High‐voltage interactions in plasma wakes: Simulation and flight measurements from the Charge Hazards and Wake Studies (CHAWS) experiment

Abstract

Abstract. The Charge Hazards and Wake Studies (CHAWS) flight experiment flew on the Wake Shield Facility (WSF) aboard STS-60 and STS-69. The experiment studied highvoltage current collection within the spacecraft wake. The wake-side sensor was a 45-cmlong, biasable cylindrical probe mounted on the 3.66-m-diameter WSF. Operations were performed in free flight and at various attitudes while on the shuttle orbiter remote manipulator system (RMS) arm. Preflight and postflight simulations were performed using the programs Potentials of Large Objects in the Auroral Region (POLAR) and Dynamic Plasma Analysis Code (DynaPAC) and are compared here with the flight results. Both programs perform three-dimensional, self-consistent, steady state plasma simulations. During high-voltage operations the wake-side probe collected current consistent with preflight predictions. In both the flight data and the steady state simulations the current collected has a power law dependence on the potential and has a less than linear dependence on density. Growth of the sheath beyond the WSF edge controls the highvoltage current collection, and kinematic and space charge effects both play important roles in attracting ions into the wake region. Measurements made at low voltage differ from the calculations. The preflight calculations for a pure oxygen plasma predict a collection threshold at -100 V bias. The flight data show little or no threshold, implying a source of ions not accounted for in the simulations. Possible sources for these ions are discussed. BackgroundLow-Earth-orbiting spacecraft have velocities higher than the thermal speed of the ions and lower than the thermal speed of the electrons of the surrounding plasma. Figure 1 shows the basic structure of a spacecraft wake. The ion and electron densities immediately behind the spacecraft are dramatically reduced because only ions with velocities comparable to the spacecraft velocity (corresponding to an energy of about 5 eV) can exist in this "deep wake" region. The electron density would be near uniform were it not for the negative potential due to electron space charge. Samir et al.

Nascap-2k Spacecraft Charging Code Overview

“…The plotted information may be displayed as text on the Text subtab and pasted into a spreadsheet for further processing. To study ion collection by a high voltage object in a spacecraft wake, the CHAWS 16 (Charging Hazards and Wake Studies) experiment was flown about the WSF (Wake Shield Facility) on STS-60 (February 1994) and STS-69 (September 1995). Originally simulated using the DynaPAC code, we use this problem as the primary example of a selfconsistent (between potentials and trajectories) calculation in Nascap-2k.…”

Plasma Density Analysis of CubeSat Wakes in the Earth’s Ionosphere

“…PIC codes are commonly employed to simulate plasma wakes for various conditions [8][9][10][11]. In general, plasma wakes have been seen to be generated by various objects in the space plasma environment: from high-velocity dust grains [8,12,13] to spacecraft [14][15][16] and planetary bodies [9,[17][18][19][20].…”

Plasma Interactions with Spacecraft. Volume 2, NASCAP-2K Scientific Documentation for Version 4.1

“…Computer modeling of flight experiments (such as SCATHA (Spacecraft Charging at High Altitude), [1] the SPEAR (Space Power Experiments Aboard Rockets) [2,3] series, and CHAWS (Charging Hazards and Wake Studies) [4]) has demonstrated excellent ability to predict both steady-state and dynamic interactions between high-voltage spacecraft and the ambient plasma. This ability was also extended to inherently dynamic problems involving threedimensional space charge sheath formation, current flow in the quasi-neutral presheath, breakdown phenomena, plasma kinetics, ionization processes, and the effect of unsteady processes on spacecraft charging.…”