103 research outputs found
The Space Infrared Interferometric Telescope (SPIRIT): The Mission Design Solution Space and the Art of the Possible
Although the Space Infrared Interferometric Telescope (SPIRIT) was studied as a candidate NASA Origins Probe mission, the real world presents a broader set of options, pressures, and constraints. Fundamentally, SPIRIT is a far-IR observatory for high-resolution imaging and spectroscopy designed to address a variety of compelling scientific questions. How do planetary systems form from protostellar disks, dousing some planets in water while leaving others dry? Where do planets form, and why are some ice giants while others are rocky? How did high-redshift galaxies form and merge to form the present-day population of galaxies? This paper takes a pragmatic look at the mission design solution space for SPIRIT, presents Probe-class and facility-class mission scenarios, and describes optional design changes. The costs and benefits of various mission design alternatives are roughly evaluated, giving a basis for further study and to serve as guidance to policy makers
Using Composite Materials in a Cryogenic Pump
Several modifications have been made to the design and operation of an extended-shaft cryogenic pump to increase the efficiency of pumping. In general, the efficiency of pumping a cryogenic fluid is limited by thermal losses which is itself caused by pump inefficiency and leakage of heat through the pump structure. A typical cryogenic pump includes a drive shaft and two main concentric static components (an outer pressure containment tube and an intermediate static support tube) made from stainless steel. The modifications made include replacement of the stainless-steel drive shaft and the concentric static stainless-steel components with components made of a glass/epoxy composite. The leakage of heat is thus reduced because the thermal conductivity of the composite is an order of magnitude below that of stainless steel. Taking advantage of the margin afforded by the decrease in thermal conductivity, the drive shaft could be shortened to increase its effective stiffness, thereby increasing the rotordynamic critical speeds, thereby further making it possible to operate the pump at a higher speed to increase pumping efficiency. During the modification effort, an analysis revealed that substitution of the shorter glass/epoxy shaft for the longer stainless-steel shaft was not, by itself, sufficient to satisfy the rotordynamic requirements at the desired increased speed. Hence, it became necessary to increase the stiffness of the composite shaft. This stiffening was accomplished by means of a carbon-fiber-composite overwrap along most of the length of the shaft. Concomitantly with the modifications described thus far, it was necessary to provide for joining the composite-material components with metallic components required by different aspects of the pump design. An adhesive material formulated specially to bond the composite and metal components was chosen as a means to satisfy these requirements
Using qualitative data to inform the adaptation of a stroke preparedness health intervention
Qualitative research methods are often used to develop health interventions, but few researchers report how their qualitative data informed intervention development. Improved completeness of reporting may facilitate the development of effective behavior change interventions. Our objective was to describe how we used qualitative data to develop our stroke education intervention consisting of a pamphlet and video. First, we created a questionnaire grounded in the theory of planned behavior to determine reasons people delay in activating emergency medical services and presenting to the hospital after stroke symptom onset. From our questionnaire data, we identified theoretical constructs that affect behavior which informed the active components of our intervention. We then conducted cognitive interviews to determine emergency department patients’ understanding of the intervention pamphlet and video. Our cognitive interview data provided insight into how our intervention might produce behavior change. Our hope is that other researchers will similarly reflect upon and report on how they used their qualitative data to develop health interventions
Science drivers and requirements for an Advanced Technology Large Aperture Space Telescope (ATLAST): Implications for technology development and synergies with other future facilities
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept
for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030
era. ATLAST will allow astronomers to answer fundamental questions at the
forefront of modern astronphysics, including "Is there life elsewhere in the
Galaxy?" We present a range of science drivers that define the main performance
requirements for ATLAST (8 to 16 milliarcsec angular resolution, diffraction
limited imaging at 0.5 {\mu}m wavelength, minimum collecting area of 45 square
meters, high sensitivity to light wavelengths from 0.1 {\mu}m to 2.4 {\mu}m,
high stability in wavefront sensing and control). We will also discuss the
synergy between ATLAST and other anticipated future facilities (e.g., TMT,
EELT, ALMA) and the priorities for technology development that will enable the
construction for a cost that is comparable to current generation
observatory-class space missions.Comment: 12 pages, 4 figures, to appear in "Space Telescopes and
Instrumentation 2010: Optical, Infrared, and Millimeter Wave," edited by
Jacobus M. Oschmann Jr., Mark C. Clampin, Howard A. MacEwen, Proc. of SPIE,
Vol. 7731, 77312
Cosmological test of the Yilmaz theory of gravity
We test the Yilmaz theory of gravitation by working out the corresponding
Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker
cosmological metrics. In the case that space is flat the theory is consistent
only with either a completely empty universe or a negative energy vacuum that
