Model supplements biological surveys of spacecraft by simulating microbial burden accumulation process during periods when surveys are not taken. Important application of model is to predict microbial loading on spacecraft landing capsule immediately prior to terminal heat sterilization

Meuser, R. F.

Nelson, B. A.

English

NASA Technical Reports Server

October 1971	 Brief 71-10401 
NASA TECH BRIEF 
NASA Pasadena Office
	
-liv 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the, Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Microbial Burden Prediction Model 
Program: Production Version 
The problem: 
To predict the number of viable micro-organisms 
accumulated on the biologically significant surfaces 
of a spacecraft at selected times during the prep-
aration and testing operations prior to launch. 
The solution: 
A mathematical model and a computer program 
that together will predict the microbial loading on 
any spacecraft. 
How it's done: 
The model supplements biological surveys of the 
spacecraft by simulating the microbial burden ac-
cumulatio.n processes during periods when surveys 
are not taken. An important application of the model 
is to predict the microbial loading on a spacecraft 
landing capsule immediately prior to terminal 
heat sterilization. 
Mathematical expressions were developed to 
represent the processes of burden accumulation and 
to reflect the effects of the parameters on each 
process. Three burden accumulation processes 
(1, 2, and 3) and one burden reduction process (4) 
were identified: (1) environment fallout; (2) personnel 
and equipment fallout; (3) contact by tools or per-
sonnel; and (4) decontamination. 
Due to uncertainties in parameter values and 
initial microbial burdens, it was necessary to treat 
these quantities as random variables. This was ac-
complished by the interval concept, a numerical 
technique for performing arithmetic operations 
of addition, multiplication and division on histograms
(probability density functions) which are not neces-
sarily from identical underlying distributions. 
The computer program logic was based on five 
requirements: (I) the ability to simulate the as-
sembly and test sequence of any spacecraft; (2) the 
ability to simulate the burden accumulation and re-
duction processes using the interval concept and the 
mathematical expressions developed; (3) the ability 
to compute and maintain statistics that describe 
the burden accumulated by each biologically signif-
icant zone at the selected points in the activity se-
quence; (4) the ability to maintain separate statistics 
for four surfaces (top, exterior, mated, and occluded) 
of each part or zone; and (5) input and output re-
quirements. 
The format of the computer input is extremely 
flexible. The input data consist of the burden 
parameters and the assembly and test sequence. The 
following inputs are supplied at appropriate 
activity levels: (1) part numbers of hardware being 
manipulated; (2) hardware area changes (e.g., the 
change from external to mated, caused by joining 
two parts); (3) environment designation; (4) number 
of personnel; (5) time to perform; (6) initial burdens 
on hardware and tools; (7) burden retention factors 
for hardware and tools; and (8) prerequisite ac-
tivities. 
The computer prints out the burden histogram 
for each surface of each part or zone whenever it 
is affected by an operation. Burden totals for each 
surface are printed at the end of each task unless 
a complete listing of burden histograms for each 
surface of every part and zone is requested.
(coritii,ucij overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000398 2020-03-17T02:30:08+00:00Z
Notes: 
1. This program is written in FORTRAN V for use 
on the UNIVAC-1108 computer. 
2. Requests for further information may be directed 
to:
COSMIC 
112 Barrow Hall 
University of Georgia 
Athens, Georgia 30601 
Reference: B71-10401
Patent status: 
No patent action is contemplated by NASA. 
Source: A. R. Hoffman of

Caltech/JPL, and

B. A. Nelson, N. D. Gorby, and L. B. Farabee of

Martin-Marietta Corp.

under contract to

NASA Pasadena Office

(NPO- l 1709) 
Brief 71-10401	 Category 09


Microbial burden prediction model program

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