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At least 631 records · Page 35

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NASA NTRS2016

The Habitability of Proxima Centauri b II. Possible Climates and Observability

Radial velocity monitoring has found the signature of a M sin i = 1.3 M(sub ⨁) planet located within the habitable zone (HZ) of Proxima Centauri. Despite a hotter past and an active host star, the planet Proxima b could have retained enough volatiles to sustain surface habitability. Here we use a 3D Global Climate Model (GCM) to simulate the atmosphere and water cycle of Proxima b for its two likely rotation modes (1:1 and 3:2 spin-orbit resonances), while varying the unconstrained surface water inventory and atmospheric greenhouse effect. Any low-obliquity, low-eccentricity planet within the HZ of its star should be in one of the climate regimes discussed here. We find that a broad range of atmospheric compositions allow surface liquid water. On a tidally locked planet with sufficient surface water inventory, liquid water is always present, at least in the substellar region. With a non-synchronous rotation, this requires a minimum greenhouse warming (~10 mbar of CO2 and 1 bar of N2). If the planet is dryer, ~0.5 bar or 1.5 bars of CO2 (for asynchronous or synchronous rotation, respectively) suffice to prevent the trapping of any arbitrary, small water inventory into polar or nightside ice caps. We produce reflection and emission spectra and phase curves for the simulated climates. We find that atmospheric characterization will be possible via direct imaging with forthcoming large telescopes. The angular separation of 7 λ/D at 1 μm (with the E-ELT) and a contrast of ~10(exp -7) will enable high-resolution spectroscopy and the search for molecular signatures, including H2O, O2, and CO2. The observation of thermal phase curves can be attempted with the James Webb Space Telescope, thanks to a contrast of 2 × 10(exp -5) at 10 μm. Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and possibly determine whether the surface of this exoplanet is habitable.

Proxima Cen↗

NASA NTRS1976

HEAO Block 2 study executive summary

An executive summary is presented of a preliminary study done on several potential High Energy Astronomy Observatory (HEAO) missions which are follow-on missions to the currently defined HEAO program. The purpose was to examine several typical missions and determine the relative complexities associated with them. The four payloads investigated were (1) a 1.2 m Diameter X-ray Telescope observatory, (2) a Large Area Moderate Angular Resolution (LAMAR) observatory, (3) a cosmic ray observatory, and (4) a gamma ray observatory. Each of the four observatories was considered a national facility. Low cost approaches were stressed throughout, with considerable use of HEAO Block I experience and designs effected to provide a high degree of confidence that such approaches were achievable. The use of the Multi-Mission Spacecraft (MMS) and the HEAO Block I spacecraft was considered as a result of this low cost emphasis. Also, NASA standard components were considered, where applicable.

Source record↗

NASA NTRS1985

Advanced 2-frequency ocean sensing radar using high resolution antenna beams

The opportunity to use a large space antenna system for remote sensing applications permits the creation of an advanced ocean sensing radar that combines the abilities of previously developed techniques. The 15 meter antenna will permit much higher angular and spatial resolution at the surface that will lead to techniques of observing ocean wave heights and the directional spectrum that had not previously been feasible from space. At the same time, sensors to measure ocean surface winds can be in operation and the data from both can be combined to increase the accuracy of each individual sensor. The existing capabilities and sensor techniques with typical data characteristics for the individual measurement of sea surface quantities are outlined.

Weissman, D. E.↗

NASA NTRS2003

Heterodyne Receiver Requirements for the Single Aperture Far-Infrared (SAFIR) Observatory

