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E Additional Related Information 103
TABLE E.1 Proposed Planet/Mission Categories and Range of Requirements Category I Category II Category III Category IV Category V Type of Any but Any but Earth return No direct contact (flyby, Direct contact (lander, prove, Earth return mission Earth return some orbiters) some orbiters) Target Sun, To be determined To be determined To be determined To be determined planet Mercury, Pluto Degree of None Record of planned impact Limit on impact Limit on probability of nominal If not safe for Earth concern probability and contamination probability impact return: control measures Passive bioload control Limit of bioload (active control) âNo impact on Earth or Moon âSterilization of returned hardware âContainment of any sample Represent- None âDocumentation only (all âDocumentation (more âDetailed documentation Outbound ative range of brief): involved than Category (substantially more involved âPer category of target require- â¢ PP plan II): than Category III): planet/ outbound mission ments â¢ Prelaunch report â¢ Contamination control â¢ Pc analysis plan â¢ Postlaunch report â¢ Organic inventory (as â¢ Microbial reduction plan Inbound â¢ Postencounter report necessary) â¢ Microbial assay plan âAll of Category IV â¢ End-of-mission report âImplementing â¢ Organics inventory requirements procedures such as: âImplementing procedures âContinual monitoring of â¢ Tragectory biasing such as: project activities â¢ Cleanroom â¢ Trajectory biasing âPreproject advanced â¢ Bioload reduction (as â¢ Cleanroom studies/research necessary) â¢ Bioload reduction If safe for Earth return: â¢ Partial sterilization None SOURCE: Reprinted with permission from De Vincenzi, D.L., and P.D. Stabekis. 1984. "Revised Planetary Protection Policy for Solar System Exploration." Adv. Space Res. 4(12):291-295.
HISTORY AND BRIEF DESCRIPTION OF THE VIKING CLEANING AND STERILIZING PROCEDURES Throughout this document, the .task group; has referred to Viking levels of cleanliness and sterilization as, representing .a reasonable standard for future Mars missions. It has distinguished between the pr preparations that may be needed for unpiloted missions that carry no in situ; extant life-detection experiments, and those that will follow later and will carry such life-detection experiments. For the former, the task group has proposed that Viking-level cleanliness will be sufficient, with the caveat that more extensive bioburden assays should be included, incorporating ,modern techniques as they are adapted for the assay of spacecraft. For missions, that include extant life-detection experiments, the task group has recommended use of the Viking sterilization program, or one equally effective in removing bioburden and contaminants. Briefly described below are the very detailed, comprehensive protocols used on Viking, along with some of the scientific and historical rationale underlying these procedures. The Viking mission was conceived and designed in general in the late 1960s and launched in 1975. It successfully landed two fairly sophisticated spacecraft on Mars (with an orbiter for each), both of which performed almost perfectly and produced an enormous amount of data, far beyond that specified, over a period of up to 3 years, depending on the experiment. The spacecraft, which were identical, emphasized the search for life on Mars and contained three different experiments, each designed specifically to look for evidence of indigenous, extant biological activity in the surface material. In addition, there was a pyrolysis gas chromatograph-mass spectrometer (GC-MS) designed to search for organic matter in the samples. The remainder of the payload included instrumentation for atmospheric analyses, collection of data on climatology and seismic activity, and preliminary geochemical analyses; a sample acquisition system; and cameras. It was clear that the life-detection experiments and the GC- MS were all extremely susceptible to contamination (both biological and chemical) from terrestrial sources and absolutely needed to be protected from contaminants that would yield false-positive data. It seemed pointless to go to Mars to detect terrestrial bacteria or terrestrial hydrocarbons that were carried there on a contaminated spacecraft. This problem was recognized in the early stages of planning for lunar and planetary exploration, and a planetary quarantine office was established at NASA Headquarters in the early 1960s. This operation included a planetary quarantine officer (a career Public Health officer) and an operating budget for the 110
