Experimental Investigation of Total Photoemission Yield from New Satellite Surface Materials

Electron photoemission influences spacecraft surface potentials and the surrounding plasma, and many modern spacecraft use new uncharacterized materials. The angle-dependent photoemission properties were measured for niobium C103 alloy, molybdenum TZM alloy, tantalum tungsten alloy, Elgiloy, graphite lubricant epoxy (DAG213) and titanium nitride at the Bending for Emission Absorption and Reflectivity beam line. The properties of tungsten were also studied to verify the method with past data. The materials were prepared similarly to flight materials. The properties were measured from 0 (normal) to 80 deg (grazing) incidence preannealed and postannealed conditioning of the samples. The yield was measured in all cases for both p and s polarization at each angle of incidence. Results are presented for the photoelectric threshold and photoelectron yield for photon energies up to 30 eV. The work function was also found for each material tested. An analytical equation was then used to fit the normal photoelectron yield for each material to help obtain photocurrents, which were calculated assuming solar illumination at 1 astronomical unit (AU) at normal incidence.