Controlling low frequency interference from direct energy transfer spacecraft power systems

Abstract

Spacecraft exploring solar and planetary plasma effects typically carry a sensitive electric-field measurement instrument operating in the tens of Hz to tens of MHz frequency range. These instruments are subject to unique, non-intuitive interference mechanisms driven by the interaction of direct energy transfer electrical power systems with the surrounding plasma. These mechanisms are not addressed by typical spacecraft EMI control programs based on MIL-STD, Aerospace TOR, or AIAA spacecraft EMI requirements.A direct energy transfer spacecraft power system controls electrical power bus voltage and battery load by switching individual solar array circuits on and off of the system power bus based on battery state of charge and spacecraft loads. This arrangement results in a direct electrical connection between solar array strings and the spacecraft power bus, providing a noise propagation path to the solar arrays.The change in solar array string voltage when switched between loaded and unloaded conditions also changes the net potential of the spacecraft surface with respect to the surrounding plasma, resulting in a "bounce" in the voltage relationship between the spacecraft and the surrounding plasma, which is detected by the e-field sensors as noise.This paper describes these phenomena and the techniques used to assess potential effects on the plasma instrument carried on the Juno spacecraft; summarizes the design approach applied to control these effects; and reviews the methods used to verify the effectiveness of the control approach.

Plasma ion composition measurements for Europa

“…The same can be said for convective flows. The spacecraft itself can be a noisy environment (see Blackburn et al, 2011) and wake effects (Lipatov et al, 2012;Ergun et al, 2010;Maynard, 1998) can further complicate the spacecraft induced electric fields to make these dc measurements very difficult. In Sittler and Strobel (1987) one sees wide swings in spacecraft potential from positive to negative values in the vicinity of Europa which will further complicate the LP measurements.…”

The Juno Waves Investigation

“…A description of all of the electromagnetic interference (EMI) mitigation techniques used on Juno on behalf of Waves is given by Blackburn et al (2011) and summarized in Sect. 4.8.…”

“…To address the sensitivity requirements of the radio instruments on board, a multipronged approach was developed to lower the ambient EMI from the spacecraft (Blackburn et al 2011). For the Waves and MWR measurements above a few MHz, passive filters were installed on each solar array string.…”

WvFEv3, An FPGA-based general purpose digital signal processor for space applications

“…The programmatic nature of the WvFEv3 has led to an implementation that is quite flexible when dealing with algorithms in digital signal processing and basic data manipulations. Table 5-1, Table 5-2 and Table 5 instrument was designed to measure [23]. In an attempt to mitigate the impact of the noise on the scientific data, spare processing cycles on the WvFEv3 were tasked to perform an adaptive noise cancellation algorithm, similar to that found in Bose noisecancelling headphone technology.…”