The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden to Department SPONSORINGMONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)AFRLNSBXT SPONSORMONITOR'S REPORT NUMBER(S) DISTRIBUTIONIAVAILABILITY STATEMENTApproved for Public Relase; distribution unlimited. SUPPLEMENTARY NOTES - ABSTRACTNascap-2k is a modem spacecraft charging code, replacing the older codes NASCAP/GEO, NASCAP/LEO, POLAR, and DynaPAC. The code builds on the physical principles, mathematical algorithms, and user experience developed over three decades of spacecraft charging research. Capabilities include surface charging in geosynchronous and interplanetary orbits, sheath and wake structure and current collection in low-Earth orbits, and auroral charging. External potential structure and particle trajectories are computed using a finite element method on a nested grid structure and may be visualized within the Nascap-2k interface. Space charge can be treated either analytically, self-consistently with particle trajectories, or by importing plume densities from an external code such as EPIC (Electric Propulsion Interactions Code). Particle-in-cell capabilities are available to study dynamic plasma effects. Auxiliary programs to Nascap-2k include Object Toolkit (for developing spacecraft surface models) and GridTool (for constructing nested grid structures around spacecraft models). The capabilities of the code are illustrated by way of three examples: charging ofa geostationary satellite, self-consistent potentials for a negative probe in a LEO spacecraft wake, and potentials associated with thruster plumes. SUBJECT TERMS Spacecraft chargingPlasma simulation, Nascap-2k AbstractNascap-2k is a modem spacecraft charging code, replacing the older codes NASCAP/GEO, NASCAP/LEO, POLAR, and DynaPAC. The code builds on the physical principles, mathematical algorithms, and user experience developed over three decades of spacecraft charging research.Capabilities include surface charging in geosynchronous and interplanetary orbits, sheath and wake structure and current collection in low-Earth orbits, and auroral charging. External potential structure and particle trajectories are computed using a finite element method on a nested grid structure and may be visualized within the Nascap-2k interface. Space charge can be treated either analytically, self-consistently with particle trajectories, or by importing plume densities from an external code such as EPIC (Electric Propulsion Interactions Code). Particle-in-cell (PIC) capabilities are available to study dynamic plasma effects.Auxiliary programs to Nascap-2k include Object Toolkit (for developing spacecr...