Backgrounds observed by JWST will be a critical parameter for overall observatory sensitivity. JWST’s background, sensitivity and other performance requirements drove the observatory’s open architecture, sunshield geometry, orbit at L2 and other unique characteristics. These requirements were verified by analysis, to be measured for the first time on-orbit. Modeling JWSTs backgrounds is complex, as JWST backgrounds have multiple components including: backgrounds from in-field sources (such as Zodiacal Light) and stray light from scattering of sky sources outside the field; thermal selfemission of optical surfaces; and scattering of thermal self-emission from other Observatory surfaces. The unbaffled telescope design allows stray light paths from multiple directions. The 5-layer sunshield passively cools and shades the telescope and science instruments; however, there are thermal paths that may affect thermal performance. In-field backgrounds and stray light from sky sources can depend on the telescope’s pointing and observation date. The thermal emission contributions will depend on the Observatory’s sun orientation and recent history. The JWST Background Tool (JBT) uses the stray light models, in-field backgrounds, and thermal models to predict the expected backgrounds. Onorbit, several positions were measured at multiple wavelengths with NIRCam and MIRI to probe JWST’s backgrounds and validate model predictions. These results may be used to update the JWST Exposure Time Calculator in preparation for the Cycle 2 proposal call. This conference proceeding will provide a summary of the modeling backgrounds and report on the measured on-orbit backgrounds.
KEYWORDS: Telescopes, James Webb Space Telescope, Image segmentation, Observatories, Mirrors, Space operations, Space telescopes, Galactic astronomy, Wavefronts, Stars
The James Webb Space Telescope (Webb) is a large, infrared space telescope that recently completed its on-orbit commissioning activities and has now embarked on its first year of approved science. Its architecture includes many first-of-its kind innovations for space, including a segmented primary mirror that is 6.6 m in diameter and a 5-layer sunshield used to passively cool the telescope and its four science instruments. Although Webb had an extensive test program, the system-level performance often relied on predictions based on integrated modeling, using conservative factors for the model uncertainties and primarily focusing on evaluating the performance at the end of life. A set of commissioning activities were designed for a system-level characterization of the performance. This proceeding will provide the status of the mission, including a discussion of the major events, on-orbit system performance, and early science highlights.
KEYWORDS: James Webb Space Telescope, Aerospace engineering, Space operations, Space telescopes, Mid-IR, Observatories, Mirrors, Infrared telescopes, Optical telescopes, Imaging systems
The James Webb Space Telescope (Webb) is the largest space telescope realized to-date, with a 6.5 m segmented primary mirror that must be folded to fit within its Ariane 5 launcher fairing. This infrared telescope is passively cooled using a five-layer sunshield that will keep the optical telescope and its four science instruments in the shade throughout the lifetime of the mission in an L2 orbit. Webb's science instruments include near- and mid- infrared imagers and spectrometers that cover the spectral range from 0.6-28.5 μ.m The Webb mission has a long history with numerous first of its kind technology developments, ground support equipment innovations, and algorithmic characterization advances. This conference proceeding summarizes the technical progress over the past two years, from the Spacecraft Element environmental testing to the Observatory integration and testing, and the final Observatory test plans leading up to launch, on-orbit commissioning, and science operations.
The James Webb Space Telescope (JWST) is a large (6.5 m) near- and mid-infrared telescope scheduled for launch in 2021. JWST will be used to explore fundamental questions in astrophysics and planetary science, including the evolution of galaxies, the first light of stars, the formation of stars and planets as well as the characterization of exoplanets. To achieve these scientific goals, NASA and its international partners, the Canadian Space Agency (CSA) and the European Space Agency (ESA), have developed four science instruments for JWST and have prepared detailed commissioning plans for each. The NASA Project Science team has also outlined activities to characterize the performance of the Observatory as a whole. These activities include: 1) monitoring of the instrument and telescope cooldown for contamination mitigation; 2) measurements of straylight and other backgrounds for validation of the JWST stray light models as well as instrument background subtraction algorithms; 3) characterization of optical thermal distortion between its hot and cold telescope pointings within the observable field of regard and 4) trending of observatory performance parameters. Each of these activities has been planned in close collaboration with the observatory wavefront, commissioning planning, and science instrument teams. Here we present the plans for these activities, the expected results and how they will impact future guest observer (GO) proposals and JWST science community.
