Very long baseline interferometry (VLBI) provides the highest-resolution images in astronomy. The sharpest resolution is nominally achieved at the highest frequencies, but as the observing frequency increases, so too does the atmospheric contribution to the system noise, degrading the sensitivity of the array and hampering detection. In this paper, we explore the limits of high-frequency VLBI observations using ngehtsim , a new tool for generating realistic synthetic data. ngehtsim uses detailed historical atmospheric models to simulate observing conditions, and it employs heuristic visibility detection criteria that emulate single- and multifrequency VLBI calibration strategies. We demonstrate the fidelity of ngehtsim’s predictions using a comparison with existing 230 GHz data taken by the Event Horizon Telescope (EHT), and we simulate the expected performance of EHT observations at 345 GHz. Though the EHT achieves a nearly 100% detection rate at 230 GHz, our simulations indicate that it should expect substantially poorer performance at 345 GHz; in particular, observations of M87* at 345 GHz are predicted to achieve detection rates of ≲20% that may preclude imaging. Increasing the array sensitivity through wider bandwidths and/or longer integration times—as enabled through, e.g., the simultaneous multifrequency upgrades envisioned for the next-generation EHT—can improve the 345 GHz prospects and yield detection levels that are comparable to those at 230 GHz. M87* and Sgr A* observations carried out in the atmospheric window around 460 GHz could expect to regularly achieve multiple detections on long baselines, but analogous observations at 690 and 875 GHz consistently obtain almost no detections at all.

We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program-the next-generation Event Horizon Telescope (ngEHT)-will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes (SMBH) and their emanating jets. This builds upon the EHT principally by deploying additional modest-diameter dishes to optimized geographic locations to enhance the current global mm/submm wavelength Very Long Baseline Interferometric (VLBI) array, which has, to date, utilized mostly pre-existing radio telescopes. The ngEHT program further focuses on observing at three frequencies simultaneously for increased sensitivity and Fourier spatial frequency coverage. Here, the concept, science goals, design considerations, station siting, and instrument prototyping are discussed, and a preliminary reference array to be implemented in phases is described.

Adjustable X-ray optics represent a potential mirror technology for the NASA Lynx X-ray observatory mission concept. Adjustable optics employ an integrated micron-thick piezoelectric film deposited on the convex side of silicon Wolter-type mirror segments. Discrete, independently addressable electrodes on the convex surface form individual actuators; the applied voltages are used to correct the shape of the mirror segments for figure errors resulting from a change in thermal environment, epoxy creep, or failure of an epoxy bond. On-orbit correction requires a metrology system to provide real-time feedback of mirror figure. We are examining the use of deposited semiconductor strain gauges to monitor mirror mechanical strains and surface temperatures. To establish requirements for monitoring we modeled a variety of thermal and mechanical disturbances to a mirror segment such as might occur on-orbit or from launch. Models are described and resulting requirements and performance discussed.

Solar Probe Cup (SPC) is a Faraday cup instrument on board NASA’s Parker Solar Probe ( PSP ) spacecraft designed to make rapid measurements of thermal coronal and solar wind plasma. The spacecraft is in a heliocentric orbit that takes it closer to the Sun than any previous spacecraft, allowing measurements to be made where the coronal and solar wind plasma is being heated and accelerated. The SPC instrument was designed to be pointed directly at the Sun at all times, allowing the solar wind (which is flowing primarily radially away from the Sun) to be measured throughout the orbit. The instrument is capable of measuring solar wind ions with an energy between 100 and 6000 V (protons with speeds from 139 to 1072 km s −1 ). It also measures electrons with an energy/charge between 100 and 1500 V. SPC has been designed to have a wide dynamic range that is capable of measuring protons and alpha particles at the closest perihelion (9.86 solar radii from the center of the Sun) and out to 0.25 au. Initial observations from the first orbit of PSP indicate that the instrument is functioning well.

