In-flight Performance and Initial Results of Plasma Energy Angle and Composition Experiment (PACE) on SELENE (Kaguya)

MAP-PACE (MAgnetic field and Plasma experiment—Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its ～1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV–9 keV and 9 eV–16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q–28 keV/q and 7 eV/q–29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the dayside of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere.     

The IMPACT Solar Wind Electron Analyzer (SWEA)

SWEA, the solar wind electron analyzers that are part of the IMPACT in situ investigation for the STEREO mission, are described. They are identical on each of the two spacecraft. Both are designed to provide detailed measurements of interplanetary electron distribution functions in the energy range 1～3000 eV and in a 120°×360° solid angle sector. This energy range covers the core or thermal solar wind plasma electrons, and the suprathermal halo electrons including the field-aligned heat flux or strahl used to diagnose the interplanetary magnetic field topology. The potential of each analyzer will be varied in order to maintain their energy resolution for spacecraft potentials comparable to the solar wind thermal electron energies. Calibrations have been performed that show the performance of the devices are in good agreement with calculations and will allow precise diagnostics of all of the interplanetary electron populations at the two STEREO spacecraft locations.     

The Solar Electron and Proton Telescope for the STEREO Mission

The Solar Electron and Proton Telescope (SEPT), one of four instruments of the Solar Energetic Particle (SEP) suite for the IMPACT investigation, is designed to provide the three-dimensional distribution of energetic electrons and protons with good energy and time resolution. This knowledge is essential for characterizing the dynamic behaviour of CME associated and solar flare associated events. SEPT consists of two dual double-ended magnet/foil particle telescopes which cleanly separate and measure electrons in the energy range from 30–400 keV and protons from 60–7?000 keV. Anisotropy information on a non-spinning spacecraft is provided by the two separate telescopes: SEPT-E looking in the ecliptic plane along the Parker spiral magnetic field both towards and away from the Sun, and SEPT-NS looking vertical to the ecliptic plane towards North and South. The dual set-up refers to two adjacent sensor apertures for each of the four view directions: one for protons, one for electrons. The double-ended set-up refers to the detector stack with view cones in two opposite directions: one side (electron side) is covered by a thin foil, the other side (proton side) is surrounded by a magnet. The thin foil leaves the electron spectrum essentially unchanged but stops low energy protons. The magnet sweeps away electrons but lets ions pass. The total geometry factor for electrons and protons is 0.52 cm²?sr and 0.68 cm²?sr, respectively. This paper describes the design and calibration of SEPT as well as the scientific objectives that the instrument will address.     

The Electron and ion Plasma Experiment for Fast

The ion and electron plasma experiment on the Fast Auroral Snapshot satellite (FAST) is designed to measure pitch-angle distributions of suprathermal auroral electrons and ions with high sensitivity, wide dynamic range, good energy and angular resolution, and exceptional time resolution. These measurements support the primary scientific goal of the FAST mission to understand the physical processes responsible for auroral particle acceleration and heating, and associated wave-particle interactions. The instrument includes a complement of 8 pairs of `Top Hat' electrostatic analyzer heads with microchannel plate (MCP) electron multipliers and discrete anodes to provide angle resolved measurements. The analyzers are packaged in four instrument stacks, each containing four analyzers. These four stacks are equally spaced around the spacecraft spin plane. Analyzers mounted on opposite sides of the spacecraft operate in pairs such that their individual 180° fields of view combine to give an unobstructed 360° field of view in the spin plane. The earth's magnetic field is within a few degrees of the spin plane during most auroral crossings, so the time resolution for pitch-angle distribution measurements is independent of the spacecraft spin period. Two analyzer pairs serve as electron and ion spectrometers that obtain distributions of 48 energies at 32 angles every 78 ms. Their standard energy ranges are 4 eV to 32 keV for electrons and 3 eV to 24 keV for ions. These sensors also have deflection plates that can track the magnetic field direction within 10° of the spin plane to resolve narrow, magnetic field-aligned beams of electrons and ions. The remaining six analyzer pairs collectively function as an electron spectrograph, resolving distributions with 16 contiguous pitch-angle bins and a selectable trade-off of energy and time resolution. Two examples of possible operating modes are a maximum time resolution mode with 16 angles and 6 energies every 1.63 ms, or a maximum energy resolution mode with 16 angles and 48 energies every 13 ms. The instrument electronics include mcp pulse amplifiers and counters, high voltage supplies, command/data interface circuits, and diagnostic test circuits. All data formatting, commanding, timing and operational control of the plasma analyzer instrument are managed by a central instrument data processing unit (IDPU), which controls all of the FAST science instruments. The IDPU creates slower data modes by averaging the high rate measurements collected on the spacecraft. A flexible combination of burst mode data and slower `survey' data are defined by IDPU software tables that can be revised by command uploads. Initial flight results demonstrate successful achievement of all measurement objectives.     

