SPIE Proceedings Vol. 1945
Space Astronomical Telescopes and Instruments II
Editor(s): Pierre Y. Bely, Space Telescope Science Institute,
Baltimore, MD, USA;
James B. Breckinridge, Jet Propulsion Lab.,
La Canada, CA, USA.
ISBN: 0-8194-1181-7, 526 pages
Published 1993
Meeting Date: 04/11 - 04/16/93, Orlando, FL, USA
Abstracts for the papers in this volume are located in this file immediately
following the contents list below. All papers are published by SPIE--The
International Society for Optical Engineering, P.O. Box 10, Bellingham,
Washington, 98227-0010, USA.
Contents:
* Commissioning of Hubble Space Telescope: the strategy for
recovery
* Hubble Space Telescope first servicing mission and observatory
recommissioning
* Status and optical performance of the corrective optics space
telescope axial replacement (COSTAR)
* System performance analysis for COSTAR design
* Effect of mirror microroughness scattering on the Hubble Space
Telescope point spread function
* Post-launch experience of the Hubble Space Telescope:
reflections upon the design and operation
* Line-of-sight jitter of the Hubble Space Telescope
* Effect of double stars on the guiding system of the Hubble space
telescope
* Calibration database for the Hubble Space Telescope
* Restoration of HST images and spectra--some lessons learned
* Lessons learned in setting up and running the European copy of
HST archive
* Edison project and radiatively cooled infrared space
observatories
* Optical design of the composite infrared spectrometer (CIRS) for
the Cassini mission
* INTEGRAL: the next major gamma-ray astronomy mission?
* Integrated structural and optical modeling of the orbiting
stellar interferometer
* Next generation space telescope: control system issues
* X-ray and gamma-ray imaging with monolithic CdZnTe detector
arrays
* Optical/UV monitor telescope on the x-ray multimirror
observatory
* High-resolution EUV spectroscopy: performance of spherical
multilayer-coated gratings operated at near normal incidence
* Limits on adaptive optics systems for lightweight space
telescopes
* Solar vector magnetograph: a candidate instrument for a lunar
solar observatory
* Conceptual design for a second generation space telescope
* Optimized performance and operations of the Faint Object Camera
* Serendipitous background monitoring of the Hubble Space
Telescope's Faint Object Spectrograph
* Thermal control of the space telescope high speed photometer
* On-orbit sky background measurements Faint Object Spectrograph
* Predicted performance of the COSTAR-corrected Faint Object
Camera
* Restoration of FOC imaging data: considerations when choosing
FOC PSFs
* In-flight performance of the Faint Object Camera of the Hubble
Space Telescope: II
* Correction of the geomagnetically induced image motion problem
on the Hubble Space Telescope's Faint Object Spectrograph
* Performance of the FOS detectors in a variable external magnetic
field
* Operations experience of the space telescope high-speed
photometer
* Instrumental artifacts: stray and scattered light in the Goddard
High-Resolution Spectrograph aboard the Hubble Space Telescope
* Scattered light characteristics of the Hubble Space Telescope
Faint Object Spectrograph
* Goddard High-Resolution Spectrograph of the Hubble Space
Telescope: operation, performance, anomalies and lessons learned
* On-orbit management of contaminants within the Hubble Space
Telescope widefield planetary camera and their effect on
instrument performance
* Contamination effects on EUV optics in the space environment
* Optimized holographic grating solution for Rowland circle
spectrographs
* System analysis for the near-infrared camera and multiobject
spectrometer cryogenic and structural design
* NICMOS flight focal plane assembly
* Optical design of NICMOS: the second-generation infrared
instrument for the Hubble Space Telescope
* FUSE microchannel plate detectors: models and data for
resolution at the pore limit
* Theoretical and measured encircled energy and wide-angle scatter
of SUMER demonstration telescope mirror in FUV
* Dimensionally stable graphite-fiber-reinforced composite mirror
technology
* Fabrication and characterization of a micromachined deformable
mirror for adaptive optics applications
* Diffractive errors in segmented adaptive optics
* Optical design of an UV camera for a Ritchey-Chretien space
telescope
* Optical design of two-mirror widefield cameras for large
telescopes
* Image reconstruction and deconvolution techniques applied to
ASCA data
* Coded mask telescope with a germanium array detector
* Ultraviolet and VUV sources for in-flight calibration of space
experiments
* Echelle class spectroscopy with a single holographic grating
* Robotic telescope systems for CCD photometry of faint objects in
crowded fields
* Spectrally selective surfaces for ground and space-based
instrumentation: support for a resource base
* Space-based CCD experiment for high-precision astrometry
Abstracts:
Commissioning of Hubble Space Telescope: the strategy for
recovery, pp.2-10
Author(s): James H. Crocker, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: When the space shuttle Endeavor rockets into orbit on
December 2, 1993, NASA will begin the last phase of a
three part program to recover from the disappointing
beginnings of Hubble Space Telescope operations. The
problem with the telescope was detected shortly after
launch in April of 1990 and in June of that year NASA
concluded that the primary mirror of the telescope had
been manufactured with the wrong figure. NASA
immediately began a detailed investigation to determine
exactly what went wrong. Next, NASA and the HST
community began a multi-effort program to maximize and
improve the science produced by the telescope in its
aberrated condition. Finally, plans were developed to
repair the telescope's problems in orbit and to restore
the observatory's full scientific potential. Much has
been written about the failure to detect this flaw
before launch. The impression of many outside the
program is that Hubble is a complete failure. Far less
has been written of the impressive efforts and
successes as the recovery from this disappointing start
evolved.!9
Hubble Space Telescope first servicing mission and observatory
recommissioning, pp.11-16
Author(s): Peg Stanley, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: HST is unique among NASA missions in the level of
preparation that has been performed for on-orbit
servicing. Planning and training for HST servicing has
been an important element HST development leading to an
observatory that is uniquely designed with servicing in
mind. An overview of the components of the first
Servicing Mission are described along with a
walkthrough of several of the planned extravehicular
activities (EVAs) including replacing solar arrays,
swapping out the WF/PC and HSP for WFPC2 and COSTAR,
replacing the gyros and installing the GHRS repair kit.
An integral part of preparing for HST's first servicing
mission is determining how to recommission the
observatory for science operations. The recommissioning
period is referred to as the Servicing Mission
Observatory Verification (SMOV) program and is a
composite of the HST deployment Orbital Verification
(OV) and Science Verification (SV) programs. We will
examine how the lessons learned from the deployment
commissioning have been addressed in development of the
SMOV plans.!0
Status and optical performance of the corrective optics space
telescope axial replacement (COSTAR), pp.17-24
Author(s): George F. Hartig, Space Telescope Science Institute,
Parkton, MD, USA;
James H. Crocker, Space Telescope Science Institute,
Baltimore, MD, USA;
Holland C. Ford, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: The Corrective Optics Space Telescope Axial Replacement
(COSTAR) is designed to restore the high image quality,
lost to a primary mirror manufacturing defect, that was
originally expected from the Hubble Space Telescope
(HST). Though its rapid development is both a technical
and programmatic challenge, COSTAR is nearing
completion at Ball Aerospace and is scheduled for
deployment during the first HST servicing shuttle
mission late this year. This paper describes the
extensive optical testing that has been planned to
assure the high quality imaging performance of the
COSTAR-corrected HST. Independent, redundant tests at
both component and system levels are employed to verify
that design tolerances are sufficient and manufacturing
tolerances are achieved. We report the results of the
critical tests which have been completed to date and
their implications for the on-orbit performance.!6
System performance analysis for COSTAR design, pp.25-35
Author(s): Paul A. Lightsey,
Ball Aerospace and Communications Group, Boulder,
CO, USA;
John D. Gerber,
Ball Aerospace and Communications Group, Boulder,
CO, USA;
Michael L. Kaplan,
Ball Aerospace and Communications Group, Boulder,
CO, USA;
Dennis A. Teusch,
Ball Aerospace and Communications Group, Boulder,
CO, USA.
Abstract: The Corrective Optics Space Telescope Axial Replacement
(COSTAR) instrument is designed to provide optical
correction for the current figure error in the Hubble
Space Telescope (HST) primary mirror to three of the
first generation instruments: Faint Object Camera
(FOC), Faint Object Spectrometer (FOS), and the Goddard
High Resolution Spectrometer. The FOC and FOS each have
two optical channels and the GHRS one optical channel
that are corrected. The optical correction is achieved
by deploying a two mirror relay into the HST hub area
in front of the Optical Telescope Assembly (OTA) focal
surface for each optical channel. Structural motion of
the mirror support system will affect alignment
producing changes in wave front error (wfe) and
line-of-sight (los). Changes of los during an exposure
will blur the image and degrade image quality in
addition to alignment degradation of wfe. The system
analyses used to perform image quality trades and
allocate budgets in the design phase and to help define
requirements for the integration and test phase will be
presented. These analyses were an integrated and
iterative process among the optical, structural, and
thermal analysis disciplines. Results of these analyses
predict COSTAR performance will meet the image quality
requirements.!3
Effect of mirror microroughness scattering on the Hubble Space
Telescope point spread function, pp.36-41
Author(s): Hashima Hasan, Space Telescope Science Institute,
Baltimore, MD, USA;
Christopher J. Burrows,
Space Telescope Science Institute and European Space
Agency, Baltimore, MD, USA.
