# Presentation: 448776

## 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

**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**

## Nascap-2K Replaces Earlier Spacecraft-Plasma Codes

_**Code**_**: NASCAP/LEO (1980-1991)**
_**Applications**_**: High Voltage Current Collection in Dense Plasma**
_**Sponsor**_**: NASA**

_**Code**_**: NASCAP/GEO (1976-1984)**
_**Applications**_**: GEO S/C Charging**
_**Sponsors**_**: NASA, Air Force**

*Nascap-2K Replaces Earlier Spacecraft-Plasma Codes*

_**Code**_**: POLAR (1978-1991)**
_**Applications**_**: Auroral Charging, Wakes**
_**Sponsor**_**: Air Force**

_**Code**_**: DynaPAC (1991-1999)**
_**Applications**_**: Complex dense plasma phenomena**
_**Sponsor**_**: AFRL**

## 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

## NASCAP2K Integrated Framework:Surface Potentials & Fields

- Surfaces in 3-D
- Object Toolkit display
- Surface Picking
- Results
- Surface #
- Normal vector
- Potential
**E**field
- Current
- Conductor #

*Surface Potentials after charging in NASA “Worst-Case” Environment*

## 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)

- 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)

- Nascap-2k* Capabilities*

**Notes:**
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.

## Object Toolkit Examples

- DMSP

- SSULI

- Users interactively size and edit standard shapes
- Construct custom primitives
- Import from common CAD programs

**Notes:**
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.

## Examples of recent NASCAP2K Models 

*STEREO: Twin spacecraft to lead/lag Earth in solar orbit*
*Concern: Engineer for positive charging to aid electron detection instruments*

*MESSENGER:  Space science mission to Mercury *
*Concern: Engineer for negative charging to aid ion detection instruments*

## 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.

## 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.

- Ion sheath conduction currents

- 5 eV ion access with 5 kV sheath