A three-dimensional (3-D), self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take o
n a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characteristic energy of the escaping photoelectrons. All of these conditions are present near the Sun. The numerical solutions also show that the spacecrafts negative potential can be amplified by an ion wake. The negative potential of the ion wake prevents secondary electrons from escaping the part of spacecraft in contact with the wake. These findings may be important for future spacecraft missions that go nearer to the Sun, such as Solar Orbiter and Solar Probe Plus.
This paper is part of the Prelaunch status LFI papers published on JINST (http://www.iop.org/EJ/journal/-page=extra.proc5/1748-0221). Plancks Low Frequency Instrument is an array of 22 pseudo-correlation radiometers at 30, 44, and 70 GHz. Before in
tegrating the overall array assembly, a first set of tests has been performed for each radiometer chain assembly (RCA), consisting of two radiometers. In this paper, we describe Rachel, a software application which has been purposely developed and used during the RCA test campaign to carry out both near-realtime on-line data analysis and data storage (in FITS format) of the raw output from the radiometric chains.
