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January 25, 1962

My. Oran W. Nicks, Director

Lunar and Planetary Programs

National Aeronautics and Space Administration
1520 H Street, Northwest

Washington 25, D. C.
Dear Mr. Nicks:

Subject: Summry of Spacecraft Sterilization Provram
I. Origin of the Sterilization Requirement

In April 1958, the International Council of Scientific
Unions, (ICSU), set up an ad hoc committee to consider the
possible effect of the chemical and biological contamination
of extra-terrestrial bodies by space probes. The CETEX,
(Committee on Contamination by Fxtraterrestrial Exploration),
decided that early landings of spacecraft on the moon or
planets might seriously interfere with subsequent research
and suggested that an internationally recognized code of
conduct be established to minimize extra~-terrestrial contam-
ination. The commi:tee recognized that risks must be taken
but recommended that they should be made as small as possible.
Special concern was expressed over biological contamination
in the form of terrestrial microorginisms and aivised that a
study of the problem of spacecraft stcrilization be immediately
undertaken.

The ‘iestex committee, (Comnittee on Exoblology), of the
Space Science Board of the National Academy of Sciences and
the iRC-Armed Forces Bioastronatuics Committee also deliber~
ated on the problem of biological contamination and expressed
deep concern over the possible camage to biologic:] investi-
gations on extra-terrestrial bod!es by inadvertantly seeding
them with terrestrial organisms. js a result, both comaittees
recommended to the “ASA that immediate steps be taken to
implement - study to develop spacecraft decontamination procedures.
Mr. oO. We Nicks - 2 ~ Jan. 25, 1962

In October 1959, the NASA adopted a policy initiating
& program for the study and application of methods for the
biological decontamination of all spacecraft having a pro-
bability of impacting or landing on the moon or planets.
Chief responsibility for this procrim was delegated to the
Jet Propulsion Laboratory, California Institute of Technology.

II. The Problem of Spacecraft Sterilisation

The problem of extra~terrestrial contamination mst be
considered for three types of missions: 1) the fly-by, in
which the spacecraft approaches the planet sufficiently
close to mak: worthwhile observations, 2) the orbiting
vehicle, 3) the lander. The flyby spacecraft need not be
subjected to direct sterilization procedures if its trajec-
tory is calculated for very low probability of impact.
Anticipated fly-by missions in the current U.5. space explor-
ation program assumes safe, non-impact trajectories so that
no spacecraft sterilization requirement is necessary.
Spacecraft which are to be put into orbit around a Planet
mst undergo a sterilization treatment, since the probability
of accidental impact will be relatively hich. likewise, all
landers must be sterilized, .

Consideration mist also be given to possible impact of
the final stage boost vehicles which have a high changes of
impacting the extra-terrestrial bodies along with the spacecraft.
Such vehicles will be prevented from impacting by including
a retro-rocket on the booster to deflect it, from an L-pact
trajectory after separation from the spacecraft.

The application of biological decontamination techniques
to spacecraft presents a number of very difficult problezs.
Since biological sterility is defined as the com lete absence
of living or viable organisms, the objective of spacecrift
sterilization is to achieve biological sterility to a very high
degree of probability. In order to accomplish this it is
necessary to apply sufficiently powerful sterilizing methods
to destroy viable microorganisms without degrading the functional
performince of the spacecraft. This is the crux of the space-
craft sterilization problem. ‘nother serious difziculty involves
the integration of these methods into very complex assembly,
test, and operational proccdures which usually :mst be performed
under a very close scheiule. fo method of sterilization existe
which is not time consuming ani which does not require some
skill and careful control in application, Therefore » sterilization
Mr. GO. We Nicks ~3- Jan. 25, 1962

imposes a severe burden on the engineering schedule and

the engineering groups responsible for the preparation
and flight of the spacecraft.

The solutions to these general problems requires tine,
money, and mich effort. Time is recuired to develop space-
craft hardware that is durable to stcrilisation methods and
to develop improved sterilisation techniques and precedurcs
which will reduce the effecte on engineering sche‘ules and
hardware. Under the conditions of the present accelerated
space prorram, research and development in this area is a
problem in Zeelf particularly because of time limitations.

III. Status of U. S. Sterilisation Program

The current procedures include methods to destroy micro-
organisms that may have become imbedded in plastic materiale
or electronic components, methods to sterilize the surfaces
which are mated during the assembly procedure, methods to
decontaminate all externally exposed surfaces of the assenbled
spacecraft, and methods to maintain the sterility of the space-
craft after the final sterilization operation.

