The Nancy Grace Roman Space Telescope will enable advances in astrophysics by providing a large-scale survey capability in infrared wavelengths. The observatory is designed to provide data that will allow astronomers to unlock mysteries of the universe, answering high-priority scientific questions related to the evolution of the universe and the habitability of exoplanets. Using a 2.4 m (7.9 ft) primary mirror, Roman will capture comparable quality images to Hubble, but with more than 200 times the field of view of Hubble’s near-infrared channel, enabling the observatory to conduct comprehensive and efficient surveys. The Wide Field Instrument (WFI) features a 300-megapixel mosaic focal plane assembly with 18 H4RG detectors. WFI includes filters that provide an imaging mode covering 0.48 - 2.0 μm and two slitless spectroscopy modes. To meet scientific objectives, WFI requires a stable structural and cryogenic environment. NASA designs and develops the WFI science data signal chain and selected Ball Aerospace as their partner to design and develop the WFI Opto-Mechanical Assembly. In this paper, we present a WFI design evolution overview from early phases of the project through the critical design review. Innovations that increased performance, improved testability, and reduced mass and power will be discussed. Moving the third telescope mirror from the instrument to the heritage telescope assembly, eliminating the cryocooler by converting from an active to passive thermal design, unfolding the optical path to eliminate the mirror in the instrument design, and changing the plane of the serviceable latch configuration to ensure a kinematic mount are presented.
The Galaxy Evolution Probe (GEP) is a concept for a mid- and far-infrared space observatory to measure key properties of large samples of galaxies with large and unbiased surveys. GEP will attempt to achieve zodiacal light and Galactic dust emission photon background-limited observations by utilizing a 6-K, 2.0-m primary mirror and sensitive arrays of kinetic inductance detectors (KIDs). It will have two instrument modules: a 10 to 400 μm hyperspectral imager with spectral resolution R = λ / Δλ ≥ 8 (GEP-I) and a 24 to 193 μm, R = 200 grating spectrometer (GEP-S). GEP-I surveys will identify star-forming galaxies via their thermal dust emission and simultaneously measure redshifts using polycyclic aromatic hydrocarbon emission lines. Galaxy luminosities derived from star formation and nuclear supermassive black hole accretion will be measured for each source, enabling the cosmic star formation history to be measured to much greater precision than previously possible. Using optically thin far-infrared fine-structure lines, surveys with GEP-S will measure the growth of metallicity in the hearts of galaxies over cosmic time and extraplanar gas will be mapped in spiral galaxies in the local universe to investigate feedback processes. The science case and mission architecture designed to meet the science requirements is described, and the KID and readout electronics state of the art and needed developments are described. This paper supersedes the GEP concept study report cited in it by providing new content, including: a summary of recent mid-infrared KID development, a discussion of microlens array fabrication for mid-infrared KIDs, and additional context for galaxy surveys. The reader interested in more technical details may want to consult the concept study report.
The Wide Field Infrared Survey Telescope (WFIRST), NASA’s next decadal astrophysics observatory, will enable advances in astrophysics by providing a large-scale survey capability in infrared wavelengths. The observatory is designed to capture data that will allow astronomers to unlock the mysteries of the universe, answering high-priority scientific questions related to the evolution of the universe and the habitability of exoplanets. Using a 2.4 m (7.9 ft) primary mirror, WFIRST will capture comparable quality images to the Hubble Space Telescope, but with more than 100 times the field of view, enabling the observatory to conduct comprehensive and efficient surveys of the infrared sky. Scientists estimate WFIRST has the potential to examine a billion galaxies over the course of its mission. Ball Aerospace was selected as NASA’s partner to design and develop the Wide Field Instrument (WFI) Opto-Mechanical Assembly for the WFIRST mission. The optical-mechanical assembly, which includes the optical bench, thermal control system, precision mechanisms, optics, electronics, and the relative calibration system, provides the stable structure and thermal environment that enables the wide-field, high quality observations of WFI. Ball's innovative design uses heritage hardware to unfold the incoming light, providing cost and schedule savings to the mission. In this paper, we present an overview of the WFI design, which completed its preliminary design review in June 2019. The overview includes a discussion of the design process, including several of the trade studies completed that led to the unfolded optical path architecture for the instrument design. The current state of the design is shown.