Abstract: The effect of internal light scattering caused by the
microroughness of the Hubble Space Telescope primary
mirror was measured and compared with theoretical
models. It was found that the effect was much smaller
than predicted and would not be a problem even in the
UV.!1
Post-launch experience of the Hubble Space Telescope: reflections
upon the design and operation, pp.42-54
Author(s): A.J. Bradley, Allied Signal Aerospace Co.,
Annapolis Junction, MD, USA;
Gerald S. Nurre, NASA Marshall Space Flight Ctr.,
Huntsville, AL, USA;
W.Ochs, NASA Goddard Space Flight Ctr., Greenbelt,
MD, USA;
J.Ryan, NASA Goddard Space Flight Ctr., Greenbelt,
MD, USA;
Hugh Dougherty, Lockheed Missiles & Space Co.,Inc.,
Sunnyvale, CA, USA;
Norman R. Bennett,
Lockheed Missiles & Space Co., Inc., Sunnyvale, CA,
USA;
Linda Abramowicz-Reed,
Hughes Danbury Optical Systems, Inc., Danbury, CT,
USA;
G.C. Andersen, Jackson & Tull, Greenbelt, MD, USA;
William G. Crabb, Allied Signal Technical Services,
Columbia, MD, USA.
Abstract: The Hubble Space Telescope (HST) is an orbiting
astronomical observatory, designed to operate as close
as possible to ground based instrumentation, given the
limitation of operating in a low earth orbit. The
spacecraft design had to accommodate an absolute
pointing accuracy of 0.01 arc seconds, a relative
pointing stability of 0.007 arc seconds rms, the
capability to maneuver 90 degrees in 18 minutes, and
operate autonomously in a safemode control scheme for
up to 72 hours. Furthermore, the design had to provide
for a flexible, stored command methodology, and
real-time command capability. This paper briefly
reviews the spacecraft engineering hardware and
software design. A detailed critique of the on-orbit
performance of the spacecraft is provided. Enhancements
and work-around, which have enabled HST to continue
implementation of a successful science plan, are
explained.!12
Line-of-sight jitter of the Hubble Space Telescope, pp.55-61
Author(s): Pierre Y. Bely, Space Telescope Science Institute,
Baltimore, MD, USA;
Olivia L. Lupie, Space Telescope Science Institute,
Baltimore, MD, USA;
John L. Hershey, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: We report on the results of a dedicated on-orbit test
which we have performed to measure the line-of- sight
jitter of the Hubble Space Telescope. The test, which
made use of one of the science instruments on board the
spacecraft, had a very high sensitivity (a fraction of
a milliarcsecond) and covered all frequencies up to 500
Hz. As was previously known from gyroscope data
analysis, the bulk of the line- of-sight jitter occurs
at frequencies lower than 5 Hz and is caused by motion
of the spacecraft body reacting against the oscillation
of its appendages. However, the test indicates that
there are also minor contributions by various modes of
the telescope structure in the 15 - 30 Hz range and the
vibration of the primary mirror at 61 Hz when it is
excited by thermally induced shocks or the running of
the tape recorder. There are also traces of a component
around 300 Hz induced by the tape recorder.!0
Effect of double stars on the guiding system of the Hubble space
telescope, pp.62-68
Author(s): John L. Hershey, Space Telescope Science Institute,
Baltimore, MD, USA;
Pierre Y. Bely, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: The interferometric system used for the guidance of HST
is sensitive to close binaries, and before the launch
of HST it was believed that up to 25% of all guide
stars pairs would lead to guidance failure due to
duplicity. After nearly 3 years of operation the actual
failure rate is below 1%. We have developed a computer
simulator to understand the causes of the discrepancy.
Our simulation results indicate a failure rate under 2%
per guide-star pair in much closer agreement with the
observed performance of the guiding system. We show
that the failure criterion originally used was much too
severe and that the proportion of guide stars in the
critical separation range had also been
overestimated.!5
Calibration database for the Hubble Space Telescope, pp.69-74
Author(s): Colin R. Cox, Space Telescope Science Institute,
Baltimore, MD, USA;
Calvin Tullos, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: We discuss the requirements and design of the
calibration data base which supports the processing of
Hubble Space Telescope observations. We describe
procedures for ensuring that, despite the continuing
changes to software and hardware, calibration files to
match the instrument configuration for any observation
are provided when needed.!0
Restoration of HST images and spectra--some lessons learned,
pp.75-82
Author(s): Hans-Martin Adorf, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany;
Richard N. Hook, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany;
Leon B. Lucy,
European Southern Observatory and European Space Agen
cy, Garching bei Muenchen,
Federal Republic of Germany.
Abstract: Images and spectra obtained with the Hubble Space
Telescope (HST) in its current configuration suffer
from severe spherical aberration and are therefore
routinely restored for visualization and scientific
evaluation. Among the non-linear, iterative restoration
methods investigated so far, the Richardson- Lucy (RL)
algorithm stands out for the quality of the
restorations it delivers at modest computational cost.
In this contribution we summarize our experience so far
with restoration methodology applied to HST imagery and
make a first attempt at drawing some general
conclusions about its usefulness.!25
Lessons learned in setting up and running the European copy of
HST archive, pp.83-90
Author(s): Benoit Pirenne, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany;
P.Benvenuti, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany;
Rudolf Albrecht, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany;
B.F. Rasmussen, European Southern Observatory,
Garching bei Muenchen, Federal Republic of Germany.
Abstract: The endeavour of Hubble Space Telescope (HST) proved
once more that arguments such as high costs, extremely
long preparation time, inherent total failure risks,
limited life time and high over- subscription rates
make each scientific space mission almost always a
unique event. The above arguments immediately point to
the need for storing all the data produced by
spacecraft in a short time for the scientific community
to re-use in the long term. This calls for the
organization of science archives. Together with the
Space Telescope Science Institute, the European
Coordinating Facility developed an archive system for
the HST data. This paper is about the experience gained
in setting up and running the European HST Science Data
Archive system. Organization, cost versus scientific
return and acceptance by the scientists are among the
aspects that will be covered. In particular, we will
insist on the 'four-pillar' structure principle that
all archive centers should have. Namely: a user
interface, a catalogue accurately describing the
content of the archive, the human scientific expertise
and of course the data. Long term prospects and
problems due to technology changes will be evaluated
and solutions will be proposed. The adaptability of the
system described to other scientific space missions our
ground-based observatories will be discussed.!7
Edison project and radiatively cooled infrared space
observatories, pp.92-99
Author(s): Harley A. Thronson, Jr.,
Wyoming Infrared Observatory, Laramie, WY, USA;
Timothy G. Hawarden, Joint Astronomy Ctr., Hilo, HI,
USA;
Tom W. Bradshaw, Rutherford Appleton Lab.,
Chilton, Didcot, Oxon, United Kingdom;
Anna H. Orlowska, Rutherford Appleton Lab.,
Chilton, Didcot, Oxon, United Kingdom;
Alan J. Penny, Rutherford Appleton Lab., Didcot,
United Kingdom;
R.F. Turner, Rutherford Appleton Lab., Didcot,
United Kingdom;
Donald Rapp, Jet Propulsion Lab., Pasadena, CA, USA.
Abstract: We describe the current design for Edison, the first
large radiatively-cooled infrared space observatory,
now under consideration by the European Space Agency.
Without the large cryogen tanks, more of the spacecraft
can be filled with light-collecting optics and, of
course, the observatory has no built-in lifetime. Our
proposal is for a telescope with a 1.7 m primary to be
launched by an Atlas, Ariane 5, or Proton. The baseline
orbit for the observatory is a 'halo' around L2, a
location which allows additional radiating area to be
placed anti-sunward. Models of the temperature behavior
of the observatory indicate an equilibrium temperature
via radiation alone of about 20 K. Use of near-future
cryo-coolers may allow optical system temperatures as
low as approximately 15 K. Consequently, Edison will be
limited in sensitivity by the celestial thermal
background at wavelengths shortward of about 60 $mu@m
and by celestial source confusion at longer
wavelengths.!10
Optical design of the composite infrared spectrometer (CIRS) for
the Cassini mission, pp.100-111
Author(s): Peter W. Maymon, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Michael G. Dittman, Swales & Associates, Inc.,
Beltsville, MD, USA;
Bert A. Pasquale, Swales & Associates, Inc.,
Beltsville, MD, USA;
Donald E. Jennings, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Kimberly I. Mehalick,
Advanced Technology & Research Corp., Burtonsville,
MD, USA;
Catherine J. Trout, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA.
Abstract: The Composite Infrared Spectrometer (CIRS) is an
instrument currently under development at NASA Goddard
Space Flight Center for the Cassini mission to Saturn.