Tropospheric New Particle Formation and the Role of Ions

The Suprathermal Electron (STE) instrument, part of the IMPACT investigation on both spacecraft of NASA’s STEREO mission, is designed to measure electrons from ～2 to ～100 keV. This is the primary energy range for impulsive electron/³He-rich energetic particle events that are the most frequently occurring transient particle emissions from the Sun, for the electrons that generate solar type III radio emission, for the shock accelerated electrons that produce type II radio emission, and for the superhalo electrons (whose origin is unknown) that are present in the interplanetary medium even during the quietest times. These electrons are ideal for tracing heliospheric magnetic field lines back to their source regions on the Sun and for determining field line lengths, thus probing the structure of interplanetary coronal mass ejections (ICMEs) and of the ambient inner heliosphere. STE utilizes arrays of small, passively cooled thin window silicon semiconductor detectors, coupled to state-of-the-art pulse-reset front-end electronics, to detect electrons down to ～2 keV with about 2 orders of magnitude increase in sensitivity over previous sensors at energies below ～20 keV. STE provides energy resolution of ΔE/E～10–25% and the angular resolution of ～20° over two oppositely directed ～80°×80° fields of view centered on the nominal Parker spiral field direction.     

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE _FWHM/E≈15 %. The dominant ion species (H⁺, He⁺, and O⁺) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.     

The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager

The IBEX-Hi Neutral Atom Imager of the Interstellar Boundary Explorer (IBEX) mission is designed to measure energetic neutral atoms (ENAs) originating from the interaction region between the heliosphere and the local interstellar medium (LISM). These ENAs are plasma ions that have been heated in the interaction region and neutralized by charge exchange with the cold neutral atoms of the LISM that freely flow through the interaction region. IBEX-Hi is a single pixel ENA imager that covers the ENA spectral range from 0.38 to 6 keV and shares significant energy overlap and overall design philosophy with the IBEX-Lo sensor. Because of the anticipated low flux of these ENAs at 1 AU, the sensor has a large geometric factor and incorporates numerous techniques to minimize noise and backgrounds. The IBEX-Hi sensor has a field-of-view (FOV) of 6.5°×6.5° FWHM, and a 6.5°×360° swath of the sky is imaged over each spacecraft spin. IBEX-Hi utilizes an ultrathin carbon foil to ionize ENAs in order to measure their energy by subsequent electrostatic analysis. A multiple coincidence detection scheme using channel electron multiplier (CEM) detectors enables reliable detection of ENAs in the presence of substantial noise. During normal operation, the sensor steps through six energy steps every 12 spacecraft spins. Over a single IBEX orbit of about 8 days, a single 6.5°×360° swath of the sky is viewed, and re-pointing of the spin axis toward the Sun near perigee of each IBEX orbit moves the ecliptic longitude by about 8° every orbit such that a full sky map is acquired every six months. These global maps, covering the spectral range of IBEX-Hi and coupled to the IBEX-Lo maps at lower and overlapping energies, will answer fundamental questions about the structure and dynamics of the interaction region between the heliosphere and the LISM.     

The THEMIS ESA Plasma Instrument and In-flight Calibration

The THEMIS plasma instrument is designed to measure the ion and electron distribution functions over the energy range from a few eV up to 30 keV for electrons and 25 keV for ions. The instrument consists of a pair of “top hat” electrostatic analyzers with common 180°×6° fields-of-view that sweep out 4π steradians each 3 s spin period. Particles are detected by microchannel plate detectors and binned into six distributions whose energy, angle, and time resolution depend upon instrument mode. On-board moments are calculated, and processing includes corrections for spacecraft potential. This paper focuses on the ground and in-flight calibrations of the 10 sensors on five spacecraft. Cross-calibrations were facilitated by having all the plasma measurements available with the same resolution and format, along with spacecraft potential and magnetic field measurements in the same data set. Lessons learned from this effort should be useful for future multi-satellite missions.     

