—such as clean-room assembly and cleaning of all components—for bioload reduction, but such spacecraft need not be sterilized.

 

 

The task group’s recommendation to reduce bioload on all spacecraft and to sterilize those spacecraft used in life-detection missions assumes the use of Viking procedures. However, the task group recommends that the Viking protocols for assessment of spacecraft bioloads be upgraded to include state-of-the-art methods for the determination of bioload. It is critical that methods for assessing bioload be compatible with methods used to detect life, with methods for both assessment and detection reflecting the same limits and sensitivity. Data on bioloads of Viking components and spacecraft are not relevant to current life-detection procedures. Modern methods of bioburden assessment should be developed for and applied to spacecraft destined for future Mars missions, especially those carrying in situ extant life-detection experiments.

Biological Contamination of Mars: Issues and Recommendations,

NRC, SSB, 1992, p. 9.

 

… the bioload of each Europa-bound spacecraft must be reduced to a sufficiently low level at launch that delivery of a viable organism to a subsurface ocean is precluded at a high level of probability. This approach allows mission planners to take advantage of the bioload reduction likely to occur en route, particularly while in Jupiter’s radiation environment. One consequence of this view is that Europa must be protected from contamination for an open-ended period, until it can be demonstrated that no ocean exists or that no organisms are present. Thus, we need to be concerned that over a time scale on the order of 10 million to 100 million years (an approximate age for the surface of Europa), any contaminating material is likely to be carried into the deep ice crust or into the underlying ocean.

Preventing the Forward Contamination of Europa,

NRC, SSB, 2000, p. 2.

 

The task group therefore recommends the following standard: for every mission to Europa, the probability of contaminating a europan ocean with a viable terrestrial organism at any time in the future should be less than 10–4 per mission. This standard calls for explicit calculation of the probability of contamination posed by each particular mission. It allows spacecraft designers to take advantage of the bioload reduction that occurs from radiation in the jovian environment. The value of 10–4 was chosen because of its historical precedents in the planetary protection resolutions issued by COSPAR.

Preventing the Forward Contamination of Europa,

NRC, SSB, 2000, p. 22.

 

NASA must devise a method for carrying out this calculation. An example of how such a calculation might be done is given in Appendix A. The task group’s suggested methodology subdivides the bioload into common microorganisms, spores, radiation-resistant spores, and highly radiation-resistant nonspore microorganisms (e.g., Deinococcus radiodurans; see Chapter 3).

Preventing the Forward Contamination of Europa,

NRC, SSB, 2000, p. 22.



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