The CIRS optical design heritage extends back to the
Infrared Interferometer Spectrometer (IRIS) which flew
on Voyager. CIRS is the next logical step in the
exploration of the atmosphere of Saturn and Titan. It
will obtain more complete sets of data with broader
spectral coverage, higher spectral and spatial
resolution, and greater sensitivity. The CIRS optical
design consists of four subassemblies: (1) a 50.8 cm
diameter Cassegrain telescope, (2) a Mid-Infrared (MIR)
Michelson interferometer, (3) a Far-Infrared (FIR)
polarizing interferometer, and (4) a Reference
interferometer (RI).!4
INTEGRAL: the next major gamma-ray astronomy mission?, pp.112-123
Author(s): Gerald K. Skinner, Univ. of Birmingham, Edgbaston,
Birmingham, United Kingdom;
S.Bergeson-Willis, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
T.Courvoisier, Observatoire de Geneve, Sauverny,
Geneva, Switzerland;
Anthony J. Dean, Univ. of Southampton, Southampton,
United Kingdom;
Ph. Durouchoux, SACLAY, Gif-sur-Yvette Cedex,
France;
N.Eismont, IKI, Moscow, Russia;
Neil Gehrels, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Jonathan E. Grindlay,
Harvard-Smithsonian Observatory, Cambridge, MA, USA;
W.A. Mahoney, Jet Propulsion Lab., Pasadena, CA,
USA;
James L. Matteson, Univ. of California/San Diego,
La Jolla, CA, USA;
B.McBreen, Univ. College, Belfield, Dublin, Ireland;
O.Pace, European Space Agency/ESTEC, Noordwijk,
Netherlands;
Thomas A. Prince,
California Institute of Technology, Pasadena, CA,
USA;
V.Schoenfelder,
Max-Planck-Institut fuer Extraterrestriche Physik,
Garching bei Muenchen, Federal Republic of Germany;
Rashid Sunyaev, Space Research Institute, Moscow,
Russia;
B.Swanenburg, SRON/ROL, Leiden, Netherlands;
Bonnard J. Teegarden,
NASA Goddard Space Flight Ctr., Greenbelt, MD, USA;
Pietro Ubertini, Istituto di Astrofisica Spaziale,
Frascati, Italy;
G.Vedrenne, Centre d'Etude Spatial des Rayonnements,
Toulouse, Cedex, France;
G.E. Villa,
Instituto per Ricerche in Fisica Cosmica, Milano,
Italy;
Serge Volonte, European Space Agency,
Paris Cedex 15, France;
C.Winkler, European Space Agency/ESTEC, Noordwijk,
Netherlands.
Abstract: The International Gamma-Ray Astrophysics Laboratory
(INTEGRAL) is a proposed joint ESA/NASA/Russia
gamma-ray astronomy mission which will provide both
imaging and spectroscopy. It is currently at the final
stages of an ESA phase-A study which it is hoped will
lead to it being adopted during 1993 as the second
'medium-class' mission within ESA's Horizon 2000 plan.
Launched in less than 10 years time it will be the
successor to the current generation of gamma-ray
spacecraft, NASA's Compton Observatory (GRO) and the
Soviet-French Granat/Sigma mission. The baseline is to
have two main instruments covering the photon energy
range 50 keV to 10 MeV, one concentrating on
high-resolution spectroscopy, the other emphasizing
imaging. In addition there will be two monitors - an
X-ray monitor which will extend the photon energy range
continuously covered down to a few keV, and an Optical
Transient Camera which will search for optical emission
from gamma-ray bursts.!34
Integrated structural and optical modeling of the orbiting
stellar interferometer, pp.124-132
Author(s): Stuart B. Shaklan, Jet Propulsion Lab., Pasadena,
CA, USA;
Jeffrey W. Yu, Jet Propulsion Lab., Pasadena, CA,
USA;
Hugh C. Briggs, Jet Propulsion Lab., Pasadena, CA,
USA.
Abstract: The Integrated Modeling of Optical Systems (IMOS)
Integration Workbench at JPL has been used to model the
effects of structural perturbations on the optics in
the proposed Orbiting Stellar Interferometer (OSI). OSI
consists of 3 pairs of interferometers and delay lines
attached to a 7.5 meter truss. They are
interferometrically monitored from a separate boom by a
laser metrology system. The spatially distributed
nature of the science instrument calls for a high level
of integration between the optics and support
structure. Because OSI is designed to achieve
micro-arcsecond astrometry, many of its alignment,
stability, and knowledge tolerances are in the
submicron regime. The spacecraft will be subject to
vibrations caused by reaction wheels and on-board
equipment, as well as thermal strain due to solar and
terrestrial heating. These perturbations affect optical
parameters such as optical path differences and beam
co-parallelism which are critical to instrument
performance. IMOS provides an environment that allows
one to design and perturb the structure, attach optics
to structural or non- structural nodes, trace rays, and
analyze the impact of mechanical perturbations on
optical performance. This tool makes it simple to
change the structure and immediately see performance
enhancement/degradation. We have employed IMOS to
analyze the effect of reaction wheel disturbances on
the optical path difference in both the science and
metrology interferometers.!10
Next generation space telescope: control system issues,
pp.133-144
Author(s): A.J. Bradley, Allied Signal Aerospace Co.,
Annapolis Junction, MD, USA;
K.Tompetrini, Allied Signal Aerospace Co.,
Teterboro, NJ, USA;
I.Steiner, Allied Signal Aerospace Co., Teterboro,
NJ, USA;
Gerald S. Nurre, NASA Marshall Space Flight Ctr.,
Huntsville, AL, USA;
J.Olivier, NASA Marshall Space Flight Ctr.,
Huntsville, AL, USA;
Max E. Nein, NASA Marshall Space Flight Ctr.,
Huntsville, AL, USA;
Abdullah S. Aljabri, Jet Propulsion Lab., Pasadena,
CA, USA;
Albert Boggess, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Laurence W. Fredrick, Univ. of Virginia,
Charlottesville, VA, USA.
Abstract: The control system requirements for the next generation
space telescope are discussed, based on the authors
experience with Hubble Space Telescope (HST), Advanced
X-Ray Astrophysics Facility (AXAF) and Space Infrared
Telescope Facility (SIRTF). Since the HST design phase,
there have been significant strides in the guidance and
control domain (i.e., fiber optic gyroscopes, solid
state star trackers and non-linear control algorithms).
The control system design will be determined by the
predicted spacecraft configuration, mirror geometry (6
to 8 meters will be considered) and science
requirements. Spacecraft dimensions have been estimated
for the telescope aperture range of interest.
Presently, the Energiya rocket can only accommodate a 6
m telescope, the proposed Heavy Lift Launch Vehicle
apparently can accommodate a 7 m telescope. A low Earth
orbit (600 Km) has been adopted for this study, the
advantage of Shuttle servicing and an accompanying long
spacecraft life, weighed heavily in this decision.
However, the possibility of a long spacecraft life in a
high altitude orbit, with the requisite attitude
control redundancy and fault tolerance, may be
feasible.!11
X-ray and gamma-ray imaging with monolithic CdZnTe detector
arrays, pp.145-151
Author(s): Fred P. Doty, Aurora Technologies Corp., San Diego,
CA, USA;
S.J. Friesenhahn, Aurora Technologies Corp.,
San Diego, CA, USA;
Jack F. Butler, Aurora Technologies Corp.,
San Diego, CA, USA;
Paul L. Hink, Univ. of California/San Diego,
San Diego, CA, USA.
Abstract: CdZnTe crystals useful for room temperature x-ray
astronomy detectors have recently been developed.
Uniform response and good energy resolution in the 3 to
300 keV range have been demonstrated for large area
detectors and monolithic arrays. Spectral resolution of
2.9 keV for the 59.5 keV $+241$/Am line, and resolved
661 keV peak from $+137$/Cs were recently achieved at
room temperature. Gain deviations of 1.2% were measured
for the elements over a large area monolithic array.
Imaging results from a 32 $MUL 32 array with active
area of 12.4 cm$+2$/ are presented. The stability,
uniformity, producibility and size of the crystals, and
the properties of the resulting nuclear radiation
detectors make CdZnTe an attractive candidate for
applications in the space sciences.!7
Optical/UV monitor telescope on the x-ray multimirror
observatory, pp.152-163
Author(s): Keith O. Mason, Mullard Space Science Lab., Dorking,
Surrey, United Kingdom;
Mark S. Cropper, Mullard Space Science Lab.,
Dorking, Surrey, United Kingdom;
John L. Fordham, Univ. College London, London,
United Kingdom;
France A. Cordova, The Pennsylvania State Univ.,
University Park, PA, USA;
David Leisawitz, The Pennsylvania State Univ.,
Greenbelt, MD, USA;
David H. Lumb, The Pennsylvania State Univ.,
University Park, PA, USA;
Cheng Ho, Los Alamos National Lab., Los Alamos, NM,
USA;
Elio Antonello, Osservatorio Astronomico di Brera,
Merate, Italy;
Claude A. Jamar, IAL-Space, Angleur, Belgium.
Abstract: The Optical/UV Monitor Telescope (XMM-OM) on the ESA
X-ray Cornerstone mission XMM is designed to provide
simultaneous optical and UV coverage of all sources
viewed by the observatory in the X-ray band. The
instrument consists of a 30 cm Ritchey-Chretien
telescope. This feeds a compact photon counting
detector that operates in the blue part of the optical
spectrum and the UV (1600 - 5500 angstroms), and
simultaneously a cooled CCD detector which registers
the red light (5500 - 10000 angstroms). The XMM-OM will
have a field of view of approximately 25 arcmin
diameter, matching that of the X-ray cameras on XMM,
and a spatial pixel size in normal operation of 1
arcsec in the blue, and about 1.8 arcsec in the red.
