May &, 1959

Mr. &. A. Berbyshire
Space Sclence Board
2101 Constitution Ave.
Washington 25, 6. C.

Dear Mr. Derbyshire:

Sur group, which met May 2nd and 3rd, spent some tine discussing
the application of lonizing radiation for the sterilization of
misstle peyloads. we had previously considered radietion technique
during our previous meetings and had felt that It might be applicable
although marginally in relation to the complete sterilization
of a payload at doses that would feave the Instrumentation Intact.
if the circultry can be subject to basic redesign, es might be
necessary for the epplication of radietion, we felt that heat
might prove to be about as effective and considerably more convenient
to use in practice. There Is, of course, considerable objection
to complete overhauling of the electronic systems to make them
amenabie to either thermal or rediation sterilization. However,
we fee! that the question should be studied as closely as possible.
The presentation was, however, somewhat narrow both from the
polat of view of the biological aspects of sterilization end cof
the effect of large radiation doses on the electrical properties
of materiel, these properties being probably more importent,
and In some cases more sensitive, than the mechanical ones which
were tabulated. There are at feast two other orgenizations
which should be considerably better qualified to study varlous
atpects of this problem than Is General Electric. One of these
is the Argonne Laboratories, operated by the University of Chi cage
under contract to the A. &. C.; the other Is the Blological —
Warfare Laboratories at Fort Setrick, Frederick, Maryland. The
Argonne Laboratories must have very auch more extensive dats on
the radiation sensitivity of mlcroorgealsas and also of materials
then ore Indicated in the 6. E. Memorandum. The Fort Detrick
Laboratories have unequalled experience In the disinfection area.
Additionally, the Army Quartermaster Corps, Ploneer Laboratory
at Natick, Massachusetts hes elso had considerable experience
in the sterilization of bulky materials by redietion end should
be consulted. we would consider that G. £. In the Hight of its
om report aad of the Indicated qualifications of Its staff would
be an acceptable choice but with e lower standing than the egencies
just Indicated to make the study called for. However, the study
should be made from an cperational point of view and these remarks
should not discourage the participation by 6. £. provided every
effort is first made to Interest the agencies IIsted.

we had some concern es to the quantitative conception of
“steritization' Indicated in the memorandum. Sterilization
is @ zero order kinetic process so that each succeeding dose
removes a constant fraction of the previous contamination load.
jn view of this consideration, the tere complete sterilization”
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, wa hesitate to suggest a tolerable level of risk at the
present time. In any case, this should represent « residual
contamination substantially less than one microorganism per
missile. If we consider payloads of the order of 10° grams and,
es Hilbert does, an Initial contamination load of 10° per gram,
our baste problem Is to reduce a load per missile from 10" to
soee number less than one. A conservative mean lethal! dose for
becteris, taking Inte account the probable existence of species
more resistant then those commonly used for calibration, would
be not tess than 105 ¢.; this gives a decimal reduction dose of
2.3 times 105 ¢. To reduce the contamination load froa 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 cnes
quoted but it should be stressed that they refer not to ‘complete
sterilization’ but to the reduction of the contamination load

to the extent indicated. tt should be stressed also that If

the procedure Is to Inactivate viruses and other more radlo-resistent
targets these figures would have to be multiplied by 10 or 100.
We agree thet these studies should be conducted In close concert
with the laboratories, such es JPL, which are actively conceraed
with the production of sclentific payloads and al6e with consul-
tation with the microblologists who have been thinking about

the problen.

We hope thet studies will be conducted that ere not confined
to radiation steriilzetion but Include other likely techniques
such as chenical fumigation and thermel sterilization.

The group asked me to take the occasion again tc stress
the vital importance of the problem and of developing practical
measures to meet It,

Yours sincerely,

Joshue Lederberg
Professor of Genetics