We present the initial design, performance improvements, and science opportunities for an upgrade to the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS). FIFI-LS efficiently measures fine structure cooling lines, delivering critical constraints of the interstellar medium and star-forming environments. The Stratospheric Observatory for Infrared Astronomy (SOFIA) provides the only far-infrared (FIR) observational capability in the world, making FIFI-LS a workhorse for FIR lines, combining optimal spectral resolution and a wide velocity range. Its continuous coverage of 51 to 203 μm makes FIFI-LS a versatile tool to investigate a multitude of diagnostic lines within our galaxy and in extragalactic environments. The sensitivity and field of view (FOV) of FIFI-LS are limited by its 90s-era photoconductor arrays. These limits can be overcome by upgrading the instrument using the latest developments in kinetic inductance detectors (KIDs). KIDs provide sensitivity gains in excess of 1.4 and allow larger arrays, enabling an increase in pixel count by an order of magnitude. This increase allows a wider FOV and instantaneous velocity coverage. The upgrade provides gains in point source observation speed by a factor >2 and in mapping speed by a factor >3.5, enabled by the improved sensitivity and pixel count. This upgrade has been proposed to NASA in response to the 2018 SOFIA Next Generation Instrumentation call.
KEYWORDS: Space operations, Space observatories, Far infrared, Observatories, Earth observing sensors, Satellites, Data processing, Calibration, Data archive systems
The Herschel Space Observatory was the fourth Cornerstone mission of ESA’s Horizon 2000 programme, and a €1Bclass far infrared space observatory. The satellite and mission were developed over an approximately 10-year period before launch in 2009 and highly successful operation for approximately four years. A Post-Operations programme continued until 2017 (and with little resources even until 2019) in order to complete the data processing, calibration and documentation activities and to populate the Herschel Science Archive with the final data products and documentation. The Herschel Science Team, which oversaw the mission over a nearly 20-year period from late 1998 until its 61st and final meeting in late 2017, has conducted a comprehensive lessons learned review of the project from start to finish, encompassing all aspects of the endeavour – programmatics and management of the spacecraft, instrument consortia and ground segment; instrument development and testing; spacecraft implementation; ground segment and operations preparation pre-launch, in-flight operation and post-operations; science management and user support; and communications. Science is not addressed here except in general terms – this is not a scientific assessment. Focusing on generic features of the mission and its management, organisation, and technical design that have potential applications and relevance to future space projects, we have identified and assessed a number of aspects in which the Herschel experience can provide valuable lessons, both positive and negative, to aid the effective development and success of future missions, especially ones that are comparable in magnitude and complexity. We outline the main findings and conclusions of this Lessons Learned exercise.
We present the initial design, performance improvements and science opportunities for an upgrade to the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS). FIFI-LS efficiently measures fine structure cooling lines, delivering critical constraints of the interstellar medium and starforming environments. SOFIA provides the only FIR observational capability in the world, making FIFI-LS a workhorse for FIR lines, combining optimal spectral resolution and a wide velocity range. Its continuous coverage from 51-203 microns makes FIFI-LS a versatile tool to investigate a multitude of diagnostic lines within our galaxy and in extragalactic environments. The sensitivity and field-of-view (FOV) of FIFI-LS are limited by its 90s-era photoconductor arrays. These limits can be overcome by upgrading the instrument using the latest developments in Kinetic Inductance Detectors (KIDs). KIDs provide sensitivity gains in excess of 1.4 and allow larger arrays, enabling an increase in pixel count by an order of magnitude. This increase allows a wider FOV and instantaneous velocity coverage. The upgrade provides gains in point source observation speed by a factor <2 and in mapping speed by a factor <3.5, enabled by the improved sensitivity and pixel count. This upgrade has been proposed to NASA in response to the 2018 SOFIA Next Generation Instrumentation call.
We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 μm. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.
Ultimately, after the Single Aperture Far-IR (SAFIR) telescope, astrophysicists will need a far-IR observatory that provides angular resolution comparable to that of the Hubble Space Telescope. At such resolution galaxies at high redshift, protostars, and nascent planetary systems will be resolved, and theoretical models for galaxy, star, and planet formation and evolution can be subjected to important observational tests. This paper updates information provided in a 2000 SPIE paper on the scientific motivation and design concepts for interferometric missions SPIRIT (the Space Infrared Interferometric Telescope) and SPECS (the Submillimeter Probe of the Evolution of Cosmic Structure). SPECS is a kilometer baseline far-IR/submillimeter imaging and spectral interferometer that depends on formation flying, and SPIRIT is a highly-capable pathfinder interferometer on a boom with a maximum baseline in the 30 - 50 m range. We describe recent community planning activities, remind readers of the scientific rationale for space-based far-infrared imaging interferometry, present updated design concepts for the SPIRIT and SPECS missions, and describe the main issues currently under study. The engineering and technology requirements for SPIRIT and SPECS, additional design details, recent technology developments, and technology roadmaps are given in a companion paper in the Proceedings of the conference on New Frontiers in Stellar Interferometry.
