A brief listing of the concerns of the working group on spacecraft charging is presented. Brief conclusions for each concern is also given

Stevens, N. John

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NASA Technical Reports Server

N89- 23568
WORKING GROUP WRITTEN PRESENTATION
SPACECRAFT CHARGING
Chairman: N. John Stevens
TRW
Issue Summary -
A. I. Materials vulnerability and orbits. Spacecraft system performance
Spacecraft Charging Interactions Couple Environment Factors To System Operations
Through Material Behavior.
The concern here is for possible interactions that result from the natural
environment action on the spacecraft materials (e.g. GEO spacecraft charging) and for
interactions caused by on-board system operations (e.g. high voltage solar arrays in
low Earth orbits). Therefore, all orbits have possible spacecraft charging
effects. This technology is still developing.
Specific effects on system performance are electromagnetic noise generation,
anomalous electronic switching, electronic parts and thermal control coating
degradation, dielectric electrical property change, power system losses and system
failures.
These effects have all been documented in previous spacecraft flight data.
Biggest data base is in GEO.
2. Correlation between theory and lab experience.
Previously defined charging interactions have been modeled and lab experiences
indicate validity of models. This includes surface and bulk dielectric charging,
effect of material configuration and some aspects of high voltage solar array/plasma
interactions. The trouble with long-term predictive capability is that the systems
are changing and what was tested in the past will not be flown in the future.
3. Can we predict for I0 or 30 years?
No, not with confidence. Present long-lived satellites are not the result of
predictive confidence; they just occurred. In families of supposedly identical
satellites, the lifetime varies because each is, in reality, individual satellites.
B. Facilities
There are facilities that can do pieces of this investigation. However, a
facility has not been identified that can do all environments required
simultaneously. Also, since these interactions are dependent on the configuration of
materials, there is no facility that can handle the size of sample necessary to
understand the very large spacecraft behavior in the space environment. Simulation
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of actual space environments is very poor as is simulation of sample grounding.
Facility ground is not the same as space. The available facilities exist at NASA-
Lewis, Hughes, TRW, Boeing, G.E., and NASA-JSC.
C. I. Synergism
Spacecraft Charging is the result of the other environmental factors acting on
spacecraft materials. Therefore, all of the other factors are important:
- Atomic Oxygen - Changes insulators, films and coatings of properties.
- Meteoroid/Debris - Erodes and punctures dielectrics allowing structure
potential electric fields to interact with plasmas.
- Trapped Radiation Charges dielectrics and structure.
- Solar Radiation Sunlit/shaded surfaces promote differential charging.
- Contamination - Changes surface properties.
Atomic oxygen and debris are low altitude phenomena (<1000 km for oxygen and 2500 km
for debris); meteoroid and solar at all altitudes; trapped radiation at >800 km and
polar orbits; contamination at all altitudes.
2. Testing of Synergism
Some aspects tested, but not all. Charging environments and solar effects
documented by ground test and flight data (SCATHA). Pinholes in insulators in high
voltage systems documented in laboratory. Influence of contamination on charged
samples observed in laboratory tests and SCATHA flight data.
3. Available Facilities for Testing Synergism
Since these interactions are so all-inclusive, there are no facilities to do
testing for all aspects of synergism.
D. Need for Space Experiments
The primary reason for space experiments is because the environment simulation
is poor. The interactions to be studied require high energy electrons and protons,
thermal plasmas, and sunlight for high orbits. For lower orbits the electrons and
protons are replaced by atomic oxygen and debris. The physical size relationships
that have to be studied, coupled with the power and voltages, demand space flight
experiments.
This does not mean that only space flights must be conducted. Ground tests of
individual aspects of interactions must be conducted. Analytical modeling of these
tests must be validated and this modeling used to extrapolate to other interactions
and size/power effects. This approach forms a data base to design meaningful
spaceflight experiments. Flight experiments will have the proper environment, but
instrumentation is limited and the experiment must be designed well to maximize the
output.
