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NASA NTRS1978

Mathematical modeling and simulation of the space shuttle imaging radar antennas

Simulations of space shuttle synthetic aperture radar antennas under the influence of space environmental conditions were carried out at L, C, and X-band. Mathematical difficulties in modeling large, non-planar array antennas are discussed, and an approximate modeling technique is presented. Results for several antenna error conditions are illustrated in far-field profile patterns, earth surface footprint contours, and summary graphs.

Campbell, R. W.↗
NASA NTRS2001

Analysis of High Contrast Imaging Techniques for Space Based Direct Planetary Imaging

We report on our ongoing investigations of a number of techniques for direct detection and imaging of Earth-like planets around nearby stellar sources. Herein, we give a quantitative analysis of these techniques and compare and contrast them via computer simulations. The techniques we will be reporting on are Bracewell Interferometry, Nisenson Apodized Square Aperture, and Coronagraphic masking techniques. We parameterize our results with respect to wavelength, aperture size, effects of mirror speckle, both mid- and high-spatial frequency, detector and photon noise as well pointing error. The recent numerous detections of Jupiter and Saturn like planets has driven a resurgence in research of space based high contrast imaging techniques for direct planetary imaging. Work is currently ongoing for concepts for NASA's Terrestrial Planet Finder mission and a number of study teams have been funded. The authors are members of one team.

Lyon, Richard G.↗
NASA NTRS1999

Achievements in the Development of Space-borne Imaging Radar

This article describes past and current achievements in the development of space-borne imaging radar technology and discusses possibilities for the future. The article focuses on space-borne capabilities for civil and scientific purposes.

space-borne imaging radar interferometry↗
NASA NTRS2006

Stellar Imager (SI) Space Mission: Stellar Magnetic Activity

The Stellar Imager (SI) is a UV-Optical, Space-Based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and stellar interiors (via asteroseismology) and of the Universe in general. SI is identified as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes: The 0.1 mas resolution of this deep-space telescope will transform point sources into extended sources, and snapshots into evolving views. SI'S science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI'S prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we will discuss the science goals of the SI Mission and a mission architecture that could meet those goals.

Carpenter, K. G.↗
NASA NTRS1987

Monsoon flood boundary delineation and damage assessment using space borne imaging radar and Landsat data

Space-borne synthetic aperture radar (SAR) data acquired by the Shuttle Imaging Radar-B (SIR-B) Program and Landsat Multispectral Scanner Subsystem (MSS) Data from Landsat 4 were used to map flood boundaries for the assessment of flood damage in the Peoples Republic of Bangladesh. The cloud penetrating capabilities of the L-band radar provided a clear picture of the hydrologic conditions of the surface during a period of inclement weather at the end of the wet phase of the 1984 monsoon. The radar image data were digitally processed to geometrically rectify the pixel geometry and were filtered to subdue radar image speckle effects. Contrast enhancement techniques and density slicing were used to create discrete land-cover categories corresponding to surface conditions present at the time of the Shuttle overflight. The radar image classification map was digitally registered to a spectral signature classification map of the area derived from Landsat MSS data collected two weeks prior to the SIR-B mission. Classification accuracy comparisons were made between the radar and MSS classification maps, and flood boundary and flood damage assessment measurements were made with the merged data by adding the classifications and inventorying the land-cover classes inundated at the time of flooding.

Imhoff, Marc L.↗
NASA NTRS2008

Technical Aspects of the Space Telescope Imaging Spectrograph Repair (STIS-R)

In August 2004, the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ceased operation, due to a failure in the Side 2 Low Voltage Power Supply (LVPS2). LVPS2 provided power to the entire instrument, including all detectors and mechanisms. Following the LVPS2 failure, a team was assembled to analyze the fault and to determine if STIS repair (STIS-R) was feasible. The team concluded that by replacing a power supply board within LVPS2, STIS could be brought back to full functionality. STIS-R will be conducted during Servicing Mission 4 (SM4), and will consist of replacing the power supply board and a new passive cooling system. STIS-R will restore full function of the instrument with one of the two redundant sides of the instrument. In this presentation, we focus on the technical aspects associated with STISR.

Rinehart, Stephen↗
NASA NTRS2008

Technical Aspects of the Space Telescope Imaging Spectrograph Repair (STIS-R)

In August 2004, the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ceased operation, due to a failure in the Side 2 Low Voltage Power Supply (LVPS2). The LVPS2 provided power to the entire instrument, including all detectors and mechanisms. The failure precluded movement of any STIS mechanism, leaving the instrument fully shuttered. The fault analysis team concluded that by replacing a board containing a new LVPS2 power supply, STIS could be brought back to full functionality. During Servicing Mission 4 (SM4), STIS-R will replace this board. STIS-R will restore full function of the instrument with one of the two redundant sides of the instrument.

