In this effort, we demonstrate the performance of a highly stable time reference for the proposed Black Hole Explorer (BHEX) mission, a space-based extension to the Event Horizon Telescope (EHT) Very Long Baseline Interferometry (VLBI) project. This precision timing system is based on the use of a space-qualified, ultralow noise laser developed as part of the Laser Interferometer Space Antenna (LISA) mission as the timing reference, and an optical frequency comb to transfer the stability of this laser to the microwave regime for instrumentation use. We describe the implementation of this system and experimental setup to characterize the stability performance. We present the results of this experiment that demonstrate the performance of this system meets requirements for the BHEX mission.
We present a baseline science operations plan for the Black Hole Explorer (BHEX), a space mission concept aiming to confirm the existence of the predicted sharp “photon ring” resulting from strongly lensed photon trajectories around black holes, as predicted by general relativity, and to measure its size and shape to determine the black hole’s spin. BHEX will co-observe with a ground-based very long baseline interferometric (VLBI) array at high-frequency radio wavelengths, providing unprecedented high resolution with the extension to space that will enable photon ring detection and studies of active galactic nuclei. Science operations require a simultaneous coordination between BHEX and a ground array of large and small radio apertures to provide opportunities for surveys and imaging of radio sources, while coordination with a growing network of optical downlink terminals provides the data rates necessary to build sensitivity on long baselines to space. Here we outline the concept of operations for the hybrid observatory, the available observing modes, the observation planning process, and data delivery to achieve the mission goals and meet mission requirements.
We present the Black Hole Explorer (BHEX), a mission that will produce the sharpest images in the history of astronomy by extending submillimeter Very-Long-Baseline Interferometry (VLBI) to space. BHEX will discover and measure the bright and narrow “photon ring” that is predicted to exist in images of black holes, produced from light that has orbited the black hole before escaping. This discovery will expose universal features of a black hole’s spacetime that are distinct from the complex astrophysics of the emitting plasma, allowing the first direct measurements of a supermassive black hole’s spin. In addition to studying the properties of the nearby supermassive black holes M87∗ and Sgr A∗ , BHEX will measure the properties of dozens of additional supermassive black holes, providing crucial insights into the processes that drive their creation and growth. BHEX will also connect these supermassive black holes to their relativistic jets, elucidating the power source for the brightest and most efficient engines in the universe. BHEX will address fundamental open questions in the physics and astrophysics of black holes that cannot be answered without submillimeter space VLBI. The mission is enabled by recent technological breakthroughs, including the development of ultra-high-speed downlink using laser communications, and it leverages billions of dollars of existing ground infrastructure. We present the motivation for BHEX, its science goals and associated requirements, and the pathway to launch within the next decade.
The Black Hole Explorer (BHEX) mission will enable the study of the fine photon ring structure, aiming to reveal the clear universal signatures of multiple photon orbits and true tests of general relativity, while also giving astronomers access to a much greater population of black hole shadows. Spacecraft orbits can sample interferometric Fourier spacings that are inaccessible from the ground, providing unparalleled angular resolution for the most detailed spatial studies of accretion and photon orbits and better time resolution. The BHEX mission concept provides space Very Long Baseline Interferometry (VLBI) at submillimeter wavelengths measurements to study black holes in coordination with the Event Horizon Telescope and other radio telescopes. This report presents the BHEX engineering goals, objectives and TRL analysis for a selection of the BHEX subsystems. This work aims to lay some of the groundwork for a near-term Explorers class mission proposal.
We have designed an Integral Field Unit for the ORCAS Keck Instrument Development II (ORKID II) Instrument. Building on the success of the ORKID camera which achieved 15.2 masec PSF FWHM visible light imaging, ORKID II will add Integral Field Spectroscopy to analyze Active Galactic Nuclei (AGN), supernovae redshift and brightness, and other observations. Several design options have been explored based on image slicers manufactured by the Canon Corporation’s machining process. Field layouts can include up to three disparate spatial sampling, with a lower limit of 6.7 masec. Spectral resolutions are considered from R 100 to R 10,000.
The Orbiting Configurable Artificial Star (ORCAS) mission in collaboration with the W. M. Keck Observatory (WMKO) is poised to deliver near diffraction limited observations in visible light. The ability to conduct such observations will enable significant scientific discoveries in fields related to Active Galactic Nuclei (AGN), Dark Energy, Flux Calibration, the High Redshift Universe, Exoplanets, and the Solar System. The ORCAS team has successfully completed three primary mission development goals to enable such observations. The performance demonstration with the ORCAS Keck Instrument Demonstrator (ORKID) captured arguably the highest resolution image at visible wavelengths from a large (10 meter) segmented telescope on the ground to date. High resolution AO imaging of the galaxy UGC 4729 in Natural Guide Star (NGS) mode was performed by locking onto a foreground asteroid passing nearby, which simulated an observation with a moving guide star validating post processing capabilities and demonstrating how regions unreachable by NGS and LGS could be explored. Additionally, the ORCAS team has successfully locked onto a laser source onboard the Laser Communications Relay Demonstration (LCRD) and closed the adaptive optics loop to perform near diffraction limited imaging at 1550 nm with the Keck 10 meter, the first demonstration of such capability with a large segmented telescope. All of these results validate the feasibility of the ORCAS mission. Following these accomplishments, ORCAS will be strongly positioned to propose a full-scale mission to upcoming opportunities.
