128 research outputs found
NASAs Orbital Debris JAO/ES-MCAT Optical Telescope Facility on Ascension Island
The NASA Orbital Debris Program Office has a long-standing optical program begun over three and a half decades ago in 1984, designed to observe the Earth-orbiting environment with optical telescopes. Photometrically calibrated optical data provides a statistical sample for input to NASA models of the debris population for understanding the current and future debris environment around the Earth. Tracked objects and orbits allow for analysis of break-up events. Both known (correlated target in the SSN catalogue, or CT) and unknown (uncorrelated target, or UCT) objects are of interest to better understand how to protect current spacecraft and design more robust future operational satellites, and advise on how policies and practices can lead to protecting the environment itself for future generations. In 2015, a joint NASA JSC Air Force Research Labs (AFRL) project culminated in the installation of the 1.3-meter Eugene Stansbery Meter Class Autonomous Telescope, ES-MCAT (a.k.a. MCAT) on Ascension Island. This DFM Engineering designed telescope provides nearly five-times greater light-collecting power than its predecessor, the 0.6-m MODEST telescope, and faster tracking capabilities by both the telescope and the 7-m ObservaDome. This allows for all orbital regimes to be easily within reach, ranging from low Earth to geosynchronous orbits. Extensive testing and commissioning activities of this custom system led to successfully reaching Initial Operational Capability in 2018, and the facility is currently on track to reach Full Operational Capability. The John Africano Observatory (JAO) comprises the primary 1.3-m ES-MCAT facility, the adjacent tower platform with a 0.4-m telescope, a sophisticated suite of weather instruments, and custom software by Euclid Research for autonomously running the entire system, including monitoring the weather and hardware, tasking all components, and collecting, processing, and analyzing the data. The mission of JAO and MCAT will be discussed, including survey and tracking tasking, a full discussion of data calibration, and both optics and weather-dependent performance
Hydration Status Effect on Anaerobic Power and Fatigue in Collegiate Female Soccer Players
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The Opacity of Spiral Galaxy Disks VIII: Structure of the Cold ISM
The quantity of dust in a spiral disk can be estimated using the dust's
typical emission or the extinction of a known source. In this paper, we compare
two techniques, one based on emission and one on absorption, applied on
sections of fourteen disk galaxies. The two measurements reflect, respectively
the average and apparent optical depth of a disk section. Hence, they depend
differently on the average number and optical depth of ISM structures in the
disk. The small scale geometry of the cold ISM is critical for accurate models
of the overall energy budget of spiral disks. ISM geometry, relative
contributions of different stellar populations and dust emissivity are all free
parameters in galaxy Spectral Energy Distribution (SED) models; they are also
sometimes degenerate, depending on wavelength coverage. Our aim is to constrain
typical ISM geometry. The apparent optical depth measurement comes from the
number of distant galaxies seen in HST images through the foreground disk. We
measure the IR flux in images from the {\it Spitzer} Infrared Nearby Galaxy
Survey in the same section of the disk that was covered by HST. A physical
model of the dust is fit to the SED to estimate the dust surface density, mean
temperature, and brightness in these disk sections. The surface density is
subsequently converted into the average optical depth estimate. The two
measurements generally agree. The ratios between the measured average and
apparent optical depths of the disk sections imply optically thin clouds in
these disks. Optically thick disks, are likely to have more than a single cloud
along the line-of-sight.Comment: 31 pages, 5 figures, 4 tables, accepted for publication in A
Spectral Mapping Reconstruction of Extended Sources
Three dimensional spectroscopy of extended sources is typically performed
with dedicated integral field spectrographs. We describe a method of
reconstructing full spectral cubes, with two spatial and one spectral
dimension, from rastered spectral mapping observations employing a single slit
in a traditional slit spectrograph. When the background and image
characteristics are stable, as is often achieved in space, the use of
traditional long slits for integral field spectroscopy can substantially reduce
instrument complexity over dedicated integral field designs, without loss of
mapping efficiency -- particularly compelling when a long slit mode for single
unresolved source followup is separately required. We detail a custom
flux-conserving cube reconstruction algorithm, discuss issues of extended
source flux calibration, and describe CUBISM, a tool which implements these
methods for spectral maps obtained with ther Spitzer Space Telescope's Infrared
Spectrograph.Comment: 11 pages, 8 figures, accepted by PAS
Integrating Orbital Debris Measurements and Modeling - How Observations and Laboratory Data are used to Help Make Space Operations Safer
The NASA Orbital Debris Program Office has been statistically surveying human-made resident space objects (RSOs) in geocentric orbits for several decades, using optical and infrared telescopes. The prime goal has been to understand the evolving population and characteristics of debris generated by RSOs. The debris population includes any non-functioning RSO that no longer serves a useful purpose. Any object that cannot be purposely maneuvered, including non-functioning satellites, rocket bodies, and any object generated by a collision, explosion, or fragmentation event, may pose a future collisional threat to active satellites. Key questions immediately surface from this knowledge: What can we do to protect our precious functioning satellites from collisions? How do we design our satellites to prevent them from being future sources of debris? And what can we do as a society to protect the environment surrounding Earth to preserve it for future generations? To begin to