Rinehart, Stephen A.↗
NASA NTRS2019

Lifetimes and Occurrence Rates of Dark Vortices on Neptune from 25 Years of Hubble Space Telescope Images

We scoured the full set of blue-wavelength Hubble Space Telescope images of Neptune, finding one additional dark spot in new Hubble data beyond those discovered in 1989, 1994, 1996, and 2015. We report the complete disappearance of the SDS-2015 dark spot, using new Hubble data taken on 2018 September 9–10, as part of the Outer Planet Atmospheres Legacy (OPAL) program. Overall, dark spots in the full Hubble data set have lifetimes of at least one to two years, and no more than six years. We modeled a set of dark spots randomly distributed in time over the latitude range on Neptune that is visible from Earth, finding that the cadence of archival Hubble images would have detected about 70% of these spots if their lifetimes are only one year, or about 85%–95% of simulated spots with lifetimes of two or more years. Based on the Hubble data set, we conclude that dark spots have average occurrence rates of one dark spot every four to six years. Many numerical models to date have simulated much shorter vortex lifetimes, so our findings provide constraints that may lead to improved understanding of Neptune’s wind field, stratification, and humidity.

Hsu, Andrew I.↗
NASA NTRS1995

Gas near the center of 30 Doradus as revealed by Hubble Space Telescope images

We present images of a 40 pc region of the 30 Doradus nebula centered about 1 arcminute north of the luminous star cluster R136 in the Large Magellanic Cloud. The region was imaged with the Hubble Space Telescope (HST) Wide Field Camera through H alpha, (S II), and stellar continuum filters. These data allow us to examine this region of star formation and the breakup of the cloud around R136 on a scale of 0.027 pc per pixel. We also present a complementary ground-based echelle spectrum of the H alpha and (N II) emission lines in this region. In the images one sees an extensive filamentary structure surrounding regions that have been hollowed out by R136 and other massive stars in the area. The (S II) image shows a sharper, more filamentary appearance than the H alpha image, and the filaments are offset in (S II) generally away from R136. These characteristics are indicative of ionization fronts that are outlining the neutral material and dust features. We also find fingers of enhanced (S II) emission located about 90 sec to the northwest of R136. The (S II) fingers appear to be readiating generally from a common region, and we suggest that they are composed of material ablated from the high density gas of the ionization fronts and entrained with the flow of the stellar winds from R136. We find that a small knot of emission resolves into two shells of about 0.5 pc diameter, each of which encircles one or two stars. One of the stars has been identified as an early main-sequence O star by Walborn & Blades (1987), and the shell could be a young wind-blown bubble. We also find a parabolic-shaped arc at the head of a long cone that opens up away from R136. The arc is located near a luminous candidate protostar identified by Hyland et al. (1992).

Hunter, Deidre A.↗
NASA NTRS1994

Hubble Space Telescope imaging of the Seyfert 2 galaxy NGC 2110

Hubble Space Telescope (HST) images of the Seyfert 2 galaxy NGC 2110 in the emission lines of (O III) lambda lambda-4959, 5007 and H-alpha + (N II) lambda lambda-6548, 6584 and the nearby continuum are presented. After deconvolution, the resolution of these images is approximately 0.1 sec, corresponding to a linear scale of approximately 23 pc at the assumed distance (46.8 Mpc) to this galaxy. The dominant line emission is associated with a strongly curved, narrow, 1 sec (230 pc) long feature emanating from the nucleus to the north. The morphology of this feature suggests that it may represent gas flowing outward from the nucleus (perhaps as a 'jet'). While this optical emission-line feature and the jetlike radio emission extend along a similar P.A., their detailed brightness distributions are loosely anticorrelated. In particular, there is no line emission associated with the off-nuclear 6 cm peaks and only weak radio emission along the optical 'jet'. On a larger scale, there is an S-shaped distribution of ionized gas (seen best in H-alpha) extending approximately 4 sec north and south of the nucleus. Ground-based kinematical data suggest this larger scale component represents normally rotating, ambient, interstellar gas photoionized by the central source. A continuum color map derived from HST observations shows evidence for an unresolved region (scale less than 23 pc) of very strong reddening at the location of the optical and radio nucleus. The location and size of the reddened region are consistent with obscuration by a dusty torus, but the observed reddening provides only a lower limit (A(sub V) greater than or equal to 4.6(sub -1.7 sup +1.2) mag) on the amount of obscuration to the nucleus. Nevertheless, this obscuration is sufficient to account for the 'energy deficit' previously reported in this object.

Mulchaey, John S.↗
NASA NTRS2010

Jupiter After the 2009 Impact: Hubble Space Telescope Imaging of the Impact-Generated Debris and Its Temporal Evolution

We report Hubble Space Telescope images of Jupiter during the aftermath of an impact by an unknown object in 2009 July, The 2009 impact-created debris field evolved more slowly than those created in 1994 by the collision of the tidally disrupted comet D/Shoemaker-Levy 9 (SL9). The slower evolution, in conjunction with the isolated nature of this single impact, permits a more detailed assessment of the altitudes and meridional motion of the debris than was possible with SL9. The color of the 2009 debris was markedly similar to that seen in 1994, thus this dark debris is likely to be Jovian material that is highly thermally processed. The 2009 impact site differed from the 1994 SL9 sites in UV morphology and contrast lifetime; both are suggestive of the impacting body being asteroidal rather than cometary. Transport of the 2009 Jovian debris as imaged by Hubble shared similarities with transport of volcanic aerosols in Earth's atmosphere after major eruptions.

