David Cooke

1
Nascap-2K Simulating the Interaction of
Spacecraft with the Plasma Environment

• David Cooke
• Adrian Wheelock
• Air Force Research Laboratory,
• Hanscom AFB, Boston, MA
• Myron J. Mandell, Victoria Davis,
• Jeffrey Hilton, Barbara Gardner
• Science Applications International Corporation
• San Diego, CA

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Nascap-2K Replaces Earlier Spacecraft-Plasma Codes
Code NASCAP/GEO (1976-1984) Applications GEO
S/C Charging Sponsors NASA, Air Force
Code POLAR (1978-1991) Applications Auroral
Charging, Wakes Sponsor Air Force
Code NASCAP/LEO (1980-1991) Applications High
Voltage Current Collection in Dense
Plasma Sponsor NASA
Code DynaPAC (1991-1999) Applications Complex
dense plasma phenomena Sponsor AFRL
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Surfaces Accumulate Chargeto Achieve Current
Balance
Physically, spacecraft surfaces are bombarded
with charged particles from the ambient plasma.
Secondary electrons are emitted from
spacecraft surfaces.
Electrically, the net plasma currents
charge spacecraft surface capacitances.
The capacitances of the surfaces to
the spacecraft chassis are much larger than those
to the plasma.
Why modeling spacecraft charging is
difficult Currents depend on potentials
fields Timescales vary by orders of
magnitude Geometrical details are
important Differential charging barriers limit
secondary electrons
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NASCAP2K Integrated FrameworkSurface Potentials
Fields
Surface Potentials after charging in NASA
Worst-Case Environment

• Surfaces in 3-D
• Object Toolkit display
• Surface Picking
• Results
• Surface
• Normal vector
• Potential
• Efield
• Current
• Conductor

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Nascap-2k Capabilities

• Tenuous Plasma
• Geosynchronous surface charging
• Solar Wind surface charging
• Potentials and Fields
• Particle Tracking
• Dense Plasma
• External Potentials
• Analytic Space Charge
• Hybrid Space Charge
• Current Collection
• EP Plumes
• Auroral Charging
• PIC
• Maxwells Eq. (Darwin approx)

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Object Toolkit Examples
Users interactively size and edit standard
shapes Construct custom primitives Import from
common CAD programs
SSULI
DMSP
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Examples of recent NASCAP2K Models
MESSENGER Space science mission to Mercury
Concern Engineer for negative charging to aid
ion detection instruments
STEREO Twin spacecraft to lead/lag Earth in
solar orbit Concern Engineer for positive
charging to aid electron detection instruments
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Success Story C/NOFSComm/Nav Outage Forecasting
System
Ram-facing experiments and E-field probes require
equipotential surfaces on ram facets.
SAIC and Spectrum-Astro used Nascap2K to show
that an innovative surface grounding scheme could
reduce ITO (conductive) coating thickness on
solar cells saving 1 M in custom processing.
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Next Success Story DSXDeployed Space Experiment

• NASCAP2K models of DSX antenna-plasma interaction
• 3D electro-dynamic PIC simulation
• Dynamic sheath structure
• Amperes law magnetic perturbations
• Sheath dissipation or radiation?
• In-house parallel processing effort
• Trajectory simulations to help place low energy
  ion and electron sensors

Points represent electron macroparticles.
5 eV ion access with 5 kV sheath
Ion sheath conduction currents