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

2. Nascap-2K Replaces Earlier Spacecraft-Plasma Codes
Code: NASCAP/GEO ( )
Applications: GEO S/C Charging
Sponsors: NASA, Air Force
Code: POLAR ( )
Applications: Auroral Charging, Wakes
Sponsor: Air Force
Code: NASCAP/LEO ( )
Applications: High Voltage Current Collection in Dense Plasma
Sponsor: NASA
Code: DynaPAC ( )
Applications: Complex dense plasma phenomena
Sponsor: AFRL

3. Surfaces Accumulate Charge to 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

4. NASCAP2K Integrated Framework: Surface 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 #

5. 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
Maxwell’s Eq. (Darwin approx)
We divide plasma interaction problems into tenuous and dense plasma regimes. New with Nascap-2k are, for tenuous plasma, charging in the solar wind, and, for dense plasma, electric propulsion plumes.

6. Object Toolkit Examples
Users interactively size and edit standard shapes
Construct custom primitives
Import from common CAD programs
Here are some examples that show the levels of complexity that can be achieved using OTk. At the top is a truss that was built within OTk and saved for use as a component for other spacecraft, as seen at top left. The MESSENGER model (lower left) shows the sunshade built by editing two concentric cylinders. The strings seen on the solar panels are build by assigning conductor numbers to the surfaces and applying appropriate bias voltage. At lower right is a DMSP model about which you will hear later in this conference.
SSULI
DMSP

7. 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

8. Success Story: C/NOFS Comm/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.

9. Next Success Story: DSX Deployed Space Experiment
NASCAP2K models of DSX antenna-plasma interaction
3D electro-dynamic PIC simulation
Dynamic sheath structure
Ampere’s 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