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E. Prioritized List of Experiments
The working group identified 10 interaction topics which are arranged in
priority order in attached sheets. These fall into materials experiments (1,3,5,8)
and materials related systems experiments (2,4,6,7,9 and |0). Since our interactions
are normally prioritized against the impact on system performance, we should have had
a better briefing on SDI system and technology requirements. It is recommendedthat
this be done.
The experiments all should be run for extended periods of time in space. Some,
like high voltage system interactions, can be done in days, while those dependent on
radiation damageto materials require years to build up total dose effects. It would
be nice to retrieve but it is not necessary. Noneof thesa experiments should be
conducted within the Shuttle bay. It should be elevated away from the sides.
This general list of experiments can be further condensed into three:
I. Material Property Determination With Time in Space Environment With Material
Under Electrical Stress
This is a radiation, UV, meteoroid-type experiment requiring high altitudes
and long life. Materials include conductors, dielectrics, composites, and
thin film coatings.
2. High Voltage System Interactions With Plasmas
This would be a low altitude experiment and would evaluate electric and
magnetic stress as well as coupling in space. This would be a material
configuration effect experiment.
3. Discharge Monitors
High altitude or polar satellites should carry these monitors along with
environment sensors to quantify effect of environmentally-induced effects.
F. Experiment Design
These are usually designed for the specific set of interactions desired. There
probably can be a generic bus with interchangeable payloads. These can be tailored
as piggyback, GASor free-flyers. Only those experiments requiring low altitude
information can be run at Shuttle/Space-Station Freedomaltitudes. Those requiring
radiation dose effects must be above 800 km.
G. Available Experiments
Concur with need for retrieving and reducing LDEFdata.
Require future flight information at available altitudes.
1. Material performance under electrical stress and space radiation
environments.
No experiment to do this has been identified.
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2. High Voltage Systems
a. SPEAR flight program underway (Space Plasma Experiments Aboard Rockets).
These are very short duration, pulsed power experiments that previde
information on system but not material behavior. Three minutes is not
adequate to design multiyear life.
b. NASA Planned Solar Array-Plasma Interaction Experiment. This must be
conducted now. Such experiments have been planned in the past, started and
then canceled. The data are mandatory.
c. Japanese plan experiment for 1992 time frame. No further information
available.
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SPACECRAFT CHARGING WORKING GROUP REPORT
CANDIDATE EXPERIMENTS
I. Material Property Changes With Electrical Stress and Time in Space
Environment
2. High Voltage System Interactions
3. Thin-Film Coating Interactions
4. Discharge Characterization
5. "Tailored" Materials
6. Heavy Stressed Power System Dielectrics
7. Pulsed Power System Interactions
8. Composite Internal Noise Generation
9. Active Charge Control
10. "Radiation Belt" Charging
Interaction: Material Property Changes With Electrical Stress and Time in Space
Environment
Why Problem:
o Stress Enhances Aging by Driving Solid State Chemical Interactions
o Radiation Induced Interface Failures
o Current Spacecraft Behavior Starting To Be Understood but Materials
and Operating Conditions Changing
o Lifetime Extended
Ground Test/Theory Correlation:
o Dielectric Community Working
o Short Term Testing Without Space Environment
What Is Still Needed: Materials Testing To Establish Range of Interaction
Why Require Spaceflight:
o Need Space Environment to Verify
o High Altitudes or Polar for Radiation
o Time in Environment
Supporting Work: Dielectric Community
Not Directed Towards Space Applications
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Interaction: High Voltage System Interactions
- High Voltage Solar Arrays
- Structure Collection in Plasmas
- Scaling Laws for Size, Voltage, Power, Frequency
- Sheath Effects
Why Problem: System Floats Electrically in Plasma Environment
Breakdowns in High Voltage Systems
Ground Test/Theory Correlation: Small Scale Sample Correlates With Theory.
What Is Still Needed: Size, Voltage, Power, Frequency Scaling.
Why Require Spaceflight: Need Complete Space Environment.
