Harvey J.E.,University of Central Florida |
Choi N.,University of Central Florida |
Krywonos A.,Florida Space Institute |
Peterson G.L.,Breault Research Organization |
Bruner M.E.,Circle Technology
Optical Engineering | Year: 2010
Image degradation due to scattered radiation is a serious problem in many short-wavelength (x-ray and EUV) imaging systems. Most currently available image analysis codes require the scattering behavior [data on the bidirectional scattering distribution function (BSDF)] as input in order to calculate the image quality from such systems. Predicting image degradation due to scattering effects is typically quite computation-intensive. If using a conventional optical design and analysis code, each geometrically traced ray spawns hundreds of scattered rays randomly distributed and weighted according to the input BSDF. These scattered rays must then be traced through the system to the focal plane using nonsequential ray-tracing techniques. For multielement imaging systems even the scattered rays spawn more scattered rays at each additional surface encountered in the system. In this paper we describe a generalization of Peterson's analytical treatment of in-field stray light in multielement imaging systems. In particular, we remove the smooth-surface limitation that ignores the scattered-scattered radiation, which can be quite large for EUV wavelengths even for state-of-the-art optical surfaces. Predictions of image degradation for a two-mirror EUV telescope with the generalized Peterson model are then numerically validated with the much more computation-intensive ZEMAX® and ASAP® codes. © 2010 SPIE.
Pinilla-Alonso N.,University of Tennessee at Knoxville |
Pinilla-Alonso N.,Florida Space Institute |
de Leon J.,Institute of Astrophysics of Canarias |
Walsh K.J.,Southwest Research Institute |
And 10 more authors.
Icarus | Year: 2016
The inner asteroid belt is an important source of near-Earth asteroids (NEAs). Dynamical studies of the inner asteroid belt have identified several families overlapping in proper orbital elements, including the Polana and Eulalia families that contain a large fraction of the low-albedo asteroids in this region.We present results from two coordinated observational campaigns to characterize this region through near-infrared (NIR) spectroscopy. These campaigns ran from August 2012 to May 2014 and used the NASA Infrared Telescope Facility and the Telescopio Nazionale Galileo. The observations focused on objects within these families or in the background, with low albedo (pv ≤ 0.1) and low inclination (iP ≤ 7°). We observed 63 asteroids (57 never before observed in the NIR): 61 low-albedo objects and two interlopers, both compatible with S- or E- taxonomical types.We found our sample to be spectrally homogeneous in the NIR. The sample shows a continuum of neutral to moderately-red concave-up spectra, very similar within the uncertainties. Only one object in the sample, asteroid (3429) Chuvaev, has a blue spectrum, with a slope (S'=-1.33± 0.21%/1000 Å) significantly different from the average spectrum (S'=0.68± 0.68%/1000 Å). This spectral homogeneity is independent of membership in families or the background population. Furthermore, we show that the Eulalia and Polana families cannot be distinguished using NIR data. We also searched for rotational variability on the surface of (495) Eulalia which we do not detect. (495) Eulalia shows a red concave-up spectrum with an average slope S'=0.91± 0.60%/1000 Å, very similar to the average slope of our sample.The spectra of two targets of sample-return missions, (101955) Bennu, target of NASA's OSIRIS-Rex and (162173) 1999 JU3 target of the Japanese Space Agency's Hayabusa-2, are very similar to our average spectrum, which would be compatible with an origin in this region of the inner belt. © 2016 Elsevier Inc..
