John Paul Andrews

Overview of the Far Ultraviolet Spectroscopic Explorer Mission

The Far Ultraviolet Spectroscopic Explorer satellite observes light in the far-ultraviolet spectral region, 905-1187 Angstrom, with a high spectral resolution. The instrument consists of four co-aligned prime-focus telescopes and Rowland spectrographs with microchannel plate detectors. Two of the telescope channels use Al :LiF coatings for optimum reflectivity between approximately 1000 and 1187 Angstrom, and the other two channels use SiC coatings for optimized throughput between 905 and 1105 Angstrom. The gratings are holographically ruled to correct largely for astigmatism and to minimize scattered light. The microchannel plate detectors have KBr photocathodes and use photon counting to achieve good quantum efficiency with low background signal. The sensitivity is sufficient to examine reddened lines of sight within the Milky Way and also sufficient to use as active galactic nuclei and QSOs for absorption-line studies of both Milky Way and extragalactic gas clouds. This spectral region contains a number of key scientific diagnostics, including O VI, H I, D I, and the strong electronic transitions of H-2 and HD.

THE COSMIC ORIGINS SPECTROGRAPH

The Cosmic Origins Spectrograph (COS) is a moderate-resolution spectrograph with unprecedented sensitivity that was installed into the Hubble Space Telescope (HST) in 2009 May, during HST Servicing Mission 4 (STS-125). We present the design philosophy and summarize the key characteristics of the instrument that will be of interest to potential observers. For faint targets, with flux F ? 1.0 ? 10?14?erg?cm?2?s?1 ??1, COS can achieve comparable signal to noise (when compared to Space Telescope Imaging Spectrograph echelle modes) in 1%-2% of the observing time. This has led to a significant increase in the total data volume and data quality available to the community. For example, in the first 20 months of science operation (2009 September-2011 June) the cumulative redshift pathlength of extragalactic sight lines sampled by COS is nine times than sampled at moderate resolution in 19 previous years of Hubble observations. COS programs have observed 214 distinct lines of sight suitable for study of the intergalactic medium as of 2011 June. COS has measured, for the first time with high reliability, broad Ly? absorbers and Ne VIII in the intergalactic medium, and observed the He II reionization epoch along multiple sightlines. COS has detected the first CO emission and absorption in the UV spectra of low-mass circumstellar disks at the epoch of giant planet formation, and detected multiple ionization states of metals in extra-solar planetary atmospheres. In the coming years, COS will continue its census of intergalactic gas, probe galactic and cosmic structure, and explore physics in our solar system and Galaxy.

Performance overview and science goals of the Cosmic Origins Spectrograph for the Hubble Space Telescope

We present an overview of the expected performance and science goals of the cosmic origins spectrograph (COS), a fourth generation instrument to be installed aborad the Hubble Space Telescope (HST) during the fourth HST servicing mission scheduled for late 2002. COS is a UV spectrograph optimized for observing faint point sources with moderate spectral resolution. The instrument has two channels: a far- UV channel that is sensitive in the 1150-1775 angstrom wavelength range and a near-UV channel that operates between 1750-3200 angstrom. The COS science team program concentrates on QSO absorption line systems and the IGM, dynamics of the ISM in galaxies and galaxy halos, UV extinction in the Milky Way, horizontal-branch stars in globular clusters, and volatile gases in the atmospheres of solar system bodies.

Design and mounting of the gratings for the Far Ultraviolet Spectroscopic Explorer (FUSE)

The far UV spectroscopic explorer grating mechanical design and analysis are discussed. These gratings are large (266 mm X 275 mm), and unique design constraints were imposed to maintain optical performance. FEM results of deflection and stress are presented. Requirements driving the unconventional grating design and its mount are addressed, including the plan to accommodate remote vacuum alignment in multiple degrees of freedom.

Southwest Research Institute intensified detector development capability

Imaging detectors for wavelengths between 10 nm and 105 nm generally rely on microchannel plates (MCPs) to provide photon detection (via the photo-electric effect) and charge amplification. This is because silicon-based detectors (CCD or APS) have near zero quantum detection efficiency (QDE) over this wavelength regime. Combining a MCP based intensifier tube with a silicon detector creates a detector system that can be tuned to the wavelength regime of interest for a variety of applications. Intensified detectors are used in a variety of scientific (e.g. Solar Physics) and commercial applications (spectroscopic test instrumentation, night vision goggles, low intensity cameras, etc.). Building an intensified detector requires the mastery of a variety of technologies involved in integrating and testing of these detector systems. We report on an internally funded development program within the Southwest Research Institute to architect, design, integrate, and test intensified imaging detectors for space-based applications. Through a rigorous hardware program the effort is developing and maturing the technologies necessary to build and test a large format (2k × 2k) UV intensified CCD detector. The intensified CCD is designed around a commercially available CCD that is optically coupled to a UV Intensifier Tube from Sensor Sciences, LLC. The program aims to demonstrate, through hardware validation, the ability to architect and execute the integration steps necessary to produce detector systems suitable for space-based applications.

Final flight grating mount design for the far ultraviolet spectroscopic explorer

ABSTRACT The Far Ultraviolet Spectroscopic Explorer grating mount design, analysis, fabrication, and test results arediscussed. The redesign of the original concept is presented as well as the fabrication and test results which necessitated thefinal design changes. Results of interferometric tests indicating optical surface sensitivity to adhesive bonding and mountattachment are reviewed. Vibration test data are presented, as well as coarse alignment and remote vacuum alignmentresults. Final test results are included, which show the mount assembly meets the FUSE distortion and stabilityrequirements.Keywords: flex pivot, FUSE, glass/metal bond, grating, holographic, spectrograph 1. INTRODUCTION The Far Ultraviolet Spectroscopic Explorer (FUSE) is a NASA sponsored low earth orbiting astrophysicalobservatory designed to provide high spectral resolution observations across the 905A to 1 195A bandpass. FUSE iscurrently in production and is scheduled to launch in late 1998.1.1. The Far Ultraviolet Spectrograph

Unique method of micropositioning as implemented in the FUSE focal plan assemblies

The Focal Plane Assemblies (FPAs), as shown in Figure 1, are a unique actuator/flexure system for space flight micropositioning. The FPAs use a High-Output Paraffm Linear Actuator (HOPLA) to actuate the X-axis compound-flexure motion stage. Closed-loop control over the linear range of motion allows for relatively static, low-frequency, micropositioning, and represents a departure from the usual binary operation of paraffm actuators. The HOPLA flexure system can achieve accurate sub-micron positioning without friction, stiction, backlash, or hysteresis. Resolution is determined by the noise-floor of the position-sensor/control electronics and the quality of the thermal management system.