Grotifer: a Profound Change in the Double-Probe Instrument Design to Provide Highly Accurate Three-Component Electric Field Measurements throughout the Heliosphere

No instrument is currently capable of consistently measuring all three components of the DC and low frequency electric field (E-field) throughout the heliosphere with sufficient accuracy to determine the smallest, and most geophysically relevant component: the E-field component parallel to the background magnetic field. E-field measurements in the heliosphere are usually made on spinning spacecraft equipped with two disparate types of double probe antennas: (1) long wire booms in the spin plane, and (2) ~10 times shorter rigid booms along the spin axis. On such systems, the potential difference (signal + noise) is divided by the boom length to produce a resultant E-field component. Because the spacecraft-associated errors are larger nearer the spacecraft, the spin plane components of the E-field are well measured while the spin axis component are poorly measured. As a result, uncertainty in the parallel E-field is usually greater than its measured value. The new design proposed by the Grotifer team is a way to overcome this difficulty. It consists of mounting detectors on two rotating plates, oriented at 90 degrees with respect to each other, on a non-rotating central body. Each rotating plate has two component measurements of the E-field such that the Twin Orthogonal Rotating Platforms provide four instantaneous measurements of the E-field, and the three E-field components are well-measured by the rotating detectors. Grotifer marks a profound change in E-field instrument design that represents the best path forward to close the observational gap that currently hampers resolution of significant science questions at the forefront of space plasma physics research. Here, we present recent advances in the development of the Grotifer design and we demonstrate the feasibility of its implementation in a 27-U CubeSat designed for a Low Earth Orbit mission.