An overview is presented of potential interactions that can occur on spacecraft operating in space environments. These interactions are discussed in detail. The environment acts on spacecraft in such a way that charging of exterior surfaces occurs. The consequences from this charging then affect system operational performance. Hence, it is the coupling of this exterior charging to system performance that is of concern here. These interactions were first discovered in the spacecraft charging phenomena in which the geomagnetic substorms charged external surfaces to a level that discharges occurred. As a result of the discharge, electronic systems either changed logic state (anomalous switching) or failed. These interactions can occur in all orbits. The type associated with geosynchronous orbits is called passive since the environment provides the charging mechanism. This type can also occur in polar orbits due to auroral charging environments. In low Earth orbits, the thermal plasma alleviates charging environment concerns, but system operations can induce similar effects

Stevens, N. John

English

NASA Technical Reports Server

N89- 23556
INFLUENCE OF CHARGING ENVIRONMENTS ON SPACECRAFT
MATERIALS AND SYSTEM PERFORMANCE
N. John Stevens
TRW Space and Technology Group
Engineering and Test Division
System Integration Laboratory
Redondo Beach, CA 90278
535
https://ntrs.nasa.gov/search.jsp?R=19890014185 2020-03-20T03:13:03+00:00Z
ENVIRONMENTALLY-INDUCEDINT RACTIONS
The purpose of this paper is to present an overview of potential interactions
that can occur on spacecraft operating in space environments. These interactions
will be discussed in more detail in the accompanyingpapers.
The environment acts on spacecraft in such a way that charging of exterior
surfaces occurs. The consequencesfrom this charging then affect system operational
performance. Hence, it is the coupling of this exterior charging to system perfor-
mancethat is of concern here. These interactions were first discovered in the
spacecraft charging phenomenain which the geomagnetic substorms charged external
surfaces to a level that discharges occurred. As a result of the discharge,
electronic systems either changed logic state (anomalousswitching) or failed.
These interactions can occur in all orbits. The type associated with geo-
synchronous orbits is called "passive" since the environment provides the charging
mechanism(Reference I). This type can also occur in polar orbits due to auroral
charging environments. In low Earth orbits, the thermal plasma alleviates charging
environment concerns, but system operations can induce similar effects ("active"
interactions).
ENVIRONMENTACTSONSURFACEMATERIALS
- RESULTSAFFECTSYSTEMPERFORMANCE
- EXTERIORSURFACEDISCHARGESCOUPLEINT0 ELECTRONICSYSTEMS
INTERACTIONSOCCURIN ALL ORBITS
- ACTIVE: DUETO SYSTEMOPERATION
EXAMPLES:HIGHVOLTAGEOPERATIONS,EFFLUENT
- P_SSIVE: DUETOENVIRONmeNT
EXAMPLES:GEOANDPOLAR-AURORALCHARGING
536
GEO SUBSTORM CHARGING OF SPACECRAFT
This phenomena has been investigated for the past ten years (References 2-5).
These studies have shown that there is a link between the exterior surface discharge
and electronic system upsets (References 6, 7). The hazards with this spacecraft
charging phenomena have been enhanced electrostatic contamination and plasma particle
measurement disturbances. These studies have generated design guideline documents
that provide guidance and suggested mitigation techniques (References 8, 9). The
recommended mitigation techniques are to analyze to ascertain the extent of charging
interaction, ground all exposed metallic surfaces to prevent discharge triggers,
select minimal charging materials, filter sensitive system inputs, shield harnesses
and control grounding techniques to minimize extraneous circuits. This document has
been included in the revised edition of Military Standard 1541A (Reference 10).
O HAZARDS ASSOCIATE WITH GEO SPACECRAFT CHARGING
- DISCHARGES
EMI, ELECTRONIC SWITCHING AND FAILURE, MATERIAL DAMAGE
- ENHANCED ELECTROSTATIC CONTAMINATION
- DISTURB SPACE SCIENCE MEASUREMENTS
MITIGATION TECHNIQUES
- ANALYZE FOR CHARGING EFFECTS
- GROUND EXTERIOR METALLIC SURFACES
- SELECT MINIMAL CHARGING EXTERIOR MATERIALS
- PROTECT INTERIOR SYSTEMS
FILTER, SHIELD AND GROUND
o INCORPORATED IN MIL STD 1541A
537
SPACECRAFT CHARGING IN FUTURE MISSIONS
The previous studies have resulted in the conclusion that the spacecraft
charging issue has been settled. In the initial stages of the spacecraft charging
investigation several companies claimed that "... there is no such thing as space-
craft charging, only bad design." These statements were wrong then just as this
belief that all issues have been resolved is wrong now. The charging investigation
covered only those materials and systems that were in use in the late seventies.
The spacecraft of the future will not use those materials or systems. Charging
anomalies arose because of the transition from relay to solid-state logic. This
innovation reduced switching transients from long pulses at 15 volts to short pulses
at less than 5 volts. The surface charging provided pulses which could switch and
damage solid-state systems. The future missions want long mission duration at very
high operating speed. In fact, the suggested operating speeds for future data buses
correspond to the ringing frequency of todays standard structures. Hence, filtering
is impossible. The future spacecraft will use new composites materials for
structures. The behavior of these materials has not vet been determined. The only
help that prior studies can provide is the recognition that the environment can
cause interactions and that these must be assessed.
o FUTURE MISSIONS REQUIRE ADDITIONAL EVALUATION
- ELECTRONIC SYSTEM SPEED INCREASING
