HEX-P is a probe-class mission concept that will combine high angular resolution (⪅ 5 ′′ at 6 keV) x-ray imaging and broad energy sensitivity (0.2 − 80 keV) to enable revolutionary new insights into black holes, neutron stars, and other extreme environments powering the high energy universe. HEX-P prioritizes broad band imagery and high resolution simultaneously, providing a wealth of information not possible with any other planned or operating observatory. HEX-P achieves its breakthrough performance by combining technologies developed by experienced partners: high resolution low energy imagery with silicon segmented mirrors provided by the Goddard Space Flight Center (GSFC, Greenbelt, MD); state of the art high energy imagery from nickel shell mirror technology developed by Media Lario (Bosisio Parini, Italy) and the National Institute for Astrophysics (INAF, Merate, Italy) through a contribution from the Italian Space Agency (ASI, Rome, Italy); high speed, high resolution Depleted P-Channel Field Effect Transistor (DEPFET) detectors through a contribution from the Max Planck Institute for Extraterrestrial Physics (MPE, Garching, Germany); photon counting high energy detectors from the NuSTAR team at the California Institute of Technology (Caltech, Pasadena CA); and a spacecraft and payload structure with a 20 m deployable boom developed by Northrop Grumman (Falls Church, VA).
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 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.
KEYWORDS: Mirrors, Amplifiers, Thermal modeling, Space telescopes, Sensors, Telescopes, Beryllium, Space operations, James Webb Space Telescope, Galaxy evolution
The Galaxy Evolution Probe (GEP) is a proposed far infrared-optimized observatory designed for zodiacal-light-limited imaging and spectroscopy in the 10 to 250 micron band. The GEP telescopes and instruments are planned to be actively cooled with the system in a sun-earth L2 halo orbit. A detailed description of the GEP mission concept is documented in [1]. Crucial to the scientific performance of GEP is the thermal architecture; it must support a range of cryogenic elements, ranging from the full telescope optical assembly at around 4 K to the far-IR focal planes consisting of kinetic inductance detector (KID) arrays cooled to 100 mK. Given the mass operating at these low temperatures, the thermal system is one of the main drivers of mission cost and complexity. We present a solution to the GEP thermal design that is realizable within a probe-class envelope. The baseline system utilizes a multi-stage adiabatic demagnetization refrigerator (ADR) for the 100mK base; the ADR system also provides an intercept at 1K. ADR systems similar to that in our design have flown, and among sub-K options, ADRs offer high Carnot efficiency. The ADR rejects heat to a hybrid Joule Thompson (JT) and Stirling or PT Cryocooler with a lowtemperature stage at 4 K as well as an intercept at 20 K. These coolers are also mature systems with flight heritage on most subcomponents.
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