Global Imaging of Proton and Electron Aurorae in the far Ultraviolet

The IMAGE spacecraft carries three FUV photon imagers, the Wideband Imaging Camera (WIC) and two channels, SI-12 and SI-13, of the Spectrographic Imager. These provide simultaneous global images, which can be interpreted in terms of the precipitating particle types (protons and electrons) and their energies. IMAGE FUV is the first space-borne global imager that can provide instantaneous global images of the proton precipitation. At times a bright auroral spot, rich in proton precipitation, is observed on the dayside, several degrees poleward of the auroral zone. The spot was identified as the footprint of the merging region of the cusp that is located on lobe field lines when IMF B_z was northward. This identification was based on compelling statistical evidence showing that the appearance and location of the spot is consistent with the IMF B_z and B_y directions. The intensity of the spot is well correlated with the solar wind dynamic pressure and it was found that the direct entry of solar wind particles could account for the intensity of the observed spot without the need for any additional acceleration. Another discovery was the observation of dayside sub-auroral proton arcs. These arcs were observed in the midday to afternoon MLT sector. Conjugate satellite observations showed that these arcs were generated by pure proton precipitation. Nightside auroras and their relationship to substorm phases were studied through single case studies and in a superimposed epoch analysis. It was found that generally there is substantial proton precipitation prior to substorms and the proton intensity only doubles at substorm onset while the electron auroral brightness increases on average by a factor of 5 and sometimes by as much as a factor of 10. Substorm onset occurs in the central region of the pre-existing proton precipitation. Assuming that nightside protons are precipitating from a quasi-stable ring current at its outer regions where the field lines are distorted by neutral sheet currents we can associate the onset location with this region of closed but distorted field lines relatively close to the earth. Our results also show that protons are present in the initial poleward substorm expansion however later they are over taken by the electrons. We also find that the intensity of the substorms as quantified by the intensity of the post onset electron precipitation is correlated with the intensity of the proton precipitation prior to the substorms, highlighting the role of the pre-existing near earth plasma in the production of the next substorm.     

Dayside Proton Aurora: Comparisons between Global MHD Simulations and IMAGE Observations

The IMAGE mission provides a unique opportunity to evaluate the accuracy of current global models of the solar wind interaction with the Earth's magnetosphere. In particular, images of proton auroras from the Far Ultraviolet Instrument (FUV) onboard the IMAGE spacecraft are well suited to support investigations of the response of the Earth's magnetosphere to interplanetary disturbances. Accordingly, we have modeled two events that occurred on June 8 and July 28, 2000, using plasma and magnetic field parameters measured upstream of the bow shock as input to three-dimensional magnetohydrodynamic (MHD) simulations. This paper begins with a discussion of images of proton auroras from the FUV SI-12 instrument in comparison with the simulation results. The comparison showed a very good agreement between intensifications in the auroral emissions measured by FUV SI-12 and the enhancement of plasma flows into the dayside ionosphere predicted by the global simulations. Subsequently, the IMAGE observations are analyzed in the context of the dayside magnetosphere's topological changes in magnetic field and plasma flows inferred from the simulation results. Finding include that the global dynamics of the auroral proton precipitation patterns observed by IMAGE are consistent with magnetic field reconnection occurring as a continuous process while the IMF changes in direction and the solar wind dynamic pressure varies. The global simulations also indicate that some of the transient patterns observed by IMAGE are consistent with sporadic reconnection processes. Global merging patterns found in the simulations agree with the antiparallel merging model, though locally component merging might broaden the merging region, especially in the region where shocked solar wind discontinuities first reach the magnetopause. Finally, the simulations predict the accretion of plasma near the bow shock in the regions threaded by newly open field lines on which plasma flows into the dayside ionosphere are enhanced. Overall the results of these initial comparisons between global MHD simulation results and IMAGE observations emphasize the interplay between reconnection and dynamic pressure processes at the dayside magnetopause, as well as the intricate connection between the bow shock and the auroral region.     