Because of the low sky background in space, the
sensitivity of the XMM-OM for detecting stars will be
comparable to that of a 4-m telescope at the Earth's
surface, and it should detect a B $EQ 24$+th$/
magnitude star with a photon counting detector in a
1000 s observation using unfiltered light.!1
High-resolution EUV spectroscopy: performance of spherical
multilayer-coated gratings operated at near normal incidence,
pp.164-175
Author(s): Michael P. Kowalski, Naval Research Lab., Laurel,
MD, USA;
John F. Seely, Naval Research Lab., Washington, DC,
USA;
Raymond G. Cruddace, Naval Research Lab.,
Washington, DC, USA;
Jack C. Rife, Naval Research Lab., Washington, DC,
USA;
C.M. Brown, Naval Research Lab., Washington, DC,
USA;
G.A. Doschek, Naval Research Lab., Washington, DC,
USA;
Uri Feldman, Naval Research Lab., Washington, DC,
USA;
Troy W. Barbee, Jr.,
Lawrence Livermore National Lab., Livermore, CA,
USA;
W.R. Hunter, SFA, Inc., Washington, DC, USA;
G.E. Holland, SFA, Inc., Washington, DC, USA;
Craig N. Boyer, Naval Research Lab., Washington, DC,
USA.
Abstract: A program is underway at the Naval Research Laboratory
(NRL) to develop a high-resolution spectrometer for the
study of astrophysical sources at EUV/soft X-ray
wavelengths. The spectrometer design is simple in that
the sole optic is a multilayer-coated spherical grating
or mosaic of co-aligned gratings used at near-normal
incidence, allowing large effective collecting area
without the strict tolerance requirements of grazing
incidence optics. Therefore, both high resolution and
high throughput can be obtained over several selected
narrow bandpasses. We present efficiency and resolving
power measurements of spherical gratings which have
parameters similar to that intended for our flight
instrument. Two gratings were replicated from the same
ruled master and then coated with a multilayer of
molybdenum and silicon. A third sister grating was used
as a control and overcoated with gold.!18
Limits on adaptive optics systems for lightweight space
telescopes, pp.176-184
Author(s): Laura Needels, Jet Propulsion Lab., Pasadena, CA,
USA;
B. Martin Levine, Jet Propulsion Lab., Arcadia, CA,
USA;
Mark Milman, Jet Propulsion Lab., Pasadena, CA, USA.
Abstract: Future space telescopes seek to maximize collecting
aperture for increased sensitivity and high spatial
resolution yet are limited in mass due to launch weight
restrictions. JPL has developed the Controlled Optics
Modelling Package (COMP) to easily facilitate analyses
of optical systems whose elements are perturbed.
Development of the computer tool, IMOS (Integrated
Modeling of Advanced Optical Systems) allows modeling
of structurally and thermally induced deformations to
interact with optical systems. Presented here are
analyses on the Segmented Reflector Telescope, (SRT),
to estimate and then minimize the effect of anticipated
disturbances on the resultant optical performance. Such
studies are a needed prerequisite for estimating the
requirements for adaptive optics due to structural
movements. A simulation study estimates the space-time
power spectral density of the residual telescope phases
from reaction wheel disturbances. Results show that
significant disturbances are concentrated in the first
few Zernike polynomials with 87% of all disturbances
described by the first 11 terms leaving a 0.35 $mu@m
rms residual. The time bandwidth of the disturbances is
between 20 - 25 Hz which placed the required
corrections in the adaptive optics regime.!17
Solar vector magnetograph: a candidate instrument for a lunar
solar observatory, pp.185-196
Author(s): Chris D. Thyen, Univ. of Minnesota/Twin Cities,
Minneapolis, MN, USA;
Mitzi Adams, NASA Marshall Space Flight Ctr.,
Huntsville, AL, USA.
Abstract: A lunar-based solar observatory (planned for expansion)
will support the Space Exploration Initiative (SEI) by
providing solar flare alerts and high quality
scientific data. One candidate instrument for the
proposed observatory, a vector magnetograph, will
provide scientists with vector magnetic field data at a
level of resolution of approximately one-half an arc
second, the scale of important physical processes.
Scientists will use the vector data from this
instrument to develop flare prediction capabilities.
The instrument, consisting of a 30 cm Cassegrain
telescope system, will be placed on the lunar nearside,
making long duration studies of solar activity (of
order 14 days) possible. The vector magnetograph will
have a temporal resolution on the order of three
minutes, an operational lifespan of five years, and
will be serviceable by crew of the First Lunar Outpost
(FLO). This instrument, based on a currently operating
vector magnetograph at NASA's Marshall Space Flight
Center, is under study for placement on the Moon using
either Johnson Space Center's Common Lunar Lander or
crew from the First Lunar Outpost. This paper will
review the scientific need to place a vector
magnetograph on the Moon, outline the design for such
an instrument, describe the preliminary requirements
for the launch vehicle and lander, and will recommend a
more penetrating study to determine the optimum optical
design for the instrument, the best materials, and the
environmental effects.!9
Conceptual design for a second generation space telescope,
pp.197-205
Author(s): John F. Bolton, NASA Goddard Space Flight Ctr.,
Columbia, MD, USA.
Abstract: Some innovative approaches to the design of a 16 meter
filled-aperture, UV to IR, high spatial resolution,
wide field-of-view space telescope are presented. The
purpose of this paper is to stimulate the discussion of
innovative concepts for a second generation space
telescope. The ideas in this paper are not tested or
analyzed. They are simply concepts that might prove to
be applicable and which will have to be tested and
developed, and possibly rejected. Comments on the
concepts presented in this paper will be welcomed by
the author.!0
Optimized performance and operations of the Faint Object Camera,
pp.206-213
Author(s): Manfred P. Miebach,
Space Telescope Science Institute, Baltimore, MD,
USA.
Abstract: The Faint Object Camera is a unique Scientific
Instrument of the Hubble Space Telescope; operating it
at top performance is critical for the quality of the
science data and a most efficient usage. This paper
describes the steps taken to optimize detector
performance, minimize the effects of thermal
variations, and maximize the allocated observing
time.!2
Serendipitous background monitoring of the Hubble Space
Telescope's Faint Object Spectrograph, pp.214-223
Author(s): John E. Fitch, Space Telescope Science Institute,
Baltimore, MD, USA;
Glenn Schneider, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: The nature of the Hubble Space Telescope's (HST) low
Earth orbit imposes scheduling restrictions and
interruptions in the data collection periods for it's
compliment of scientific instruments. During many of
these times the Faint Object Spectrograph (FOS) is in a
full operational configuration and is taking detector
background measurements which are continually reported
in HST's engineering telemetry stream. These data are
primarily used to monitor the instrument for changes in
behavior resulting, principally, from intermittently
noisy diodes in its digicon arrays. These same data may
be used to monitor temporal changes in the charged
particle environment of HST's near-earth orbit. We
present here the results of a study of two years of
on-orbit FOS background data obtained serendipitously
during periods while the FOS in an operational state,
but not exposing on external, or calibration targets.
These in situ data, which represent more than 100,000
discrete samples (equivalent to more than 1100 orbits)
have allowed us to accurately measure variations in the
background proton flux seen by the FOS. An analysis of
these variations have permitted us to model the
geomagnetic environment of the South Atlantic Anomaly
(SAA) as a function of time as well as the change in
detector background as a function of geomagnetic
latitude.!2
Thermal control of the space telescope high speed photometer,
pp.224-231
Author(s): Evan E. Richards, Univ. of Wisconsin/Madison,
Madison, WI, USA;
Jeffrey W. Percival, Univ. of Wisconsin/Madison,
Madison, WI, USA;
Jerry C. Sitzman, Univ.of Wisconsin/Madison,
Madison, WI, USA;
Tom Jones, Univ. of Wisconsin/Madison, Madison, WI,
USA.
Abstract: The Hubble Space Telescope High Speed Photometer (HSP)
thermal control system uses a software control system
instead of mechanical thermostats to control heaters.
The most unreliable part of a conventional thermal
control system, the thermostat, is eliminated in this
design. In addition, the software control design
provides great operational flexibility impossible to
obtain with thermostats. The heaters can be controlled
by a 'software thermostat' with its in-flight
adjustable set points. The control system can also be
operated in a variety of other modes, namely, a
constant power mode, a power profile mode, and a direct
commanding mode. The system can provide a given amount
of energy into the heaters over a wide range of input
bus voltages because bus voltage is sensed by the
control software. Heater power is switched by the same
relays that are needed in a thermostat system for power
control. The system has proven to be adaptable to the
changing needs of the Hubble Space Telescope mission. A
similar system was designed and built into the Diffuse
X-Ray Spectrometer instrument that was launched in
January 1993. Experience from that mission is also
described.!5
On-orbit sky background measurements Faint Object Spectrograph,
pp.232-243
Author(s): Ron W. Lyons, Univ. of California/San Diego,
La Jolla, CA, USA;
William A. Baity, Univ. of California/San Diego,
Solana Beach, CA, USA;
Edward A. Beaver, Univ. of California/San Diego,
La Jolla, CA, USA;
Ross D. Cohen, Univ. of California/San Diego,
La Jolla, CA, USA;
Vesa T. Junkkarinen, Univ. of California/San Diego,
La Jolla, CA, USA;
J.B. Linsky, Univ. of California/San Diego,
La Jolla, CA, USA;
R.Bohlin, Space Telescope Science Institute,
Baltimore, MD, USA.