To ensure that plastic materials and electronic compon-
ents arc free of viable microorganisas, all materials, components
and sub-systems which are ot degraded by thermal exposure are
subjected to a dry heat sterilization cycle of 125% for 24
hours. If a sub-system contains one or more components which
will not endure the thermal exposure, it ‘sa. first heated with-
out the heat sensitive elements. The sensitive element is
separately sterilised by other methods such as radiation
exposure or sterile fabrication. In a very small nuaber of
cases, neithcr heat, radiation, or sterile fabrication is
possible. The sensitive component is then added to the huat
sterilized sub-aystom by sterile aseembly procedures. This
requires placing the sub-assembly and the component in a
suitable transparent isolator which permits a technician to
perform the assembly with rubber gloves sealed to holes in
the wall of the box. The surfaces of all mterials are —
sterilised just prior to asseably by a sterilizing gas. The
component is then added to the subsystem under completely
sterile conditions.

Surfaces that are mtcd during the assembly procedure
are thoroughly scrubbed with isopropyl alconol before joining
them together. However, much more powerful liquid sterilizing
agents are under study which will be available in the near future.
Mr. 0. W. Nicks ad 4 - Jan. 255 1962

After the conclusion of the assembly and test operations,
all exposed surfaces of the spacecraft are subjected to a
sterilising gas mixture conposed of 12 per cent ethylene oxide
and &8 per cent Freon-12, for 11 kours, at 35 to 45 per cent
relative humidity and at room temperature. This operation is
performed by placing the spacecraft within a chamber consist~
ing of tho vehicle nose cone which has bsen designed with
sufficient sealing to function us a gassing chamber and as
a protection against décontaminition after sterilisation.
The nose cone is rot removed until the spacecraft 4s ejected
beyond the atmosnhere of the earth.

Using the above methods, the present sterilization pro-
cedure for lunar spacecraft c sists of first heating the
largest sub-assemblies consist with the number of heat
sensitive parts in the system. ileat sensitive components
are then added to the sub-assumblies by sterile assembly
techniques. Sub-assembiks are then fitted together using
liquid sterilante to stcrilize mating surfaces before join-
ing. After final test operations are performed » the spacecraft
is exposed to the sterilizing gas mixture for eleven hours
after which the gas is purged from the chamber with nitrogen
sterilized by passage through a bacteriological filter. The
spacecraft is thereafter protected from further contamination
during field operations and launch.

Although the current sterilization procedures are con-
sidered adequate for the varly lunar missions, more stringent
methods are boing contemplated for future planetary spacecraft.

Current studies have shown that the dry heat sterilisation
oyele of 125 derrees cuntifrado for 24 hours appears to be
adequate for destroying organiems dceply imbedded in Plastics
and electronic components. However, further studies will be
made to assure that this techniqe is entirely adequate in all
cases, or whether longer times and higher temp:ratures will
be renuired to sterilize with certainty.

The use of licuid sterilants in assembly operations is
considcred undesirable for planetary spacecraft sterilization
or whenever the highest decree of decontamination is required,
It is intended that the use of this method will be minimised.
The use of liquid storilents involves hundreds of individual
sterilizing operations and consequently reduces the certainty
of sterility due to the chances of errors in application. In
cases where they must be used, it will be necessary to enforce
strict control over the procedure. Although gaseous sterili-~
aation is one of the best available methods, it is time consuming
and will not penetrate deep into materials to sterilize imbedded
microorganisms.
Mr.. 0. W. Nicks bl 5 = Jan. 25; 1962

The present thinking on achieving highly efficient
decontamination involves the concept of thermal sterili-
zation of the completely assembled spacecraft under a
sealed nose cone or shroud. Under these conditions, both
aurface and internal sterilization could be performed
simitaneously. This technique would greztly increase
the probability of achieving complete biological decon-~
tamination of the spacecraft by reducing the procedure
to a single, controlled operation, instead of many
operations. It would relieve the engineering groups
of the responsibility of integrating sterilization into
each individual sub-system aesembly and testing pro-
cedure, and would reduce the decontamination process
to the minimum of operational complexity.

However, in order to accomplish this objective a
considerably large engineering effort will be involved
in order to develop a spacecraft system composed completely
of thermally stable elements. In existing lunar spacecraft
an estimated 99 percent of the electronic components can
survive and function after the heat sterilization cycle.
Many of the components are designed to operate at high
temperatures without special fabrication. At least 99 per
cent of the plastic materials included in these spacecraft
will also endure this cycle. Ffforte are being made to
initiate hardware development in a few areas that will not
permit sterilization by heat. The most important heat
sensitive components are batteries, solid propellants,
transistors and diodes, magnetic tapes, and pyrotechnic
actuators. Although the relative number of thermally
sensitive devices is small, the engineering effort required
to replace them with stable devices will be large.

Other problem areas which will be investigated are
the long term effects of the heat cycle on components, i.e.,
effects on the expected life of the component after heating,
and the effects on system calibration, because with a final
thermal sterilization technioue, systems that have drifted
out of calibration cannot be directly recalibrated.