- CPERATIONS AT STRUCTURE RESONANT FREQUENCY
- CAN'T FILTER OUT NOISE
- MATERIAL SELECTIONS
- COMPOSITE BEHAVIOR UNKNO_£N
- COATING SE]_ECTION PROVIDENCE OF THERmal, DESIGN
- LONG TERM AGING EFFECTS ON MATERIAL PROPERTIES UNKNOWN
o GUIDES EXIST BUT MAY NOT BE DIRECTLY APPLICABLE
538
LEO ORBIT INTERACTIONS
NASA is planning to build a very large Space Station* that will orbit at about
400 km. This Station will incorporate solar arrays that will generate 200 kw of
power at a nominal operating voltage of 160 volts. This is the largest system yet
conceived operating at a voltage larger than any previous satellite. This array
voltage will determine the spacecraft floating potential relative to space. Whether
or not this is serious has to be determined. Todays technology has trouble under-
standing its present data base of solar cell interactions obtained with 2 X 2 cm
and 2 X 4 cm silicon cell segments tested only in limited areas of up to i000 sq.
cm. (References 11-13). The Station has baselined 8 X 8 cm solar cell for which
there is no data on plasma effects.
The size of the Station also presents concerns for environmental interactions.
There will be high voltage that may or may not be distributed over very large areas
moving at orbital speeds through the Earth's magnetic field. The electronic systems
must function at high operational rates. This Station is a complicated system and
its interaction has to be understood in order to assure safe operations over the
lifetime of the Station.
As complicated as the Space Station may appear, the SDI missions are far more
complex. Here, the power levels rise to gigawatt levels which would be required
instantaneously, anytime in their i0 year mission life. Clearly, this is a
challenge to understanding complex interactions between space environments and
spacecraft systems.
NASA SPACE STATION IN LEO
- LONG MISSION LIFE (30 YEARS) AT HIGH POWER
- 160 VOLT OPERATIONS
- COMPLEX INTERACTION WITH ENVIRONMENT
TECHNOLOGY TO PREDICT BEHAVIOR UNPROVEN
- NO LARGE SOLAR CELL DATA
- NO LARGE STRUCTURE DATA
- NO HIGH VOLTAGE DATA
- NO LARGE COMPLEX STRUCTURE DATA
o SDI MISSION AT HIGHER POWER LEVELS
VERY HIGH VOLTAGE PHENOMENA
- EFFLUENTS FROM OPEN CYCLE OPERATIONS
- LONG STORAGE TIME IN SPACE DIELECTRIC AGING
*Space Station Freedom
539
GROUND SIMULATION TECHNIQUES
Environmentally-induced effects have been studied in the past in ground
simulation facilities (References 13-15). Such facilities allow a more complete
testing of phenomena under controlled conditions. However, they suffer since they
are normally poor simulations of the Earth's environment.
Geomagnetic substorm facilities normally operate with a monoenergetic electron
beam irradiating a dielectric mounted on a grounded metal plate. Such tests can
generate meaningful data on dielectric properties, but they can not be used to
demonstrate space behavior. Floating or biasing the metal plate can be done, but
this can influence the results.
Low Earth orbit simulation of the plasma environment also suffers in comparison
to the actual environment. The space plasma temperature cannot be reproduced in
chambers and the influence of the higher, ground simulation particle temperatures
has not been determined. These facilities also limit the size of the sample that
can be tested before the tank walls dominate the interaction.
Flight experiments _rovide the environment but the instrumentation is limited;
the cost is high and the opportunities few.
The ideal situation would be to have the tools to model the interaction
(engineering level as well as the more detailed techniques), conduct ground
simulation tests to obtain needed information for the models, conduct flight
experiments to validate the modeling technique and then use the models to predict
the impact of the interaction on spacecraft systems behavior.
o SUBSTORM SIMULATORS
- MONOENERGETIC ELECTRON BEAMS
- SMALL AREAS EXPOSED
- TANK GROUND POTENTIAL REFERENCE
o LEO SIMULATORS
- POOR PLASMA ENVIRONMENT SIMULATION
- SHEATH EFFECTS DOMINATE
FACILITY SMALL FOR PROJECTED SPACECRAFT DIMENSIONS
- EFFLUENT FLOW CONSTRAINED BY WALLS
o INTERPRETATION OF RESULTS DIFFICULT
o ANALYTICAL MODELING TECHNIQUES NEEDED
- SUPPORTED BY GROUND AND FLIGHT EXPERIMENTS
540
SUMMARY
This paper is intended to present an overview of the possible interactions bet-
ween spacecraft system and charging environment. Encounters with such envirom_ents
have resulted in system upsets and failure in the past and it is naive to believe
that future systems would be immune to these interactions. The state of the art is
not as well developed as the technical community believes. All spacecraft interact
with the environment, many have had system difficulties, but only a limited number
of events have been reported. A program leading to an analytical modeling technique
is required to ascertain the impact of interactions on system designs. This program
must be supported by ground and flight experiments.
"4
O
O
SPACECRAFT SYSTEMS RESPOND TO ENVIRONMENTAL CONDITIONS
- ELECTRONIC SWITCHING UPSETS, COMPONENT FAILURES AND MATERIAL
DEGRADATION OCCURS
- MOST SPACECRAFT HAVE ANOMALIES
- FEW INCIDENTS ARE WELL-KNOWN
FUTURE SPACECRAFT ARE LARGER, USE FASTER ELECTRONIC SYSTEMS AND
HAVE LONGER MISSION LIFE
- ANOMALOUS BEHAVIOR WILL INCREASE
- TECHNIQUES FOR MITIGATION UNPROVEN
DEVELOPMENT OF CONTROL TECHNIQUE REQUIRED
- BASED ON UNDERSTANDING INTERACTION
- DEMONSTRATED CAPABILITY TO PREDICT BEHAVIOR
- DOCUMENTED MITIGATION TECHNIQUES
54]
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Space Systems and Their Interactions with Earth's Space Environment. H.B.
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Influence of charging environments on spacecraft materials and system performance

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