May 4, 1959

Mr. G. A. Derbyshire
Space Sclence Board
21d! Constitution Ave.
Washington 25, 8. C.

Dear Mr. Derbyshire:

Our group, which met May 2nd and 5rd, spent some time discussing
the application of lonizing radiation for the sterilization of
missiie payloads. we had previcusty considered radiation techal que
during cur previous meetings and had felt that it might be applicable
although marginally in relation to the complete sterilization
of a peyload at doses that would feave the Instrumentation Intact.
If the circultry can be subject to basic redesign, as might be
necessary for the application of radiation, we felt that heat
might prove to be about as effective and considerably more convenient
to use In practice. Yhere is, of course, considerable objection
to complete overhauling of the electronic systems to make them
amenable to elther therma! or radiation sterilization. However,
we feel that the question should be studied as clasely as possible.
The presentation was, however, somewhat narrow both from the
polnt of view of the bloiogical aspects of sterilization and of
the effect of large radiation doses on the electrical properties
of material, these properties being probably more important,
and In some cases more sensitive, then the mechanical ones which
were tabulated. There are at least two other organizations
which should be considerably better qualified to study various
aspects of this problem than Is General Electric. + One of these
is the Argonne Laboratories, operated by the University of Chicago
under contract to the A. E. €.; the other Is the Blological
Warfare Laboratories at Fort Detrick, Frederick, Maryland. The
Argonne Laboratories must have very much more extensive data on
the radiation sensitivity of microorganisas and also of materials
than are Indicated In the G. E. Memorandum. The Fort Detrick
Laboratories heve unequalled experience In the disinfection area.
Additionally, the Army Quartermaster Corps, Ploneer Laboratory
at Natick, Messachusetts has also had considerable experience
jn the sterliization of bulky materials by radiation and should
be consulted. We would consider that G. E. In the light of its
own report and of the Indicated qualifications of its staff would
be an acceptable choice but with a lower standing than the egencies
just indicated to make the study called for. However, the study
should be made from an operational polnat of view and these remarks
should not discourage the participation by 6. E. provided every
effort is first made to Interest the agencies !isted.

we had some concern a3 to the quantitetive conception of
“sterilization indicated In the memorandum. Steril lzation
is @ zero order kinetic process so that each succeeding dose
= 2 «

removes a constant fraction of the previous contamination load.
In view of this consideration, the term “complete sterl!fzation"
is hardly meaningful. what can be looked for Is the reduction of
the contamination load to some figure which presents what wil]

be considered an acceptable risk. In view of many Intangible
factors, we hesitate to Suggest a tolerable level of risk at the
present time. In any case, this should represent a residual
contamination substantially less than one microorganism per
missile. If we consider payloads of the order of 10> grams and,
as Hilbert does, an initial contamination load of 10° per gram,
our basic problem Is to reduce a load per missile from 10! to
some number less than one. A conservative mean lethal dose for
bacteria, taking Into account the probable existence of species
more resistant than those commonly used for calibration, would

be not less than 10° r.; this gives a decimal reduction dose of
2.3 times 10° r. To reduce the contamination load from 10” to
one organism per missile would then require local doses of the
order of 2 times 10° r. These figures are comparable to the ones
quoted but It should be stressed that they refer not to "comlete
sterllizatlon" but to the reduction of the contamination load

to the extent Indicated. it should be stressed also that If

the procedure Is to InactIivate viruses and other more radio-resistant
targets these figures would have to be multiptted by 10 or 100,
We agree that these studies should be conducted In close concert
with the laboratories, such as JPL, which are actively concerned
with the production of sclentific payloads and alee with consul-
tation with the microblologists who have been thinking about

the problem,

We hope that studies will be conducted that ere not confined
to radiation sterilization but Include other likely techniques
such as chemical fumigation and thermal sterilization.

The group asked me to take the occasion again,to stress
the vital Importance of the problem and of developing practical
measures to meat It.

Yours sincerely,

Joshua Lederberg
Professor of Genetics