In the next few years, work will commence in earnest on the development of technology for the next generation large cryogenic far-infrared telescope: the Single Aperture Far- Infrared (SAFIR) Observatory. SAFIR's science goals are driven by the fact that youngest stages of almost all phenomena in the universe are shrouded in absorption by cool dust, resulting in the energy being emitted primarily in the far-infrared. The earliest stages of star formation, when gas and dust clouds are collapsing and planets forming, can only be observed in the far-infrared. Spectral diagnostics in the far-infrared are typically quite narrow (approx. 1 km/s) and require high sensitivity to detect them. SAFIR is a 10 m-class telescope designed for cryogenic operation at L2, removing all sources of thermal emission from the telescope and atmosphere. Despite its limited collecting area and angular resolution as compared to the ALMA interferometer, its potential for covering the entire far-infrared band cannot be matched by any ground-based or airborne observatory. This places a new challenge on heterodyne receivers: broad frequency coverage. The ideal mixer would be able to detect frequencies over several octaves (e.g., 0.6 THz - 12 THz) with near quantum-limited performance at all frequencies. In contrast to ground-based observatories, it may not be necessary to strive for high instantaneous bandwidth, as direct detection spectroscopy is preferable for bandwidths of Delta v/ v greater than or equal to 10(exp -4) (e.g., 1 GHz at 10 THz). We consider likely directions for technology development for heterodyne receivers for SAFIR.

Benford, Dominic J.↗

DOE OSTI2021

Self-Consistent Field Methods for Excited States in Strong Magnetic Fields: A Comparison Between Energy - and Variance-based Approaches

An efficient implementation of geometrical derivatives at the Hartree–Fock (HF) and current-density functional theory (CDFT) levels is presented for the study of molecular structure in strong magnetic fields. The required integral derivatives are constructed using a hybrid McMurchie–Davidson and Rys quadrature approach, which combines the amenability of the former to the evaluation of derivative integrals with the efficiency of the latter for basis sets with high angular momentum. In addition to its application to evaluating derivatives of four-center integrals, this approach is also applied to gradients using the resolution-of-the-identity approximation, enabling efficient optimization of molecular structure for many-electron systems under a strong magnetic field. The CDFT contributions have been implemented for a wide range of density functionals up to and including the meta-GGA level with current-density dependent contributions and (range-separated) hybrids for the first time. Illustrative applications are presented to the OH and benzene molecules, revealing the rich and complex chemistry induced by the presence of an external magnetic field. Challenges for geometry optimization in strong fields are highlighted, along with the requirement for careful analysis of the resulting electronic structure at each stationary point. The importance of correlation effects is examined by comparison of results at the HF and CDFT levels. The present implementation of molecular gradients at the CDFT level provides a cost-effective approach to the study of molecular structure under strong magnetic fields, opening up many new possibilities for the study of chemistry in this regime.

Comparison↗

NASA NTRS1982

Spectral photometry of extreme helium stars: Ultraviolet fluxes and effective temperature

Ultraviolet flux distributions are presented for the extremely helium rich stars BD +10 deg 2179, HD 124448, LSS 3378, BD -9 deg 4395, LSE 78, HD 160641, LSIV -1 deg 2, BD 1 deg 3438, HD 168476, MV Sgr, LS IV-14 deg 109 (CD -35 deg 11760), LSII +33 deg 5 and BD +1 deg 4381 (LSIV +2 deg 13) obtained with the International Ultraviolet Explorer (IUE). Broad band photometry and a newly computed grid of line blanketed model atmospheres were used to determine accurate angular diameters and total stellar fluxes. The resultant effective temperatures are in most cases in satisfactory agreement with those based on broad band photometry and/or high resolution spectroscopy in the visible. For two objects, LSII +33 deg 5 and LSE 78, disagreement was found between the IUE observations and broadband photometry: the colors predict temperatures around 20,000 K, whereas the UV spectra indicate much lower photospheric temperatures of 14,000 to 15,000 K. The new temperature scale for extreme helium stars extends to lower effective temperatures than that of Heber and Schoenberner (1981) and covers the range from 8,500 K to 32,000 K.

Drilling, J. S.↗

NASA NTRS1999

Design and Performance of the HESSI Cryostat

The High Energy Solar Spectroscopic Imager (HESSI) spacecraft, to be launched in July 2000, will be used to observe the Sun with the finest angular and energy resolutions ever achieved from a few keV to hundreds of keV. The spacecraft will use an array of nine germanium (Ge) detectors, each 7.1 cm in diameter and 8.5 cm long, operating at 75K. The detectors are mounted in a cryostat on a common cold plate, and cooled by a small Stirling-cycle cryocooler. This paper describes the design of the cryostat, special accommodations for the Ge detectors, interfaces with the cryocooler, and thermal performance of the engineering test unit.