Kehoe A.J.E.,University of Central Florida |
Kehoe T.J.J.,University of Aveiro |
Kehoe T.J.J.,Florida Space Institute |
Colwell J.E.,University of Central Florida |
Dermott S.F.,University of Florida
Astrophysical Journal | Year: 2015
We have performed detailed dynamical modeling of the structure of a faint dust band observed in coadded InfraRed Astronomical Satellite data at an ecliptic latitude of 17°that convincingly demonstrates that it is the result of a relatively recent (significantly less than 1 Ma) disruption of an asteroid and is still in the process of forming. We show here that young dust bands retain information on the size distribution and cross-sectional area of dust released in the original asteroid disruption, before it is lost to orbital and collisional decay. We find that the Emilkowalski cluster is the source of this partial band and that the dust released in the disruption would correspond to a regolith layer ∼3 m deep on the ∼10 km diameter source body's surface. The dust in this band is described by a cumulative size-distribution inverse power-law index with a lower bound of 2.1 (implying domination of cross-sectional area by small particles) for dust particles with diameters ranging from a few μm up to a few cm. The coadded observations show that the thermal emission of the dust band structure is dominated by large (mm-cm size) particles. We find that dust particle ejection velocities need to be a few times the escape velocity of the Emilkowalski cluster source body to provide a good fit to the inclination dispersion of the observations. We discuss the implications that such a significant release of material during a disruption has for the temporal evolution of the structure, composition, and magnitude of the zodiacal cloud. © 2015. The American Astronomical Society. All rights reserved..
Agency: Department of Defense | Branch: Air Force | Program: STTR | Phase: Phase I | Award Amount: 99.97K | Year: 2002
Research Support Instruments, Inc., with the aid of the Princeton University Photonics and Optoelectronic Materials (POEM) group and the Florida Space Institute (FSI), proposes the development of a revolutionary, high specific impulse, microchip-sizedthruster for nanosatellite propulsion. This project will combine recent advances in two areas: larger-sized Electron Cyclotron Resonance Heating (ECRH) ion sources developed for ion propulsion (Satori et. al 1996), and a microchip-sized microwave plasmagenerator (Siebert et. al., 1998). The result will be the Microwave ElectroMagneto-Static (MEMS) thruster, an ECRH-ionized electrostatic thruster with a specific impulse appropriate for a xenon-based ion thruster (~2000 seconds). In addition, the MEMSthruster technology will be immediately applicable as an extremely compact electron source for neutralization in other microthrusters such as the micro-ion, micro-Hall, and FEEP thrusters.FSI will develop new sub-micron models and scaling laws for microwave ionization, ECRH heating, and electrostatic acceleration. RSI will design and fabricate a laboratory model of the MEMS thruster/neutralizer at the POEM Micro-Fabrication Laboratories.An array of MEMS thrusters will provide high specific impulse thruster in microchip form. The development of the MEMS thruster will take advantage of an open, underdeveloped market - compact thruster neutralization - to provide immediate commercial application while development and validation of the actual thruster continues. The MEMSthruster represents a unique opportunity to satisfy the need for high specific impulse micro-machined thrusters onboard nanosatellites, as well as a commercially attractive need for compact neutralization in a variety of existing microthrusters.
Eastes R.W.,Florida Space Institute |
Eastes R.W.,University of Central Florida |
Murray D.J.,University of Central Florida |
Aksnes A.,Florida Space Institute |
And 4 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011
A thorough understanding of how the N2 Lyman-Birge-Hopfield (LBH) band emissions vary with altitude is essential to the use of this emission by space-based remote sensors. In this paper, model-to-model comparisons are first performed to elucidate the influence of the solar irradiance spectrum, intrasystem cascade excitation, and O2 photoabsorption on the limb profile. Next, the observed LBH emissions measured by the High resolution Ionospheric and Thermospheric Spectrograph aboard the Advanced Research and Global Observation Satellite are compared with modeled LBH limb profiles to determine which combination of parameters provides the best agreement. The analysis concentrates on the altitude dependence of the LBH (1,1) band, the brightest LBH emission in the observations. In the analysis, satellite drag data are used to constrain the neutral densities used for the data-to-model comparisons. For the average limb profiles on two of the three days analyzed (28, 29, and 30 July 2001), calculations using direct excitation alone give slightly better agreement with the observations than did calculations with cascading between the singlet electronic N2 states (a 1IIg, a′Σ- u, and w 1Δu); however, the differences between the observed profiles and either model are possibly greater than the differences between the models. Nevertheless, both models give excellent agreement with the observations, indicating that current models provide an adequate description of the altitude variation of the N2 LBH (1,1) band emissions. Consequently, when using the LBH bands to remotely sense thermospheric temperatures, which can be used to provide an unprecedented view of the thermosphere, the temperatures derived have a negligible dependence on the model used. Copyright 2011 by the American Geophysical Union.