The Rapid infrared IMAger-Spectrometer (RIMAS) is a near-infrared (NIR) imager and spectrometer that will quickly follow up gamma-ray burst afterglows on the 4.3-meter Discovery Channel Telescope (DCT). RIMAS has two optical arms which allows simultaneous coverage over two bandpasses (YJ and HK) in either imaging or spectroscopy mode. RIMAS utilizes two Teledyne HgCdTe H2RG detectors controlled by Astronomical Research Cameras, Inc. (ARC/Leach) drivers. We report the laboratory characterization of RIMAS's detectors: conversion gain, read noise, linearity, saturation, dynamic range, and dark current. We also present RIMAS's instrument efficiency from atmospheric transmission models and optics data (both telescope and instrument) in all three observing modes.
The Rapid Infrared Imager/Spectrometer (RIMAS) is designed to perform follow-up observations of transient
astronomical sources at near infrared (NIR) wavelengths (0.9 - 2.4 microns). In particular, RIMAS will be used to
perform photometric and spectroscopic observations of gamma-ray burst (GRB) afterglows to compliment the Swift
satellite’s science goals. Upon completion, RIMAS will be installed on Lowell Observatory’s 4.3 meter Discovery
Channel Telescope (DCT) located in Happy Jack, Arizona. The instrument’s optical design includes a collimator lens
assembly, a dichroic to divide the wavelength coverage into two optical arms (0.9 - 1.4 microns and 1.4 - 2.4 microns
respectively), and a camera lens assembly for each optical arm. Because the wavelength coverage extends out to 2.4
microns, all optical elements are cooled to ~70 K. Filters and transmission gratings are located on wheels prior to each
camera allowing the instrument to be quickly configured for photometry or spectroscopy. An athermal optomechanical
design is being implemented to prevent lenses from loosing their room temperature alignment as the system is cooled.
The thermal expansion of materials used in this design have been measured in the lab. Additionally, RIMAS has a guide
camera consisting of four lenses to aid observers in passing light from target sources through spectroscopic slits. Efforts
to align these optics are ongoing.
The Rapid infrared IMAger-Spectrometer (RIMAS) is a rapid gamma-ray burst afterglow instrument that will provide photometric and spectroscopic coverage of the Y, J, H, and K bands. RIMAS separates light into two optical arms, YJ and HK, which allows for simultaneous coverage in two photometric bands. RIMAS utilizes two 2048 x 2048 pixel Teledyne HgCdTe (HAWAII-2RG) detectors along with a Spitzer Legacy Indium- Antimonide (InSb) guiding detector in spectroscopic mode to position and keep the source on the slit. We describe the software and hardware development for the detector driver and acquisition systems. The HAWAII- 2RG detectors simultaneously acquire images using Astronomical Research Cameras, Inc. driver, timing, and processing boards with two C++ wrappers running assembly code. The InSb detector clocking and acquisition system runs on a National Instruments cRIO-9074 with a Labview user interface and clocks written in an easily alterable ASCII file. We report the read noise, linearity, and dynamic range of our guide detector. Finally, we present RIMAS’s estimated instrument efficiency in photometric imaging mode (for all three detectors) and expected limiting magnitudes. Our efficiency calculations include atmospheric transmission models, filter models, telescope components, and optics components for each optical arm.
Douglas Leviton, Thomas Anderjaska, James Badger, Tom Capon, Clinton Davis, Brent Dicks, William Eichhorn, Mario Garza, Corina Guishard, Shadan Haghani, Claef Hakun, Paul Haney, David Happs, Lars Hovmand, Madhu Kadari, Jeffrey Kirk, Richard Nyquist, F. David Robinson, Joseph Sullivan, Erin Wilson
The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity
ground characterization and calibration of JWST’s flight instruments. OSIM and its associated Beam Image Analyzer
(BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the
instruments according to the same optical prescription as the flight telescope will image stars – correct in focal surface
position and chief ray angle. OSIM’s and BIA’s fifteen axes of mechanisms navigate according to redundant, cryogenic,
absolute, optical encoders – 32 in all operating at or below 100 K. OSIM’s encoder subsystem, the engineering
challenges met in its development, and the encoders’ sub-micron and sub-arcsecond performance are discussed.
The Observational Cosmology Laboratory at NASA’s Goddard Space Flight Center (GSFC), in collaboration with the
University of Maryland, is building the Rapid Infrared Imager/Spectrometer (RIMAS) for the new 4.3 meter Discovery
Channel Telescope (DCT). The instrument is designed to observe gamma-ray burst (GRB) afterglows following their
initial detection by the Swift satellite. RIMAS will operate in the near infrared (0.9 – 2.4 microns) with all of its optics
cooled to ~60 K. The primary optical design includes a collimator lens assembly, a dichroic dividing the wavelength
coverage into the “YJ band” and “HK band” optical arms, and camera lens assemblies for each arm. Additionally, filters
and dispersive elements are attached to wheels positioned prior to each arm’s camera, allowing the instrument to quickly
change from its imaging modes to spectroscopic modes. Optics have also been designed to image the sky surrounding
spectroscopic slits to help observers pass light from target sources through these slits. Because the optical systems are
entirely cryogenic, it was necessary to account for changing refractive indices and model the effects of thermal
contraction. One result of this work is a lens mount design that keeps lenses centered on the optical axis as the system is
cooled. Efforts to design, tolerance and assemble these cryogenic optical systems are presented.
