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NASA NTRS2019

LUVOIR: Engineering Design & Technology Overview

The Large Ultraviolet / Optical / Infrared Surveyor (LUVOIR) is one of four large mission concepts being study by NASA in preparation for the 2020 Decadal Survey in Astronomy and Astrophysics. Over the past three and a half years, the LUVOIR Science and Technology Definition Team (STDT) and Study Office at NASA's Goddard Space Flight Center have developed a broad, compelling science case for LUVOIR, and detailed engineering point designs to achieve it. In this paper, we provide an overview of the two LUVOIR concepts: LUVOIR-A, a 15-m segmented, obscured aperture observatory, and LUVOIR-B, an 8-m segmented, unobscured aperture observatory. Both versions of LUVOIR cover a broad spectral range between 100 nm and 2.5 µm with a suite of imagers and spectrographs, including the High Definition Imager (HDI), the LUVOIR Ultraviolet Multi-object Spectrograph (LUMOS), and the Extreme Coronagraph for Living Planetary Systems (ECLIPS). LUVOIR-A will carry an additional fourth instrument, Pollux, a high-resolution UV spectropolarimeter being studied by the Centre National d'Etudes Spatiales (CNES). Both versions of LUVOIR are also designed to be serviceable and upgradeable. We will also provide a summary of the LUVOIR technology development program, which identifies critical enabling technologies, enhancing technologies, and a development plan to mature those technologies to TRL 6.

technology↗
NASA NTRS1990

A search for Beta Pictoris analogs

The results are presented of the survey of known shell stars detected by the Infrared Astronomy Satellite (IRAS) at sufficient bandpasses to permit evaluation of the nature of the infrared excess, and having archival International Ultraviolet Explorer (IUE) high dispersion spectra suitable for identifying stars with infalling circumstellar plasma. Detection of infall in shell stars with infrared signatures of circumstellar dust is described. One star which shows infalling plasma, but apparently no circumstellar dust is described. The implications for the understanding of Beta Pictoris and similar systems are discussed.

Cheng, Kwang-Ping↗
NASA NTRS1988

Far Ultraviolot Space Telescope (FAUST)

The Far Ultraviolet Space Telescope is a compact, wide field-of-view, far ultraviolet instrument designed for observations of extended and point sources of astronomical interest. It was originally used in sounding rocket work by both French and American investigators. The instrument was modified for flight on the space shuttle and flew on the Spacelab 1 mission as a joint effort between the Laboratoire d'Astronomie Spatiale and the University of California, Berkeley. The prime experiment objective of this telescope on the Atmospheric Laboratory Applications and Science (ATLAS 1) NASA mission is to observe faint astronomical sources in the far ultraviolet with sensitivities far higher than previously available. The experiment will cover the 1300 to 1800 A band, which is inaccessible to observers on earth. The observing program during the mission consists of obtaining deep sky images during spacecraft nighttime. The targets will include hot stars and nebulae in our own galaxy, faint diffuse galactic features similar to the cirrus clouds seen by the Infrared Astronomical Satellite (IRAS), large nearby galaxies, nearby clusters of galaxies, and objects of cosmological interest such as quasars and the diffuse far ultraviolet background.

Bowyer, S.↗
NASA NTRS1989

The origin of micrograins

Using ultraviolet and infrared techniques, researchers investigated the origins of the tiny (approx. 10A) grains whose presence in the interstellar medium (ISM) is inferred from near-infrared photometry (Sellgren, Werner, and Dinerstein 1983; Sellgren 1984). The authors consider two possibilities: (1) that the grains are formed by condensation in stellar atmospheres; or (2) that they are formed by fragmentation of larger grains in interstellar shocks. They searched for evidence of very small grains in circumstellar environments by analyzing ultraviolet extinction curves in binaries containing hot companions, and by searching for the 3.3-micron emission feature in similar systems. The ultraviolet extinction curve analysis could be applied only to oxygen-rich systems, where small carbonaceous grains would not be expected, so these results provide only indirect information. Researchers find a deficiency of grains smaller than 800A in oxygen-rich systems, consistent with theoretical models of grain condensation which suggest that grains grow to large sizes before injection into the interstellar medium. More direct information on carbonaceous micrograins was obtained from the search for the 3.3-micron feature in carbon-rich binaries with hot companions, whose ultraviolet flux should excite the tiny grains to emit in the infrared. No 3.3-micron feature was found, suggesting that the micrograins are absent in these systems. In addition to the negative search for micrograins in circumstellar environments, researchers have also studied the possible association of these grains with shocks in the diffuse interstellar medium. Using Infrared Astronomy Satellite (IRAS) colors as indicators of the presence or absence of the small grains (e.g., Ryter, Puget, and Perault 1987 and references cited therein), researchers systematically searched for them in regions (reflection nebulae) expected to have sufficient ultraviolet flux to make them glow in the infrared. They found that the distribution is not uniform. The researchers propose that production of micrograins by fragmentation of larger grains in shocks could explain this uneven distribution.