Abstract: Observations of the sky background obtained with the
Faint Object Spectrograph during 1991 - 1992 are
discussed. Sky light can be an important contributor to
the observed count rate in several of the instrument
configurations especially when large apertures are
used. In general, the sky background is consistent with
the pre-launch expectations and showed the expected
effects of zodiacal light and diffuse galactic light.
In addition to these sources, there is, particularly
during the daytime, a highly variable airglow component
which includes a number of emission lines. The sky
background will have an impact on the reduction and
possibly the interpretation of some spectra.!11
Predicted performance of the COSTAR-corrected Faint Object
Camera, pp.244-251
Author(s): Robert Jedrzejewski,
Space Telescope Science Institute, Baltimore, MD,
USA;
George F. Hartig, Space Telescope Science Institute,
Parkton, MD, USA;
Anatonella Nota,
Space Telescope Science Institute and European Space
Agency, Baltimore, MD, USA;
Perry E. Greenfield,
Space Telescope Science Institute, Baltimore, MD,
USA;
David A. Baxter, Space Telescope Science Institute,
Baltimore, MD, USA;
Warren Hack, Space Telescope Science Institute,
Baltimore, MD, USA;
Francesco Paresce,
Space Telescope Science Institute and European Space
Agency and Osservatorio Astronomico d, Baltimore,
MD, USA.
Abstract: The installation of COSTAR will improve the imaging
performance of the Hubble Space Telescope such that the
Faint Object Camera performance will approach that
predicted before the discovery of the spherical
aberration. However, this is not achieved without some
undesirable side-effects. Despite these, it will be
possible to achieve scientific goals with the
COSTAR-corrected Faint Object Camera that are not
currently feasible.!8
Restoration of FOC imaging data: considerations when choosing FOC
PSFs, pp.252-262
Author(s): David A. Baxter, Space Telescope Science Institute,
Baltimore, MD, USA;
Perry E. Greenfield,
Space Telescope Science Institute, Baltimore, MD,
USA;
Warren Hack, Space Telescope Science Institute,
Baltimore, MD, USA;
Anatonella Nota,
Space Telescope Science Institute and European Space
Agency, Baltimore, MD, USA;
Robert Jedrzejewski,
Space Telescope Science Institute, Baltimore, MD,
USA;
Francesco Paresce,
Space Telescope Science Institute, European Space Age
ncy, Osservatorio Astronomico di Tori, Baltimore,
MD, USA.
Abstract: We present a discussion of the various sources of FOC
Point Spread Functions (PSFs), and the problems
associated with their use. In particular, we highlight
the time variability of the PSF halo structure and
indicate some of the causes. We examine the usefulness
of the PSF modelling software, TinyTim, and show that
although this software creates visually similar images,
these similarities are to a large extent superficial.
We conclude by showing that the theoretical PSFs
produced by TinyTim are inadequate for the restoration
of high S/N FOC point source images. We also conclude
that, because of 'breathing', there is a strong
likelihood that empirical PSFs, whether pre-existing or
specifically obtained, may not be sufficient either.!7
In-flight performance of the Faint Object Camera of the Hubble
Space Telescope: II, pp.264-275
Author(s): Perry E. Greenfield,
Space Telescope Science Institute, Baltimore, MD,
USA;
Anatonella Nota,
Space Telescope Science Institute and European Space
Agency/ESTEC, Baltimore, MD, USA;
Robert Jedrzejewski,
Space Telescope Science Institute, Baltimore, MD,
USA;
Warren Hack, Space Telescope Science Institute,
Baltimore, MD, USA;
Hashima Hasan, Space Telescope Science Institute,
Baltimore, MD, USA;
Phil Hodge, Space Telescope Science Institute,
Baltimore, MD, USA;
David A. Baxter, Space Telescope Science Institute,
Baltimore, MD, USA;
W.Baggett, Space Telescope Science Institute,
Baltimore, MD, USA;
Francesco Paresce,
Space Telescope Science Institute and European Space
Agency/ESTEC and Osservatorio Astrono, Baltimore,
MD, USA.
Abstract: This paper gives an update on the performance of the
Faint Object Camera - launched with the Hubble Space
Telescope - since the last report two years ago. The
primary camera, the f/96 relay, continues to work well,
but the f/48 relay has recently developed serious
problems. The stability of the f/96 relay has been very
good with the only change being a small apparent
decrease in UV sensitivity. Preliminary results for the
f/48 DQE are presented. In-orbit UV flat fields have
been obtained and the f/96 objective prisms and
polarizers have been calibrated.!5
Correction of the geomagnetically induced image motion problem on
the Hubble Space Telescope's Faint Object Spectrograph,
pp.276-286
Author(s): John E. Fitch, Space Telescope Science Institute,
Baltimore, MD, USA;
George F. Hartig, Space Telescope Science Institute,
Parkton, MD, USA;
Edward A. Beaver, Univ. of California/San Diego,
La Jolla, CA, USA;
Richard G. Hier, Univ. of California/San Diego,
San Diego, CA, USA.
Abstract: During the Science Verification phase of the Hubble
Space Telescope mission, it was determined that the
Faint Object Spectrograph's (FOS) Red detector
displayed significant image motions which correlated
with orbital changes in the geomagnetic field. The Blue
detector exhibited similar but less pronounced motions.
The cause of this motion was determined to be
inadequate magnetic shielding of the instrument's
Digicon detectors. The results of these motions were
decreases in onboard target acquisition accuracy,
spectral resolution, and photometric accuracy. The
Space Telescope Science Institute and the FOS
Investigation Definition Team, set about correcting
this Geomagnetically-induced Image Motion Problem
(GIMP) through a real-time on-board correction scheme.
This correction required modifications to almost all
aspects of the HST ground system as well as additional
NSSC1 flight software and the use of an existing
software 'hook' in the FOS microprocessor firmware.
This paper presents a detailed description of the
problem, the proposed solution, and results of on-orbit
testing of the correction mechanism.!1
Performance of the FOS detectors in a variable external magnetic
field, pp.287-300
Author(s): William A. Baity, Univ. of California/San Diego,
Solana Beach, CA, USA;
Edward A. Beaver, Univ. of California/San Diego,
La Jolla, CA, USA;
Ross D. Cohen, Univ. of California/San Diego,
La Jolla, CA, USA;
Vesa T. Junkkarinen, Univ. of California/San Diego,
La Jolla, CA, USA;
Ron W. Lyons, Univ. of California/San Diego,
La Jolla, CA, USA;
John E. Fitch, Space Telescope Science Institute,
Baltimore, MD, USA;
George F. Hartig, Space Telescope Science Institute,
Parkton, MD, USA;
Don J. Lindler, Advanced Computer Concepts, Inc.,
Potomac, MD, USA.
Abstract: We present the results of an investigation of the
in-orbit performance of the Digicon detectors in the
Faint Object Spectrograph (FOS), conducted as part of
the commissioning phase of the Hubble Space Telescope.
This paper includes orbital results on detector
background noise, sensor image stability, and
photometric stability along with several typical FOS
observations. This information should be of general
interest to designers of future spacecraft detectors
and to astronomers observing with the FOS
instrument.!26
Operations experience of the space telescope high-speed
photometer, pp.301-307
Author(s): Evan E. Richards, Univ. of Wisconsin/Madison,
Madison, WI, USA;
Jeffrey W. Percival, Univ. of Wisconsin/Madison,
Madison, WI, USA;
Matthew Nelson, Univ. of Wisconsin/Madison, Madison,
WI, USA;
L.C. Townsley, Univ. of Wisconsin/Madison,
Baltimore, MD, USA;
Edward Hatter, Jackson & Tull, Lanham, MD, USA.
Abstract: The Hubble Space Telescope High Speed Photometer (HSP)
has successfully completed orbital and science
verification testing and is currently executing
scientific proposals. The performance of the HSP has
been satisfactory except for sensitivity of one of the
detectors and low transmission of the prism apertures
used for two color photometry. The impact of the
telescope performance and ground system limitations on
instrument performance is discussed. The HSP's use of
the telescope is unique in several respects. Target
acquisition depends critically on knowledge of aperture
locations and the ability to execute precise small
angle maneuvers. The HSP requires precise spacecraft
scans for occultation observations. The photometric
performance of the HSP is especially dependent on
spacecraft pointing stability. The HSP's time series
data do not naturally fit into the image oriented data
format of HST.!3
Instrumental artifacts: stray and scattered light in the Goddard
High-Resolution Spectrograph aboard the Hubble Space Telescope,
pp.308-317
Author(s): Dennis C. Ebbets, Ball Aerospace Systems Group,
Boulder, CO, USA.
Abstract: The scientific goals of the Goddard High Resolution
Spectrograph (GHRS) require data of very high
integrity, with high S/N, spectral resolution,
wavelength calibration and photometric accuracy. The
instrument was designed to have optical, structural,
thermal and detector performance capable of delivering
nearly photon limited ultraviolet spectra. Many
important characteristics such as geometrical formats,
sensitivity functions, resolving power and linearity
were predicted from design specifications, and were
tested and verified. Instrumental properties which may
limit the ultimate performance, such as stray light,
distortions and geometrical instabilities were
anticipated but not precisely modeled. A careful test
program, comprising several distinct pre- and
post-launch phases identified, characterized and in
several cases eliminated potentially troublesome
aspects. In the spirit of 'lessons learned' this paper
describes a number of optical and detector related
artifacts, how they were identified and measured, and
either eliminated by reworking the hardware, or
calibrated and compensated for during data reduction.
