With the advent of the Space Exploration Initiative, the possibility of designing and using systems on scales heretofore unattempted presents exciting new challenges in systems design and space science. The environments addressed by the Space Exploration Initiative include the surfaces of the Moon and Mars, as well as the varied plasma and field environments which will be encountered by humans and cargo enroute to these destinations. Systems designers will need to understand environmental interactions and be able to model these mechanisms from the earliest conceptual design stages through design completion. To the end of understanding environmental interactions and establishing robotic precursor mission requirements, an Environmental Interactions Working Group was established as part of the Robotic Missions Working Group. The working group is described, and its current activities are updated

Hillard, G. Barry

Kolecki, Joseph C.

English

NASA Technical Reports Server

i"t9 2- 22 382
ENVIRONMENTAL INTERACTIONS IN SPACE EXPLORATION:
ENVIRONMENTAL INTERACTIONS WORKING GROUP
Joseph C. Kolecki
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
G. Barry Hillard
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
INTRODUCTION
With the advent of the Space Exploration Initiative as
mandated by the President of the United States in his
twentieth anniversary speech commemorating the first
Moon landing, the possibility of designing and using new
space systems on scales not heretofore attempted opens
before us exciting new challenges in systems design and
space science. The environments addressed by the Space
Exploration Initiative include the surfaces of the moon
and Mars, as well as the varied plasma and field
environments which will be encountered by humans and
cargo en-route to these destinations from the surface of
the Earth, or from low Earth orbit. It is fully expected
that systems designers will have to take into account the
environmental characteristics for which they are designing.
They will need to understand the interaction mechanisms
to which their systems will be subject and be able to
model them from the earliest conceptual design stages
through to design completion.
Planetary and space environments are interactive with
man-made systems in a variety of ways, as experience has
already shown. Lunar dust physics is dominated by
electrostatic forces. The martian surface environment
differs from that of the moon in that it consists both of
sand and dust, and a dust-laden, low pressure atmosphere
in which Paschen electrical breakdown can occur at
voltages ranging from a few hundred volts upward. The
space environment is dominated by plasmas and fields
with a wide range of energies and other physical
characteristics. In addition to these natural environments,
humans will produce local environments of their own
which will modify what is already there and have to be
dealt with on their own terms. The characteristics of
system/environmental interactions depends on both the
characteristics of the local environment, and those of the
system. Different system scale sizes lead to different types
of interactions and require different mathematical models
to enable understanding, evaluation, and prediction.
To the end of understanding environmental interactions
for the Exploration Initiative, an Environmental
Interactions Working Group has been established as part
of the Engineering Requirements Subgroup. This working
group is chaired by Joe Kolecki of NASA Lewis and draws
its membership from a broad scope of disciplines. The
current paper describes the working group and gives an
update on its current activities. The working group
charter and operation are reviewed, background
information on the environmental interactions and their
characteristics as we understand them is offered, and the
current status of the group's activities are presented along
with anticipations for the future.
ENVIRONMENTAL INTERACTIONS WORKING
GROUP
Space system/environmental interactions comprise a set of
phenomena which occur when a system is placed into an
environment whose local characteristics are such that the
system and the environment are able to exchange
"information" in some way and thereby influence or modify
each other. Put another way, one can imagine the various
environments of concern to be characterized each by some
parameter set (like an Earth Standard Atmosphere
model), and the various systems likewise. An
environmental interaction is what occurs when one takes
a system from shelf "A," an environment from shelf "B,"
places them into a sealed bag and shakes well. It is the
objective of an environmental interactions team to classify,
prioritize, and model interactions, to advocate and/or
conduct all necessary experiments whether in space or on
the laboratory, and to place into the hands of systems
designers the best possible user friendly codes and/or
design guideline documents possible. This will enable
those designers to optimize their systems to the
environments in which they must function, from the
earliest design stages through to completion and use.
This type of work is already being carried out in a number
of discipline areas, some of which have been ongoing for
a considerable time. Some of these areas include