A far ultraviolet imager for the International Solar-Terrestrial Physics Mission

The aurorae are the result of collisions with the atmosphere of energetic particles that have their origin in the solar wind, and reach the atmosphere after having undergone varying degrees of acceleration and redistribution within the Earth's magnetosphere. The global scale phenomenon represented by the aurorae therefore contains considerable information concerning the solar-terrestrial connection. For example, by correctly measuring specific auroral emissions, and with the aid of comprehensive models of the region, we can infer the total energy flux entering the atmosphere and the average energy of the particles causing these emissions. Furthermore, from these auroral emissions we can determine the ionospheric conductances that are part of the closing of the magnetospheric currents through the ionosphere, and from these we can in turn obtain the electric potentials and convective patterns that are an essential element to our understanding of the global magnetosphere-ionosphere-thermosphere-mesosphere. Simultaneously acquired images of the auroral oval and polar cap not only yield the temporal and spatial morphology from which we can infer activity indices, but in conjunction with simultaneous measurements made on spacecraft at other locations within the magnetosphere, allow us to map the various parts of the oval back to their source regions in the magnetosphere. This paper describes the Ultraviolet Imager for the Global Geospace Sciences portion of the International Solar-Terrestrial Physics program. The instrument operates in the far ultraviolet (FUV) and is capable of imaging the auroral oval regardless of whether it is sunlit or in darkness. The instrument has an 8° circular field of view and is located on a despun platform which permits simultaneous imaging of the entire oval for at least 9 hours of every 18 hour orbit. The three mirror, unobscured aperture, optical system (f/2.9) provides excellent imaging over this full field of view, yielding a per pixel angular resolution of 0.6 milliradians. Its FUV filters have been designed to allow accurate spectral separation of the features of interest, thus allowing quantitative interpretation of the images to provide the parameters mentioned above. The system has been designed to provide ten orders of magnitude blocking against longer wavelength (primarily visible) scattered sunlight, thus allowing the first imaging of key, spectrally resolved, FUV diagnostic features in the fully sunlit midday aurorae. The intensified-CCD detector has a nominal frame rate of 37 s, and the fast optical system has a noise equivalent signal within one frame of 10R. The instantaneous dynamic range is >1000 and can be positioned within an overall gain range of 10⁴, allowing measurement of both the very weak polar cap emissions and the very bright aurora. The optical surfaces have been designed to be sufficiently smooth to permit this dynamic range to be utilized without the scattering of light from bright features into the weaker features. Finally, the data product can only be as good as the degree to which the instrument performance is characterized and calibrated. In the VUV, calibration of an an imager intended for quantitative studies is a task requiring some pioneering methods, but it is now possible to calibrate such an instrument over its focal plane to an accuracy of ±10%. In summary, very recent advances in optical, filter and detector technology have been exploited to produce an auroral imager to meet the ISTP objectives.     

The Ultraviolet Spectrograph on NASA’s Juno Mission

The ultraviolet spectrograph instrument on the Juno mission (Juno-UVS) is a long-slit imaging spectrograph designed to observe and characterize Jupiter’s far-ultraviolet (FUV) auroral emissions. These observations will be coordinated and correlated with those from Juno’s other remote sensing instruments and used to place in situ measurements made by Juno’s particles and fields instruments into a global context, relating the local data with events occurring in more distant regions of Jupiter’s magnetosphere. Juno-UVS is based on a series of imaging FUV spectrographs currently in flight—the two Alice instruments on the Rosetta and New Horizons missions, and the Lyman Alpha Mapping Project on the Lunar Reconnaissance Orbiter mission. However, Juno-UVS has several important modifications, including (1) a scan mirror (for targeting specific auroral features), (2) extensive shielding (for mitigation of electronics and data quality degradation by energetic particles), and (3) a cross delay line microchannel plate detector (for both faster photon counting and improved spatial resolution). This paper describes the science objectives, design, and initial performance of the Juno-UVS.     