Builders of future instruments should be aware of the
types of anomalies we encountered so they may be
avoided in the design phases, or well calibrated in the
testing phase. We will discuss aspects of the testing
programs, both technical and programmatic, which
contributed to the successful commissioning of the GHRS
and its current return of high quality spectroscopic
data.!17
Scattered light characteristics of the Hubble Space Telescope
Faint Object Spectrograph, pp.318-327
Author(s): Frank Bartko, Bartko Science & Technology,
Littleton, CO, USA;
Geoffrey Burks, Univ. of Colorado/Boulder, Boulder,
CO, USA;
Gerry Kriss, Johns Hopkins Univ., Baltimore, MD,
USA;
Arthur Davidsen, Johns Hopkins Univ., Baltimore, MD,
USA;
Ross D. Cohen, Univ. of California/San Diego,
La Jolla, CA, USA;
Vesa T. Junkkarinen, Univ. of California/San Diego,
La Jolla, CA, USA;
Ron W. Lyons, Univ. of California/San Diego,
La Jolla, CA, USA;
Richard J. Harms, Applied Research Corp., Landover,
MD, USA.
Abstract: Observations of a standard star (BD$PLU@75D325) have
been used to measure the Hubble Space Telescope
(HST)/Faint Object Spectrograph (FOS) scattering
characteristics in the wavelength range 115 to 250 nm.
Spectra of the standard star were obtained as the star
was progressively offset from the optical line of sight
axis of the telescope, both in the in-dispersion and
cross-dispersion directions. These data have been
reduced and analyzed to determine the scattering
function of the telescope- spectrograph combination.
Two primary results have been obtained. (1) The
resulting scattering function exhibits three
characteristics: (a) the inner core ($theta $LS 4') is
dominated by the large Point Spread Function (PSF) of
the HST; (b) the outer wings of the scattering function
(4' $LS $theta $LS 32') show a $theta$+$MIN@3$/
dependence consistent with predictions for the HST Airy
disc; and (c) the wavelength dependence of this
scattering function follows $lambda$+$MIN@1$/,
suggesting that the ultraviolet (UV) micro roughness
contribution to the scatter is quite small, and hence
the HST primary mirror is very smooth at ultraviolet
wavelengths. (2) The FOS scattering contribution is
limited only by grating scatter, and is consistent with
pre-launch grating calibration measurements.!11
Goddard High-Resolution Spectrograph of the Hubble Space
Telescope: operation, performance, anomalies and lessons learned,
pp.328-339
Author(s): Joseph P. Skapik, Space Telescope Science Institute,
Baltimore, MD, USA;
Harry W. Garner, Ball Aerospace Systems Group,
Boulder, CO, USA.
Abstract: The Goddard High Resolution Spectrography, (GHRS), has
been in operation since the launch of the Hubble Space
Telescope in April 1989. While this instrument has
proven it's value to the scientific community, a number
of operational and hardware problems had to be
addressed to enable it's continued use. This paper will
detail the symptoms, analysis and resolution of each of
these problems. Issues to be covered include the effect
of spherical aberration on the target acquisition
software routines, performance of the optical element
carrousel motor and electronics, and the impact of a
failure in the side one low voltage power supply.!0
On-orbit management of contaminants within the Hubble Space
Telescope widefield planetary camera and their effect on
instrument performance, pp.340-345
Author(s): John W. MacKenty, Space Telescope Science Institute,
Baltimore, MD, USA;
Glenn Schneider,
Computer Sciences Corp. and Space Telescope Science I
nstitute, Baltimore, MD, USA;
Sylvia M. Baggett,
Space Telescope Science Institute, Baltimore, MD,
USA;
Dana D. Mitchell, Space Telescope Science Institute,
Towson, MD, USA;
Christine E. Ritchie,
Space Telescope Science Institute, Baltimore, MD,
USA;
William B. Sparks,
Space Telescope Science Institute, Baltimore, MD,
USA.
Abstract: The Wide Field Planetary Camera (WF/PC) onboard the
Hubble Space Telescope contains contaminants which
condense on the windows in front of each CCD detector.
These contaminants are UV opaque and increase with time
to the extent that after several months they block 50%
of the flux at 300 nm. Also, when the contaminants are
warmed above $MIN@40$DGR@C and then returned to the
normal CCD operating temperature of $MIN@87$DGR@C,
particles form and severely degrade the image quality.
The windows may be temporarily cleaned by raising their
temperature to 0$DGR@C. However, this results in a
change in the structure of the flat field due to the
partial removal of the UV flood which was applied after
launch to suppress Quantum Efficiency Hysteresis in the
CCDs. Repeated decontaminations will reintroduce the
QEH and necessitate another time consuming UV flood and
recalibration of the instrument. After 22 months of
on-orbit operation, the contaminants could no longer be
fully removed by the decontamination procedure. This
paper describes the current state of the contaminants,
what has been deduced concerning their properties and
sources, the results of our efforts to remove them, and
some lessons for future space-based instruments using
cryogenic UV sensitive detectors.!2
Contamination effects on EUV optics in the space environment,
pp.348-360
Author(s): Barry J. Kent, Rutherford Appleton Lab.,
Chilton Didcot, Oxfordshire, United Kingdom;
Bruce M. Swinyard, Rutherford Appleton Lab.,
Chilton Didcot, Oxon, United Kingdom;
D.Hicks, Rutherford Appleton Lab., Chilton Didcot,
Oxon, United Kingdom.
Abstract: The Coronal Diagnostic Spectrometer (CDS) to be carried
on the joint ESA/NASA solar observatory satellite,
SOHO, in late 1995 operates in the extreme ultra-violet
(15 - 80 nm) and is thus particularly vulnerable to
molecular contamination of the optical surfaces. Such
contamination arises from materials present in the
assembly and test environment and also from outgasses
products from the various elastomers and other
non-metals used for instrument construction. The need
for secure surfaces free from contamination and the
requirement for very low optical scatter drives the
need for a comprehensive system of contamination
control. We present our current work from a study in
which we are attempting to identify typical
contaminants found in space instrumentation, to
understand and characterize their properties and to
measure effects on the performance of an EUV optical
system.!9
Optimized holographic grating solution for Rowland circle
spectrographs, pp.361-364
Author(s): Scott P. Sarlin, Univ. of Colorado/Boulder, Boulder,
CO, USA;
Webster C. Cash, Univ. of Colorado/Boulder, Boulder,
CO, USA;
James C. Green, Univ. of Colorado/Boulder, Boulder,
CO, USA.
Abstract: A new solution to the holographic grating equations
designed for use in high resolution FUV applications is
presented. The solution is shown through ray tracing to
provide a sizable resolution enhancement over
conventional Rowland circle grating solutions through
the minimization of various aberration terms,
especially astigmatism. This new design promises to
also provide diffraction limited performance across a
very large wavelength range.!3
System analysis for the near-infrared camera and multiobject
spectrometer cryogenic and structural design, pp.365-370
Author(s): Paul A. Lightsey, Ball Aerospace Systems Group,
Boulder, CO, USA;
John D. Gerber, Ball Aerospace Systems Group,
Boulder, CO, USA;
Chris D. Miller, Ball Aerospace Systems Group,
Boulder, CO, USA.
Abstract: The requirements for a second generation Hubble Space
Telescope (HST) Science Instrument (SI) are similar to
those of other space-borne instruments: the shuttle
launch loads must be survived; the instrument must have
specific dynamic characteristics; mass, size envelope,
and electrical power constraints are imposed; thermal
interfaces are defined; and a minimum on-orbit lifetime
is required. The Near Infrared Camera and Multi-Object
Spectrometer (NICMOS) differs from first generation and
other second generation HST SIs in that it is an
infrared instrument. The NICMOS detectors must be
cooled to 58 K. This leads to a demanding instrument
design that includes as an integral part of the optical
bench design, a solid nitrogen (SN$-2$/) cryogen dewar
with a five year minimum lifetime goal. The dewar
requires over 50% of the total instrument weight budget
and occupies a significant portion of the available
size envelope. Designing for five year cryogen lifetime
while achieving a structural design that will meet
launch loads and optical stability led to many design
conflicts. The system level trades along with the
structural and cryogenic lifetime analyses used to
resolve these conflicts and arrive at the innovative
NICMOS design will be discussed.!2
NICMOS flight focal plane assembly, pp.371-382
Author(s): Lloyd Shin, Rockwell International Corp., Anaheim,
CA, USA;
Gregory S. Winters,
Steward Observatory/Univ. of Arizona, Tucson, AZ,
USA.
Abstract: This paper discusses the mechanical design and assembly
of the Near Infrared Camera and Multi- Object
Spectrometer (NICMOS) focal plane assembly (FPA). The
FPA consists of a mercury- cadmium-telluride (MCT)
detector array hybridized to a silicon multiplexer
(MUX), a sapphire carrier, an alumina ceramic
multi-layer board (CMLB) including electrical
components, a base plate, and flex cables. The FPA is
designed for the following conditions; (1) shock and
vibration during launch, (2) Coefficient of Thermal
Expansion (CTE) of dissimilar materials at cryogenic
temperature, (3) outgassing limitations to meet NASA's
specifications, and (4) optical assembly tolerances.