The James Webb Space Telescope (JWST) is a NASA flagship mission that will address multiple science themes including our Universe’s first light, the assembly of galaxies, the birth of stars and planetary systems, and planets and the origins of life. The JWST is a large (6.5 m) segmented aperture telescope equipped with near- and mid-infrared instruments (0.6-28 microns), all of which are passively cooled to ~40 K by a 5-layer sunshield while the mid-infrared instrument is actively cooled to 7 K. The JWST will be launched to an L2 orbit aboard a European Space Agency (ESA) supplied Ariane 5 rocket, whose payload volume constraints require that the JWST structure is stowed for launch. The JWST telescope recently completed its cryogenic test program and the sunshield has been fully integrated and deployed. JWST is currently in the final stages of the test program at the Observatory level. The current estimated JWST performance metrics will be presented, such as the image quality, pointing stability, sensitivity, and stray light backgrounds. The JWST development status and future plans will be described for the final testing, launch, and commissioning. JWST is an international project with contributions from NASA, ESA, and the Canadian Space Agency (CSA). Northrop Grumman Aerospace Systems is the prime contractor for the JWST, and the Space Telescope Science Institute will serve as the science operations center.
In preparation of the 2020 Astrophysics Decadal Survey, National Aeronautics and Space Administration (NASA) has commenced a process for the astronomical community to study several large mission concepts leveraging the lessons learned from past Decadal Surveys. This will enable the Decadal Survey committee to make more informed recommendations to NASA on its astrophysics science and mission priorities with respect to cost and risk. Four
astrophysics large mission concepts were identified. Each of them had a Science and Technology Definition Teem (STDT) chartered to produce scientifically compelling, feasible, and executable design reference mission (DRM) concepts to present to the 2020 Decadal Survey. In addition, The Aerospace Corporation will perform an independent cost and technical evaluation (CATE) of each of these mission concept studies in advance of the 2020 Decadal Survey,
by interacting with the STDTs to provide detailed technical details on certain areas for which “deep dives” are appropriate. This paper presents the status and path forward for one of the four large mission concepts, namely, the Large UltraViolet, Optical, InfraRed surveyor (LUVOIR).
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the world’s largest airborne observatory, featuring a
2.5 meter effective aperture telescope housed in the aft section of a Boeing 747SP aircraft. SOFIA’s current instrument
suite includes: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), a 5-40 μm dual band
imager/grism spectrometer developed at Cornell University; HIPO (High-speed Imaging Photometer for Occultations), a
0.3-1.1μm imager built by Lowell Observatory; GREAT (German Receiver for Astronomy at Terahertz Frequencies), a
multichannel heterodyne spectrometer from 60-240 μm, developed by a consortium led by the Max Planck Institute for
Radio Astronomy; FLITECAM (First Light Infrared Test Experiment CAMera), a 1-5 μm wide-field imager/grism
spectrometer developed at UCLA; FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), a 42-200 μm IFU grating
spectrograph completed by University Stuttgart; and EXES (Echelon-Cross-Echelle Spectrograph), a 5-28 μm highresolution
spectrometer designed at the University of Texas and being completed by UC Davis and NASA Ames
Research Center. HAWC+ (High-resolution Airborne Wideband Camera) is a 50-240 μm imager that was originally
developed at the University of Chicago as a first-generation instrument (HAWC), and is being upgraded at JPL to add
polarimetry and new detectors developed at Goddard Space Flight Center (GSFC). SOFIA will continually update its
instrument suite with new instrumentation, technology demonstration experiments and upgrades to the existing
instrument suite. This paper details the current instrument capabilities and status, as well as the plans for future
instrumentation.
