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E
Additional Related Information
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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) —No impact on Earth or
Moon
—Sterilization of returned
hardware
—Containment of any
sample
Represent- None —Documentation only (all —Documentation (more —Detailed documentation Outbound
ative range of brief): involved than Category (substantially more involved —Per category of target
require- II): than Category III): planet/ outbound mission
• PP plan
ments • Contamination control • Pc analysis plan
• Prelaunch report
Inbound
• Organic inventory (as • Microbial reduction plan
• Postlaunch report
—All of Category IV
necessary) • Microbial assay plan
• Postencounter report
requirements
—Implementing • Organics inventory
• End-of-mission report
—Continual monitoring of
procedures such as: —Implementing procedures
project activities
such as:
• Tragectory biasing
—Preproject advanced
• Cleanroom • Trajectory biasing
studies/research
• Bioload reduction (as • Cleanroom
necessary) • Bioload reduction
If safe for Earth return:
• 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.
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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
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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
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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
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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.
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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 Bodies—Asteroids, 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
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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
2015—Planetary 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
2015—Life 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 Programs—1991. 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).
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