address these questions, and to better understand this population as well as break-up events contributing to it, NASA has developed a suite of models and experimental laboratory data to work in tandem with observational and laboratory measurements of RSOs. These models include the Orbital Debris Engineering Model (ORDEM), the Standard Satellite Break-up Model (SSBM), and an evolutionary model of the environment from LEO to GEO (LEGEND). Ground-based data have been collected from the infrared telescope UKIRT (UK Infrared Telescope) in Hawaii, as well as the 1.3m Eugene Stansbery Meter Class Autonomous Telescope, ES-MCAT, historically called MCAT, on Ascension Island. MCAT will be tasked to collect GEO (Geosynchronous) survey data, scanning orbits to search for uncatalogued objects (e.g. fragmentation/break-up events (SSBM)), and targeted observations of catalogued objects for more intensive studies, e.g. when a break-up or anomalous event occurs. Laboratory experimental data includes DebriSat, a satellite impacted at ~6.9 km/s in an impact laboratory on Earth, and optical photometry from the Optical Measurements Center at NASA JSC. An integrated view will be discussed of how our telescopic observations and lab measurements interplay with models to understand the current (ORDEM) and future (LEGEND) environment, the evolution of satellite breakups (SSBM), and how this knowledge can help to promote an environment that is safer for operations
The Mid-Infrared Spectrum of Star-Forming Galaxies: Global Properties of PAH Emission
We present a sample of low-resolution 5-38um Spitzer IRS spectra of the inner
few square kiloparsecs of 59 nearby galaxies spanning a large range of star
formation properties. A robust method for decomposing mid-infrared galaxy
spectra is described, and used to explore the behavior of PAH emission and the
prevalence of silicate dust extinction. Evidence for silicate extinction is
found in ~1/8 of the sample, at strengths which indicate most normal galaxies
undergo A_V < ~3 magnitudes averaged over their centers. The contribution of
PAH emission to the total infrared power is found to peak near 10% and extend
up to ~20%, and is suppressed at metallicities Z < ~Z_sun/4, as well as in
low-luminosity AGN environments. Strong inter-band PAH feature strength
variations (2-5x) are observed, with the presence of a weak AGN and, to a
lesser degree, increasing metallicity shifting power to the longer wavelength
bands. A peculiar PAH emission spectrum with markedly diminished 5-8um features
arises among the sample solely in systems with relatively hard radiation fields
harboring low-luminosity AGN. The AGN may modify the emitting grain
distribution and provide the direct excitation source of the unusual PAH
emission, which cautions against using absolute PAH strength to estimate star
formation rates in systems harboring active nuclei. Alternatively, the low star
formation intensity often associated with weak AGN may affect the spectrum. The
effect of variations in the mid-infrared spectrum on broadband infrared surveys
is modeled, and points to more than a factor of two uncertainty in results
which assume a fixed PAH emission spectrum, for redshifts z=0-2.5.Comment: Accepted for publication in ApJ, 24 pages (abstract typo fixed,
reference added
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The relations among 8, 24 and 160 mu m dust emission within nearby spiral galaxies
We investigate the relations among the stellar continuum-subtracted 8 µm polycyclic aromatic hydrocarbon (PAH 8 µm) emission, 24 µm hot dust emission and 160 µm cold dust emission in 15 nearby face-on spiral galaxies in the Spitzer Infrared Nearby Galaxies Survey sample. The relation between PAH 8 and 24 µm emission measured in ~2 kpc regions is found to exhibit a significant amount of scatter, and strong spatial variations are observed in the (PAH 8 µm)/24 µm surface brightness ratio. In particular, the (PAH 8 µm)/24 µm surface brightness ratio is observed to be high in the diffuse interstellar medium and low in bright star-forming regions and other locations with high 24 µm surface brightness. PAH 8 µm emission is found to be well-correlated with 160 µm emission on spatial scales of ~2 kpc, and the (PAH 8 µm)/160 µm surface brightness ratio is generally observed to increase as the 160 µm surface brightness increases. These results suggest that the PAHs are associated with the diffuse, cold dust that produces most of the 160 µm emission in these galaxies, and the variations in the (PAH 8 µm)/160 µm ratio may generally be indicative of either the intensity or the spectrum of the interstellar radiation field that is heating both the PAHs and the diffuse interstellar dust
Gaps in the cloud cover? Comparing extinction measures in spiral disks
Dust in galaxies can be mapped by either the FIR/sub-mm emission, the optical
or infrared reddening of starlight, or the extinction of a known background
source. We compare two dust extinction measurements for a set of fifteen
sections in thirteen nearby galaxies, to determine the scale of the dusty ISM
responsible for disk opacity: one using stellar reddening and the other a known
background source. In our earlier papers, we presented extinction measurements
of 29 galaxies, based on calibrated counts of distant background objects
identified though foreground disks in HST/WFPC2 images. For the 13 galaxies
that overlap with the Spitzer Infrared Nearby Galaxies Survey (SINGS), we now
compare these results with those obtained from an I-L color map. Our goal is to
determine whether or not a detected distant galaxy indicates a gap in the dusty
ISM, and hence to better understand the nature and geometry of the disk
extinction.
We find that distant galaxies are predominantly in low-extinction sections
marked by the color maps, indicating that their number depends both on the
cloud cover of {\it Spitzer}-resolved dust structures --mostly the spiral
arms--and a diffuse, unresolved underlying disk. We note that our infrared
color map (E[I-L]) underestimates the overall dust presence in these disks
severely, because it implicitly assumes the presence of a dust screen in front
of the stellar distribution.Comment: 22 pages, 2 figures, 3 tables, accepted for publication in A
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