Origins of Anisotropic 40–300 keV Electron Events Observed at Low and High Latitudes

Using a survey of anisotropic electron events in the energy range of ～40–300 keV observed by HI-SCALE on Ulysses, we have selected several time intervals during 1999 when Ulysses traveled from about 20° S at 5.2 AU (January 1999) to 42° S at 4.2 AU (January 2000). We compare these events with observations at ～1 AU using the nearly identical instrument, EPAM on ACE. In order to study the solar origins of these electrons using the imaging Nançay Radioheliograph, we further restricted the list of events to those in which interplanetary magnetic field lines with origins on the visible solar disk, intersected Ulysses. We find that not all the anisotropic electron events are observed by both spacecraft and there exists a strong dependence on the spacecraft's magnetic connection back to the Sun. We have identified the solar origin for five electron events using radio observations, and correlate these with interplanetary type-III radio emissions using the WIND/WAVES experiment.     

The Burst Alert Telescope (BAT) on the SWIFT Midex Mission

he burst alert telescope (BAT) is one of three instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution, a sensitivity of ∼10⁻⁸ erg s⁻¹ cm⁻², and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor.     

The Jupiter Energetic Particle Detector Instrument (JEDI) Investigation for the Juno Mission

The Jupiter Energetic Particle Detector Instruments (JEDI) on the Juno Jupiter polar-orbiting, atmosphere-skimming, mission to Jupiter will coordinate with the several other space physics instruments on the Juno spacecraft to characterize and understand the space environment of Jupiter’s polar regions, and specifically to understand the generation of Jupiter’s powerful aurora. JEDI comprises 3 nearly-identical instruments and measures at minimum the energy, angle, and ion composition distributions of ions with energies from H:20 keV and O: 50 keV to >1 MeV, and the energy and angle distribution of electrons from <40 to >500 keV. Each JEDI instrument uses microchannel plates (MCP) and thin foils to measure the times of flight (TOF) of incoming ions and the pulse height associated with the interaction of ions with the foils, and it uses solid state detectors (SSD’s) to measure the total energy (E) of both the ions and the electrons. The MCP anodes and the SSD arrays are configured to determine the directions of arrivals of the incoming charged particles. The instruments also use fast triple coincidence and optimum shielding to suppress penetrating background radiation and incoming UV foreground. Here we describe the science objectives of JEDI, the science and measurement requirements, the challenges that the JEDI team had in meeting these requirements, the design and operation of the JEDI instruments, their calibrated performances, the JEDI inflight and ground operations, and the initial measurements of the JEDI instruments in interplanetary space following the Juno launch on 5 August 2011. Juno will begin its prime science operations, comprising 32 orbits with dimensions 1.1×40 RJ, in mid-2016.     

The STEREO Mission: An Introduction

The twin STEREO spacecraft were launched on October 26, 2006, at 00:52 UT from Kennedy Space Center aboard a Delta 7925 launch vehicle. After a series of highly eccentric Earth orbits with apogees beyond the moon, each spacecraft used close flybys of the moon to escape into orbits about the Sun near 1 AU. Once in heliospheric orbit, one spacecraft trails Earth while the other leads. As viewed from the Sun, the two spacecraft separate at approximately 44 to 45 degrees per year. The purposes of the STEREO Mission are to understand the causes and mechanisms of coronal mass ejection (CME) initiation and to follow the propagation of CMEs through the inner heliosphere to Earth. Researchers will use STEREO measurements to study the mechanisms and sites of energetic particle acceleration and to develop three-dimensional (3-D) time-dependent models of the magnetic topology, temperature, density and velocity of the solar wind between the Sun and Earth. To accomplish these goals, each STEREO spacecraft is equipped with an almost identical set of optical, radio and in situ particles and fields instruments provided by U.S. and European investigators. The SECCHI suite of instruments includes two white light coronagraphs, an extreme ultraviolet imager and two heliospheric white light imagers which track CMEs out to 1 AU. The IMPACT suite of instruments measures in situ solar wind electrons, energetic electrons, protons and heavier ions. IMPACT also includes a magnetometer to measure the in situ magnetic field strength and direction. The PLASTIC instrument measures the composition of heavy ions in the ambient plasma as well as protons and alpha particles. The S/WAVES instrument uses radio waves to track the location of CME-driven shocks and the 3-D topology of open field lines along which flow particles produced by solar flares. Each of the four instrument packages produce a small real-time stream of selected data for purposes of predicting space weather events at Earth. NOAA forecasters at the Space Environment Center and others will use these data in their space weather forecasting and their resultant products will be widely used throughout the world. In addition to the four instrument teams, there is substantial participation by modeling and theory oriented teams. All STEREO data are freely available through individual Web sites at the four Principal Investigator institutions as well as at the STEREO Science Center located at NASA Goddard Space Flight Center.     