The Event Horizon Explorer (EHE) is a mission concept to extend the Event Horizon Telescope via an additional space-based node. We provide highlights and overview of a concept study to explore the feasibility of such a mission. We present science goals and objectives, which include studying the immediate environment around supermassive black holes, and focus on critical enabling technologies and engineering challenges. We provide an assessment of their technological readiness and overall suitability for a NASA Medium Explorer (MIDEX) class mission.
Over its more than 30-year history, the Advanced Technologies and Instrumentation (ATI) program has provided grants to support technology development and instrumentation for ground-based astronomy. Through a combination of automated literature assessment and in-depth literature review, we present a survey of ATI-funded research and its impact on astronomy and society. Award acknowledgment and literature citation statistics for ATI are comparable to a comparison astronomy grant program that does not support technology development. Citation statistics for both NSF-funded programs exceed those of the general astronomical literature. Numerous examples demonstrate the significant, long-term impact of ATI-supported research in astronomy. As part of this impact, ATI grants have provided many early career researchers the opportunity to gain critical professional experience. However, technology development unfolds over a time period that is longer than an individual grant. A longitudinal perspective shows that investments in technology and instrumentation have led to extraordinary scientific progress.
Over its more than thirty-year history, the Advanced Technologies and Instrumentation (ATI) program has provided grants to support technology development for ground-based astronomy. Research from this program has advanced adaptive optics, high resolution and multi-object spectroscopy, optical interferometry and synoptic surveys, to name just a few. Previous and ongoing scientific advances span the entire field of astronomy, from studies of the Sun to the distant universe. Through a combination of literature assessment and individual case studies, we present a survey of ATI funded research for optical-infrared astronomy. We find that technology development unfolds over a time period that is longer than an individual grant. A longitudinal perspective shows that substantial scientific gains have resulted from investments in technology.
The Large Synoptic Survey Telescope (LSST) will explore the entire southern sky over 10 years starting in 2022 with unprecedented depth and time sampling in six filters, ugrizy. Artificial power on the scale of the 3.5 deg LSST field-of-view will contaminate measurements of baryonic acoustic oscillations (BAO), which fall at the same angular scale at redshift z ~ 1. Using the HEALPix framework, we demonstrate the impact of an “un- dithered” survey, in which 17% of each LSST field-of-view is overlapped by neighboring observations, generating a honeycomb pattern of strongly varying survey depth and significant artificial power on BAO angular scales. We find that adopting large dithers (i.e., telescope pointing o sets) of amplitude close to the LSST field-of-view radius reduces artificial structure in the galaxy distribution by a factor of ~10. We propose an observing strategy utilizing large dithers within the main survey and minimal dithers for the LSST Deep Drilling Fields. We show that applying various magnitude cutos can further increase survey uniformity. We find that a magnitude cut of r < 27:3 removes significant spurious power from the angular power spectrum with a minimal reduction in the total number of observed galaxies over the ten-year LSST run. We also determine the effectiveness of the observing strategy for Type Ia SNe and predict that the main survey will contribute ~100,000 Type Ia SNe. We propose a concentrated survey where LSST observes one-third of its main survey area each year, increasing the number of main survey Type Ia SNe by a factor of ~1.5, while still enabling the successful pursuit of other science drivers.
Membrane deformable mirror devices consist of a single large membrane that is suspended above an array of actuating electrodes. A transparent electrode is incorporated into the membrane mirror device in the optical path in an effort to provide significantly greater control of the membrane, and hence improved performance in an adaptive optics system. The devices presented here were fabricated from 1 mm thickness SOI; devices were bonded to electrode arrays with 1024 electrodes, packaged in ceramic pin grid arrays and driven by off chip D/A electronics. The transparent electrodes consist of glass that is ITO coated for electrical conductivity and visible light transmission. An electrode is inserted into a recessed cavity of each membrane chip, and is positioned 70 mm above the membrane. With 2x2 binned electrodes, the device demonstrates 10 mm deflection toward the electrode array at 40 V. Large deflection at low voltage is obtained because of the low intrinsic stress of the silicon membrane. These data also demonstrate modest deflection toward the transparent electrode, which may be improved with better alignment of the transparent electrode with the underlying membrane and electrode array in future devices.