development of a research program aimed at establishing the necessary technology to prevent planetary contamination. Help was solicited from a wide spectrum of expertise in the country such as the U.S. Public Health Service, the Center for Disease Control, the Department of Agriculture, the food canning industry, and others, and an interagency committee was established to oversee NASA's activities. At the same time the cooperation of the international community was. solicited-through the Committee on Space Research (COSPAR), and an international agreement to prevent contamination was produced. The former Soviets are party to this agreement, and although we have never seen their protocols for spacecraft cleaning and sterilization, their officials have assured us that their Mars probes were sterilized. During the 1960s, a great deal of research was done in universities and in government laboratories to find methods for cleaning and, if necessary, sterilizing spacecraft. Research was done in the area of survivability of microorganisms under extremely adverse conditions, including simulated martian environments. Expert advisory committees were assembled, and guidelines were developed that led to the formulation of the Viking cleaning and sterilization protocols. Many techniques were studied, evaluated, and rejected or accepted. These included most of the contemporary methods for sterilizing found in the biology laboratory, in hospitals, and in the food (particularly canning) industry, as well as techniques for the control of disease. Since large structures, such as spacecraft, had never been sterilized before, many of the seemingly simple questions took on unusual complexities. These problems were compounded by the need to sterilize materials and components that had never undergone such treatment and would very likely be sensitive to it. This necessitated an extensive heat-testing program and the replacement of some standard spacecraft parts with new materials. Although this was a costly undertaking, there is reason to believe that it led to a family of new and more reliable materials for the spacecraft industry. Sterilization techniques such as gaseous sterilization with "fumigants" such as ethylene oxide were rejected because of the corrosive and potentially explosive nature of the gases. Spacecraft irradiation was rejected because of the sensitivity of many spacecraft components and scientific instruments to irradiation, and because of the great difficulty in implementing such a technique. Furthermore, it had been determined that surface sterilization was inadequate because viable organisms were found in the interiors of components and materials (including plastics) and in cracks and crevices not reached by gases. It was reasoned that such organisms could be released by the impact of landing, thus providing a source of contamination for the surface to be sampled. The biology 111
instrumentation was the system most sensitive to contamination and was the driver in the development of sterilization techniques. Surface samples were to be acquired by a sampling arm, transported to a sample-processing system where they could be sifted and sized, and then moved into whatever instrument was scheduled to receive them. These instruments included the three life-detection instruments, the GC-MS, and the inorganic analytical instrument. Since there was no realistic way to totally isolate the life-detection instruments, there was no way to sterilize only those instruments, and so the entire spacecraft had to be sterilized. Heat sterilization proved to be the most satisfactory method available for use. Two methods were considered: wet heat (autoclaving) and dry heat. Since wet heat was too destructive (particularly for electronic components), dry heat was ultimately used. Briefly, after assembly and testing, the Viking spacecraft was disassembled and treated as follows: 1. Surfaces were rigorously cleaned to reduce the starting bioburden on the spacecraft, thus reducing the time required for sterilization at high temperature. 2. Instruments were cleaned and assembled in cleanrooms by workers in surgical attire; laminar flow hoods were used, and the rooms had appropriate filters to remove virtually all microorganisms from the air. Both the lander and orbiter were treated in this way. 3. The entire lander and its payload were assembled under the same conditions. The Ian-der was packaged inside a sealed "bioshield" that prevented recontamination between the period of time from assembly and subsequent sterilization, through launch, until departure from Earth's atmosphere. 4. The lander was then placed in an oven and subjected to dry heat in cycles. In order to assure that the interior of the spacecraft reached sufficient temperature for sterilization, a liquid was pumped to the interior. The precise heating cycle was indicated by the calculated bioburden on the lander as determined by surface sampling with standard laboratory techniques (cotton swabbing, culturing, and microbial colony counting). The temperatures used and the duration of the heat application were calculated to be sufficient to sterilize the entire lander and all of its parts. The success of this rather cumbersome procedure is found in the success of the mission: no instruments failed. The lander worked perfectly, and no problems were induced by sterilization. The biology instruments and the GC-MS were not contaminated in any detectable way. Although the procedure certainly had an impact on the cost of the mission (it has been estimated at between 5 and 15 percent of the total cost), perhaps the financial aspect was not too serious considering that the scientific potential was preserved. In addition, a catalog of highly resistant and reliable materials and 112