Far ultraviolet imaging from the IMAGE spacecraft. 2. Wideband FUV imaging

The Far Ultraviolet Wideband Imaging Camera (WIC) complements the magnetospheric images taken by the IMAGE satellite instruments with simultaneous global maps of the terrestrial aurora. Thus, a primary requirement of WIC is to image the total intensity of the aurora in wavelength regions most representative of the auroral source and least contaminated by dayglow, have sufficient field of view to cover the entire polar region from spacecraft apogee and have resolution that is sufficient to resolve auroras on a scale of 1 to 2 latitude degrees. The instrument is sensitive in the spectral region from 140–190 nm. The WIC is mounted on the rotating IMAGE spacecraft viewing radially outward and has a field of view of 17° in the direction parallel to the spacecraft spin axis. Its field of view is 30° in the direction perpendicular to the spin axis, although only a 17°×17° image of the Earth is recorded. The optics was an all-reflective, inverted Cassegrain Burch camera using concentric optics with a small convex primary and a large concave secondary mirror. The mirrors were coated by a special multi-layer coating, which has low reflectivity in the visible and near UV region. The detector consists of a MCP-intensified CCD. The MCP is curved to accommodate the focal surface of the concentric optics. The phosphor of the image intensifier is deposited on a concave fiberoptic window, which is then coupled to the CCD with a fiberoptic taper. The camera head operates in a fast frame transfer mode with the CCD being read approximately 30 full frames (512×256 pixel) per second with an exposure time of 0.033 s. The image motion due to the satellite spin is minimal during such a short exposure. Each image is electronically distortion corrected using the look up table scheme. An offset is added to each memory address that is proportional to the image shift due to satellite rotation, and the charge signal is digitally summed in memory. On orbit, approximately 300 frames will be added to produce one WIC image in memory. The advantage of the electronic motion compensation and distortion correction is that it is extremely flexible, permitting several kinds of corrections including motions parallel and perpendicular to the predicted axis of rotation. The instrument was calibrated by applying ultraviolet light through a vacuum monochromator and measuring the absolute responsivity of the instrument. To obtain the data for the distortion look up table, the camera was turned through various angles and the input angles corresponding to a pixel matrix were recorded. It was found that the spectral response peaked at 150 nm and fell off in either direction. The equivalent aperture of the camera, including mirror reflectivities and effective photocathode quantum efficiency, is about 0.04 cm². Thus, a 100 Rayleigh aurora is expected to produce 23 equivalent counts per pixel per 10 s exposure at the peak of instrument response.     

Validation of techniques for space based remote sensing of auroral precipitation and its ionospheric effects

Knowledge of the spatial distribution of auroral precipitation and its associated ionospheric effects is important both to scientific studies of the Earth's environment and successful operation of defense and communication systems. Observations with the best spatial and temporal coverage are obtained through remote sensing from space-based platforms. Various techniques have been used, including the detection of visible, ultraviolet and X-ray emissions produced by the precipitating particles. Interpretation of the measurements is enabled through theoretical modeling of the interaction of precipitating particles with atmospheric constituents. A great variety of auroral precipitation exists, with each kind differing in the type and energy distribution of the particles, as well as in its spatial and temporal behavior. Viable remote sensing techniques must be able to distinguish at least the species of particle, the total energy flux, and the average energy. Methods based on visible, ultraviolet and X-ray emissions meet these requirements to varying degrees. These techniques and the associated space instrumentation have evolved in parallel over the last two decades. Each of the methods has been tested using simultaneous measurements made by space-based imaging systems and ground-based measurements made by radars and optical instruments. These experiments have been extremely helpful in evaluating the performance and practicality of the instruments and the results have been crucial in improving instrument design for future remote sensing platforms. The next decade will see continued development and test of remote sensing instruments and the measurements, in addition to providing important operational data, will be increasingly more critical in addressing a number of scientific problems in auroral and atmospheric physics.     

Auroral flares and solar flares

The morphology of development of auroral flares (magnetospheric substorms) for both electron and proton auroras is summarized, based on ground-based as well as rocket-borne and satellite-borne data with specific reference to the morphology of solar flares.The growth phase of an auroral flare is produced by the inflow of the solar wind energy into the magnetosphere by the reconnection mechanism between the solar wind field and the geomagnetic field, thus the neutral and plasma sheets in the magnetotail attaining their minimum thickness with a great stretch of the geomagnetic fluxes into the tail.The onset of the expansion phase of an auroral flare is represented by the break-up of electron and proton auroras, which is associated with strong auroral electrojets, a sudden increase in CNA, VLF hiss emissions and characteristic ULF emissions. The auroral break-up is triggered by the relaxation of stretched magnetic fluxes caused by cutting off of the tail fluxes at successively formed X-type neutral lines in the magnetotail.The resultant field-aligned currents flowing between the tailward magnetosphere and the polar ionosphere produce the field-aligned anomalous resistivity owing to the electrostatic ion-cyclotron waves; the electrical potential drop thus increased further accelerates precipitating charged particles with a result of the intensification of both the field-aligned currents and the auroral electrojet. It seems that the rapid building-up of this positive feedback system for precipitating charged particles is responsible for the break-up of an auroral flare.     