Low stress membrane mirrors will allow improved wave front correction in vision science and astronomical adaptive optics systems. We have fabricated low stress membrane mirrors from single crystal silicon, and flip chip bonded membranes to electrode arrays. These devices operate at lower voltage and have greater stroke than existing membrane mirror devices; they have 256 control electrodes, and are driven by off chip electronics. Devices have a single electrode plane and are pre-biased to allow full wave front correction. We have demonstrated these devices in an adaptive optics system consisting of a coherent source, and a Shack-Hartmann wave front sensor. We compare the experimental performance of the devices to computer simulations and theoretical calculations.
The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.
We are developing membrane mirrors for use in adaptive optics, particularly in astronomy and vision science. We have micro-fabricated membrane mirrors from single crystal silicon using wet chemical etching and reactive ion etching. Membrane size, tension and operating voltage were selected to allow greater deformation of the mirror surface at low operating voltage than previous membrane mirror designs. Mirror devices consist of independently fabricated membrane and electrode array chips that are flip chip bonded together. We have fabricated electrode arrays with 256 and 1024 electrodes, and active diameters ranging from 6-10 mm (comparable to the size of the human pupil). Membrane-electrode hybrids are mounted to ceramic packages, wire bonded, and driven by off chip, D/A electronics. These devices are milestones in the development of an electret membrane mirror.
Adaptive optics provides a means to measure and correct aberrations in human vision. This technology is being used to diagnose vision problems, study the mechanism of human vision, and extend the capabilities of nature's optics. The ideal wavefront corrector for vision science adaptive optics would have greater stroke, and more degrees of freedom than is currently available. Micromachined deformable mirrors may soon meet these demands. Membrane mirrors in particular offer a promising alternative to other MEMS deformable mirror designs. A new type of mirror, employing a bound charge layer on the membrane, may overcome some of the limitations of previous membrane mirrors.
The burst and all sky imaging survey (BASIS) is a proposed mission to provide plus or minus 3 arc-second locations of an estimated 90 gamma-ray bursts (GRBs) per year. The BASIS coded aperture imaging system requires a segmented detector plane able to detect the position of photon absorption to less than 100 microns. To develop prototype detector arrays with such fine position resolution we have fabricated many 15 mm by 15 mm by 2 mm 100 micron pitch CdZnTe strip detectors. A 2 by 2 prototype 100 micron CdZnTe strip detector array has been fabricated and has been used to test the capabilities of the BASIS imaging system. Preliminary shadowgrams of a 1 mm wide gap between two tungsten straight edges indicate that our position resolution is on the order of 69 micrometers. Both the array and imaging tests are described. A 6 by 6 element CdZnTe detector array is also being fabricated at GSFC. The assembly of this flight prototype array is discussed as well as applications for BASIS.
The burst and all-sky imaging survey (BASIS) project is a proposed small explorer (SMEX) mission to image the gamma-ray sky in the 10 - 150 keV energy range with high angular and energy resolution. It will be able to determine the locations of gamma-ray bursts (GRBs) to within a few arcseconds, sending accurate positions to ground-based telescopes for simultaneous and follow-up observations within seconds of the beginning of the GRB. It will also produce all-sky maps with 30 arcsecond resolution and 2 milliCrab sensitivity. The instrument uses a two-scale coded aperture mask to modulate gamma-rays falling on a cadmium zinc telluride (CZT) detector plane consisting of both 100 micrometer pitch strip detectors and 4 mm square spectroscopy detectors. The spatial pattern of gamma-rays will be deconvolved with the mask pattern to produce an image. This paper presents results from a prototype of this system, using a mask and strip detectors to produce an image of a radioactive source. The prototype functions as expected, producing images which, when scaled to the dimensions of the proposed instrument, achieve the desired resolution.
CdZnTe strip detectors have been fabricated and tested to show the ability for arc second imaging and spectroscopy. Two dimensional CdZnTe strip detectors with 100 micron pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 22 to 122 keV photons to less than 100 microns. Good spectral resolution has also been achieved. The uniformity and relative efficiency of the strip detector are discussed. Radiation damage effects by intermediate energy neutrons and low energy protons on the surface and bulk performance of CdZnTe devices have been investigated and are presented. Activation and annealing of radiation effects have been seen and are discussed.
We exposed a CdZnTe detector to MeV neutrons from a 252Cf source and found no performance degradation for fluences below 1010 neutrons cm-2. Detector resolution did show significant degradation at higher neutron fluences. There is evidence of room temperature annealing of the radiation effects over time. Activation lines were observed and the responsible isotopes were identified by the energy and half-life of the lines. These radiation damage studies allow evaluation of the robustness of CdZnTe detectors in high neutron and radiation environments.
A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy is being developed for a space flight gamma-ray burst instrument. Two dimensional strip detectors with 100 micrometers pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 22 to 122 keV photons to less than 100 micrometers. In addition, good spectral resolution has been achieved. The uniformity of response and relative efficiency of the strip detector will be discussed. Results form electrical characterization which include strip leakage current and strip capacitance will be presented.
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