Snow, Theodore P., Jr.↗
NASA NTRS1978

Center and limb solar spectrum in high spectral resolution 225.2 nm to 319.6 nm

The atlas has been designed to fulfill the need in solar and stellar astronomy, in aeronomy, and in space science for a convenient reference source that provides a detailed and accurate record of the measured solar ultraviolet spectrum in high spectral resolution for the wavelength range from 225.2 nm to 319.6 nm. The atlas also contains a preliminary synthetic solar spectrum with a legend for identifying and describing the features of the synthetic spectrum. Attention is given to aspects of instrumentation, the radiometric calibration, the wavelength scale, background noise random fluctuations and data filtering, intermittent noise, the observational conditions, the experimental uncertainty, the atlas format, references, tables, and plots.

Kohl, J. L.↗
NASA NTRS1986

Application of wedge and strip image readout systems to detectors for astronomy

Microchannel plate (MCP) detector systems that use wedge and strip anodes for imaging radiation in the range 50 A to 8000 A are described. Test data, obtained from the calibration of the Extreme Ultraviolet Explorer Satellite detectors and the ARIA EUV aeronomy sensor is presented. The long-term performance characteristics of Z-stack microchannel plates are investigated and it is shown that stable operation is achieved after an initial settling period. Conventional and new anode designs and their potential for increasing the position resolution are discussed. Position resolution of better than 80 microns FWHM has been attained for 50 mm devices, and this is shown to be essentially independent of event location. Image nonlinearity of less than 0.3 percent has been achieved with stability to better than 0.1 percent. Differential nonlinearity of less than 1 percent and stability to better than 1 percent have been obtained. Measurements of the quantum efficiency of a CsI photocathode on an MCP are presented, demonstrating efficiencies as high as 47 percent.

Siegmund, O. H. W.↗
NASA NTRS1996

STS-80 Flight Day 6

On this sixth day of the STS-80 mission, the flight crew, Cmdr. Kenneth D. Cockrell, Pilot Kent V. Rominger, Mission Specialists, Tamara E. Jernigan, Thomas D. Jones, and F. Story Musgrave, are awakened to news from Mission Control that the ORFEUS-SPAS astronomy satellite may be closing in on the Wake Shield Facility satellite slightly faster than originally predicted. The Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer, or ORFEUS-SPAS satellite, has conducted 77 different astronomical observations since being deployed on launch day. Jernigan reports that the VIEW-CAPL experiment, designed by students at the University of Maryland, is working well. The experiment tests capillary pumped loop technology that one day may be used for more reliable spacecraft cooling systems. The crew also sends down television pictures of the flight deck and address half a dozen questions posed via the NASA Shuttle Web on the Internet.

Source record↗
NASA NTRS2002

Evolution of Galaxies and the Star Formation Rate in the Infrared

A central goal of extragalactic observational astronomy is to understand how normal galaxies evolve with redshift, and particularly when galaxies formed their stars. While optical and rest-frame UV (ultraviolet) observations have begun to address these issues, the interpretation of such data is particularly challenging because of the sensitivity to dust obscureness (at optical and UV wavelengths). The absorbed light is re-radiated at IR (infrared) wavelengths, hence the optimal indicators of the star formation rate (SFR) is at a rest-frame of (lambda) (is approximately equal to) 60 microns. The SIRTF (space infrared telescope facility) mission will revolutionize the study of the global evolution of the SFR by providing mass-selected, complete samples of galaxies and fares estimators of the SFR. This research program is to study the SFR using statistical samples of galaxies in the local universe, at intermediate redshifts, and set the stage for continuing studies up to z = 5.