Boyle, R.↗

NASA NTRS2012

Design and Status of the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): An Interferometer at the Edge of Space

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infraredinterferometer designed to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer tosimultaneously obtain spatial and spectral information on science targets; the long baseline permits subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. Here, we present key aspects of the overall design of the mission and provide an overview of the current status of the project. We also discuss briefly the implications of this experiment for future space-based far-infrared interferometers.

Balloon↗

NASA NTRS2015

X-Ray Optics at NASA Marshall Space Flight Center

NASA's Marshall Space Flight Center (MSFC) engages in research, development, design, fabrication, coating, assembly, and testing of grazing-incidence optics (primarily) for x-ray telescope systems. Over the past two decades, MSFC has refined processes for electroformed-nickel replication of grazing-incidence optics, in order to produce high-strength, thin-walled, full-cylinder x-ray mirrors. In recent years, MSFC has used this technology to fabricate numerous x-ray mirror assemblies for several flight (balloon, rocket, and satellite) programs. Additionally, MSFC has demonstrated the suitability of this technology for ground-based laboratory applications-namely, x-ray microscopes and cold-neutron microscopes and concentrators. This mature technology enables the production, at moderately low cost, of reasonably lightweight x-ray telescopes with good (15-30 arcsecond) angular resolution. However, achieving arcsecond imaging for a lightweight x-ray telescope likely requires development of other technologies. Accordingly, MSFC is conducting a multi-faceted research program toward enabling cost-effective production of lightweight high-resolution x-ray mirror assemblies. Relevant research topics currently under investigation include differential deposition for post-fabrication figure correction, in-situ monitoring and control of coating stress, and direct fabrication of thin-walled full-cylinder grazing-incidence mirrors.

X-ray Optics↗

NASA NTRS2015

X-Ray Optics at NASA Marshall Space Flight Center

X-ray telescope↗

NASA NTRS1983

Speckle interferometry of IRC +10216 in the fundamental vibration-rotation lines of CO

The largest fraction of the matter returned by stars to the interstellar medium is probably provided by red giants. The carbon star IRC +10216 is an example of an evolved giant with a large mass loss rate. One plausible mechanism for the acceleration of the gas in stars like IRC +10216 is radiation pressure on dust grains which then collide with and transfer their momentum to the gas. However, at the present time neither infrared nor microwave observations provide a clear picture of the distribution of matter near cool red giant stars. There exists one method which may be used to obtain more information about the distribution of matter very close to the star. This method involves the measurement of the spatial extent of near-infrared lines by employing a combination of very high spatial and high spectral resolution. The present investigation is concerned with an application of this method. Speckle interferometry is used to measure the radial distribution of CO molecules on angular scales of 1 sec near IRC +10216.

Dyck, H. M.↗

NASA NTRS2012

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII)

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer to simultaneously obtain spatial and spectral information on science targets; the long baseline provides subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. Here, we present key aspects of the overall design of the mission and provide an overview of the current status of the project. We also discuss briefly the implications of this experiment for future space-based far-infrared interferometers.

Rinehart, Stephen↗

NASA NTRS1982

Topography and stratigraphy of Martian polar layered deposits

The first samples of high resolution Viking Orbiter topographic and stratigraphic data for the layered polar deposits of Mars are presented, showing that these deposits are with respect to both slopes and angular relief similar to those in the south. It is also demonstrated that, in conjunction with stereophotogrammetry, photoclinometry holds promise as a tool for detailed layered deposit studies. The spring season photography, which lends itself to photoclinometric analysis, covers the entire area of the north polar deposits. Detailed tests of layered terrain evolution hypotheses will be made, upon refinement of the data by comparison with stereo data. A more promising refining technique will make use of averaging perpendicular to selected sections to enhance SNR. Local reliefs of 200-800 m, and slopes of 1-8 deg, lead to initial calculations of average layer thickness which yields results of 14-46 m, linearly correlated with slope.