decays to produce a constant density of matter. In both cases the total energy
remains zero at all times, and in the latter case the acceleration of the
expansion is always negative. To obtain a more flexible and potentially more
realistic cosmology, the equation of state relating the pressure and energy
density of the matter creation process must be different from the vacuum, as
for example is the case in the steady-state models of Gold, Bondi, Hoyle and
others. The theory does not support the cosmological principle for curved space
K =/= 0 cosmological metrics
The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers, Technology Developments, and Synergies with Other Future Facilities
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers that define the main performance requirements for ATLAST (8 to 16 milliarcsec angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We will also discuss the synergy between ATLAST and other anticipated future facilities (e.g., TMT, EELT, ALMA) and the priorities for technology development that will enable the construction for a cost that is comparable to current generation observatory-class space missions
The Advanced Technology Large Aperture Space Telescope (ATLAST): Science Drivers and Technology Developments
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8-meter to 16-meter UVOIR space observatory for launch in the 2025-2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including "Is there life elsewhere in the Galaxy?" We present a range of science drivers and the resulting performance requirements for ATLAST (8 to 16 milliarcsecond angular resolution, diffraction limited imaging at 0.5 m wavelength, minimum collecting area of 45 square meters, high sensitivity to light wavelengths from 0.1 m to 2.4 m, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to current generation observatory-class space missions. Keywords: Advanced Technology Large-Aperture Space Telescope (ATLAST); ultraviolet/optical space telescopes; astrophysics; astrobiology; technology development
Hypersurface homogeneous locally rotationally symmetric spacetimes admitting conformal symmetries
All hypersurface homogeneous locally rotationally symmetric spacetimes which
admit conformal symmetries are determined and the symmetry vectors are given
explicitly. It is shown that these spacetimes must be considered in two sets.
One set containing Ellis Class II and the other containing Ellis Class I, III
LRS spacetimes. The determination of the conformal algebra in the first set is
achieved by systematizing and completing results on the determination of CKVs
in 2+2 decomposable spacetimes. In the second set new methods are developed.
The results are applied to obtain the classification of the conformal algebra
of all static LRS spacetimes in terms of geometrical variables. Furthermore all
perfect fluid nontilted LRS spacetimes which admit proper conformal symmetries
are determined and the physical properties some of them are discussed.Comment: 15 pages; to appear in Classical Quantum Gravity; some misprints in
Tables 3,5 and in section 4 correcte
Advanced Technology Large-Aperture Space Telescope (ATLAST): A Technology Roadmap for the Next Decade
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of
mission concepts for the next generation of UVOIR space observatory with a
primary aperture diameter in the 8-m to 16-m range that will allow us to
perform some of the most challenging observations to answer some of our most
compelling questions, including "Is there life elsewhere in the Galaxy?" We
have identified two different telescope architectures, but with similar optical
designs, that span the range in viable technologies. The architectures are a
telescope with a monolithic primary mirror and two variations of a telescope
with a large segmented primary mirror. This approach provides us with several
pathways to realizing the mission, which will be narrowed to one as our
technology development progresses. The concepts invoke heritage from HST and
JWST design, but also take significant departures from these designs to
minimize complexity, mass, or both.
Our report provides details on the mission concepts, shows the extraordinary
scientific progress they would enable, and describes the most important
technology development items. These are the mirrors, the detectors, and the
high-contrast imaging technologies, whether internal to the observatory, or
using an external occulter. Experience with JWST has shown that determined
competitors, motivated by the development contracts and flight opportunities of
the new observatory, are capable of achieving huge advances in technical and
operational performance while keeping construction costs on the same scale as
prior great observatories.Comment: 22 pages, RFI submitted to Astro2010 Decadal Committe
The Space Infrared Interferometric Telescope (SPIRIT): High-resolution imaging and spectroscopy in the far-infrared
We report results of a recently-completed pre-Formulation Phase study of
SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and
spectral interferometer with an operating wavelength range 25 - 400 microns.
SPIRIT will provide sub-arcsecond resolution images and spectra with resolution
R = 3000 in a 1 arcmin field of view to accomplish three primary scientific
objectives: (1) Learn how planetary systems form from protostellar disks, and
how they acquire their inhomogeneous composition; (2) characterize the family
of extrasolar planetary systems by imaging the structure in debris disks to
understand how and where planets of different types form; and (3) learn how
high-redshift galaxies formed and merged to form the present-day population of
galaxies. Observations with SPIRIT will be complementary to those of the James
Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All
three observatories could be operational contemporaneously.Comment: 20 pages, 12 figures, accepted for publication in J. Adv. Space Res.
on 26 May 200
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