Pahre, Michael, A.↗
NASA NTRS1993

Initial results from the extreme ultraviolet explorer

Data obtained during the first five months of calibration and science operation of the Extreme Ultraviolet Explorer (EUVE) are presented. Spectra of an extragalactic object were obtained; the object is detectable to wavelenghts longer than 100 A, demonstrating that extragalactic EUV astronomy is possible. Spectra of a hot white dwarf, and a late-type star in quiescence and flaring are shown as examples of the type of spectrographic data obtainable with EUVE. Other objects for which broad band photometric mode data have been obtained and analyzed include an RS CVn star and several late-type stars. The backgrounds in the EUVE detectors are quite low and the character of the diffuse astronomical EUV background has been investigated using these very low rates. Evidence is presented showing that, contrary to previously published reports, EUVE is about three times more sensitive than the English Wide Field Camera in the short wavelength bandpass covered by both instruments. Only limited information has been extracted from the longer bandpasses coered only by EUVE. Nonetheless, the brightest EUV source in the sky, a B star, has been discovered and is detected only in these longer bandpasses.

Bowyer, S.↗
NASA NTRS1999

The interstellar 4.62 micron band

We present new 4.5-5.1 micron (2210-1970 cm-1) spectra of embedded protostars, W33 A, AFGL 961 E, AFGL 2136, NGC 7538 IRS 9, and Mon R2 IRS 2, which contain a broad absorption feature located near 4.62 micron (2165 cm-1), commonly referred to in the literature as the "X-C triple bond N" band. The observed peak positions and widths of the interstellar band agree to within 2.5 cm-1 and 5 cm-1, respectively. The strengths of the interstellar 4.62 micrometers band and the ice absorption features in these spectra are not correlated, which suggests a diversity of environmental conditions for the ices we are observing. We explore several possible carriers of the interstellar band and review possible production pathways through far-ultraviolet photolysis (FUV), ion bombardment of interstellar ice analog mixtures, and acid-base reactions. Good fits to the interstellar spectra are obtained with an organic residue produced through ion bombardment of nitrogen-containing ices or with the OCN- ion produced either through acid-base reactions or FUV photolysis of NH3-containing ices.

NASA Center ARC↗
NASA NTRS1986

Calibration of photon counting imaging microchannel plate detectors for EUV astronomy

The calibration of photon counting imaging detectors for satellite based EUV astronomy is a complex process designed to ensure the validity of the data received 'in orbit'. The methods developed to accomplish calibration of microchannel plate detectors for the Extreme Ultraviolet Explorer are described and illustrated. The characterization of these detectors can be subdivided into three categories: stabilization, performance tests, and environmental tests.

Siegmund, O. H. W.↗
NASA NTRS1994

A new systems engineering approach to streamlined science and mission operations for the Far Ultraviolet Spectroscopic Explorer (FUSE)

The Mission Operations and Data Systems Directorate (MO&DSD, Code 500), the Space Sciences Directorate (Code 600), and the Flight Projects Directorate (Code 400) have developed a new approach to combine the science and mission operations for the FUSE mission. FUSE, the last of the Delta-class Explorer missions, will obtain high resolution far ultraviolet spectra (910 - 1220 A) of stellar and extragalactic sources to study the evolution of galaxies and conditions in the early universe. FUSE will be launched in 2000 into a 24-hour highly eccentric orbit. Science operations will be conducted in real time for 16-18 hours per day, in a manner similar to the operations performed today for the International Ultraviolet Explorer. In a radical departure from previous missions, the operations concept combines spacecraft and science operations and data processing functions in a single facility to be housed in the Laboratory for Astronomy and Solar Physics (Code 680). A small missions operations team will provide the spacecraft control, telescope operations and data handling functions in a facility designated as the Science and Mission Operations Center (SMOC). This approach will utilize the Transportable Payload Operations Control Center (TPOCC) architecture for both spacecraft and instrument commanding. Other concepts of integrated operations being developed by the Code 500 Renaissance Project will also be employed for the FUSE SMOC. The primary objective of this approach is to reduce development and mission operations costs. The operations concept, integration of mission and science operations, and extensive use of existing hardware and software tools will decrease both development and operations costs extensively. This paper describes the FUSE operations concept, discusses the systems engineering approach used for its development, and the software, hardware and management tools that will make its implementation feasible.