IMAGE mission overview

The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission is the first mission in NASA's MIDEX (Mid-size Explorer) program. It is the first satellite mission that is dedicated to imaging the Earth's magnetosphere. IMAGE will utilize the techniques of ultraviolet imaging, neutral atom imaging, and radio plasma imaging to map out global distributions of the electron and proton aurora; the helium ions of the plasmasphere; the ionospheric ion outflow; the medium-energy ions of the near-Earth plasma sheet, ring current, and polar cusp; the high-energy ions of the ring current and trapped radiation belts; and the total plasma density from the ionosphere out to the magnetopause. The imaging perspective is from an elliptical polar orbit with apogee at latitudes from 40° to 90° in the northern hemisphere. For ultraviolet and neutral atom imaging, the time resolution is set by the two-minute spin period of the IMAGE spacecraft, which will be sufficient to track the development of magnetospheric substorms. An important feature of the IMAGE mission is its completely open data set with no proprietary data or intervals. All data, along with software needed for plotting and analysis, will be available within 24 hours of acquisition.     

The Far Ultra-Violet Imager on the Icon Mission

ICON Far UltraViolet (FUV) imager contributes to the ICON science objectives by providing remote sensing measurements of the daytime and nighttime atmosphere/ionosphere. During sunlit atmospheric conditions, ICON FUV images the limb altitude profile in the shortwave (SW) band at 135.6 nm and the longwave (LW) band at 157 nm perpendicular to the satellite motion to retrieve the atmospheric O/N₂ ratio. In conditions of atmospheric darkness, ICON FUV measures the 135.6 nm recombination emission of \(\mathrm{O}^{+}\) ions used to compute the nighttime ionospheric altitude distribution. ICON Far UltraViolet (FUV) imager is a Czerny–Turner design Spectrographic Imager with two exit slits and corresponding back imager cameras that produce two independent images in separate wavelength bands on two detectors. All observations will be processed as limb altitude profiles. In addition, the ionospheric 135.6 nm data will be processed as longitude and latitude spatial maps to obtain images of ion distributions around regions of equatorial spread F. The ICON FUV optic axis is pointed 20 degrees below local horizontal and has a steering mirror that allows the field of view to be steered up to 30 degrees forward and aft, to keep the local magnetic meridian in the field of view. The detectors are micro channel plate (MCP) intensified FUV tubes with the phosphor fiber-optically coupled to Charge Coupled Devices (CCDs). The dual stack MCP-s amplify the photoelectron signals to overcome the CCD noise and the rapidly scanned frames are co-added to digitally create 12-second integrated images. Digital on-board signal processing is used to compensate for geometric distortion and satellite motion and to achieve data compression. The instrument was originally aligned in visible light by using a special grating and visible cameras. Final alignment, functional and environmental testing and calibration were performed in a large vacuum chamber with a UV source. The test and calibration program showed that ICON FUV meets its design requirements and is ready to be launched on the ICON spacecraft.     

Atmosphere-magnetosphere-ionosphere system mami

The effects on the terrestrial atmosphere and ionosphere of energy and momentum sources of magnetospheric origin are investigated theoretically. Parameters measured by instruments on board the GGS spacecraft and by the GGS ground-based networks are used as inputs to the models that quantify the magnetosphere-ionosphere-thermosphere coupling. Images of the aurora acquired at ultraviolet, visible and X-ray wavelengths by instruments on board the POLAR spacecraft are particularly useful in this investigation by yielding good spatial coverage and high time resolution of the aurora.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

ATS-6 Solar Cosmic Ray and Trapped Particle Experiment

The Solar Cosmic Ray and Trapped Particle Experiment was designed to study the entry, propagation, and loss of solar cosmic rays and the acceleration and loss of trapped electrons and protons in the magnetosphere. Two orthogonal proton and alpha partical telescopes measure protons from 300 keV to 250 MeV and alphas from 2 MeV to 200 MeV. Electron spectrometers measure electrons from 50 keV to 1 MeV and are used in conjunction with the 300-keV to 1.2-MeV proton channels to study the injection of electrons and protons into the magnetosphere during substorms. Two solar cosmic ray events were observed during the first four months of operation. The first of these began on July 3, 1974, and is probably one of the more complicated events in recent years. There were numerous flares and sudden commencements as well as intense fluxes of low energy plasma with a severly perturbed magnetosphere. The second solar cosmic ray event was smaller and was associated with an isolated east limb flare. The first increase was observed on September 11, 1974.     

