Extreme Ultraviolet Reflective Grating Characterization and Simulationsfor the Aspera SmallSat Mission

The Aspera SmallSat mission is designed to detect and map the warm-hot gaseous component of the halos of nearby galaxies through long-slit spectroscopy of the ionized O VI emission line (103.2 nm) for the first time. The Aspera Rowland circle type spectrograph uses a toroidal grating coated with a multilayer film consisting of aluminum, lithium fluoride, and magnesium fluoride capping to optimize reflectivity in the extreme ultraviolet (EUV) waveband from 103 to 104nm. We discuss the grating characterization test setup at the University of Arizona (UA), which will validate the multilayer coating and grating efficiency in a UV vacuum chamber. We also simulate the reflectivity of the multilayer thin film coating using IMD IDL software to compare simulated results with measured reflectivity. Additionally, non-sequential ray trace simulations and 3D CAD modeling are used for verification of the test setup. Finally, the implications of the differences between the measured and simulated reflectivity and grating efficiencies are considered, including impact to the mission

Neutron detector development for microsatellites

We present a preliminary design for a novel neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide ((LiInSe2)-Li-6), the first crystal to include Li-6 in the crystalline structure, and a silicon avalanche photodiode (Si-APD). The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha, gamma and neutron radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10 cm x 10 cm x 15 cm, weighs 670 grams and requires 5 V direct current at 3 Watts.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Composition of northern low-albedo regions of Mars: Insights from the Mars Odyssey Gamma Ray Spectrometer

Analysis of data acquired by the Mars Global Surveyor Thermal Emission Spectrometer (TES) instrument led to the identification of two distinct surface types. Surface type 1, lying mostly within southern low-albedo terrain, is likely to be composed of basalt. However, there are several competing mineralogical models for surface type 2, which is found primarily in northern low-albedo terrain. We attempt to identify which models better agree with element concentrations determined through the Gamma Subsystem (GS) of the Gamma Ray Spectrometer (GRS) instrument suite aboard the Mars Odyssey spacecraft. We have binned GS data over threshold regions derived from maps of surface types 1 and 2 and examined the spatial correlation of element concentrations with surface type 2. The elements we have examined are Cl, Fe, H, K, Si, and Th. Our results show that K concentration, Th concentration, and the areal abundance of surface type 2 are strongly correlated, with significant enrichment of both K and Th in regions representative of surface type 2. In addition, Si does not appear to be significantly enriched in surface type 2. These results are more consistent with surface type 2 originating from a compositionally distinct mantle source than the aqueous alteration of basalts. Copyright 2006 by the American Geophysical Union

Equatorial and midlatitude distribution of chlorine measured by Mars Odyssey GRS

The 2001 Mars Odyssey Gamma Ray Spectrometer (GRS) has made the first measurement of the equatorial and midlatitude distribution of C1 at the near-surface of Mars. A mean concentration value of 0.49 wt% C1 has been determined from a grand sum of GRS spectra collected over the planet excluding high-latitude regions. C1 is significantly enriched within the upper few tens of centimeters of the surface relative to the Martian meteorites and estimates for the bulk composition of the planet. However, C1 is not homogeneously distributed and varies by a factor of ∼4 even after smoothing of data with a 10°-arc-radius filter. Several contiguous, geographically large (\u3e20°) regions of high and low C1 concentrations are present. In particular, a region centered over the Medusae Fossae Formation west of Tharsis shows significantly elevated C1. A large region north of Syrtis Major extending into Utopia Planitia in the northern hemisphere shows the lowest C1 concentrations. On the basis of hierarchical multivariate correlations, C1 is positively associated with H while negatively associated with Si and thermal inertia. We discuss four possible geologic mechanisms (aeolian, volcanic, aqueous, and hydrothermal) that may have affected the C1 distribution seen by GRS. While some of the distribution may be due to C1-rich dust deposits transported by aeolian processes, this mechanism does not appear to account for all of the observed variability. We propose that reactions with volcanic exhalations may have been important for enriching C1 in Medusae Fossae Formation material. Copyright 2006 by the American Geophysical Union

Bulk composition and early differentiation of Mars

We report the concentrations of K, Th, and Fe on the Martian surface, as determined by the gamma ray spectrometer onboard the 2001 Mars Odyssey spacecraft. K and Th are not uniformly distributed on Mars. K ranges from 2000 to 6000 ppm; Th ranges from 0.2 to 1 ppm. The K/Th ratio varies from 3000 to 9000, but over 95% of the surface has K/Th between 4000 and 7000. Concentrations of K and Th are generally higher than those in basaltic Martian meteorites (K = 200-2600 ppm; Th = 0.1-0.7 ppm), indicating that Martian meteorites are not representative of the bulk crust. The average K/Th in the crust is 5300, consistent with the Wänke-Dreibus model composition for bulk silicate Mars. Fe concentrations support the idea that bulk Mars is enriched in FeO compared to Earth. The differences in K/Th and FeO between Earth and Mars are consistent with the planets accreting from narrow feeding zones. The concentration of Th on Mars does not vary as much as it does on the Moon (where it ranges from 0.1 to 12 ppm), suggesting that the primary differentiation of Mars differed \u27from that of the Moon. If the average Th concentration (0.6 ppm) of the surface is equal to the average of the entire crust, the crust cannot be thicker than about 118 km. If the crust is about 57 km thick, as suggested by geophysical studies, then about half the Th is concentrated in the crust. Copyright 2006 by the American Geophysical Union