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NASA NTRS2017

Advanced Environmentally Resistant Lithium Fluoride Mirror Coatings for the Next Generation of Broadband Space Observatories

Recent advances in the physical vapor deposition (PVD) of protective fluoride films have raised the far-ultraviolet (FUV: 912-1600 A) reflectivity of aluminum-based mirrors closer to the theoretical limit. The greatest gains, at more than 20%, have come for lithium fluoride-protected aluminum, which has the shortest wavelength cutoff of any conventional overcoat. Despite the success of the NASA FUSE mission, the use of lithium fluoride (LiF)-based optics is rare, as LiF is hygroscopic and requires handling procedures that can drive risk. With NASA now studying two large mission concepts for astronomy, Large UV-Optical-IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HabEx), which mandate throughput down to 1000 , the development of LiF-based coatings becomes crucial. This paper discusses steps that are being taken to qualify these new enhanced LiF-protected aluminum (eLiF) mirror coatings for flight. In addition to quantifying the hygroscopic degradation, we have developed a new method of protecting eLiF with an ultrathin (10-20 A) capping layer of a nonhygroscopic material to increase durability. We report on the performance of eLiF-based optics and assess the steps that need to be taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space missions.

Fleming, Brian↗

NASA NTRS1973

Optical space astronomy and goals of the large space telescope.

Optical astronomy now means the study of EM radiation in the very near IR and vacuum UV in addition to the visible wavelengths. Practical constraints presently define the IR limit at about 11000 A, where photoemissive cathodes become ineffective, and the UV limit at 912 A, where the hydrogen of the interstellar medium limits the view to very nearby objects. Salient events of the first decade of optical space astronomy are discussed together with the orbiting astronomical observatories. Particular attention is given to the large space telescope (LST) project, taking into account the physical characteristics of the LST and the scientific program.

O'Dell, C. R.↗

NASA NTRS1984

An all-reflective wide-angle flat-field telescope for space

An all-reflective wide-angle flat-field telescope (WAFFT) designed and built at Goddard Space Flight Center demonstrates the markedly improved wide-angle imaging capability which can be achieved with a design based on a recently announced class of unobscured 3-mirror optical systems. Astronomy and earth observation missions in space dictate the necessity or preference for wide-angle all-reflective systems which can provide UV through IR wavelength coverage and tolerate the space environment. An initial prototype unit has been designed to meet imaging requirements suitable for monitoring the ultraviolet sky from space. The unobscured f/4, 36 mm efl system achieves a full 20 x 30 deg field of view with resolution over a flat focal surface that is well matched for use with advanced ultraviolet image array detectors. Aspects of the design and fabrication approach, which have especially important bearing on the system solution, are reviewed; and test results are compared with the analytic performance predictions. Other possible applications of the WAFFT class of imaging system are briefly discussed. The exceptional wide-angle, high quality resolution, and very wide spectral coverage of the WAFFT-type optical system could make it a very important tool for future space research.

Hallam, K. L.↗

NASA NTRS1982

Good imaging with very fast paraboloidal primaries - An optical solution and some applications

Attention is given to the imaging performance improvement obtainable in telescopes with fast parabolic primaries by means of two-mirror correctors of the Paul-Baker type. Images with 80 percent of the energy concentrated within 0.2 arcsec are projected for an f/1 primary relaying to an f/2 final focus, over a 1 deg-diameter field. It is noted that the mechanical structure and enclosure of a large telescope built with these fast optics should be significantly smaller and less expensive than those for conventional optics. The application of the Paul-Baker corrector system is explored for such diverse telescope types as those employing six off-axis primary mirrors, UV astronomy telescopes with no chromatic aberration, a low emissivity IR astronomy instrument with an off-axis f/1 parent primary mirror part, and thin rectangular aperture telescopes which are useful for spectroscopy and photometry.

Angel, J. R. P.↗

NASA NTRS2004

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 observations have begun to address these issues, the interpretation of such data is particularly challenging because of the sensitivity to dust obscuration (at optical and UV wavelengths). The absorbed light is reradiated at IR wavelengths, hence the optimal indicators of the star-formation rate (SFR) is at a rest-frame wavelength of approx. 60 microns. The Spitzer Space Telescope mission is beginning to revolutionize the study of the global properties and evolution of galaxies. Spitzer reaches nearly two orders of magnitude more sensitivity than previous IR space missions. 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. The overall research program is divided into three main investigations: A Mid-IR Hubble Atlas and SFR estimators in the local universe, Evolution of the SFR at 0 < z < 1 using pencil beam redshift surveys, and Galaxy formation and evolution at 1 < z < 5. The Spitzer Space Telescope launched during the past year and the first papers from it are currently being submitted to The Astrophysical Journal. This is clearly an exciting time for IR astronomy!