We present a status report and early commissioning results for FLITECAM, the 1-5 micron imager and spectrometer for
SOFIA (the Stratospheric Observatory for Infrared Astronomy). In February 2014 we completed six flights with
FLITECAM mounted in the FLIPO configuration, a co-mounting of FLITECAM and HIPO (High-speed Imaging
Photometer for Occultations; PI Edward W. Dunham, Lowell Observatory). During these flights, the FLITECAM modes
from ~1-4 μm were characterized. Since observatory verification flights in 2011, several improvements have been made
to the FLITECAM system, including the elimination of a light leak in the FLITECAM filter wheel enclosure, and
updates to the observing software. We discuss both the improvements to the FLITECAM system and the results from the
commissioning flights, including updated sensitivity measurements. Finally, we discuss the utility of FLITECAM in the
FLIPO configuration for targeting exoplanet transits.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory, carrying a 2.5 m telescope onboard a heavily modified Boeing 747SP aircraft. SOFIA is optimized for operation at infrared wavelengths, much of which is obscured for ground-based observatories by atmospheric water vapor. The SOFIA science instrument complement consists of seven instruments: FORCAST (Faint Object InfraRed CAmera for the SOFIA Telescope), GREAT (German Receiver for Astronomy at Terahertz Frequencies), HIPO (High-speed Imaging Photometer for Occultations), FLITECAM (First Light Infrared Test Experiment CAMera), FIFI-LS (Far-Infrared Field-Imaging Line Spectrometer), EXES (Echelon-Cross-Echelle Spectrograph), and HAWC (High-resolution Airborne Wideband Camera). FORCAST is a 5–40 μm imager with grism spectroscopy, developed at Cornell University. GREAT is a heterodyne spectrometer providing high-resolution spectroscopy in several bands from 60–240 μm, developed at the Max Planck Institute for Radio Astronomy. HIPO is a 0.3–1.1 μm imager, developed at Lowell Observatory. FLITECAM is a 1–5 μm wide-field imager with grism spectroscopy, developed at UCLA. FIFI-LS is a 42–210 μm integral field imaging grating spectrometer, developed at the University of Stuttgart. EXES is a 5–28 μm high-resolution spectrograph, developed at UC Davis and NASA ARC. HAWC is a 50–240 μm imager, developed at the University of Chicago, and undergoing an upgrade at JPL to add polarimetry capability and substantially larger GSFC detectors. We describe the capabilities, performance, and status of each instrument, highlighting science results obtained using FORCAST, GREAT, and HIPO during SOFIA Early Science observations conducted in 2011.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) has recently concluded a set of engineering flights for Observatory performance evaluation. These in-flight opportunities have been viewed as a first comprehensive assessment of the Observatory's performance and will be used to address the development activity that
is planned for 2012, as well as to identify additional Observatory upgrades. A series of 8 SOFIA Characterization
And Integration
flights have been conducted from June to December 2011. The HIPO science instrument in
conjunction with the DSI Super Fast Diagnostic Camera (SFDC) have been used to evaluate pointing stability,
including the image motion due to rigid-body and
flexible-body telescope modes as well as possible aero-optical
image motion. We report on recent improvements in pointing stability by using an Active Mass Damper system
installed on Telescope Assembly. Measurements and characterization of the shear layer and cavity seeing, as
well as image quality evaluation as a function of wavelength have been performed using the HIPO+FLITECAM
Science Instrument conguration (FLIPO). A number of additional tests and measurements have targeted basic
Observatory capabilities and requirements including, but not limited to, pointing accuracy, chopper evaluation
and imager sensitivity. This paper reports on the data collected during these
flights and presents current SOFIA
Observatory performance and characterization.
HIPO is a special purpose science instrument for SOFIA that was also designed to be used for Observatory test work. It
was used in a series of flights from June to December 2011 as part of the SOFIA Characterization and Integration
(SCAI) flight test program. Partial commissioning of HIPO and the co-mounted HIPO-FLITECAM (FLIPO)
configuration were included within the scope of the SCAI work. The commissioning measurements included such
things as optical throughput, image size and shape as a function of wavelength and exposure time, image motion
assessment over a wide frequency range, scintillation noise, photometric stability assessment, twilight sky brightness,
cosmic ray rate as a function of altitude, telescope pointing control, secondary mirror control, and GPS time and position
performance. As part of this work we successfully observed a stellar occultation by Pluto, our first SOFIA science data.
We report here on the observed in-flight performance of HIPO both when mounted alone and when used in the FLIPO
configuration.
This paper describes the current status of FLITECAM, the near-infrared (1 - 5 μm) camera and spectrometer for
NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). Due to a change in schedule FLITECAM’s
delivery was advanced, allowing it to be co-mounted with the HIPO instrument and used on four flights in October 2011
for observatory verification. Although not part of FLITECAM’s commissioning time, some preliminary performance
characteristics were determined. Image size as a function of wavelength was measured prior to the installation of active
mass dampers on the telescope. Preliminary grism spectroscopy was also obtained. In addition, FLITECAM was used to
measure the emissivity of the telescope and warm optics in the co-mounted configuration. New narrow band filters were
added to the instrument, including a Paschen alpha filter for line emission. Results are illustrated.
KEYWORDS: Sensors, James Webb Space Telescope, Electronics, Near infrared, Calibration, Infrared sensors, Space telescopes, Infrared telescopes, Infrared radiation, Astronomy
The James Webb Space Telescope, an infrared-optimized space telescope being developed by NASA for launch in 2014,
will utilize cutting-edge detector technology in its investigation of fundamental questions in astrophysics. JWST's near
infrared spectrograph, NIRSpec utilizes two 2048 × 2048 HdCdTe arrays with Sidecar ASIC readout electronics
developed by Teledyne to provide spectral coverage from 0.6 microns to 5 microns. We present recent test and
calibration results for the "pathfinder NIRSpec detector subsystem" as well as data processing routines for noise
reduction and cosmic ray rejection.
