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STANFORD UNIVERSITY MEDICAL CENTER
STANFORD, CALIFORNIA 94305 © (415) 321-1200

 

 

STANFORD UNIVERSITY SCHOOL OF MEDICINE
Department of Genetics

Instrumentation Research Laboratories
(et iS is : May 21, 1971

Mr. C. H. Robbins

NASA Langley Research Center
Langley Station

Hampton, Virginia 23365

RE: Viking '75 Project Mission Design Requirements,
Objectives and Constraints, Document No. IR-3720055

Dear Mr. Robbins:

Last week, upon receiving this document, I called you to express my concern
that the document did not either describe the ground data handling requirements
necessary to carry out the mission or make clear that they were meant to be
excluded from this document. It is the adaptive parts of the mission that
impose the most stringent requirements. This is obvious in connection with
site certification by the orbiter and should be made more explicit in
connection with landed imaging requirements. Tables 4.2.1.1-1 and 4.2.1.2-1
of the requirements and objectives are a very good first guess of imaging
sequences. The ground data handling and ground command capability must
exist to provide adaptive variations from the sequence to take advantage

of opportunities that are observed and unpredicted requirements.

In addition, I would like to make some comments about paragraph 2.4.6 entitled
“Planetary Quarantine Constraint". As you may be aware, there is considerable
dispute concerning the rationale and validity of the 17 year criteria which
leads to the January 1, 1989 date. The 17 years were chosen to provide a
basis of calculating the number of missions that might be used to carry out
biological explorations. This permits spreading the risks of contamination
over these missions. It does not follow from this that it should be used

as the basis for calculating lifetime in orbit. I am enclosing a copy of a
letter that Lederberg and I wrote to Dr. Herbert Friedman of the Space

Science Board, November 4, 1969. This letter discusses this matter more
fully. From a pragmatic point of view it may be possible to take care of

the issue quite simply. My understanding of Paragraph 2.4.6 is that the

a priori probability of violating the 17-year lifetime in orbit will be less
than 2 x 10-8 for each Centaur and less than 3 x 1075 for the Viking Orbiter
and less than some number still to be determined for the bioshield cap and
base. If this is true, based on the significant uncertainties that are bound
to exist in a knowledge of the atmosphere and the solar radio flux, it
Mr. C. H. Robbins Page 2 May 21, 1971

follows that orbits will be chosen which are likely to provide a reasonably
high probability of lifetimes greater than 50 years. I think it would

Satisfy even the most conservative point of view, including mine, if the
probability were greater than .95 that the lifetime-in-orbit would exceed

50 years. If my understandings are correct, this is not likely to be
incompatible with the constraints of paragraph 2.4.6 because of the steepness
of the lifetime-in-orbit curves and their sensitivity to atmospheric parameters.
I urge, however, that this matter not be left ambiguous. An additional
boundary condition asserting a reasonable probability that the lifetime in
orbit would exceed 50 years should be added as an additional constraint.

I am forwarding a copy of this letter to Mr. Lawrence Hall for his comments
on this matter.

Very truly yours,

Elliott Levinthal
ECL/mia

ec: Mr. Lawrence Hall
Dr. John Findlay
Dr. Richard Young
Dr. Thomas Mutch