Ground Test for Spacecraft Charging and Discharging at NRIAG-Egypt

National Space Plasma Interactions Unit (N-SPI-U) at NRIAG, EGYPT has been constructed five years ago to investigate the spacecraft charging/discharging phenomena under the effect of the ambient plasma environment in LEO. This is the first time to initiate such tests in Egypt which are very important for the ambitious Egyptian Space Program. Argon gas is used to generate plasma for simulating the plasma properties. The application of this plasma flowing gives the threshold in voltage and current at which potential the current is cut off in the connector. The effect of the plasma on different aluminum alloys (Al-6061, Al-7075, Al-2024) is considered, and results shown that the material deformation and surface degradation can be occurred due to discharge of the ambient plasma and the arc current. In addition we tested the arc and degradation occurred on solar array besides its electric performance after the effects of space plasma.The performance of Si solar cells as a consequence of exposure to LEO plasma environment are investigated. The operating point of the filament of the source is 13 A at 5 V. The potential difference between the filament and the surrounding anode is 450 V and the flowing current is 0.5 A. Diagnostic tools such as Longmuir probe, spectrophotometer and CCD camera are used to describe the plasma properties. Six square shaped Si cells samples of side length of 1cm are supported on a holder located inside the chamber. Three of them are back- connected to a power supply of -100 V, while the others are unbiased. Si solar cells (biased and unbiased) are exposed to the simulated plasma fluency for different times up to 14 h and their alternating current (AC) properties are measured. The results shown the shift of the junction profile toward the front surface and the decreasing in resistance of cell series. However, decreasing of a parasitic Schottky barrier between the front surface and metal grid indicate that, The exposure of the cells after simulated LEO plasma caused a structural change in the diffused donor layer, leading to an increase in the number of electrically active doping atoms.