The USAF Communication/Navigation Outage
Forecast System satellite, launched into an eccentric low earth
orbit (401 km perigee by 867 km apogee) of 13° inclination on
April 16, 2008, has a set of dc electric field probes that constitute
part of the Vector Electric Field Investigation (VEFI). In order to
obtain the ambient electric field, the v ×B component of electric
field must be subtracted from the VEFI measurements. After
this subtraction and the subtraction of the ambient dc electric
components, a residual dc offset directed toward the spacecraft
wake is still observed, which varies somewhat within an orbit
and on longer timescales. One of the interesting features of these
offsets is that when the satellite is occasionally rotated, the offsets
are reset to their baseline values, only to come back within a
month or so. Various hypotheses have been proposed to explain
the residual dc offsets. In this paper, we explore the possibilities
that either the influence of the spacecraft wake on the sensors or
that modified surface layers on the probe surfaces are producing
the offsets. Nascap-2k and EWB models are used to show the
various influences of the wake and of surface materials. Finally,
a hypothesis is produced that quantitatively explains many of the
salient features of the offsets. The feasibility of using dc electric
field probes in space is reaffirmed. Recommendations for probe
construction on future spacecraft to ameliorate spurious effects
are presented.
The USAF Communication/Navigation OutageForecast System satellite, launched into an eccentric low earthorbit (401 km perigee by 867 km apogee) of 13° inclination onApril 16, 2008, has a set of dc electric field probes that constitutepart of the Vector Electric Field Investigation (VEFI). In order toobtain the ambient electric field, the v ×B component of electricfield must be subtracted from the VEFI measurements. Afterthis subtraction and the subtraction of the ambient dc electriccomponents, a residual dc offset directed toward the spacecraftwake is still observed, which varies somewhat within an orbitand on longer timescales. One of the interesting features of theseoffsets is that when the satellite is occasionally rotated, the offsetsare reset to their baseline values, only to come back within amonth or so. Various hypotheses have been proposed to explainthe residual dc offsets. In this paper, we explore the possibilitiesthat either the influence of the spacecraft wake on the sensors orthat modified surface layers on the probe surfaces are producingthe offsets. Nascap-2k and EWB models are used to show thevarious influences of the wake and of surface materials. Finally,a hypothesis is produced that quantitatively explains many of thesalient features of the offsets. The feasibility of using dc electricfield probes in space is reaffirmed. Recommendations for probeconstruction on future spacecraft to ameliorate spurious effectsare presented.
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