Also, the FPA is designed to be easily integrated into
its dewar with provisions for mechanical as well as
optical alignment. The FPA is assembled by building up
two subassemblies in a parallel path, and then
integrating the two subassemblies with the flex cables
for the final assembly. These procedures are described
in this paper, including alignment tolerances required
and measured.!2
Optical design of NICMOS: the second-generation infrared
instrument for the Hubble Space Telescope, pp.383-389
Author(s): Eric Ramberg, Ball Aerospace Systems Group, Boulder,
CO, USA.
Abstract: NICMOS is the near infrared second generation
instrument for the Hubble Space Telescope. The NICMOS
instrument consist of three infrared cameras with
spectral response between 1 and 2.5 micrometers whose
fields of view are 11, 19.3 and 51.1 arc seconds. Each
camera has an independent filter wheel with 20
positions. In the wide field camera, two grisms will be
substituted for two of the filters. Some unique
challenges arise because (1) NICMOS must interface with
HST, (2) it is a low background infrared device with
warm optics and (3) it has a large cryogenic dewar
enveloping the detectors. This paper summarizes the
optical configuration of the instrument as well as some
of the requirements that drive the design. Expected
performance will be presented.!1
FUSE microchannel plate detectors: models and data for resolution
at the pore limit, pp.390-397
Author(s): David J. Sahnow, Johns Hopkins Univ., Baltimore, MD,
USA;
Charles W. Bowers, Johns Hopkins Univ., Baltimore,
MD, USA;
Oswald H. Siegmund, Univ. of California/Berkeley,
Berkeley, CA, USA;
Joseph M. Stock, Univ. of California/Berkeley,
Walnut Creek, CA, USA;
Mark A. Gummin, Univ. of California/Berkeley,
Berkeley, CA, USA.
Abstract: For detectors using microchannel plates (MCPs), the
nonuniform response introduced by the finite size of
the MCP pores has a significant effect when the size of
a resolution element is comparable to the spacing
between the pores (approximately 10 - 15 $mu@m). For
the Far Ultraviolet Spectroscopic Explorer (FUSE)
spectrograph, which will employ a delay line detector,
the instrument plate scale, nominal slit width (1
arcsecond), and well-corrected optical design combine
to produce slit-limited images 25 $mu@m in width with
resolution elements 32 $mu@m wide, and a nominal
resolution of $lambda@/$Delta$lambda $EQ 30,000. At
these scales, the MCPs will sparsely sample spectral
line images, resulting in significant pixellation
effects. We have constructed a computer model of a
microchannel plate detector to simulate these effects
and evaluate the performance that can be expected from
the FUSE detector. These simulations have been compared
to actual images obtained with a laboratory version of
a delay line detector. Slit patterns imaged onto the
detector were chosen to simulate the resolution
expected from the FUSE spectrograph in order to provide
an estimate of the expected resolving power and test
the effects of several detector parameters on
resolution. Details of the model are described, and a
comparison of the results with laboratory data is made.
The implications for FUSE are also discussed.!8
Theoretical and measured encircled energy and wide-angle scatter
of SUMER demonstration telescope mirror in FUV, pp.398-409
Author(s): Timo T. Saha, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Douglas B. Leviton, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA.
Abstract: The theoretical encircled energy and wide angle scatter
of the SUMER Demonstration Telescope (SDT) mirror was
analyzed at the wavelength of 123.6 nm. The modeling
was accomplished with two software packages: (1)
Metrology Data Processor (METDAT) and (2) Optical
Surface Analysis Code (OSAC). The modeling is based on
measured mirror surface figure error data and roughness
characteristics covering all important spatial
frequencies affecting the imaging in the Far
Ultraviolet (FUV) wavelength region. The performance of
the SDT mirror including the encircled energy and wide
angle scatter was also directly measured at 123.6 nm.
We found an excellent agreement between the measured
and theoretical encircled energy up to about 3
arcseconds from the peak and wide angle scatter up to
about 20 arcminutes from the peak at 123.6 nm. The 80
percent encircled energy diameter of the SDT mirror is
about 2.6 arcseconds and the amount of scattered light
drops to about 5.0 $MUL 10$+$MIN@10$/ of peak
irradiance 20 arcminutes from the peak. The performance
of the mirror in the FUV is degraded by the
mid-frequency errors.!13
Dimensionally stable graphite-fiber-reinforced composite mirror
technology, pp.410-420
Author(s): James P. Gormican, Composite Optics, Inc.,
San Diego, CA, USA;
Shel Kulick, Composite Optics, Inc., San Diego, CA,
USA;
Eldon P. Kasl, Composite Optics, San Diego, CA, USA;
Laura B. Abplanalp, Eastman Kodak Co., Rochester,
NY, USA.
Abstract: Lightweight, high performance optical systems have
historically relied upon ultralightweight optical
components to achieve high stiffness, low weight, high
quality optical surfaces exhibiting high thermal
stability. Composite Optics, Incorporated (COI) has
independently pursued state-of-the-art graphite fiber
reinforce composite (GFRC) substrates for microwave and
infrared (IR) applications. Eastman Kodak Company
(Kodak) and COI have participated in a joint evaluation
of hybrid optical mirrors fabricated from low
coefficient of thermal expansion (CTE) graphite
composite materials and ULE$+TM$/ low CTE glass. While
glass can be polished to achieve an optical quality
surface, relative to other mirror substrates, GFRC
attractively offers high specific stiffness and low
steady state and transient distortion characteristics
as shown. This joint effort between Kodak and COI has
resulted in the demonstration of processed optical
surfaces within 0.05 waves rms (at 0.63 $mu@m). Optical
surfaces have remained stable to within 2 waves rms
over a wide range of temperatures ($MIN@13 to
65$DGR@C). The optical performance demonstrated meets
the requirements for long wavelength systems, with
promise of satisfying visible wavelength performance
with further development.!5
Fabrication and characterization of a micromachined deformable
mirror for adaptive optics applications, pp.421-430
Author(s): Linda M. Miller, Jet Propulsion Lab., Pasadena, CA,
USA;
Michael L. Agronin, Jet Propulsion Lab., Pasadena,
CA, USA;
Randall K. Bartman, Jet Propulsion Lab., Pasadena,
CA, USA;
William J. Kaiser, Jet Propulsion Lab., Pasadena,
CA, USA;
Thomas W. Kenny, Jet Propulsion Lab., Pasadena, CA,
USA;
Robert L. Norton, Jet Propulsion Lab., Pasadena, CA,
USA;
Erika C. Vote, Jet Propulsion Lab., Pasadena, CA,
USA.
Abstract: A novel micromachined electrostatically controlled
deformable mirror has been fabricated and
characterized. This device combines the fields of
microinstruments, adaptive optics and controls to form
a silicon-based mirror assembly that is relatively
simple to process, inexpensive, lightweight, and
integrable with drive and sensing electronics.
Electrostatic control of a thin membrane mirror is
demonstrated with low voltage actuation and without the
need for complex construction of PZT or other
translator-type arrays. In addition, the low-stress
Si-rich Si$-x$/N$-y$/ film used as the deformable
membrane mirror is thermally matched to the silicon
supporting frame. Custom design of the mirror shape can
be implemented by redesigning the electrode pattern on
an insulating substrate separate from the thin film
mirror. Test results from a pull-only circular mirror
with a single actuator are presented as a proof of
concept for low voltage actuation of a low-stress
Si$-x$/N$-y$/ flexible membrane. The Si$-x$/N$-y$/
which forms the membrane is under tensile stress. This
tensile stress increase the voltage required for
deflection of the membrane, but insures a linear
relationship between the center deflection of the
mirror and the applied pressure. This should
significantly simplify the controls algorithm required
for closed-loop operation of this device.!19
Diffractive errors in segmented adaptive optics, pp.431-434
Author(s): S.Enguehard,
Applied Mathematical Physics Research, Inc.,
Lexington, MA, USA;
Brian Hatfield,
Applied Mathematical Physics Research, Inc.,
Lexington, MA, USA.
Abstract: Segmentation of the primary mirror offers an
inexpensive method to produce large, active telescopes
or beam directors. We discuss the goal of segment
control and our analytic solution configuration
functional. We show that the nature of the
segmentation, control, and solution generates an
additional source of diffractive errors that must be
accounted for in the design of these systems. These
diffractive errors and not r$-0$/ ultimately set the
segment size.!3
Optical design of an UV camera for a Ritchey-Chretien space
telescope, pp.435-442
Author(s): Roberto Ragazzoni,
Astronomical Observatory of Padova, Padova, Italy;
R.Falomo, Astronomical Observatory of Padova,
Padova, Italy;
G.Corrain, Astronomical Observatory of Padova,
Padova, Italy.
Abstract: A study for the optical design of an UV-imaging camera
is briefly reported. We emphasize the guidelines that
drove the design choices adopted, as trade-off between
optical quality and efficiency. Optical solutions for
an additional long focal length channel are also given.
This study is performed in the framework of the SUV
project, a 170 cm Ritchey-Chretian space telescope to
be made with the collaboration of Russia, Ukraine,
Italy and Germany.!18
Optical design of two-mirror widefield cameras for large
telescopes, pp.443-452
Author(s): Paul G. Hannan, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Mark E. Wilson, NASA Goddard Space Flight Ctr.,
College Park, MD, USA.