The Relativistic Proton Spectrometer (RPS) for the Radiation Belt Storm Probes Mission

The Relativistic Proton Spectrometer (RPS) on the Radiation Belt Storm Probes spacecraft is a particle spectrometer designed to measure the flux, angular distribution, and energy spectrum of protons from ～60 MeV to ～2000 MeV. RPS will investigate decades-old questions about the inner Van Allen belt proton environment: a nearby region of space that is relatively unexplored because of the hazards of spacecraft operation there and the difficulties in obtaining accurate proton measurements in an intense penetrating background. RPS is designed to provide the accuracy needed to answer questions about the sources and losses of the inner belt protons and to obtain the measurements required for the next-generation models of trapped protons in the magnetosphere. In addition to detailed information for individual protons, RPS features count rates at a 1-second timescale, internal radiation dosimetry, and information about electrostatic discharge events on the RBSP spacecraft that together will provide new information about space environmental hazards in the Earth’s magnetosphere.     

Far ultraviolet imaging from the IMAGE spacecraft. 3. Spectral imaging of Lyman-α and OI 135.6 nm

Two FUV Spectral imaging instruments, the Spectrographic Imager (SI) and the Geocorona Photometer (GEO) provide IMAGE with simultaneous global maps of the hydrogen (121.8 nm) and oxygen 135.6 nm components of the terrestrial aurora and with observations of the three dimensional distribution of neutral hydrogen in the magnetosphere (121.6 nm). The SI is a novel instrument type, in which spectral separation and imaging functions are independent of each other. In this instrument, two-dimensional images are produced on two detectors, and the images are spectrally filtered by a spectrograph part of the instrument. One of the two detectors images the Doppler-shifted Lyman- while rejecting the geocoronal `cold Ly-, and another detector images the OI 135.6 nm emission. The spectrograph is an all-reflective Wadsworth configuration in which a grill arrangement is used to block most of the cold, un-Doppler-shifted geocoronal emission at 121.567 nm. The SI calibration established that the upper limit of transmission at cold geocoronal Ly- is less than 2%. The measured light collecting efficiency was 0.01 and 0.008 cm² at 121.8 and at 135.6 nm, respectively. This is consistent with the size of the input aperture, the optical transmission, and the photocathode efficiency. The expected sensitivity is 1.8×10^–2 and 1.3×10^–2 counts per Rayleigh per pixel for each 5 s viewing exposure per satellite revolution (120 s). The measured spatial resolution is better than the 128×128 pixel matrix over the 15°×15° field of view in both wavelength channels. The SI detectors are photon counting devices using the cross delay line principle. In each detector a triple stack microchannel plate (MCP) amplifies the photo-electronic charge which is then deposited on a specially configured anode array. The position of the photon event is measured by digitizing the time delay between the pulses detected at each end of the anode structures. This scheme is intrinsically faster than systems that use charge division and it has a further advantage that it saturates more gradually at high count rates. The geocoronal Ly- is measured by a three-channel photometer system (GEO) which is a separate instrument. Each photometer has a built in MgF₂ lens to restrict the field of view to one degree and a ceramic electron multiplier with a KBr photocathode. One of the tubes is pointing radially outward perpendicular to the axis of satellite rotation. The optic of the other two subtend 60° with the rotation axis. These instruments take data continuously at 3 samples per second and rely on the combination of satellite rotation and orbital motion to scan the hydrogen cloud surrounding the earth. The detective efficiencies (effective quantum efficiency including windows) of the three tubes at Ly- are between 6 and 10%.     

The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) NASA Mission-of-Opportunity

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a NASA Explorer Mission-of-Opportunity to stereoscopically image the Earth’s magnetosphere for the first time. TWINS extends our understanding of magnetospheric structure and processes by providing simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes ENAs from 1–100 keV with high angular (～4°×4°) and time (～1-minute) resolution. The TWINS Ly-α monitor measures the geocoronal hydrogen density to aid in ENA analysis while environmental sensors provide contemporaneous measurements of the local charged particle environments. By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft, TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the magnetosphere for the first time. This “instrument paper” documents the TWINS design, construction, calibration, and initial results. Finally, the appendix of this paper describes and documents the Southwest Research Institute (SwRI) instrument calibration facility; this facility was used for all TWINS instrument-level calibrations.     