The Relativistic Electron-Proton Telescope (REPT) Instrument on Board the Radiation Belt Storm Probes (RBSP) Spacecraft: Characterization of Earth’s Radiation Belt High-Energy Particle Populations

Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of radiation belt science. In order to measure cleanly and separately both the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to ～20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above E=100 MeV. The instrument has a large geometric factor (g=0.2 cm²?sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10^?2–10⁶ particles/cm²?s?sr?MeV) and energy spectra (ΔE/E～25 %) throughout the slot and outer radiation belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT.     

The STEREO/IMPACT Magnetic Field Experiment

The magnetometer on the STEREO mission is one of the sensors in the IMPACT instrument suite. A single, triaxial, wide-range, low-power and noise fluxgate magnetometer of traditional design—and reduced volume configuration—has been implemented in each spacecraft. The sensors are mounted on the IMPACT telescoping booms at a distance of ～3 m from the spacecraft body to reduce magnetic contamination. The electronics have been designed as an integral part of the IMPACT Data Processing Unit, sharing a common power converter and data/command interfaces. The instruments cover the range ±65,536 nT in two intervals controlled by the IDPU (±512 nT; ±65,536 nT). This very wide range allows operation of the instruments during all phases of the mission, including Earth flybys as well as during spacecraft test and integration in the geomagnetic field. The primary STEREO/IMPACT science objectives addressed by the magnetometer are the study of the interplanetary magnetic field (IMF), its response to solar activity, and its relationship to solar wind structure. The instruments were powered on and the booms deployed on November 1, 2006, seven days after the spacecraft were launched, and are operating nominally. A magnetic cleanliness program was implemented to minimize variable spacecraft fields and to ensure that the static spacecraft-generated magnetic field does not interfere with the measurements.     

Solar Wind Electron Proton Alpha Monitor (SWEPAM) for the Advanced Composition Explorer

The Solar Wind Electron Proton Alpha Monitor (SWEPAM) experiment provides the bulk solar wind observations for the Advanced Composition Explorer (ACE). These observations provide the context for elemental and isotopic composition measurements made on ACE as well as allowing the direct examination of numerous solar wind phenomena such as coronal mass ejections, interplanetary shocks, and solar wind fine structure, with advanced, 3-D plasma instrumentation. They also provide an ideal data set for both heliospheric and magnetospheric multi-spacecraft studies where they can be used in conjunction with other, simultaneous observations from spacecraft such as Ulysses. The SWEPAM observations are made simultaneously with independent electron and ion instruments. In order to save costs for the ACE project, we recycled the flight spares from the joint NASA/ESA Ulysses mission. Both instruments have undergone selective refurbishment as well as modernization and modifications required to meet the ACE mission and spacecraft accommodation requirements. Both incorporate electrostatic analyzers whose fan-shaped fields of view sweep out all pertinent look directions as the spacecraft spins. Enhancements in the SWEPAM instruments from their original forms as Ulysses spare instruments include (1) a factor of 16 increase in the accumulation interval (and hence sensitivity) for high energy, halo electrons; (2) halving of the effective ion-detecting CEM spacing from ∼5° on Ulysses to ∼2.5° for ACE; and (3) the inclusion of a 20° conical swath of enhanced sensitivity coverage in order to measure suprathermal ions outside of the solar wind beam. New control electronics and programming provide for 64-s resolution of the full electron and ion distribution functions and cull out a subset of these observations for continuous real-time telemetry for space weather purposes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)

The Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) is a five telescope package, which has been developed for the Solar Terrestrial Relation Observatory (STEREO) mission by the Naval Research Laboratory (USA), the Lockheed Solar and Astrophysics Laboratory (USA), the Goddard Space Flight Center (USA), the University of Birmingham (UK), the Rutherford Appleton Laboratory (UK), the Max Planck Institute for Solar System Research (Germany), the Centre Spatiale de Leige (Belgium), the Institut d’Optique (France) and the Institut d’Astrophysique Spatiale (France). SECCHI comprises five telescopes, which together image the solar corona from the solar disk to beyond 1 AU. These telescopes are: an extreme ultraviolet imager (EUVI: 1–1.7 R_⊙), two traditional Lyot coronagraphs (COR1: 1.5–4 R_⊙ and COR2: 2.5–15 R_⊙) and two new designs of heliospheric imagers (HI-1: 15–84 R_⊙ and HI-2: 66–318 R_⊙). All the instruments use 2048×2048 pixel CCD arrays in a backside-in mode. The EUVI backside surface has been specially processed for EUV sensitivity, while the others have an anti-reflection coating applied. A multi-tasking operating system, running on a PowerPC CPU, receives commands from the spacecraft, controls the instrument operations, acquires the images and compresses them for downlink through the main science channel (at compression factors typically up to 20×) and also through a low bandwidth channel to be used for space weather forecasting (at compression factors up to 200×). An image compression factor of about 10× enable the collection of images at the rate of about one every 2–3 minutes. Identical instruments, except for different sizes of occulters, are included on the STEREO-A and STEREO-B spacecraft.     

Overview of the New Horizons Science Payload

The New Horizons mission was launched on 2006 January 19, and the spacecraft is heading for a flyby encounter with the Pluto system in the summer of 2015. The challenges associated with sending a spacecraft to Pluto in less than 10 years and performing an ambitious suite of scientific investigations at such large heliocentric distances (>32 AU) are formidable and required the development of lightweight, low power, and highly sensitive instruments. This paper provides an overview of the New Horizons science payload, which is comprised of seven instruments. Alice provides moderate resolution (～3–10 Å FWHM), spatially resolved ultraviolet (～465–1880 Å) spectroscopy, and includes the ability to perform stellar and solar occultation measurements. The Ralph instrument has two components: the Multicolor Visible Imaging Camera (MVIC), which performs panchromatic (400–975 nm) and color imaging in four spectral bands (Blue, Red, CH₄, and NIR) at a moderate spatial resolution of 20 μrad/pixel, and the Linear Etalon Imaging Spectral Array (LEISA), which provides spatially resolved (62 μrad/pixel), near-infrared (1.25–2.5 μm), moderate resolution (λ/δ λ～240–550) spectroscopic mapping capabilities. The Radio Experiment (REX) is a component of the New Horizons telecommunications system that provides both radio (X-band) solar occultation and radiometry capabilities. The Long Range Reconnaissance Imager (LORRI) provides high sensitivity (V<18), high spatial resolution (5 μrad/pixel) panchromatic optical (350–850 nm) imaging capabilities that serve both scientific and optical navigation requirements. The Solar Wind at Pluto (SWAP) instrument measures the density and speed of solar wind particles with a resolution ΔE/E<0.4 for energies between 25 eV and 7.5 keV. The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) measures energetic particles (protons and CNO ions) in 12 energy channels spanning 1–1000 keV. Finally, an instrument designed and built by students, the Venetia Burney Student Dust Counter (VB-SDC), uses polarized polyvinylidene fluoride panels to record dust particle impacts during the cruise phases of the mission.     

Solar Origin of Anisotropic Electron Events observed by ULYSSES and ACE

We investigate the solar origin of energetic collimated electron events observed in situ by the EPAM and/or HISCALE particle experiments aboard the ACE and ULYSSES spacecraft, respectively. This study has been performed for two months, September and October 1999 when Ulysses was magnetically connected to the solar disk at heliolongitudes visible at the Earth. The two spacecraft were separated by about 35° in latitude and up to 60° in longitude. In this paper, results are described for one period only, October 24–November 1, 1999. It is found that not all the anisotropic events are observed by both spacecrafts; there exists a strong dependence on the spacecraft's magnetic connection back to the Sun. This revised version was published online in August 2006 with corrections to the Cover Date.