components was produced, which should greatly simplify dealing with the problem of cleaning spacecraft for future missions, as well as substantially reduce future costs. It is likely that other existing techniques appropriate to future missions may be simpler to implement and more effective. Viking sterilization protocols were settled on in the early 1970s and based on technology developed in the 1960s and earlier. An appropriate, properly funded research program could greatly enhance the prospect of simplifying procedures and reducing costs. This task group urges NASA to proceed with such a program. 113
SELECTED BIBLIOGRAPHY OF SPACE STUDIES BOARD PUBLICATIONS Space Science Board. 1967. "Study on the Biological Quarantine of Venus." Report of an ad hoc panel, January 9. National Academy of Sciences, Washington, D.C. Space Science Board. 1970. "Review of Sterilization Parameter Probability of Growth (Pg)." Report an ad hoc review group, July 16-17. National Academy of Sciences, Washington, D.C. Space Science Board. 1976. "Recommendations on Quarantine Policy for Uranus, Neptune, and Titan." Report of the Panel on Exobiology, May 24. National Academy of Sciences, Washington, D.C. Space Science Board. 1976. "On Contamination of the Outer Planets by Earth Organisms." Report of the Ad Hoc Committee on Biological Contamination of Outer Planets and Satellites, Panel on Exobiology, March 20. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1977. Post-Viking Biological Investigations of Mars. Committee on Planetary Biology and Chemical Evolution. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1978. Strategy for Exploration of the Inner Planets: 1977-1987. Committee on Planetary and Lunar Exploration. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1978. Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan. Committee on Planetary Biology and Chemical Evolution. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1980. Strategy for the Exploration of Primitive Solar-System BodiesâAsteroids, Comets, and Meteoroids: 1980-1990. Committee on Planetary and Lunar Exploration. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1981. Origin and Evolution of Life-Implications for the Planets: A Scientific Strategy for the 1980's. Committee on Planetary Biology and Chemical Lvolution. National Academy of Sciences, Washington, D.C. Space Science Board, National Research Council. 1986. Strategy for the Exploration of the Outer Planets: 1986-1996. Committee on Planetary and Lunar Exploration. National Academy Press, Washington, D.C. Space Science Board, National Research Council. 1986. Report of the NAS/EST Joint Working Group: A Strategy for U.S./European 114
Cooperation in Planetary Exploration. National Academy Press, Washington, D.C. Space Science Board, National Research Council. 1988. Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015âPlanetary and Lunar Exploration. National Academy Press, Washington, D.C. Space Science Board, National Research Council. 1988. Space Science in the Twenty-First Century: Imperatives for the Decades 1995 to 2015âLife Sciences. National Academy Press, Washington, D.C. Space Studies Board, National Research Council. 1990. International Cooperation for Mars Exploration and Sample Return. Committee on Cooperative Mars Exploration and Sample Return. National Academy Press, Washington, D.C. Space Studies Board, National Research Council. 1990. The Search for Life's Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution. Committee on Planetary Biology and Chemical Evolution. National Academy Press, Washington, D.C. Space Studies Board, National Research Council. 1990. Strategy for the Detection and Study of Other Planetary Systems and Extrasolar Planetary Materials: 1990-2000. Committee on Planetary and Lunar Exploration. National Academy Press, Washington, D.C. Space Studies Board, National Research Council. 1990. Update to Strategy for Exploration of the Inner Planets. Committee on Planetary and Lunar Exploration. National Academy Press, Washington, D.C. Space Studies Board, National Research Council. 1991. Assessment of Solar System Exploration Programsâ1991. Committee on Planetary and Lunar Exploration. National Academy Press, Washington, D.C. Letter report from SSB Chairman Thomas Donahue to NASA Office of Space Science and Applications Associate Administrator Burton I. Edelson regarding planetary protection policy, November 22, 1985 (unpublished). Letter report from Committee on Planetary Biology and Chemical Evolution to Arnauld E. Nicogossian, director, Life Sciences Division, NASA, regarding the planetary protection categorization of the Comet Rendezvous-Asteroid Flyby mission, May 16, 1986 (unpublished). Letter report from Committee on Planetary Biology and Chemical Evolution to John D. Rummel, chief, Planetary Quarantine Program, Office of Space Science and Applications, NASA, regarding a formal recommendation on planetary protection categorization of the Comet Rendezvous-Asteroid Flyby mission and the TitanCassini mission, July 6, 1988 (unpublished). 115