Lynx, one of the four strategic mission concepts under study for the 2020 Astrophysics Decadal Survey, provides leaps in capability over previous and planned x-ray missions and provides synergistic observations in the 2030s to a multitude of space- and ground-based observatories across all wavelengths. Lynx provides orders of magnitude improvement in sensitivity, on-axis subarcsecond imaging with arcsecond angular resolution over a large field of view, and high-resolution spectroscopy for point-like and extended sources in the 0.2- to 10-keV range. The Lynx architecture enables a broad range of unique and compelling science to be carried out mainly through a General Observer Program. This program is envisioned to include detecting the very first seed black holes, revealing the high-energy drivers of galaxy formation and evolution, and characterizing the mechanisms that govern stellar evolution and stellar ecosystems. The Lynx optics and science instruments are carefully designed to optimize the science capability and, when combined, form an exciting architecture that utilizes relatively mature technologies for a cost that is compatible with the projected NASA Astrophysics budget. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

We have been studying Lynx, an X-ray Observatory with factors of 10 to 1000 greater imaging and spectroscopic capabilities than any other existing or planned facility. We present a Design Reference Mission (DRM) driven by the need to solve fundamental problems in three broad areas of astrophysics. The Lynx Observatory will provide discovery space for all of astrophysics, and also address questions which will only be revealed as our knowledge increases. Studies supported by the Advanced Concepts Office at MSFC for the observatory design and operations take advantage of the highly successful architecture of the Chandra Observatory. A light-weight mirror with 30 times the Chandra effective area, and modern microcalorimeter and CMOS based X-ray imagers will exploit the 0.5 arcsec imaging capability. Operating at Sun/Earth L2, we expect 85% to 90% of the time to be spent acquiring data from celestial targets. Designed for a five year baseline mission, there are no expected impediments to achieving a 20 year goal. This paper presents technical details of the Observatory and highlights of the mission operations.

The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are rotated relative to one another so their broad fields of view combine like the seams on a baseball to view the entire sky except for the region obscured by the heat shield and covered by SPC. Observations by SPC and SPAN produce the combined field of view and measurement capabilities required to fulfill the science objectives of SWEAP and Solar Probe Plus. SWEAP measurements, in concert with magnetic and electric fields, energetic particles, and white light contextual imaging will enable discovery and understanding of solar wind acceleration and formation, coronal and solar wind heating, and particle acceleration in the inner heliosphere of the solar system. SPC and SPAN are managed by the SWEAP Electronics Module (SWEM), which distributes power, formats onboard data products, and serves as a single electrical interface to the spacecraft. SWEAP data products include ion and electron velocity distribution functions with high energy and angular resolution. Full resolution data are stored within the SWEM, enabling high resolution observations of structures such as shocks, reconnection events, and other transient structures to be selected for download after the fact. This paper describes the implementation of the SWEAP Investigation, the driving requirements for the suite, expected performance of the instruments, and planned data products, as of mission preliminary design review.

Three metallic coatings with textured surfaces, made of rhenium, tungsten and molybdenum, were studied in the frame of the Solar Probe Plus mission (NASA) as candidate materials. The role of these coatings is to dissipate a maximum of energy from a hot instrument facing the Sun, by the mean of their high total hemispherical emissivity. The total hemispherical emissivity of the three coatings was measured in the temperature range 1100-1900 K, as well as over time in order to study their high temperature stability. Various emissivity levels were obtained depending on the surface texture. The highest total hemispherical emissivity was obtained on a rhenium coating, with an emissivity of 0.8 in the temperature range 1300-1700 K. However, this rhenium coating with a fine, sharp surface texture, presented an instability at high temperature, which might limit its optimal operating temperature to about 1500 K. As for the tungsten coating, the total hemispherical emissivity was increased by a factor 2 due to the enhanced surface texturation and its great stability over the whole temperature range was shown. (C) 2015 Elsevier Ltd. All rights reserved.

Addressing the astrophysical problems of the 2020's requires sub-arcsecond x-ray imaging with square meter effective area. Such requirements can be derived, for example, by considering deep x-ray surveys to find the young black holes in the early universe (large redshifts) which will grow into the first super-massive black holes. We have envisioned a mission, the Square Meter Arcsecond Resolution Telescope for X-rays (SMART-X), based on adjustable x-ray optics technology, incorporating mirrors with the required small ratio of mass to collecting area. We are pursuing technology which achieves sub-arcsecond resolution by on-orbit adjustment via thin film piezoelectric "cells" deposited directly on the non-reflecting sides of thin, slumped glass. While SMART-X will also incorporate state-of-the-art x-ray cameras, the remaining spacecraft systems have no requirements more stringent than those which are well understood and proven on the current Chandra X-ray Observatory.