A new calorimetric absolute power meter has been developed for THz radiation. This broad band THz power meter measures average power at ambient temperature and pressure, does not use a window, and is insensitive to polarization and time structure of THz radiation. The operation of the power meter is based on the calorimetric method: in order to determine the power of a beam of THz radiation, the beam is used to illuminate a highly absorbing surface with known BRDF characteristics until a stable temperature is reached. The power in the incident beam can then be determined by measuring the electric power needed to cause the sample temperature rise. The new power meter was used with laser calorimetry to measure the absorptivity, and thus the emissivity, of aluminum-coated silicon carbide mirror samples produced during the coating qualification run of the Herschel Space Observatory telescope to be launched by the European Space Agency in 2007. The samples were measured at 77 Kelvin to simulate the operating temperature of the telescope in its planned orbit around the second Lagrangian point, L2, of the Earth-Sun system. The absorptivity of both clean and dust-contaminated samples was measured at 70, 118, 184 and 496 mm and found to be in the range 0.2 - 0.8%.
In order to extend the US Naval Observatory (USNO) small-angle astrometric capabilities to near infrared wavelengths we have designed and manufactured a 1024 x 1024 InSb re-imaging infrared camera equipped with an array selected from the InSb ALADDIN (Advanced Large Area Detector Development in InSb) development
program and broadband and narrowband 0.8 - 3.8 μm filters. Since the USNO 1.55-m telescope is optimized for observations at visible wavelengths with an oversized secondary mirror and sky baffles, the straylight rejection capabilities of the ASTROCAM Lyot stop and baffles are of critical importance for its sensitivity and flat-
fielding capabilities. An Offner relay was chosen for the heart of the system and was manufactured from the same melt of aluminum alloy to ensure homologous contraction from room temperature to 77 K. A blackened cone was installed behind the undersized hole (the Lyot stop) in the Offner secondary. With low distortion, a well-sampled point spread function, and a large field of view, the system is well suited for astrometry. It is telecentric, so any defocus will not result in a change of image scale. The DSP-based electronics allow readout of the entire array with double-correlated sampling in 0.19 seconds, but shorter readout is possible with single sampling or by reading out only small numbers of subarrays. In this paper we report on the optical, mechanical, and electronic design of the system and present images and results on the sensitivity and astrometric stability obtained with the system, now operating routinely at the 1.55-m telescope with a science-grade ALADDIN array.
We have developed optical measurement and control techniques that allow stable, precise adjustment and tracking of Fabry-Perot plate parallelism and spacing over a distance of many fringes with a precision of 20 nm. This extension of the range of optical position sensing has proved useful in controlling a cryogenic, electromagnetically driven, infrared spectrometer for astronomy.
The design concept of a wide-field astronomical imaging telescope for use as a payload on an unmanned space platform, a Space Station attached payload, or a Delta-class Explorer is described. The instrument is based on a space Schmidt telescope concept studied by NASA and ESA (1979) for Spacelab missions. The astrophysical objectives include all-sky surveys in the UV and NIR ranges. Objects of interest include very hot and very cool stars and the interstellar medium. The UV range is inaccessible from the ground, and large-area surveys and sensitive imagery of diffuse sources are impractical with current or planned UV space telescopes. The NIR range is severely compromised in ground-based observations, particularly of diffuse sources, by airglow emissions, and no wide-field NIR space telescopes are currently approved for flight.
Possible optical designs of imaging detectors for the spaceborne Schmidt telescope proposed by Carruthers et al. (1990) are discussed, surveying the currently or potentially available technology. Consideration is given to FUV electrographic detectors of large format (e.g., 120 mm with 10-micron resolution) using CsI photocathodes, the possible extension of the same technology to the mid-UV using Cs2Te instead of CsI, large CCD arrays for the visible and NIR, electron-bombarded CCDs for the FUV and mid-UV, and the data handling and processing requirements of these detectors.
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