The Reionization And Transients Infra-Red camera has been built for rapid Gamma-Ray Burst followup and
will provide simultaneous optical and infrared photometric capabilities. The infrared portion of this camera
incorporates two Teledyne HgCdTe HAWAII-2RG detectors, controlled by Teledyne’s SIDECAR ASICs. While
other ground-based systems have used the SIDECAR before, this system also utilizes Teledyne’s JADE2 interface
card and IDE development environment. Together, this setup comprises Teledyne’s Development Kit, which is
a bundled solution that can be efficiently integrated into future ground-based systems. In this presentation, we
characterize the system’s read noise, dark current, and conversion gain.
The Reionization And Transients InfraRed (RATIR) camera has been built for rapid Gamma-Ray Burst (GRB)
followup and will provide quasi-simultaneous imaging in ugriZY JH. The optical component uses two 2048 × 2048
pixel Finger Lakes Imaging ProLine detectors, one optimized for the SDSS u, g, and r bands and one optimized
for the SDSS i band. The infrared portion incorporates two 2048 × 2048 pixel Teledyne HgCdTe HAWAII-2RG
detectors, one with a 1.7-micron cutoff and one with a 2.5-micron cutoff. The infrared detectors are controlled by
Teledyne's SIDECAR (System for Image Digitization Enhancement Control And Retrieval) ASICs (Application
Specific Integrated Circuits). While other ground-based systems have used the SIDECAR before, this system
also utilizes Teledyne's JADE2 (JWST ASIC Drive Electronics) interface card and IDE (Integrated Development
Environment). Here we present a summary of the software developed to interface the RATIR detectors with
Remote Telescope System, 2nd Version (RTS2) software. RTS2 is an integrated open source package for remote
observatory control under the Linux operating system and will autonomously coordinate observatory dome,
telescope pointing, detector, filter wheel, focus stage, and dewar vacuum compressor operations. Where necessary
we have developed custom interfaces between RTS2 and RATIR hardware, most notably for cryogenic focus stage
motor drivers and temperature controllers. All detector and hardware interface software developed for RATIR
is freely available and open source as part of the RTS2 distribution.
The Reionization and Transients InfraRed camera (RATIR) is a simultaneous optical/NIR multi-band imaging
camera which is 100% time-dedicated to the followup of Gamma-ray Bursts. The camera is mounted on the
1.5-meter Johnson telescope of the Mexican Observatorio Astronomico Nacional on Sierra San Pedro Martir in
Baja California. With rapid slew capability and autonomous interrupt capabilities, the system will image GRBs
in 6 bands (i, r, Z, Y, J, and H) within minutes of receiving a satellite position, detecting optically faint afterglows
in the NIR and quickly alerting the community to potential GRBs at high redshift (z>6-10). We report here
on this Spring's first light observing campaign with RATIR. We summarize the instrumental characteristics,
capabilities, and observing modes.
The James Webb Space Telescope Observatory will consist of three flight elements: (1) the Optical Telescope Element
(OTE), (2) the Integrated Science Instrument Module Element (ISIM), and (3) the Spacecraft Element. The ISIM
element consists of a composite bench structure that uses kinematic mounts to interface to each of the optical benches of
the three science instruments and the guider. The ISIM is also kinematically mounted to the telescope primary mirror
structure. An enclosure surrounds the ISIM structure, isolates the ISIM region thermally from the other thermal regions
of the Observatory, and serves as a radiator for the science instruments and guider. Cryogenic optical testing of the ISIM
Structure and the Science Instruments will be conducted at Goddard Space Flight Center using an optical telescope
simulator that is being developed by a team from Ball Aerospace and Goddard Space Flight Center, and other local
contractors. This simulator will be used to verify the performance of the ISIM element before delivery to the Northup
Grumman team for integration with the OTE. In this paper, we describe the O
OTE Sim TE Simulator (OSIM) and provide a brief
overview of the optical test program.
ulator
This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with a standard uncertainty below 2nm rms. Two developmental silicon carbide mirrors were tested: both were spheres with radius of curvature of 600 mm, and clear apertures of 150 mm. The mirrors were cooled within a cryostat, and the surface figure error measured through a fused-silica window. The GSFC team developed methods to measure the change in surface figure with temperature (the cryo-change) with a combined standard uncertainty below 1 nm rms. This paper will present the measurement facility, methods, and uncertainty analysis.
This report describes the equipment, experimental methods, and first results at a new facility at the Goddard Space Flight Center Optics Branch for interferometric measurement of cryogenically-cooled spherical mirrors. A mirror is cooled to 80 K and 20 K within a cryostat; and its surface figure error is measured through a fused-silica window using standard phase-shifting interferometry. The first mirror tested was a concave spherical silicon foam-core mirror with a clear aperture of 120 mm. The optic surface was measured at room temperature outside the dewar using standard "absolute" techniques; and then the change in surface figure error within the dewar from room temperature to 80 K was measured, and the two measurements added to create a representation of the two-dimensional surface figure error at 80 K, with a combined standard uncertainty of 3.4 nm rms. The facility and techniques will be used to measure the surface figure error at 20K of prototype lightweight silicon carbide and Cesic mirrors developed by Galileo Avionica (Italy) for the European Space Agency (ESA).
