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The proposed Inner Magnetosphere Imager mission will obtain the first simultaneous images of the component regions of the inner magnetosphere and will enable scientists to relate these global images to internal and external influences, as well as local observations. They are performing at the George C. Marshall Space Flight Center a concept definition study of the proposed mission. The baseline mission calls for an instrument complement of approximately seven imagers to fly in an elliptical Earth orbit with an apogee of seven Earth radii (R[sub e]) and a perigee of approximately 4,800 km. Several spacecraft concepts are being considered for the mission. The first concept utilizes a spinning space-craft with a despun platform. The second concept splits the instruments onto two smaller satellites--a spinning spacecraft and a complementary three-axis stabilized spacecraft. Launch options being assessed for the spacecraft range from a Delta 2, for the single- and dual-spacecraft concepts, to dual Taurus launches, for the two smaller spacecraft. An additional option, that of downsizing the mission to fit within the guidelines of the Space Physics Division's new class of solar terrestrial probes, is also being considered.

We present a small Explorer mission, Imagers for the Magnetosphere, Aurora, and Plasmasphere (IMAP), to provide the first global magnetospheric images that will allow a systematic study of major regions of the magnetosphere, their dynamics, and their interactions. The mission objective is to obtain simultaneous images of the inner magnetosphere (ring current and trapped particles), the plasmasphere, the aurora, and auroral upflowing ions. The instruments are (1) a Low Energy Neutral Particle Imager for imaging H and O atoms, separately, in the energy range of ~1 to 30 keV, in several energy passbands; (2) an Energetic Neutral Particle Imager for imaging H atoms in the energy range ~15 to 200 keV and, separately, O atoms in the energy range ~60 to 200 keV, each in several energy passbands; (3) an Extreme-Ultraviolet Imager to obtain images of the plasmasphere (the distribution of cold He + ) by means of He + (30.4 nm) emissions; and (4) a Far-Ultraviolet Imaging Monochromator to provide images of the aurora and the geocorona. All images will be obtained with time and spatial resolutions appropriate to the global and macroscale structures to be observed. IMAP promises new quantitative analyses that will provide great advances in insight and knowledge of global and macroscale magnetospheric parameters. The results expected from IMAP will provide the first large-scale visualization of the ring current, the trapped ion populations, the plasmasphere, and the upflowing auroral ion population. Such images, coupled with simultaneously obtained auroral images, will also provide the initial opportunity to globally interconnect these major magnetospheric regions. The time sequencing of IMAP images will also provide the initial large-scale visualization of magnetospheric dynamics, both in space and time.

Imaging of the terrestrial magnetosphere is possible through the detection of low-energy neutral atoms (LENA5) produced by charge exchange between magnetospheric plasma ions and neutral atoms of the Earth's geocorona. We present calculations of both hydrogen and oxygen line-of-sight LENA fluxes expected on orbit for various plasma regimes as predicted by the Rice University Magnetospheric Specification Model. To decrease the required computation time, we are in the process of adapting our code for massively parallel computers. The speed gains achieved from parallel algorithms are substantial, and we present results from computational runs on the Connection Machine CM-2 data parallel supercomputer. We also estimate expected image count rates and image quality based on realistic instrument geometric factors, energy passbands, neutral atom scattering in the instrument, and image accumulation intervals. The results indicate that LENA imaging instruments will need a geometric factor ( G ) on the order of 0.1 cm 2 sr eV/eV to be capable of imaging storm time ring currents, and a G of 1.0 cm 2 sr eV/eV in order to image the quiet time ring current fluxes, ion injections from the tail, and subsequent ion drifts toward the dayside magnetopause.

The measurement of neutral atom fluxes generated by charge exchange with the Earth's geocorona has recently been shown to provide the capability to image the magnetosphere. We investigate neutral oxygen fluxes produced by charge exchange from the cusp/cleft ion fountain population. Using an empirical cusp/cleft ion fountain model, an empirical variation of the geocoronal neutral hydrogen density with distance, and typical values for charge-exchange cross sections, line-of-sight integrations are performed to calculate the neutral oxygen flux at arbitrary locations in space. The resulting images are evaluated for a set of orbital positions of the proposed HI-LITE small explorer spacecraft. The resulting neutral oxygen fluxes are high enough for imaging with a low-energy neutral atom imaging instrument (ILENA) onboard the spacecraft.

Magnetospheric imaging by remote detection of low-energy neutral atoms (LENA5) that are created by charge exchange between magnetospheric plasma ions and neutral geocoronal atoms has been proposed as a method to provide global information of magnetospheric dynamics. For LENA detection, carbon foils can be implemented to (1) ionize the LENAs and electrostatically remove them from the large background of solar UV scattered by the geocorona to which LENA detectors (e.g. , microchannel plates) are sensitive and (2) generate secondary electrons to provide coincidence and/or LENA trajectory information. Quantification of LENA-foil interactions are crucial in defining LENA imager performance. We present equilibrium charge state and angular scatter distributions for 1- to 30-keV atomic hydrogen, helium, and oxygen transiting nominal 0.5 μg cm2 carbon foils. Results obtained after coating the exit surface of foils with either aluminum or gold suggest that the intended alteration of the exit surface chemistry has no effect on the charge state distributions due to foil contamination from exposure to air. Angular scattering that results from the projectile-foil interaction is quantified and is shown to be independent of the charge state distribution.