12 research outputs found
Spacecraft potential control for Double Star
International audienceThe spacecraft potential of Double Star TC-1 is positive in large parts of the orbits due to the photo-effect from solar EUV irradiation. These positive potentials typically disturb low energy plasma measurements on board. The potential can be reduced, and thereby the particle measurements improved, by emitting a positive ion beam. This method has successfully been applied on several other spacecraft and it has also been chosen for TC-1. The instrument TC-1/ASPOC is a derivative of the Cluster/ASPOC instruments, from which it has inherited many features. The paper describes the adaptations and further developments made for the ion emitters and the electronics. The instrument performs very well and can support higher beam currents than on Cluster. The expected significant improvement of the low energy particle measurements on board was indeed observed. The modifications of the electron distributions are analysed for a one-time interval when the spacecraft was located in the magnetosheath. The change in the potential due to the ion beam was determined, and first studies of the 3-D electron distributions in response to the spacecraft potential control have been performed, which indicate that the method works as expected
Active spacecraft potential control for Cluster ? implementation and first results
International audienceElectrostatic charging of a spacecraft modifies the distribution of electrons and ions before the particles enter the sensors mounted on the spacecraft body. The floating potential of magnetospheric satellites in sunlight very often reaches several tens of volts, making measurements of the cold (several eV) component of the ambient ions impossible. The plasma electron data become contaminated by large fluxes of photoelectrons attracted back into the sensors. The Cluster spacecraft are equipped with emitters of the liquid metal ion source type, producing indium ions at 5 to 9 keV energy at currents of some tens of microampere. This current shifts the equilibrium potential of the spacecraft to moderately positive values. The design and principles of the operation of the instrument for active spacecraft potential control (ASPOC) are presented in detail. Experience with spacecraft potential control from the commissioning phase and the first two months of the operational phase are now available. The instrument is operated with constant ion current for most of the time, but tests have been carried out with varying currents and a "feedback" mode with the instrument EFW, which measures the spacecraft potential . That has been reduced to values according to expectations. In addition, the low energy electron measurements show substantially reduced fluxes of photoelectrons as expected. The flux decrease in photoelectrons returning to the spacecraft, however, occurs at the expense of an enlarged sheath around the spacecraft which causes problems for boom-mounted probes
Spacecraft potential control for Double Star
The spacecraft potential of Double Star TC-1 is positive in large parts
of the orbits due to the photo-effect from solar EUV irradiation. These
positive potentials typically disturb low energy plasma measurements on
board. The potential can be reduced, and thereby the particle measurements
improved, by emitting a positive ion beam. This method has successfully been
applied on several other spacecraft and it has also been chosen for TC-1.
The instrument TC-1/ASPOC is a derivative of the Cluster/ASPOC
instruments, from which it has inherited many features. The paper describes
the adaptations and further developments made for the ion emitters and the
electronics. The instrument performs very well and can support higher beam
currents than on Cluster. The expected significant improvement of the low
energy particle measurements on board was indeed observed. The modifications
of the electron distributions are analysed for a one-time interval when the
spacecraft was located in the magnetosheath. The change in the potential due
to the ion beam was determined, and first studies of the 3-D electron
distributions in response to the spacecraft potential control have been
performed, which indicate that the method works as expected
Spacecraft potential control aboard Equator-S as a test for Cluster-II
The payload of Equator-S was complemented by
the potential control device (PCD) to stabilise the electric potential of the
spacecraft with respect to the ambient plasma. Low potentials are essential for
accurate measurements of the thermal plasma. The design of PCD is inherited from
instruments for Geotail and Cluster and utilises liquid metal ion sources
generating a beam of indium ions at several keV. The set-up of the instrument
and its interaction with the plasma instruments on board is presented. When the
instrument was switched on during commissioning, unexpectedly high ignition and
operating voltages of some ion emitters were observed. An extensive
investigation was initiated and the results, which lead to an improved design
for Cluster-II, are summarised. The cause of the abnormal behaviour could be
linked to surface contamination of some emitters, which will be monitored and
cured by on-board procedures in future. The mission operations on Equator-S were
not at all affected, because of the high redundancy built into the instrument so
that a sufficient number of perfectly operating emitters were available and were
turned on routinely throughout the mission. Observations of the effect of
spacecraft potential control on the plasma remained limited to just one event on
January 8, 1998, which is analysed in detail. It is concluded that the ion beam
lead to the predicted improvement of the particle measurements even outside the
low density regions of the magnetosphere where the effect of spacecraft
potential control would have been much more pronounced, and that the similar
instruments for the four Cluster-II spacecraft to be launched in 2000 will be
very important to ensure accurate plasma data from this mission.Key words. Space plasma physics (active perturbation
experiments; spacecraft sheaths · wakes · charging; instruments and
techniques
Cassini Plasma Spectrometer electron spectrometer measurements during the Earth swing-by on August 18, 1999
On August 18, 1999, Cassini flew by the Earth on its way to Saturn. The Cassini Earth swing-by was the fastest traversal of the Earth's magnetosphere to date. The spacecraft was traveling at 9.1 R-E hr(-1) (16.1 km s(-1)) and made rapid traversals of several regions of the terrestrial magnetosphere. During the Cassini Earth swing-by the Electron Spectrometer (ELS) collected almost 9 hours of data in the Earth's magnetosphere and almost 10 hours of solar wind data upstream of the Earth. During the pass, Cassini ELS sampled electrons in the solar wind, bow shock, magnetosheath, magnetopause, radiation belts, plasmasphere, plasma sheet, lobes, and crossings of the tail magnetopause. The purpose of this paper is (1) to give a summary of electron observations including the locations of magnetosphere boundary crossings and (2) to assess how the ELS is functioning as it takes measurements in the greatly differing plasma regimes encountered. Results are shown to be mainly consistent with previous observations with a few exceptions. In addition to anticipated results we present evidence of a low-energy field-aligned beam in the plasma sheet and evidence of asymmetry on the dayside and nightside plasmapause position. Preliminary calculations of density and temperature for the solar wind, magnetosheath, and plasma sheet are also presented