Blasius, K. R.↗

NASA NTRS1985

Observations of potential ultra high energy gamma-ray sources above 10(15) eV

The Haverah Park 50 m water-Cerenkov array has been used to examine a number of periodic sources for ultra high energy gamma-ray emission above 10 to the 15th power eV. The data, recorded between 1 Jan. 1979 and 31 Dec. 1984, feature a modest angular resolution of approx 3 deg with millisecond arrival time resolution post 1982. The sources investigated include the Crab pulsar, Her X-1, Au0115 + 63 and Geminga. All objects have been detected by workers in the TeV region, with varying degrees of confidence.

Lambert, A.↗

NASA NTRS1981

A Wolter type I LAMAR

Observational objectives for the LAMAR and their influence on the instrument design are discussed. It is concluded that the most important design parameter is the angular resolution of the LAMAR modules since it so strongly influences sensitivity, optical identifications, source confusion, spectral resolution for objective gratings and the ability to resolve small extended sources. A high resolution Wolter Type I LAMAR module is described, its hardware status discussed, and the performance of a LAMAR observatory presented. A promising technique for enhancing the reflectivity of Wolter Type I X-ray optics in a selected bandpass at high energy has been investigated and the performance of the LAMAR module, utilizing this method, has been calculated.

Catura, R. C.↗

NASA NTRS1984

Dependence of NOAA-AVHRR recorded radiance on scan angle, atmospheric turbidity and unresolved cloud

Experimental evidence on the scan angle and sun angle dependence of radiance recorded by the Advanced Very High Resolution Radiometer (AVHRR) devices on the NOAA-6 and NOAA-7 satellites is presented. The effects of atmospheric turbidity at various scan angles is shown, and simulations of angular anisotropy and recorded radiance are compared with the recorded digital data from the AVHRR obtained over the Great Plains area of the US. Evidence is presented on the effects of unresolved cloud on the recorded radiance and vegetative indices from uniform, vegetative targets.

Piwinski, D. J.↗

NASA NTRS1991

The Gamma Ray Observatory

The Gamma Ray Observatory (GRO), scheduled for launch by the Space Shuttle in April 1991, weighs 35,000 lbs and will offer 10 to 20 times better sensitivity than any previous gamma ray mission. The four instruments aboard GRO are described. The Burst and Transient Source Experiment (BATSE) will continuously monitor the entire sky for transient gamma-ray events using eight identical, wide-field detectors capable of measuring brightness variations lasting only milliseconds at energies from about 50,000 to 600,000 eV. The Oriented Scintillation Spectrometer Experiment (OSSE) will make comprehensive observations of discrete sources at energies from 100,000 to 10 million eV, where many radioactive elements have emission lines. The observatory's Imaging Compton Telescope will conduct a deep survey of the entire sky at gamma-ray energies between 1 and 30 MeV. The Energetic Gamma Ray Experiment Telescope will cover a broad high-energy spectral range, from about 20 million to 30 billion eV and conduct a sensitive all-sky survey with a wide field of view and good angular resolution.

Kniffen, Donald A.↗

NASA NTRS1993

From bipolar to quadrupolar - The collimation processes of the Cepheus A outflow

Results of new K-band observations of the (1, 1) and (2, 2) ammonia lines toward Cepheus A are reported. The lines are mapped with approximately 2 arcsec of angular resolution and 0.3 km/s of velocity resolution. A sensitivity of 10 mJy has been achieved. The observations reveal details of the spatial and kinematics structure of the ambient high-density gas. It is suggested that the interstellar high-density gas is diverting and redirecting the outflow in the sense that the quadrupolar structure of the molecular outflow is produced by the interaction with the ammonia condensationss, with Cep A-1 and Cep A-3 splitting in two halves, respectively the blue- and redshifted lobes of an east-west bipolar molecular outflow.

Torrelles, Jose M.↗