Proc. SPIE. 9910, Observatory Operations: Strategies, Processes, and Systems VI
KEYWORDS: Stars, Cameras, Sensors, Calibration, Spectroscopy, Spectroscopy, Imaging spectroscopy, Molybdenum, Target acquisition, James Webb Space Telescope, James Webb Space Telescope, Camera shutters
The Near-Infrared Spectrograph (NIRSpec) is the work-horse spectrograph at 1-5microns for the James Webb Space Telescope (JWST). A showcase observing mode of NIRSpec is the multi-object spectroscopy with the Micro-Shutter Arrays (MSAs), which consist of a quarter million tiny configurable shutters that are 0. ′′20×0. ′′46 in size. The NIRSpec MSA shutters can be opened in adjacent rows to create flexible and positionable spectroscopy slits on prime science targets of interest. Because of the very small shutter width, the NIRSpec MSA spectral data quality will benefit significantly from accurate astrometric knowledge of the positions of planned science sources. Images acquired with the Hubble Space Telescope (HST) have the optimal relative astrometric accuracy for planning NIRSpec observations of 5-10 milli-arcseconds (mas). However, some science fields of interest might have no HST images, galactic fields can have moderate proper motions at the 5mas level or greater, and extragalactic images with HST may have inadequate source information at NIRSpec wavelengths beyond 2 microns. Thus, optimal NIRSpec spectroscopy planning may require pre-imaging observations with the Near-Infrared Camera (NIRCam) on JWST to accurately establish source positions for alignment with the NIRSpec MSAs. We describe operational philosophies and programmatic considerations for acquiring JWST NIRCam pre-image observations for NIRSpec MSA spectroscopic planning within the same JWST observing Cycle.
We explore the design of a space mission called Project Lyman that has the goal of quantifying the ionization history of the universe from the present epoch to a redshift of z ~ 3. Observations from WMAP and SDSS show that before a redshift of z (Symbol not available. See manuscript.) 6 the first collapsed objects, possibly dwarf galaxies, emitted Lyman continuum (LyC) radiation shortward of 912 Å that reionized most of the universe. Theoretical estimates of the LyC escape fraction ( fesc ) required from these objects to complete reionization is fesc ~10%. How LyC escapes from galactic environments, whether it induces positive or negative feedback on the local and global collapse of structures, and the role played by clumping, molecules, metallicity and dust are major unanswered theoretical questions, requiring observational constraint. Numerous intervening Lyman limit systems frustrate the detection of LyC from high z objects. They thin below z ~ 3 where there are reportedly a few cases of apparently very high fesc. At low z there are only controversial detections and a handful of upper limits. A wide-field multi-object spectroscopic survey with moderate spectral and spatial resolution can quantify fesc within diverse spatially resolved galactic environments over redshifts with significant evolution in galaxy assemblage and quasar activity. It can also calibrate LyC escape against Lyα escape, providing an essential tool to JWST for probing the beginnings of reionization. We present calculations showing the evolution of the characteristic apparent magnitude of star-forming galaxy luminosity functions at 900 Å, as a function of redshift and assumed escape fraction. These calculations allow us to determine the required aperture for detecting LyC and conduct trade studies to guide technology choices and balance science return against mission cost. Finally we review our efforts to build a pathfinding dual order multi-object spectro/telescope with a (0.5°)2 field-of-view, using a GSFC microshutter array, and crossed delay-line micro-channel plate detector.
Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE) has had a profound impact on many areas of astrophysics. Although the prime scientific instrument continues to perform well, numerous hardware failures on the attitude control system, particularly those of gyroscopes and reaction wheels, have made science operations a challenge. As each new obstacle has appeared, it has been overcome, although sometimes with changes in sky coverage capability or modifications to pointing performance. The CalFUSE data pipeline has also undergone major changes to correct for a variety of instrumental effects, and to prepare for the final archiving of the data. We describe the current state of the FUSE satellite and the challenges of operating it with only one reaction wheel and discuss the current performance of the mission and the quality of the science data.
Shull et al. have asserted that the contribution of stars, relative to quasars, to the metagalactic
background radiation that ionizes most of the baryons in the universe
remains almost completely unknown at all epochs. The potential to
directly quantify this contribution at low redshift has recently become
possible with the identification by GALEX of large numbers of
sparsely distributed faint ultraviolet galaxies. Neither STIS nor
FUSE nor GALEX have the ability to efficiently survey these sparse
fields and directly measure the Lyman continuum radiation that may leak
into the low redshift (z < 0.4) intergalactic medium. We present
here a design for a new type of far ultraviolet spectrograph, one that
is more sensitive, covers wider fields, and can provide spectra and
images of a large number of objects simultaneously, called the
Far-ultraviolet Off Rowland-circle Telescope for Imaging and
Spectroscopy (FORTIS). We intend to use a sounding rocket flight to
validate the new instrument with a simple long-slit observation of the
starburst populations in the galaxy M83. If however, the long-slit
were replaced with microshutter array, this design could isolate the
chains of blue galaxies found by GALEX over an ~30' diameter
field-of-view and directly address the Lyman continuum problem in a
long duration orbital mission. Thus, our development of the sounding
rocket instrument is a pathfinder to a new wide field spectroscopic
technology for enabling the potential discovery of the long
hypothesized but elusive Lyman continuum radiation that is thought to leak from low redshift galaxies and contribute to the ionization of the universe.
The Far Ultraviolet Spectroscopic Explorer satellite (FUSE)
is a NASA Origins mission launched on 1999 June 24 and
operated from the Johns Hopkins University Homewood campus in
Baltimore, MD. FUSE consists of four aligned telescopes feeding
twin far-ultraviolet spectrographs that achieve a spectral
resolution of R=20,000 over the 905-1187 Å spectral region.
This makes FUSE complementary to the Hubble Space Telescope
and of broad general interest to the astronomical community.
FUSE is operated as a general-purpose observatory with
proposals evaluated and selected by NASA.
The FUSE mission concept evolved dramatically over time. The
version of FUSE that was built and flown was born out of the
"faster, better, cheaper" era, which drove not only the
mission development but also plans for operations. Fixed price
contracts, a commercial spacecraft, and operations in the
University environment were all parts of the low cost strategy.
The satellite performs most functions autonomously, with ground
contacts limited typically to seven 12-minute contacts per
day through a dedicated ground station. All support functions
are managed by a staff of 40 scientists and engineers located at
Johns Hopkins. In this configuration, we have been able to achieve
close to 30% average on-target science efficiency. In short, FUSE is a successful example of the "faster, better, cheaper" philosophy.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched on June 24, 1999. FUSE is designed to make high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstrom). Its high effective area, low background and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. FUSE has now been in orbit for one year. We discuss the accomplishments of the FUSE mission during this time, and look ahead to the future now that normal operations are under way.
The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite was launched into orbit on June 24, 1999. FUSE is now making high resolution ((lambda) /(Delta) (lambda) equals 20,000 - 25,000) observations of solar system, galactic, and extragalactic targets in the far ultraviolet wavelength region (905 - 1187 angstroms). Its high effective area, low background, and planned three year life allow observations of objects which have been too faint for previous high resolution instruments in this wavelength range. In this paper, we describe the on- orbit performance of the FUSE satellite during its first nine months of operation, including measurements of sensitivity and resolution.