radiation effects, having to do with particles and fields;
collision effects, having to do with micrometeoroids and
orbital debris; effects connected with dusty plasmas, like
those found on the moon or in the vicinity of comet
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nuclei; plasma and spacecraft charging effects, chemical
processes, Martian aeolian processes, and temperature
cycling effects. Systems which have historically been
impacted by interactions with their local environments
include the "big" missions systems like those associated
with Apollo, Viking, and the planetary and cometary
probes of the past few decades, geostationary satellites,
which displayed anomalous behavior most readily
accounted for by charge/discharge phenomena, the Space
Shuttle, which has carried various payloads to determine
environmental parameters at LEO (some of which were
used in development of computer models) and the Space
Station, whose size and complexity has led to a
reconsideration of environmental interactions in LEO.
The evolution in our knowledge of environmental
interactions has been driven by the growth and variety of
space infrastructure elements placed onto Earth orbit and
elsewhere. Systems of increasing size and complexity, and
placement of those systems into active new environmental
regimes has repeatedly necessitated the development of
new interactions knowledge and system design guidelines.
The President's Exploration Initiative is orders of
magnitude larger than anything attempted in space to this
point in time. Therefore, our understanding of
environmental interactions must again grow to meet the
challenge of the future.
The environments of concern to the Exploration Initiative
include at least the surface environments of the Moon and
Mars, the martian atmosphere, and the space
environments through which humans and cargo will travel
to reach these destinations. Least known among these
environments are the martian surface and atmosphere.
Interactions to be anticipated when systems are placed cn
the martian surface include Paschen breakdown from
moderate to high voltage surfaces, charge/discharge
phenomena associated with electrostatically charged dust,
modification of discharge onset characteristics depending
on wind and wind-borne dust conditions, and
charge/discharge phenomena during descent and ascent of
man-made vehicles. Dust deposition will modify surface
optical, electrical, and thermal properties, and wind borne
dust will produce mechanical erosion over long periods of
time. Chemical effects are also to be anticipated with
active species in the martian atmosphere and soil.
Additional thoughts on martian environmental effects are
included in the appendix to this abstract.
Better known is the lunar environment in which dust
dynamics are driven by electrical forces, and result in
copious contamination of external and internal surfaces
and volumes. Since the moon has no atmosphere,
radiation and plasma effects are also important lunar
surface considerations. Long term human occupation of
the Moon and Mars necessitates development of systems
in which interactions with the environment are understood
in the earliest design phases, and taken into account
throughout the design process. Similar arguments exist for
translunar and interplanetary space through which humans
and cargo must pass en-route to lunar and Martian
destinations, as well as to low Earth orbit which may be
the site of semi-permanent human occupation in an Earth
orbiting Space Station. The size and complexity of the
Space Station have already been cited as drivers for
developing new environmental interactions knowledge, and
the issues which have arisen (with such design parameters
as Space Station structure to solar array grounding) must
serve as fair warning of the need for constantly updating
our interactions models and/or developing and
experimentally validating new ones, as necessity
determines.
To date, environmental interactions work has been carried
out in several specific areas and completed to varying
degrees. But this work has not been carried out in the
"Integrated Program" fashion necessary to the scope and
magnitude of a Space Exploration Initiative. The
respective disciplines have evolved semi-autonomously,
that is, to a large extent independently of each other.
Cross fertilization of ideas has occurred only as needed, as
when the question of a plasma interaction arose around
the issue of a solid object like a meteoroid impacting or
penetrating a spacecraft bumper shield and generating a
hot transient gas as a by-product. No forum yet exists in
which system/plasma interactions are discussed on a large
scale, with cross-disciplinary exchange of ideas, and
development of integrated program elements which both
insures minimal overlap of funded efforts and fills all of
the programmatic "holes."
An integrated, coordinated approach is required for future
work in this area, allowing programs to develop with
mutual knowledge of each other and knowledge of the
mission and system definition activities already under way.
To that end, a working group has been established to
address issues and make recommendations, defining
agency-wide areas of need for predicting and evaluating
interactions, establishing what information is already
