Contamination Control Far Outside the Cleanroom (Space Exploration)
Barbara Kanegsberg and Ed Kanegsberg, January 2004
We must consider contamination control inside and outside of the cleanroom.
In fact, some of the frontiers of contamination control efforts are taking
place far outside the confines of the typical fab facility - outer space. Space
exploration efforts bring into sharp focus the limits of contamination control,
both biological and non-biological, and the related issue of contamination
measurements, particularly technique sensitivity and measurement near the detection
limits.
Mars and Ecosystem Management
Three probes are due to land on Mars during January, 2004; two from the
U.S. and one from the European Space Agency. The mission
statement for the two U.S.
landers is to "follow the water." Because water is
necessary for life, the working hypothesis is that if evidence
of water is
found, life is
or was possible.
One overall contamination minimization goal in space programs
is referred to as ìplanetary protection,î preventing
cross-contamination between Earth and entities in space. Introduction
of microbes or other contaminants
from spacecraft to another planet is referred to as forward
contamination. Back
contamination refers to contamination of earth by returning
spacecraft. The need for interplanetary contamination control
has been known for over
three decades. However, our increasing understanding of the
potential for contamination
makes these goals an ever increasing challenge.
One issue is the ìwallî of absolute cleanliness.
Complete, utter cleanliness is a goal toward which we approach,
but one which
will probably
never be achieved. At the May, 2003 ASTM conference to develop
cleanliness standards for biomedical devices, many speakers and
attendees commented
that it is impossible to define zero contamination.1
The same principle applies to hardware for space exploration.
Detecting the presence of one single particle, and then
eliminating that particle, would
not seem to be reasonable. Similarly, we cannot detect
contamination down to one spore or one cell. While biologists tacitly
assume
that a certain
di minimus
contamination can be tolerated, the potential (albeit very
low) of cross-contaminating interplanetary ecosystems calls
for perhaps unprecedented efforts to minimize
viable contaminants. Certainly, cross-fertilization of
the space exploration community with the medical community might
prove productive. For example,
as with ASTM efforts, it may be possible to extrapolate
from contamination studies
on successful, long-term biomedical implants. NASA standards
for managing outbound hardware and for containing returning
materials have been established.
Solar Wind and Low-level Detection
The Genesis mission is a current effort to collect atomic particles from the
sun, the solar wind, over a two year period. The samples
will be returned to Earth for analysis in 2004. The project illustrates
techniques required
to
determine low levels of analyte and illustrates problems
associated
with chemical analysis near the detection limits.
The technique of collecting samples for long periods of time
to obtain a significant, representative sample of low
levels of material is analogous
to the technique
of collecting witness samples for analysis of Airborne
Molecular Contamination (AMC) in fabrication facilities for wafers,
optics, and biomedical devices.2
Spurious interferences near the detection limits presents
yet another challenge in contamination control. In
the solar wind project, for example, plasticizers
in the walls of a nitrogen cabinet were found to
outgas at
sufficiently high levels to interfere with analysis.
A specially designed cabinet is required
to minimize potentially interfering contaminants.
The potential for contamination is inseparable from
efforts to fabricate, measure, or explore, at the
microscopic
or intergalactic level. Approaches
to achieving
accurate sample collection in space and preventing
interplanetary ecosystem contamination have many
commonalities with
preparation of a small stent or
of an implantable pharmaceutical delivery device
with well-defined surface properties. Both communities
require
accurate,
precise, sensitive measurements.
Each community can benefit from the experiences
and approaches used by the other. Such cross-fertilization
has the potential
for obvious benefits both
in and out of the cleanroom.
Thanks to Mary Sue Bell, Lockheed Martin, Science,
Engineering, Test, and Analysis at Johnson Space
Center, Houston,
TX for her helpful contributions
to and review
of this column.
References:
1. Kanegsberg and Kanegsberg, A2C2, October,
20032. Kanegsberg and Chawla, A2C2, April,
2001.
Barbara Kanegsberg and Ed Kanegsberg are independent consultants in critical cleaning, precision cleaning, surface preparation, and contamination control. They are the editors of “Handbook for Critical Cleaning,” CRC Press. Contact them at BFK Solutions LLC., 310-459-3614; info@bfksolutions.com; www.bfksolutions.com.