Pahre, Michael A.↗

NASA NTRS2000

Acousto-Optic Imaging Spectrometers for Mars Surface Science

NASA's long term plan for Mars sample collection and return requires a highly streamlined approach for spectrally characterizing a landing site, documenting the mineralogical make-up of the site and guiding the collections of samples which represent the diversity of the site. Ideally, image data should be acquired at hundreds of VIS and IR wavelengths, in order to separately distinguish numerous anticipated species, using principal component analysis and linear unmixing. Cameras with bore-sighted point spectrometers can acquire spectra of isolated scene elements, but it requires 10(exp 2) to 10(exp 2) successive motions and precise relative pointing knowledge in order to create a single data cube which qualifies as a spectral map. These and other competing science objectives have to be accomplished within very short lander/rover operational lifetime (a few sols). True, 2-D imaging spectroscopy greatly speeds up the data acquisition process, since the spectra of all pixels in the scene are collected at once. This task can be accomplished with cameras that use electronically tunable acousto-optic tunable filters (AOTFs) as the optical tuning element. AOTFs made from TeO2 are now a mature technology, and operate at wavelengths from near-UV to about 5 microns. Because of incremental improvements in the last few years, present generation devices are rugged, radiation-hard and operate at temperatures down to at least 150K so they can be safely integrated into the ambient temperature optics of in-situ instruments such as planetary or small-body landers. They have been used for ground-based astronomy, and were also baselined for the ST-4 Champollion IR comet lander experiment (CIRCLE), prior to cancellation of the ST-4 mission last year. AIMS (for Acousto-optic Imaging spectrometer), is a prototype lander instrument which is being built at GSFC with support by the NASA OSS Advanced Technologies and Mission Studies, Mars Instrument Definition and Development Program (MIDP). AIMS is capable of tunable spectroscopic imaging of surface mineralogy, ices and dust between 0.5 and 2.4 microns, at a resolving power (lambda/delta lambda) which is typically several hundred. The design spatial resolution, similar to IMP and SSI, will allow mapping at scales down to about 1 cm.

Glenar, D. A.↗

NASA NTRS2003

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 observations have begun to address these issues, the interpretation of such data is particularly challenging because of the sensitivity to dust obscuration (at optical and UV wavelengths). The absorbed light is re-radiated at IR wavelengths, hence the optimal indicators of the star formation rate (SFR) is at a rest-frame wavelength of approx. 60 microns. The SIRTF mission will revolutionize the study of the global evolution of the SFR by providing mass-selected, complete samples of galaxies and far-IR estimators of the SFR. SIRTF will be two orders of magnitude more sensitive than previous IR space missions, and therefore will open up a completely new region of parameter space in sensitivity and angular resolution. This research program will 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. The overall research program is divided into three main investigations: a Mid-IR Hubble Atlas and SFR estimators in the local universe, evolution of the SFR at 0 less than z less that 1 using pencil beam redshift surveys, and Galaxy formation and evolution at 1 less than z less than 5.

Pahre, Michael A.↗

NASA NTRS2005

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 observations have begun to address these issues, the interpretation of such data is particularly challenging because of the sensitivity to dust obscuration (at optical and UV wavelengths). The absorbed light is re-radiated at IR wavelengths, hence the optimal indicators of the star formation rate (SFR) is at a rest-frame wavelength of approx. 60 microns. The Spitzer Space Telescope mission is revolutionizing the study of the global properties and evolution of galaxies. Spitzer reaches nearly two orders of magnitude more sensitivity than previous IR space missions. 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. The overall research program is divided into three main investigations: A Mid-IR Hubble Atlas and SFR estimators in the local universe, Evolution of the SFR at 0 < z < 1 using pencil beam redshift surveys, and Galaxy formation and evolution at 1 < z < 5. The first papers from Spitzer were published during the last year, including ten refereed journal papers where the PI was first or co-author.

Pahre, Michael A.↗

NASA NTRS2002

Evolution of Galaxies and the Star Formation Rate in the Infrared

Pahre, Michael, A.↗

NASA NTRS1995

High Resolution IRAS Maps and IR Emission of M31 -- II. Diffuse Component and Interstellar Dust

Large-scale dust heating and cooling in the diffuse medium of M31 is studied using the high resolution (HiRes) IRAS maps in conjunction with UV, optical (UBV), and the HI maps. A dust heating/cooling model is developed based on a radiative transfer model which assumes a 'Sandwich' configuration of dust and stars takes account of the effect of dust grain scattering.

infrared astronomy galaxies interstellar grains ph↗