This paper describes the implementation of a solar simulator, know as the Solar Environment Simulator (SES), that can simulate solar flux levels up to those encountered at 9.8 solar radii. The paper outlines the design, and the challenges of realizing the SES. It also describes its initial uses for proving out the design of the Solar Winds Electrons, Alphas, and Protons (SWEAP) Faraday cup. The upcoming Solar Probe Plus (SPP) mission requires that its in-situ plasma instrument (the Faraday Cup) survive and operate over an unprecedented range of temperatures. One of the key risk mitigation activities during Phase B has been to develop and implement a simulator that will enable thermal testing of the Faraday Cup under flight-like conditions. While still in the initial start-up, the SES has proven to be an instrumental component in the process of predicting the inflight performance of the SWEAP Faraday Cup. With near continuously variable power control above the threshold of 1.6kW/lamp up to approximately 6.5kW/lamp, the SES has been used to determine the system response to a wide range of incoming flux, thereby making it possible to correlate detailed thermal models to a high degree of certainty (see Ref. [1], Figure 1.1). The SES consists of a set of repurposed, and slightly re-designed standard movie projectors. The projectors have proven to be an economical and effective means to safely hold and control the xenon short-arc lamps that are the basis of the SES. This paper outlines the key challenges controlling the extremely high flux levels (~70w/cm^2) necessary to make the SES a useful test facility.

The upcoming Solar Probe Plus (SPP) mission requires novel approaches for in-situ plasma instrument design. SPP's Solar Probe Cup (SPC) instrument will, as part of the Solar Wind Electrons, Alphas, and Protons (SWEAP) instrument suite, operate over an enormous range of temperatures, yet must still accurately measure currents below 1 pico-amp, and with modest power requirements.This paper discusses some of the key technology development aspects of the SPC, a Faraday Cup and one of the few instruments on SPP that is directly exposed to the solar disk, where at closest approach to the Sun (less than 10 solar radii (R-s) from the center of the Sun) the intensity is greater than 475 earth-suns. These challenges range from materials characterization at temperatures in excess of 1400 degrees C to thermal modeling of the behavior of the materials and their interactions at these temperatures. We discuss the trades that have resulted in the material selection for the current design of the Faraday Cup. Specific challenges include the material selection and mechanical design of insulators, particularly for the high-voltage (up to 8 kV) grid and coaxial supply line, and thermo-optical techniques to minimize temperatures in the SPC, with the specific intent of demonstrating Technology Readiness Level 6 by the end of 2013.

The NASA Solar Probe Plus (SPP) mission will be the first spacecraft to pass through the sub-Alfvenic solar corona. The objectives of the mission are to trace the flow of energy that heats and accelerates the solar corona and solar wind, to determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, and to explore mechanisms that accelerate and transport energetic particles. The Solar Wind Electrons, Alphas, and Protons (SWEAP) Investigation instrument suite on SPP will measure the bulk solar wind conditions in the inner heliosphere. SWEAP consists of the Solar Probe Cup (SPC), a sun-pointing Faraday Cup, and the Solar Probe ANalyzers (SPAN), a set of 3 electrostatic analyzers that will reside in the penumbra of SPP's thermal protection system and measure solar wind ions and electrons. SPP is scheduled to launch in 2018 into an equatorial solar orbit where a sequence of Venus gravity assists will gradually lower its closest solar approach to within 9.5 solar radii (R-S) of the center of the Sun. The photon flux at 9.5 R-S is more than 500 times greater than at 1 AU and therefore presents a design challenge for SPC, which will point directly at the Sun. SPC is derived from the Faraday cup instruments successfully flown on spacecraft from the beginning of the space age, but updated with high temperature materials to operate through the solar encounters. Current work includes both instrument design and the development of a testing approach capable of demonstrating adequate performance in encounter conditions. This paper will briefly discuss the suite as a whole, and then focus on the design and capabilities of SPC. We will also present the planned calibration and characterization of the instrument and the testing required to demonstrate the technological readiness of the design.

