A probe for measuring spacecraft surface potentials using a direct-gate field effect transistor

Experimental research aimed at the development of a solid state electrostatic field and surface potential sensor has been performed. The overall goal has been to obtain a sensor that overcomes the deficiencies of existing field sensors, including the need for mechanical moving parts and relatively high power consumption. As a result, both the Floating Gate Field Effect Transistor (FGFET) and Direct Gate Field Effect Transistor (DGFET) have been developed and tested. Both devices have been successfully used to measure electrostatic fields over extened periods of time on the order of hours, and a plausible theory for device behavior has been formulated and corroborated with experimental data. Device shortcomings include substantial sensitivity to temperature changes and to extraneous sources of light (DGFET). A moderate amount of random operating point drift has also been observed.