| Popis: |
Summary form only given. The USAF Phillips Lab. Experiment, CHAWS (Charge Hazard And Wake Studies), was flown on two recent Space Shuttle missions as a cooperative experiment on the Univ. of Houston Wake Shield Facility (WSF). CHAWS was designed to investigate the current-voltage (IV) characteristic of a charged object in the wake of another larger body in Low Earth Orbit (LEO), an issue relevant to spacecraft design and operation. The CHAWS experiment measures the WSF ram side plasma by means of three Retarding Potential Analyzers (RPA) which determine the density, temperature and flow direction of the plasma stream. On the wake side, similar RPAs are housed in a large Langmuir probe and used to measure the distribution of wake ions. The Langmuir probe bias is swept up to -5 Kilo Volts and measures the ion current-voltage (IV) characteristic. High voltage sweeps were conducted on both missions in free flight and on the Shuttle Manipulator Arm, providing IV characteristics over a wide range of attitudes and plasma conditions. The numerical plasma simulation of CHAWS is challenging because the plasma density is high enough to require an accurate Poisson solution, time and length scales are large, the geometry is 3D asymmetric with small features, and the ions are collisionless with high relative angular momentum. The Air Force has sponsored the development of two plasma simulation codes that are well suited to modeling CHAWS, POLAR, and more recently DynaPAC. Both codes were used to make preflight predictions, and post Right analysis. This talk will review both the methods and the experiment, and provide a critical comparison. In generally, the code-experiment agreement is quite good. |