FLITECAM is a 1-5 micron spectrometer and camera developed at UCLA for NASA's Stratospheric Observatory for
Infrared Astronomy (SOFIA). On SOFIA, FLITECAM will take advantage of lower backgrounds from 3-5 microns and
will provide access to spectral regions completely or partially absorbed by water vapor at even the best ground-based
sites. FLITECAM employs large cryogenic optics and an ALADDIN III 1024 × 1024 InSb detector to inscribe an 8
arcminute field of view with 0.48 arcsec/pixel spatial resolution. The optical components are cooled with liquid nitrogen
and a liquid helium reservoir is used to establish an operational temperature of 30 K for the InSb array. FLITECAM has
two primary observing modes, imaging and spectroscopy. A pupil-viewing mode, for examination of the primary mirror
surface, and a high-speed snapshot mode for occultation observations are also provided. Ground-based commissioning
of the instrument using the Shane 3-meter telescope at UCO/Lick Observatory has been completed successfully. In
addition to broad-band filters, the imaging mode accommodates several narrow-band filters. A data reduction pipeline
processes dithered image sets in real-time during the flight. The grism spectroscopy mode employs three direct-ruled
KRS-5 grisms and fixed slits of either 1" × 60" or 2 × 60" to yield resolving powers (FWHM) of R~1700 and 900
respectively. Observations are scripted using AORs (Astronomical Observation Requests) in both modes. A pilot survey
of 3.3 micron emission in planetary nebulae performed with FLITECAM at UCO/Lick Observatory demonstrates the
potential of the grism mode.
FLITECAM is a 1-5 micron infrared camera for NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA).
A 1024 ×1024 InSb ALADDIN III detector and large refractive optics provide a field of view of almost 8 arc minutes
in diameter with a scale of just under 0.5 arc seconds per pixel. The instrument is cooled by a double liquid helium and
liquid nitrogen cryostat. Using a collimated beam of about 26 mm diameter, a low resolution spectroscopic mode is also
available using direct-ruled KRS5 grisms and fixed slits of either 1" or 2" width and 60" length to yield resolving
powers of R~1700 and 900 respectively. FLITECAM has been partially commissioned at the 3-m Shane telescope of
Lick Observatory where the f/17 optics of this telescope provides almost the same plate scale as SOFIA. Astronomical
observing requests (scripts) and a real-time data reduction pipeline (DRP) for dithered image patterns have been
demonstrated. The performance of the instrument during ground-based trials is illustrated.
FLITECAM, a near-infrared instrument being developed at the UCLA Infrared lab, will be the first light infrared instrument for NASA's SOFIA aircraft. In addition to its imaging capability, FLITECAM has been equipped with three direct-ruled KRS-5 grisms, allowing observations in 9 spectral bands, and giving nearly continuous spectral coverage from 1 to 5.5 microns. The design favors regions of the spectrum that are heavily attenuated except at high altitudes. The grisms are used with a dual-width long slit to yield a spectral resolution of R~1700 at high resolution and R~900 at low resolution. This resolution is better than that of the IRAS, ISO or KAO spectrometers, and covers a spectral regime left unsampled by the Spitzer Space Telescope. When used on the SOFIA, FLITECAM's spectroscopic mode will allow astronomical investigation of near-infrared features at a low water vapor overburden. The grism spectroscopic mode has been demonstrated on the Shane 120 inch telescope at Lick Observatory by observations of astronomical targets of interest, especially the PAH feature at 3.3 microns in HII regions and young planetary nebulae.
Highly efficient Volume phase holographic (VPH) gratings do not lend themselves to use in existing spectrographs except for grism spectrographs where VPH grisms can be designed that disperse but do not deviate the light. We discuss our program to outfit existing spectrographs [the Imaging grism instrument (IGI) on the McDonald Observatory Smith Reflector, and the Hobby-Eberly Telescope Marcario Low Resolution Spectrograph (LRS)] with efficient VPH grisms. We present test data on sample gratings from Ralcon Development Lab, and compare them to theoretical predictions. We have created a simple test bench for efficiency measurements of VPH gratings, which we describe. Finally we present first results from the use of VPH grisms in IGI and the LRS, the latter being the largest grism ever deployed in an astronomical spectrograph. We also look forward to using VPH grisms in the LRS infrared extension, which covers the wavelength range from 0.9 to 1.3 microns.
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