This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with an uncertainty goal of 6 nm rms. The mirrors to be tested will be spheres with radius of curvature of 600 mm, and clear apertures of 120 - 150 mm. The optic surface will first be measured at room temperature using standard "absolute" techniques with an uncertainty of 2.6 nm rms; and then the change in surface figure error between room temperature and 20 K will be measured with an uncertainty goal of 5.4 nm rms. The mirror will be cooled within a cryostat, and its surface figure error measured through a fused-silica window. The facility and techniques are being developed to measure the cryogenic surface figure error of prototype lightweight mirrors being developed by the European Space Agency (ESA) and by US companies in SBIR's for NASA. This paper will present the measurement facility, methods and uncertainty analysis.
The Burst Alert Telescope (BAT) on Swift has a graded-Z Shield that closes out the volume between the coded aperture mask and the Cadmium-Zinc-Telluride (CZT) detector array. The purpose of the 37-kilogram shield is to attenuate gamma rays that have not penetrated the coded aperture mask of the BAT instrument and are therefore a major source of noise on the detector array. Unlike previous shields made from plates and panels, this shield consists of multiple layers of thin metal foils (lead, tantalum, tin, and copper) that are stitched together much like standard multi-layer insulation blankets. The shield sections are fastened around BAT, forming a curtain around the instrument aperture. Strength tests were performed to validate and improve the design, and the shield will be vibration tested along with BAT in late 2002. Practical aspects such as the layup design, methods of manufacture, and testing of this new kind of graded-Z Shield are presented.
The 2.6 square meter coded aperture mask is a vital part of the Burst Alert Telescope on the Swift mission. A random, but known pattern of more than 50,000 lead tiles, each 5 mm square, was bonded to a large honeycomb panel which projects a shadow on the detector array during a gamma ray burst. A two-year development process was necessary to explore ideas, apply techniques, and finalize procedures to meet the strict requirements for the coded aperture mask. Challenges included finding a honeycomb substrate with minimal gamma ray attenuation, selecting an adhesive with adequate bond strength to hold the tiles in place but flexible enough to allow the tiles to expand and contract without distorting the panel under large temperature gradients, and eliminating excess adhesive from all untiled areas. Finding an efficient way to bond the > 50,000 lead tiles to the panel while maintaining positional tolerances within +0.1 mm was no small task. In order to generate the desired bondline, adhesive was applied and allowed to cure to each tile. The 'pre-cured' tiles were located in a tool to maintain positional accuracy, wet adhesive was applied to the panel, and the wetted substrate was lowered to the tile surface with synchronized actuators. Using this procedure, the entire tile pattern was transferred to the large honeycomb panel in a single bond. The pressure for the bond was achieved by enclosing the entire system in a vacuum bag. Thermal vacuum and acoustic tests validated this approach. This paper discusses the methods, materials, and techniques used to fabricate this very large and unique coded aperture mask for the Swift mission.
The Infrared Array Camera (IRAC) is one of three science instruments that will fly aboard the Space Infrared Telescope Facility mission scheduled for launch in December, 2001. This paper summarizes the `as built' design of IRAC along with important integration and testing results.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
A method of minimizing the optical distortion from gravity sag on a suspended large autocollimating flat mirror has been devised. This method consists of an inverted nine- point Hindle-Mount. A conventional Hindle-mount is located underneath a sky-viewing mirror and is primarily under compression loads from the weight of the mirror. It is not suitable for the situation where the mirror is viewing the ground, since a mirror would tend to fall out of the mount when in an inverted position. The inverted Hindle-Mount design consists of bonded joints on the backside of the mirror that allow the mirror to be held or suspended above an object to be viewed. This ability is useful in optical setups such a s a calibration test where a flat mirror is located above a telescope so that the telescope may view a known optic.
The CIRS instrument to be flown on the Cassini mission to Saturn is a cryogenic spectrometer with far-IR (FIR) and mid-IR (MIR) channels. The CIRS FIR channel is a polarizing interferometer that contains three polarizing grid components. These components are an input polarizer, a polarizing beamsplitter, and an output polarizer/analyzer. THey consist of a 1.5 micron thick substrate with 2 micrometers wide copper wires, with 2 micrometers spacing, photolithographically deposited on the substrate. Mylar and polypropylene were chosen as the flight candidate substrates. After the testing was performed, mylar was chosen over polypropylene for the CIRS instrument due to a better cryogenic reflectance performance. These elements were fabricated at Queen Mary and Westfield College in London. This paper details the flight qualification of the mylar substrate and the characterization of the polypropylene substrate. Performance tests included cryogenic optical flatness, cryogenic polarization sensitive reflectance and transmittance measurements. Environmental tests included vibration, acoustic, humidity, and radiation survivability.
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