available, and formulating and implementing a program to
develop and experimentally validate models for use by
system design engineers. As a point of ingress into a
potentially infinite area of study, the Environmental
Interactions Working Group will begin by establishing
requirements for robotic missions to Mars. The group will
establish a data base of currently available information on
the Martian surface environment, and understand in broad
terms the expected operating parameters of systems
intended for use on the martian surface. It will then
define and prioritize martian surface interactions, and
establish those parameter sets most critical to developing
interactions models. The parameter sets will be compared
against existing data, and used to define instruments,
sensors, and/or experiments to be carried to the martian
surface as part of the robotic precursor "package." These
items will be documented in the form of a set of
recommendations, and delivered to the Engineering
Requirements Working Group being established at the
Johnson Space Flight Center. The working group will
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expand its activities to embrace the broader charter
described above as appropriate. It will meet by
videoconference approximately every six weeks, and more
frequently on an as-needed basis.
E. Concerns include spacecraft surface charging,
sputtering from charged surfaces, spacecraft
floating potentials, oxygen degradation of
materials, and spacecraft system grounding
APPENDIX: OUTLINE OF PRELIMINARY
THOUGHTS ON MARS SURFACE
INTERACTIONS
The following outline represents preliminary thoughts on
electrical system/environment interactions on the planet
Mars. These types of interactions should be of interest to
system designers at every stage of system design.
I. ATMOSPHERIC INTERACTIONS
A. Paschen electrical breakdown from high voltage
surfaces: (The 7-9 Torr atmospheric pressure
at the martian surface is ideal for Paschen
breakdown over mm to cm distances at a few
hundred volts, and cm to m at a few kilovolts)
1. breakdown to other spacecraft surfaces
2. breakdown to air
3. breakdown to ground
4. source of system power loss
5. source of electromagnetic noise
B. Sparks, arcs, and other sustained or transient
discharge phenomena
1. electrical power loss
2. sputter erosion of surfaces
3. transport and redeposition of materials
(contamination)
C. Electrical discharge phenomena during descent
and ascent (unknown)
1. electrical breakdown of low pressure
atmosphere and local gases due to thruster
firing
2. differential charging of surfaces during
thruster firings
3. analogous to discharge events seen during
terrestrial launches
II. MARTIAN IONOSPHERE/SPACECRAFT
INTERACTIONS IN LMO (100-300KM)
A. Plasma phenomena are functions of system
voltage, system configuration, and local particle
populations
B. Max neutral number density = 109 and 10" cm -3
for monatomic oxygen and CO2 respectively
(compare 109 cm -3 for monatomic oxygen in
LEO)
C. Max electron density = 104 to 10_ cm 3
(compare 10_ to 10_ cm 3 in LEO)
D. Max ion density -- 104 to 105cm 3 for CO, ÷ and
Oz* respectively (compare l& to l& cm -3for N ÷
and O* respectively in LEO)
1. PIX II showed evidence of arcing and
parasitic current collection at 104 cm -3
electron number density
2. PIX II operating voltages -- +/- 750 volts
III. DUST RELATED ELECFRICAL INTERACrlONS
A. Surface dust
1. charging due to solar ultraviolet
2. charging due to induced dipole effects
from exposed high voltage surfaces
3. deposition on surfaces due to electrostatic
attraction
4. modification of surface thermal, optical,
and dielectric properties
5. contamination of clean volumes
B. Wind borne dust
1. charging due to frictional mechanisms
2. charging due to differential settling after
dust storms
3. deposition of electrically charged dust on
surfaces
4. modification of surface thermal, optical,
and dielectric properties
5. contamination of clean volumes
IV. INTERAC'rlON MODELS: WHAT HAPPENS
WHEN YOU ADD A SYSTEM TO AN
ENVIRONMENT AND "SHAKE WELL?" HOW
DOES ONE CHARACrERIZE THE RESULTING
INTERACTION AND USE THAT KNOWLEDGE
TO PRODUCE THE BEST DESIGN? SOME
AREAS FOR CONSIDERATION/
DEVELOPMENT ARE THE FOLLOWING:
A. Identify relevant physical mechanisms/equations
B. Produce, and (where necessary) experimentally
verify mathematical models
1. identify existing interaction models where
applicable
2. identify and direct models currently under
development in related areas
3. identify areas for which model
development needs to be initiated (SEI
specific models, or working modules for
use with existing models)
C. Understand user needs and establish
appropriate user interfaces
1. system designers are the most likely users
2. interaction models are a bridge between
standard environment models and
engineers who wish to understand how
their new system will play in a given
environment
D. Establish appropriate input/output formats
E. Identify/performrelevantlaboratory/spacetests
and analyses
F. Deliver user-friendly software with appropriate
interfaces
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Environmental interactions in space exploration: Environmental interactions working group

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