Auroral Plasma Acceleration Above Martian Magnetic Anomalies

Aurora is caused by the precipitation of energetic particles into a planetary atmosphere, the light intensity being roughly proportional to the precipitating particle energy flux. From auroral research in the terrestrial magnetosphere it is known that bright auroral displays, discrete aurora, result from an enhanced energy deposition caused by downward accelerated electrons. The process is commonly referred to as the auroral acceleration process. Discrete aurora is the visual manifestation of the structuring inherent in a highly magnetized plasma. A strong magnetic field limits the transverse (to the magnetic field) mobility of charged particles, effectively guiding the particle energy flux along magnetic field lines. The typical, slanted arc structure of the Earth’s discrete aurora not only visualizes the inclination of the Earth’s magnetic field, but also illustrates the confinement of the auroral acceleration process. The terrestrial magnetic field guides and confines the acceleration processes such that the preferred acceleration of particles is frequently along the magnetic field lines. Field-aligned plasma acceleration is therefore also the signature of strongly magnetized plasma. This paper discusses plasma acceleration characteristics in the night-side cavity of Mars. The acceleration is typical for strongly magnetized plasmas – field-aligned acceleration of ions and electrons. The observations map to regions at Mars of what appears to be sufficient magnetization to support magnetic field-aligned plasma acceleration – the localized crustal magnetizations at Mars (Acuña et al., 1999). Our findings are based on data from the ASPERA-3 experiment on ESA’s Mars Express, covering 57 orbits traversing the night-side/eclipse of Mars. There are indeed strong similarities between Mars and the Earth regarding the accelerated electron and ion distributions. Specifically acceleration above Mars near local midnight and acceleration above discrete aurora at the Earth – characterized by nearly monoenergetic downgoing electrons in conjunction with nearly monoenergetic upgoing ions. We describe a number of characteristic features in the accelerated plasma: The “inverted V” energy-time distribution, beam vs temperature distribution, altitude distribution, local time distribution and connection with magnetic anomalies. We also compute the electron energy flux and find that the energy flux is sufficient to cause weak to medium strong (up to several tens of kR 557.7 nm emissions) aurora at Mars. Monoenergetic counterstreaming accelerated ions and electrons is the signature of field-aligned electric currents and electric field acceleration. The topic is reasonably well understood in terrestrial magnetospheric physics, although some controversy still remains on details and the cause-effect relationships. We present a potential cause-effect relationship leading to auroral plasma acceleration in the nightside cavity of Mars – the downward acceleration of electrons supposedly manifesting itself as discrete aurora above Mars.     

Advanced Technologies Demonstrated by the Miniature Integrated Camera and Spectrometer (MICAS) Aboard Deep Space 1

MICAS is an integrated multi-channel instrument that includes an ultraviolet imaging spectrometer (80–185 nm), two high-resolution visible imagers (10–20 μrad/pixel, 400–900 nm), and a short-wavelength infrared imaging spectrometer (1250–2600 nm). The wavelength ranges were chosen to maximize the science data that could be collected using existing semiconductor technologies and avoiding the need for multi-octave spectrometers. It was flown on DS1 to validate technologies derived from the development of PICS (Planetary Imaging Camera Spectrometer). These technologies provided a novel systems approach enabling the miniaturization and integration of four instruments into one entity, spanning a wavelength range from the UV to IR, and from ambient to cryogenic temperatures with optical performance at a fraction of a wavelength. The specific technologies incorporated were: a built-in fly-by sequence; lightweight and ultra-stable, monolithic silicon-carbide construction, which enabled room-temperature alignment for cryogenic (85–140 K) performance, and provided superb optical performance and immunity to thermal distortion; diffraction-limited, shared optics operating from 80 to 2600 nm; advanced detector technologies for the UV, visible and short-wavelength IR; high-performance thermal radiators coupled directly to the short-wave infrared (SWIR) detector optical bench, providing an instrument with a mass less than 10 kg, instrument power less than 10 W, and total instrument cost of less than ten million dollars. The design allows the wavelength range to be extended by at least an octave at the short wavelength end and to ∼50 microns at the long wavelength end. Testing of the completed instrument demonstrated excellent optical performance down to 77 K, which would enable a greatly reduced background for longer wavelength detectors. During the Deep Space 1 Mission, MICAS successfully collected images and spectra for asteroid 9969 Braille, Mars, and comet 19/P Borrelly. The Borrelly encounter was a scientific hallmark providing the first clear, high resolution images and excellent, short-wavelength infrared spectra of the surface of an active comet’s nucleus.     

