Hybrid Method of Remote Sensing of Electrostatic Potential for Proximity Operations

Touchless determination of electrostatic potential is an enabling technology for a wide variety of orbital robotics applications. This concept is useful for characterizing satellite surfaces during servicing missions, preventing electrostatic discharge during initial contact, and accounting for electrostatic perturbations that affect the relative motion during proximity operations. The electrostatic tractor concept proposes using these forces and torques to detumble or tow uncontrolled satellites to graveyard orbits. All of these applications require the ability to remotely sense the voltage on another spacecraft prior to any physical contact. Two methods have been proposed for remote monitoring of spacecraft electrostatic potential from a co-orbiting craft. This paper considers fusing data from both sensing methods to mitigate the limitations of each method and produce a robust estimate of the surface voltage. The methods involve observing x-ray and electron spectra emitted when energetic electrons, such as those from an electron gun, strike the surface of the target. The electron method provides a highly accurate estimate but is strongly sensitive to the relative geometry of the spacecraft which limits the times during which a usable signal is received. The x-ray method produces a less accurate estimate but is less affected by the target geometry. Experimental results demonstrate that fusing the datasets produces significant improvements in accuracy and geometrical coverage of the voltage estimate across a wide range of conditions, including a rotating target plate. These results are important for future missions which must remotely monitor the potential on a nearby object to ensure mission success.