Meet Grotifer: a CubeSat that Will Provide Highly Accurate
Three-Component Electric Field Measurements throughout the Heliosphere
Abstract
No existing instrument is 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. Grotifer leverages more than fifty
years of expertise in delivering highly accurate spin plane E-field
measurements, while overcoming inaccuracies generated by spin axis
E-field measurements. Its design consists of mounting detectors on two
rotating plates, oriented at 90° 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 (TORPs) provide four instantaneous measurements of the
E-field, and the three E-field components are well-measured by the
rotating detectors. Grotifer (Giant rotifer) is a reference to the
rotifer, also known as the “wheel animalcule”, which has twin crowns
of antenna-like cilia that appear to rotate in all directions. 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 the Grotifer design concept
implemented as a 27-U CubeSat, discuss the important features in the
design and operation of Grotifer, and demonstrate the feasibility of
implementing Grotifer using existing sub-systems and technologies.