The Galaxy Evolution Probe (GEP) is a concept for a mid and far-infrared space observatory designed to survey sky for star-forming galaxies from redshifts of z = 0 to beyond z = 4. Furthering our knowledge of galaxy formation requires uniform surveys of star-forming galaxies over a large range of redshifts and environments to accurately describe star formation, supermassive black hole growth, and interactions between these processes in galaxies. The GEP design includes a 2 m diameter SiC telescope actively cooled to 4 K and two instruments: (1) An imager to detect star-forming galaxies and measure their redshifts photometrically using emission features of polycyclic aromatic hydrocarbons. It will cover wavelengths from 10 to 400 μm, with 23 spectral resolution R = 8 filter-defined bands from 10 to 95 μm and five R = 3.5 bands from 95 to 400 μm. (2) A 24 – 193 μm, R = 200 dispersive spectrometer for redshift confirmation, identification of active galactic nuclei, and interstellar astrophysics using atomic fine-structure lines. The GEP will observe from a Sun-Earth L2 orbit, with a design lifetime of four years, devoted first to galaxy surveys with the imager and second to follow-up spectroscopy. The focal planes of the imager and the spectrometer will utilize KIDs, with the spectrometer comprised of four slit-coupled diffraction gratings feeding the KIDs. Cooling for the telescope, optics, and KID amplifiers will be provided by solar-powered cryocoolers, with a multi-stage adiabatic demagnetization refrigerator providing 100 mK cooling for the KIDs.
The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development of extreme lightweighted large optomechanical structures. Sparse apertures, shell optics, and membrane optics are a few of the approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for many years. The MOIRE approach in which the membrane is used as a transmissive diffractive optical element (DOE) offers a significant relaxation in the control requirements on the membrane surface figure, supports extreme lightweighting of the primary collecting optic, and provides a path for rapid low cost production of the primary optical elements. Successful development of a powered meter-scale transmissive membrane DOE was reported in 2012. This paper presents initial imaging results from integrating meter-scale transmissive DOEs into the primary element of a 5- meter diameter telescope architecture. The brassboard telescope successfully demonstrates the ability to collect polychromatic high resolution imagery over a representative object using the transmissive DOE technology. The telescope includes multiple segments of a 5-meter diameter telescope primary with an overall length of 27 meters. The object scene used for the demonstration represents a 1.5 km square complex ground scene. Imaging is accomplished in a standard laboratory environment using a 40 nm spectral bandwidth centered on 650 nm. Theoretical imaging quality for the tested configuration is NIIRS 2.8, with the demonstration achieving NIIRS 2.3 under laboratory seeing conditions. Design characteristics, hardware implementation, laboratory environmental impacts on imagery, image quality metrics, and ongoing developments will be presented.
The desire to field space-based telescopes with apertures in excess of 10 meter diameter is forcing the development
of extreme lightweighted large optics. Sparse apertures, shell optics, and membrane optics are a few of the
approaches that have been investigated and demonstrated. Membrane optics in particular have been investigated for
many years. The majority of the effort in membrane telescopes has been devoted to using reflective membrane
optics with a fair level of success being realized for small laboratory level systems; however, extending this
approach to large aperture systems has been problematic. An alternative approach in which the membrane is used as
a diffractive transmission element has been previously proposed, offering a significant relaxation in the control
requirements on the membrane surface figure. The general imaging principle has been demonstrated in 50-cm-scale
laboratory systems using thin glass and replicated membranes at long f-number (f/50). In addition, a 5-meter
diameter f/50 transmissive diffractive optic has been demonstrated, using 50-cm scale segments arrayed in a
foldable origami pattern. In this paper we discuss Membrane Optical Imager Real-time Exploitation (MOIRE)
Phase 1 developments that culminated in the development and demonstration of an 80 cm diameter, off-axis, F/6.5
phase diffractive transmissive membrane optic. This is a precursor for an optic envisioned as one segment of a 10
meter diameter telescope. This paper presents the demonstrated imaging wavefront performance and collection
efficiency of an 80 cm membrane optic that would be used in an F/6.5 primary, discusses the anticipated areal
density in relation to existing space telescopes, and identifies how such a component would be used in previously
described optical system architectures.
In August 2004, the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ceased operation
due to a failure of the 5V mechanism power converter in the Side 2 Low Voltage Power Supply (LVPS2). The failure
precluded movement of any STIS mechanism and, because of the earlier (2001) loss of the Side 1 electronics chain, left
the instrument shuttered and in safe mode after 7.5 years of science operations. A team was assembled to analyze the
fault and to determine if STIS repair (STIS-R) was feasible. The team conclusively pinpointed the Side 2 failure to the
5V mechanism converter, and began studying EVA techniques for opening STIS during Servicing Mission 4 (SM4) to
replace the failed LVPS2 board. The restoration of STIS functionality via surgical repair by astronauts has by now
reached a mature and final design state, and will, along with a similar repair procedure for the Advanced Camera for
Surveys (ACS), represent a first for Hubble servicing. STIS-R will restore full scientific functionality of the
spectrograph on Side 2, while Side 1 will remain inoperative. Because of the high degree of complementarity between
STIS and the new Cosmic Origins Spectrograph (COS, to be installed during SM4)), successful repair of the older
spectrograph is an important scientific objective. In this presentation, we focus on the technical aspects associated with
STIS-R.
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