The Solar Probe Cup (SPC) Instrument is a Sun-facing Faraday Cup instrument slated for launch aboard the Solar Probe Plus (SPP) spacecraft in 2018. SPC is one of two instruments onboard the Solar Wind Electrons Alphas Protons (SWEAP) instrument suite and is the only SPP charged particle instrument that will not be shielded behind the spacecraft’s Thermal Protection System (TPS). The 7-year SPP mission will take SPC on 24 solar encounters at perihelia ranging from 35 to 9.86 solar radii (RS). The SPC components will encounter a large range of temperatures, from in excess of 1500°C at perihelion to -130°C at or near aphelion. This paper details the derived mechanical and structural requirements on the primary SPC mechanical assemblies including its thermal shield, the sensor unit and the strut/adapter assembly. An example of sensor requirements derivation to the component level is provided by the modulator flex ring. Preliminary requirements derivation, definition, and compliance are provided for these assemblies and components.

We describe an X-ray Observatory mission with 0.5” angular resolution, comparable to the Chandra X-ray Observatory, but with 30 times more effective collecting area. The concept is based on developing the new technology of adjustable X-ray optics for ultra thin (0.4 mm), highly nested grazing incidence X-ray mirrors. Simulations to date indicate that the corrections for manufacturing and mounting can be determined on the ground and the effects of gravity release can be calculated to sufficient accuracy, so that all adjustments are applied only once on-orbit, without the need of any on-orbit determination of the required corrections. The mission concept is based on the Chandra Observatory, and takes advantage of the technology studies which have taken place over the past fifteen years developing large area, light weight mirrors.

In the half century since the initial discovery of an astronomical (non-solar) x-ray source, the observation time required to achieve a given sensitivity has decreased by eight orders of magnitude. Largely responsible for this dramatic progress has been the refinement of the (grazing-incidence) focusing x-ray telescope, culminating with the exquisite subarcsecond imaging performance of the Chandra X-ray Observatory. The future of x-ray astronomy relies upon the development of x-ray telescopes with larger aperture areas (< 1 m2) and comparable or finer angular resolution (< 1″). Combined with the special requirements of grazing-incidence optics, the mass and envelope constraints of space-borne telescopes render such advances technologically challenging—requiring precision fabrication, alignment, and assembly of large areas (< 200 m2) of lightweight (≈ 1 kg m-2 areal density) mirrors. Achieving precise and stable alignment and figure control may entail active (in-space adjustable) x-ray optics. This paper discusses relevant programmatic and technological issues and summarizes current progress toward active x-ray telescopes.

Future x-ray observatories will require high-resolution (< 1 '') optics with very-large-aperture (> 25 m(2)) areas. Even with the next generation of heavy-lift launch vehicles, launch-mass constraints and aperture-area requirements will limit the areal density of the grazing-incidence mirrors to about 1 kg/m(2) or less. Achieving sub-arcsecond x-ray imaging with such lightweight mirrors will require excellent mirror surfaces, precise and stable alignment, and exceptional stiffness or deformation compensation. Attaining and maintaining alignment and figure control will likely involve active (in-space adjustable) x-ray optics. In contrast with infrared and visible astronomy, active optics for x-ray astronomy is in its infancy. In the middle of the past decade, two efforts began to advance technologies for adaptive x-ray telescopes: The Smart X-ray Optics (SXO) Basic Technology project in the United Kingdom (UK) and the Generation-X (Gen-X) concept studies in the United States (US). This paper discusses relevant technological issues and summarizes progress toward active x-ray telescopes.

We are developing adjustable X-ray optics to use on a mission such as SMART-X (see posters 38.02, 38.03 and Presentation 30.03). To satisfy the science problems expected to be posed by the next decadal survey, we anticipate requiring effective area greater than 1 square meter and Chandra-like angular resolution: approximately equal to 0.5 inches. To achieve such precise resolution we are developing adjustable mirror technology for X-ray astronomy application. This uses a thin film of piezoelectric material deposited on the back surface of the mirror to correct for figure distortions, including manufacturing errors and deflections due to gravity and thermal effects. We present here a plan to raise this technology from its current Level 2, to Level 6, by 2018.