Can't Simulate On Ground
Supporting Work: Ground Support Work
Japanese Space Experiment
Interaction: Thin-Film Coatings
Stability of Thin-Film Optical and Electrical Coatings in Space
Environment
Applied for Specific Optical or Electrical Purpose
Charging Interaction Coupled With Sputtering or Contamination May
Destroy
Ground Test/Theory Correlation:
Short-Term Testing
Flight Data Not Instrumented For Detailed Examination
What Is Still Needed:
Identification of Coatings
Why Require Spaceflight:
Need Space Environment
Interaction: Discharge Characterization
Sources - Conditions for Discharge Initiation, High Power
Character - Frequency, Amplitudes, Rep Rate, Transfer Function and
Changes With Time in Space
Why Problem: Protection of System Circuits Depends on Knowledge of Discharges
Ground Test/Theory Correlation:
- Deducing Discharge Behavior in Space by Effect
- Characteristics Not Repeatable
Why Problem:
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What Is Still Needed:
Theory and Test Correlation
Why Require Spaceflight: Need Total Environment and Spacecraft Configurations
Interaction: "Tailored" Materials
Materials Developed for Properties To Minimize Charging Levels
- Conductivities in Range 10 .8 to 10 -10 S/cm 2
Why Problem: Can Mitigate Charging Concerns
Ground Test/Theory Correlation:
- Quasi-Conductive Materials Under Development
What Is Still Needed: o Better Materials for This Application
o Demonstrate Stability in Space Environment
Why Require Spaceflight: Demonstrate Behavior in Space Environment
Supporting Work: GSFC, VA. Tech
Interaction: Heavy Stressed Power System Dielectric SDI Applications Under High
Voltage and Large Current
Why Problem: Strong Electrical Stress and Induced Magnetic for Reduce Breakdown
Thresholds
Ground Test/Theory Correlation:
- Pieces Under Study
What Is Still Needed: Combined System Effects
Space Environment Demonstration
Why Require Spaceflight: Total Space Environment Effect
Time in Space
Interaction:
Why Problem:
Pulsed Power Interaction
System Dynamic Response to I to 100 _sec Power Pulse
Behavior in Plasma Uncertain
Affects System Performance
Flashover
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Ground Test/Theory Correlation: Theory Being Developed
What Is Still Needed: Theory and Test Demonstration
Why Require Spaceflight: Need Space Environment
Radiation Environment Important
Supporting Work: SPEAR II
Texas Tech and Maxwell (Testing)
Interaction: Noise Generated in Composites
Space Induced Charging Coupled With
Radiation Generates Noise in Materials
Why Problem: RF Noise Can Couple Into Communications and Sensors
Ground Test/Theory Correlation: Measure RF Levels in Small Samples Under Electrical
Stress and Radiation Theory Adequate but Number
of Pulses Unknown
What Is Still Needed: Pulses Expected in Samples Scaling
Why Require SpaceFlight: Need Spaceflight Environment
Auroral or High Altitude
Can Be Added to Existing S/C
Systems Having R.F. Detection
Interaction: Active Charge Control Interactions
Why Problem: Mitigation Technique but Can Degrade Coatings by Bombardment - Time
Effect
Ground Test/Theory Correlation: Short Term Testing
Model Exists but Not Validated
Why Require Spaceflight: Long Term Study in Space Without Walls
Supporting Work: AFGL Charge Control System (Xenon)
IAPS (Mercury)
Interaction: "Radiation Bolt" Charging
Energetic Proton and Electron Environment Variable in Orbits
Why Problem: Upsets Seem To Occur on GPS
No Charging Model Evaluation
Ground Test/Theory Correlation:
Should Be Able To Treat but Hasn't Been Yet
What Is Still Needed: Evaluation of Effect of Environment
Why Require Spaceflight: Need Environment and Time In Space
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SPACECRAFT CHARGING WORKING GROUP REPORT
SUMMARY
o Identified Interactions That Would Affect System Performance
o Better Definition of System/Missions Required
o General Approach for This Area:
Small Scale Ground Tests
- Modeling of Interaction
o Understanding
o Scaling
- Flight Verification Test
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Working group written presentation: Spacecraft charging

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