Butler, Madeline J.↗
NASA NTRS1980

Radial diffusion in Io's torus - Some implications from Voyager I

Data from several Voyager 1 experiments are used to determine the magnitude and L dependence of the radial diffusion coefficient for low-energy charged particles outside of Io's orbit under steady-state conditions. The extreme ultraviolet observations near 685A are inverted to produce an ion density profile for L greater than 6. This normalized ion profile as well as the (equatorial) electron density profile estimated from the planetary radio astronomy (PRA) observations falls off as L to the -5th. Such a density gradient would make possible centrifugally driven cross-L diffusion outside of Io's orbit without ruling out the presence of an atmospherically driven mechanism. A lower limit for the radial diffusion coefficient DLL is 1.5 x 10 to the -10th L to the 5th (Jupiter radii squared per sec), yielding a characteristic diffusion time from 6RJ to 7RJ of less than 10 days, much shorter than previously anticipated. Steady-state diffusion is not a good assumption inside of Io's orbit, where the particle densities decrease sharply from 6 Jupiter radii to 5 Jupiter radii; the diffusion time in that region is probably longer than outside of Io's orbit.

Froidevaux, L.↗
NASA NTRS1987

Search for ultraviolet Shuttle glow

In January 1986, the Space Shuttle Columbia carried two ultraviolet experiments (UVX) in an attempt to observe very weak diffuse emission from various astronomical sources at wavelengths below 3200 A with moderate spectral resolution. The experiment attested to the feasibility of low cost astronomy from the Space Shuttle using Get Away Special canisters. Emissions from O2, O, and NO were detected and shown to be consistent with an atmospheric origin.

Tennyson, P. D.↗
NASA NTRS2008

Stereo and Solar Cycle 24

The twin STEREO spacecrafi, launched in October 2006, are in heliocentric orbits near 4 AU with one spacecraft (Ahead) leading Earth in its orbit around the Sun and the other (Behind) trailing Earth. As viewed from the Sun, the STEREO spacecraft are continually separating from one another at about 45 degrees per year with Earth biseding the angle. At present, th@spaser=raft are a bit more than 45 degrees apart, thus they are able to each 'vie@ ground the limb's of the Sun by about 23 degrees, corresponding to about 1.75 days of solar rotation. Both spameraft contain an identical set of instruments including an extreme ultraviolet imager, two white light coronagraphs, tws all-sky imagers, a wide selection of energetic particle detectors, a magnetometer and a radio burst tracker. A snapshot of the real time data is continually broadcast to NOW-managed ground stations and this small stream of data is immediately sent to the STEREO Science Center and converted into useful space weather data within 5 minutes of ground receipt. The resulting images, particle, magnetometer and radio astronomy plots are available at ~ ~ j ~ g ~ ~ ~ i t , : gAs~ timqe~ co~n~ting ue~s ijnto~ ~ ~ ~ ~ . ~ g ~ solar cycle 24, the separation angle becomes 90 degrees in early 2009 and 180 degrees in early 201 1 as the activity heads toward maximum. By the time of solar maximum, STEREO will provide for the first time a view of the entire Sun with the mronagraphs and e*reme ultraviolet instruments. This view wilt allow us to follow the evolution of active regions continuously and also detect new active regions long before they pose a space weather threat to Earth. The in situ instruments will be able to provide about 7 days advanced notice of co-rotating structures in the solar wind. During this same intewal near solar maximum, the wide-angle imagers on STEREB will both be ;able to view EarlCP-dirsted CMEs in their plane-oPsky. When combined with Eat-lhorbiting assets available at that time, it seems solar cycle 24 will mark a great increase in our ability to understand and predict space weather.

Kaise,r Michael L.↗
NASA NTRS1965

Space astronomy.

Space astronomy, considering UV spectra of Jupiter and Venus, stellar energy distributions, interstellar scattering and X-ray observations

PLANETARY RADIATION↗
NASA NTRS1990

Multiwavelength studies of southern early type galaxies

Observations from an in progress program to study early type galaxies are presented. International Ultraviolet Explorer (IUE) spectra of the southern galaxies NGC 1326 and 1808 are presented and compared to IUE archival spectra of four galaxies of approximately similar morphological type. The targets were selected on the basis of their infrared astronomy satellite emission, peculiarities in their dust structure as revealed from charge coupled device frames and the presence of H I from 21 cm data. Preliminary results show large differences in stellar populations, and the presence of early spectral type stars are correlated with UV extinction and IR excess. Interpretation of the data is presented, discussing the correlations between extinction, gas content and stellar populations.

Danks, A. C.↗
NASA NTRS1999

UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers

Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.

NASA Center ARC↗