The Juno Radiation Monitoring (RM) Investigation

The Radiation Monitoring Investigation of the Juno Mission will actively retrieve and analyze the noise signatures from penetrating radiation in the images of Juno’s star cameras and science instruments at Jupiter. The investigation’s objective is to profile Jupiter’s \(>10\mbox{-MeV}\) electron environment in regions of the Jovian magnetosphere which today are still largely unexplored. This paper discusses the primary instruments on Juno which contribute to the investigation’s data suite, the measurements of camera noise from penetrating particles, spectral sensitivities and measurement ranges of the instruments, calibrations performed prior to Juno’s first science orbit, and how the measurements may be used to infer the external relativistic electron environment.     

Energetic Particles Investigation (EPI)

The Energetic Particles Investigation (EPI) instrument operates during the pre-entry phase of the Galileo Probe. The major science objective is to study the energetic particle population in the innermost regions of the Jovian magnetosphere — within 4 radii of the cloud tops — and into the upper atmosphere. To achieve these objectives the EPI instrument will make omnidirectional measurements of four different particle species — electrons, protons, alpha-particles, and heavy ions (Z > 2). Intensity profiles with a spatial resolution of about 0.02 Jupiter radii will be recorded. Three different energy range channels are allocated to both electrons and protons to provide a rough estimate of the spectral index of the energy spectra. In addition to the omnidirectional measurements, sectored data will be obtained for certain energy range electrons, protons, and alpha-particles to determine directional anisotropies and particle pitch angle distributions. The detector assembly is a two-element telescope using totally depleted, circular silicon surfacebarrier detectors surrounded by a cylindrical tungsten shielding with a wall thickness of 4.86 g cm^-2. The telescope axis is oriented normal to the spherical surface of the Probe's rear heat shield which is needed for heat protection of the scientific payload during the Probe's entry into the Jovian atmosphere. The material thickness of the heat shield determines the lower energy threshold of the particle species investigated during the Probe's pre-entry phase. The EPI instrument is combined with the Lightning and Radio Emission Detector (LRD) such that the EPI sensor is connected to the LRD/EPI electronic box. In this way, both instruments together only have one interface of the Probe's power, command, and data unit.     

Galileo Ultraviolet Spectrometer experiment

The Galileo ultraviolet spectrometer experiment uses data obtained by the Ultraviolet Spectrometer (UVS) mounted on the pointed orbiter scan platform and from the Extreme Ultraviolet Spectrometer (EUVS) mounted on the spinning part of the orbiter with the field of view perpendicular to the spin axis. The UVS is a Ebert-Fastie design that covers the range 113–432 nm with a wavelength resolution of 0.7 nm below 190 and 1.3 nm at longer wavelengths. The UVS spatial resolution is 0.4 deg × 0.1 deg for illuminated disc observations and 1 deg × 0.1 deg for limb geometries. The EUVS is a Voyager design objective grating spectrometer, modified to cover the wavelength range from 54 to 128 nm with wavelength resolution 3.5 nm for extended sources and 1.5 nm for point sources and spatial resolution of 0.87 deg × 0.17 deg. The EUVS instrument will follow up on the many Voyager UVS discoveries, particularly the sulfur and oxygen ion emissions in the Io torus and molecular and atomic hydrogen auroral and airglow emissions from Jupiter. The UVS will obtain spectra of emission, absorption, and scattering features in the unexplored, by spacecraft, 170–432 nm wavelength region. The UVS and EUVS instruments will provide a powerful instrument complement to investigate volatile escape and surface composition of the Galilean satellites, the Io plasma torus, micro- and macro-properties of the Jupiter clouds, and the composition structure and evolution of the Jupiter upper atmosphere.