Abstract: Many large optical telescopes have a wide field camera
as one of their primary instruments. Camera designs
with all reflective surfaces are useful because they
give stable image quality over a broad spectral band.
Systems with two conic mirrors can correct the residual
aberrations, field curvature and astigmatism, of
Ritchey-Chretien telescopes. We present first- and
third-order optical design relations which can
facilitate the formation of design concepts during
preliminary trade studies. We apply the relations to
the Hubble Space Telescope in the design of a new wide
field camera which compensates the existing spherical
aberration, as well as the astigmatism and field
curvature, of the telescope.!3
Image reconstruction and deconvolution techniques applied to ASCA
data, pp.453-464
Author(s): Lalit Jalota, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Eric V. Gotthelf, NASA Goddard Space Flight Ctr.,
Greenbelt, MD, USA;
Saeid Zoonematkermani, SUNY/Stony Brook,
Stony Brook, NY, USA.
Abstract: The Advanced Satellite for Cosmology and Astrophysics,
ASCA, is a joint Japanese-United State X-ray
astrophysics observatory which was launched on February
20th 1993. The scientific payload comprises four
identical grazing incidence X-ray mirrors complemented
by two charge-coupled devices and two gas scintillation
proportional counters as the focal plane detectors.
This paper presents the latest work carried out to
improve the quality of ASCA images using the
Lucy-Richardson deconvolution method. The ability to
resolve two point sources is studied under various
conditions of separation, relative intensity, and
signal-to-noise. The method is also tested with an
extended source. The minimum separation which can be
resolved is 30 arcseconds, corresponding approximately
to the radius of the core of the PSF. There is also
some advantage to be gained in the relative orientation
of the sources. Sources of unequal intensity must be
separated further in order to be resolved, for example,
when one source is half the intensity of the other
source the minimum separation is 45 arcseconds. A
signal-to- noise ratio of 5$sigma is the lower limit
for resolving two sources of equal strength 30
arcseconds apart. Deconvolution of the simulated image
of the supernova remnant CAS-A is successfully carried
out and the resulting image has about one arcminute
resolution, limited by the PSF core width.!13s
Coded mask telescope with a germanium array detector, pp.465-477
Author(s): Gerald K. Skinner, Univ. of Birmingham, Edgbaston,
Birmingham, United Kingdom;
J.R. Herring, Univ. of Birmingham, Edgebaston,
Birmingham, United Kingdom;
R.L. Balthazor, Univ. of Birmingham, Edgbaston,
Birmingham, United Kingdom.
Abstract: Coded mask X-ray and gamma-ray telescopes are the only
way of obtaining true images in the photon energy range
from approximately 10 keV to a few MeV. The detectors
used must be position sensitive, and the types employed
in gamma-ray coded mask telescopes up to now have had
limited energy resolution. With a view to developing
position sensitive detectors which have the energy
resolution attainable with Germanium we have procured
and characterized in the laboratory a detector
comprising a small array of high purity Germanium
elements each 15 $MUL 15 $MUL 50 mm. Although having
only nine elements, its construction is such that is
should later be possible to build larger modules in the
same way and finally to assemble modules into a large
detector plane array. The nine element array is being
incorporated into a coded mask telescope which will be
tested in a balloon flight. Laboratory tests on the
array detector and comparisons with simulations are
reported and the anticipated performance of the small
array telescope considered. The feasibility of a large
instrument based on this approach, which is under study
for a space mission, and its expected capabilities are
discussed.!24
Ultraviolet and VUV sources for in-flight calibration of space
experiments, pp.478-483
Author(s): Molly L. Morrow, Resonance Ltd., Cookstown, Ontario,
Canada;
William H. Morrow, Resonance Ltd., Alliston,
Ontario, Canada;
Lawrence N. Majorana, Jet Propulsion Lab., Ontario,
CA, USA.
Abstract: The importance of calibration subsystems as part of
overall system design has grown with the increasing
sophistication and complexity of remote sensing and
imaging instruments. In general they provide spectral
and radiometric reference data in-situ under remote and
sometimes unpredictable instrument conditions which are
used to correct electronic, optical and detector
nonlinearities. The recent difficulties with GOES
satellites underline the importance of reliable
calibration sources for space applications. Although
the calibration component is a small fraction of the
budget of any space qualified instrument, its failure
can result in a catastrophic loss of data. A group of
sources will be described which have been developed for
in-flight and pre-flight calibration of a variety of
space astronomy and space physics experiments with
different requirements in terms of wavelength coverage,
power budget, size requirements and radiation
hardness.!1
Echelle class spectroscopy with a single holographic grating,
pp.484-487
Author(s): James C. Green, Univ. of Colorado/Boulder, Boulder,
CO, USA;
Scott P. Sarlin, Univ. of Colorado/Boulder, Boulder,
CO, USA;
Webster C. Cash, Univ. of Colorado/Boulder, Boulder,
CO, USA.
Abstract: There are several problems in astrophysics that cannot
be addressed until very high resolution spectroscopy
($lambda@/$Delta$lambda $GRT 100,000) in the far
ultraviolet ($lambda $LS 2000 angstroms) can be
achieved simultaneously with high efficiency. Issues
such as atomic isotopic abundances in the interstellar
medium, velocity structure in interstellar clouds, and
fine and hyperfine line structure in atomic transitions
require 100,000 - 200,000 class resolution and high
sensitivity; a capability that currently does not
exist. Historically, resolutions this high have been
obtained with echelle spectrographs, which require two
gratings, and must suffer the losses due to reflective
efficiency and diffraction efficiency on both gratings.
These losses are much more significant in the far
ultraviolet than in the visible. We present a means of
obtaining very high resolution spectroscopy in the far
ultraviolet with a single, holographic grating, which
should be significantly more efficient than classic
echelle designs.!2
Robotic telescope systems for CCD photometry of faint objects in
crowded fields, pp.488-496
Author(s): John E. Baruch, Univ. of Bradford,
Bradford, West Yorkshire, United Kingdom;
Janice Da Luz Vieira, Univ. of Bradford,
Bradford, West Yorkshire, United Kingdom.
Abstract: This paper first considers the design of robotic
telescopes to monitor faint objects in crowded fields.
It shows that the mechanical design problems have been
solved by the use of precision control and modelling
software developed for the latest large telescopes.
Modern design methods mean that these telescopes can be
produced relatively cheaply. The largest part of the
cost of a robotic telescope is the software to enable
it to work as an autonomous robot. Conventional
software techniques are inadequate and inefficient for
many purposes associated with robotic operation. These
include: to optimize and monitor their operation and
efficiency, to schedule their observing, to evaluate
their environment, to generate confidence in the target
acquisition pattern recognition parameters, to evaluate
the quality of the CCD images and the photometry of the
objects within the images, and to return reduced data
to the astronomer with the required indices to gives
the astronomer confidence in the data. The paper
evaluates AI, neural nets and fuzzy logic techniques
applied to these different problems.!17
Spectrally selective surfaces for ground and space-based
instrumentation: support for a resource base, pp.497-504
Author(s): Susan H. McCall,
Stellar Optics Labs. Ltd. and Univ. of Toronto,
Thornhill, ON, Canada;
R.L. Sinclair, Spar Aerospace Ltd., Brampton,
Ontario, Canada;
Stephen M. Pompea, Gemini 8-M Telescopes Project,
Tucson, AZ, USA;
Robert P. Breault,
Breault Research Organization, Inc., Tucson, AZ,
USA.
Abstract: The performance of space telescopes, space instruments,
and space radiator systems depends critically upon the
selection of appropriate spectrally selective surfaces.
Many space programs have suffered severe performance
limitations, schedule setbacks, and spent hundreds of
thousands of dollars in damage control because of a
lack of readily-accessible, accurate data on the
properties of spectrally selective surfaces,
particularly black surfaces. A Canadian effort is
underway to develop a resource base (database and
support service) to help alleviate this problem. The
assistance of the community is required to make the
resource base comprehensive and useful to the end
users. The paper aims to describe the objectives of
this project. In addition, a request for information
and support is made for various aspects of the project.
The resource base will be useful for both ground and
space-based instrumentation.!14
Space-based CCD experiment for high-precision astrometry,
pp.505-511
Author(s): Stuart B. Shaklan, Jet Propulsion Lab., Pasadena,
CA, USA;
Steven H. Pravdo, Jet Propulsion Lab., Pasadena, CA,
USA.
Abstract: The Astrometric Imaging Telescope, an orbiting 1.5 m
low-distortion Ritchey-Chretien, will use a large
format CCD to record star trails as the CCD is dragged
across the image plane. Star-trail separations, when
averaged over thousands of pixels, yield photon-noise
limited centroids with 10 micro-arcsecond accuracy. In
this paper, we will discuss the important CCD and
optical design parameters that affect astrometric
accuracy. For the CCD, these include charge transfer
efficiency, pixel-to-pixel relative quantum efficiency,
sub-pixel QE gradients, and systematic pixel
dislocations. For optical design, they are tolerancing
to parameters such as secondary mirror decenter and
tilt, and conic constants. We present a point design
for a system that can achieve 10 micro-arcsecond
accuracy over a long-term mission. End-to-end modeling,
including high precision diffraction calculations, is
used to validate the design.!9