IV. Evaluation of the Sterilization Reouirements

Because of the hardship introduced into the engineering
phases of the national space program, and the high cost. in
dollars and man hours, which are impiied in the sterilization
requirements, consideration of the recessity of this requirement
should be made.
Mr. 0. Ww. Nicks - 6 - Jan. 25, 1962

The scientific value of the sterilization program is
undeniable despite objections to the contrary by one or
two reputable scientists. The essence for the defence of
spacecraft sterilization rests in the fact that no direct
knowledge is available about the surface environments of
extra~terrestrial bodies, rug.rdless of the theoretical
considerations upon which the importance of sterilisation
is denied. The possibilities which concern reputuible bio-
logiste do exist, and it will be im ssible to determine
if there really is a sterilisation problem until actual
observations are obtained at the surface of these bodies.
Early space probe experiments should be designed to do
this. Due to the extreme importance that information on
extra-terrestrial biolo;y would have on umderatanding the
nature and origin of life, and the fact that a single
space probe bearing a single viable micreorganiam could
potentially destroy forever, the validity of this infor~
mation, the sterilization of such spacecraft seems necessary
from a moral and political standpoint as well as a scientific
one.

However, reasonable riske will be necessary because
it will be impossible to land on the moon or the Planets
without some chance of introducing a biological contaminate.
No method is perfect no matter how well thought out and
tested. Nevertheless, our methods should be made as perfect
as possible so that every reasonable precaution will have
been taken to ersure the integrity of our studies.

Even though detailed knowledge of the Junar surface is
small, knowledge about the atmosphere, surface temperatures
and ultru-violet radiation levels are know to a high degree
of confidence. On the basis of this k-owledge, most bio-~
logists agree that risks to scientific exploration are not
dangerously high if sufficiently small amounts of biological
material were :ccidentally landed on the moon. Microorganisms
landed on the lunar surface would not be expected to grow
because of the lack of water, nor would they survive for long
because of the intense ultraviolet radiation striking the
surface and the high surface temperatures. However, micro-
organiems which were imbedded beneath a layer of dust would
be protected against both ultraviolet and high temperatures.
Under these conditions some microorganisms might be expected
to survive in a dormant state for very long periods of time.
The emiy danger to subsequent investigations would be in the
re-detection of these dormant contaminants. If such contam
inants were kept very small and confined to small areas of
Mr. 0. W. Nicks -7- Jan. 25, 1962

the moon's surface, the probability of detecting then at a
later time would be insignificant. Nevertheless, strict
requirements for keeping the contamination of the moon to
an absolute minimus has im ortant side benefite. Ffforts
to decontaminate lunar spacecraft are important in develop-

ing stcrilization techniques of the highest efficiency
for planetary missions.

The sterilisation requiroments for the planets, however,
whould be made as stringent as possible. while recent temp-
eraturu measurements on the surface of Venus indLoate, temperature
incompatible with the existence of any know fora of terrestrial
life, there is yot/iiicertainty ubout the observations. Several
kinds of observations are indicative of an endogenous Martian
biology which will be important to protect from contaminated
spacecraft. Also, our current knowledge of Mare indicates that
some form of terrestrial microorganisns might be active if landed.
The validity of this can only Le determined by a closcr examine
ation of the planet.

The cost of sterilisation in dollirs and cents, is trivial
compared with the total space budget. The cost in time spent
on special engineering problezs appears fairly large. However,
the development of heat sterilisable spacecraft could produce
important incidental benefits. Such spacecraft would undoubt-
edly have inoreased reliability, and would be co::siderably
more durable to the espace environment. In the long tera thie
could advance spacccraft technology significantly.

The time and money expended in spacecraft sturilisation
must be considered an investacnt. If sti:rilisation proves
to be necessary it will have been north all of the time,
money and effort. If 1t proves unnecessary we will have
obtaincd some side benefits and the assurance that we have
conscicntiously performed our duty to scie:ce and society.

However, if we do not exert serious efforts in this
area, and it turns out to have be:n necessiry after all, we
may be in the rosition of having destroyed the most signi-
ficant scientific discoveries in human history.

Ve Summary

The most reputable national and international scientific
organisations have recommended that sterilisation of space~
craft Le made an important part of the space exploration
Mr. 0. W. Nicks -~ 8- Jane 25, 1962

program. In response to these recommendations the NASA has
initiated the study and execution of a program to decontam-
inate all lunar and planetary spacecraft. Difficult engincering
and biological problems are involved in the execution of this
program ineluding the development of effective sterilisation
methods, and ace elorment of methods for integrating the
engineering asterilisation proc-duree. Very good progruss
has been made in sterilising early lunar sprcecraft using
heat to sterilize electronic components and materials, liquids
to sterilise surfacce during asevmbly, and ethylene oxide gas
mixtures for the final sterilisation of the surfacos of the
completely assombled spacocraft. Efrorts are buing made te
siw:lify proccdures and increase the effectivences of steri-
vation methods for future spacecraft. Such efforts, although
expensive in the absolute scnse coat little in terms of the
total space budget and the moral, political and scientific
obligations to future generations.

Sineerely yours,
JET PROPULSION LABORATORY

George L. Hobby,
Group Supervisor
Space Biology Group

GLH/d1.j