Hammel, H. B.↗
NASA NTRS2003

Space Telescope Imaging Spectrograph Co-Investigator Support

The purpose of this contract has been to support investigation of astronomical problems primarily using data from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST). As a Co-investigator on STIS, I participated in several projects, which will be described below. The research resulted in 19 papers in refereed journals, 8 papers published in conference proceedings, and 27 papers presented at meetings. There are still at least four papers submitted or in press, as well as some additional research yet to be written up for publication. The research has also produced one master's thesis and two PhD dissertations currently underway, with one to be completed Spring 2003. Undergraduates have participated in the analysis of supporting observations. One student has published some of his results in a web- based refereed publication for undergraduate research (www.jyi.org). I have given several talks to the general public describing results from the HST as well as the results of my research. I have been named the UNLV Regents' Outstanding Faculty Member for 1995 and received the 2002 College of Science Distinguished Researcher's Award as a result of these activities.

Weistrop, Donna↗
NASA NTRS1994

Hubble Space Telescope imaging of super-star clusters in NGC 1569 and NGC 1705

We examine the structural properties of three super-star clusters in the nearby, H I-rich galaxies NGC 1569 and NGC 1705. The clusters, which have total absolute V magnitudes between -13.3 and -14.1, appear to be point sources on ground-based images but are partially resolved in new images obtained with the Hubble Space Telescope (HST) Planetary Camera. From deconvolved V- and I-band images we find that the three clusters have very compact cores with extended halos that are partially resolved into individual stars. Using new distances to the galaxies derived from color-magnitude diagrams for field stars, we find that the half-light radii are 2.2-3.4 pc. The cluster in NGC 1705 is barely resolved in the HST images. The clusters in NGC 1569, on the other hand, show significant substructure in their cores and ellipticities that are comparable to the flattenings seen in young clusters in the Large Magellanic Cloud (LMC). The clusters show internal (V-I) color gradients. The properties of these clusters are similar to R136, the core of the luminous star-forming complex 30 Doradus in the LMC, except that R136 has a lower luminosity and central surface brightness. The half-light surface brightness of the brightest cluster (NGC 1569 A) is 1.3 x 10(exp 6) L(sub v) solar/ sq cm, which is over 65 times higher than R136 and 1200 times higher than the mean rich LMC star cluster other than R136 after allowing for aging effects. The next brightest clusters in each of these galaxies are greater than or = 2 mag fainter. Thus, the super-star clusters represent an extreme but uncommon mode of star formation. In terms of luminosity and size, they appear to be good analogs of young globular clusters.

O'Connell, Robert W.↗
NASA NTRS1994

Hubble Space Telescope imaging of the central star forming region in NGC 1140 (exp 1)

We present broadband images taken with the Hubble Space Telescope's Planetary Camera of the central supergiant H II region in the amorphous galaxy NGC 1140. These images allow observations to a resolution of about 13 pc at the galaxy, and they reveal that its central 1/2 kpc contains 6-7 blue, luminous, compact super star clusters, many of which would be comparable in luminosity to globular clusters at the same age. A blue arc-shaped structure near the center may be a grouping of less luminous, R136/NGC 2070-sized clusters or a sheet of OB stars. Additional somewhat less luminous and redder clusters are also found farther out from the center. If these clusters are older, they too could have had luminosities comparable to those of the central six clusters at a comparable age. Thus, we find that NGC 1140 is remarkable in the number of extreme clusters that it has formed recently in a relatively small area of the galaxy. Since NGC 1140 exhibits global characteristics that are consistent with a recent merger, these clusters are likely to be a product of that event. This galaxy adds to the number of cases where rapid star formation has evidently produced super star clusters.

Hunter, Deidre A.↗
NASA NTRS2003

Correlation of the Hubble Space Telescope (HST) Space Telescope Imaging Spectrometer (STIS) On-Orbit Data with Pre-launch Predictions and Ground Contamination Controls

The Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) was deployed on-orbit in February 1997. The contamination program for STIS was stringently controlled as the five-year end-of-life deposition was set at 158, per optical element. Contamination was controlled through materials selection, extensive vacuum outgassing certifications, cleaning techniques, and environmental controls. In addition to ground contamination controls, on-orbit contamination controls were implemented for both the HST servicing mission activities and early post-servicing mission checkout. The extensive contamination control program will be discussed and the STIS on-orbit data will be correlated with the prelaunch analytical predictions.

Hansen, Patricia A.↗
NASA NTRS1990

Volumetric imaging of space debris using sun microsystem's TAAC-1 application accelerator board

Analysis of space debris requires the researcher to have a three-dimensional spatial framework and understanding. By using computers to image and display the space debris volumes, the researcher is provided with an added visual analysis tool. This paper describes volumetric visualization of space debris. Two imaging approaches are used. The first method visualizes the cube faces of the volumetric image. The second method uses a ray-tracing technique to display surfaces within the volume. Three examples of space debris volumes are described.

Luetkemeyer, Kelly G.↗