arXiv subjects

Ewan S. Douglas

Publications and source records attributed to Ewan S. Douglas.

71 records · Page 4Linked to original sources

arXiv2021

Updated simulation tools for Roman coronagraph PSFs

The Nancy Grace Roman Space Telescope Coronagraph Instrument will be the first large scale coronagraphmission with active wavefront control to be operated in space and will demonstrate technologies essential tofuture missions to image Earth-like planets. Consisting of multiple coronagraph modes, the coronagraph isexpected to characterize and image exoplanets at 1E-8 or better contrast levels. An object-oriented physicaloptics modeling tool called POPPY provides flexible and efficient simulations of high-contrast point spreadfunctions (PSFs). As such, three coronagraph modes have been modeled in POPPY. In this paper, we presentthe recent testing results of the models and provide quantitative comparisons between results from POPPY andexisting tools such as PROPER/FALCO. These comparisons include the computation times required for PSFcalculations. In addition, we discuss the future implementation of the POPPY models for the POPPY front-endpackage WebbPSF, a widely used simulation tool for JWST PSFs.

astro-ph.IM↗

arXiv2021

The Versatile CubeSat Telescope: Going to Large Apertures in Small Spacecraft

The design of a CubeSat telescope for academic research purposes must balance complicated optical and structural designs with cost to maximize performance in extreme environments. Increasing the CubeSat size (eg. 6U to 12U) will increase the potential optical performance, but the cost will increase in kind. Recent developments in diamond-turning have increased the accessibility of aspheric aluminum mirrors, enabling a cost-effective regime of well-corrected nanosatellite telescopes. We present an all-aluminum versatile CubeSat telescope (VCT) platform that optimizes performance, cost, and schedule at a relatively large 95 mm aperture and 0.4 degree diffraction limited full field of view stablized by MEMS fine-steering modules. This study features a new design tool that permits easy characterization of performance degradation as a function of spacecraft thermal and structural disturbances. We will present details including the trade between on- and off-axis implementations of the VCT, thermal stability requirements and finite-element analysis, and launch survival considerations. The VCT is suitable for a range of CubeSat borne applications, which provides an affordable platform for astronomy, Earth-imaging, and optical communications.

astro-ph.IM↗

arXiv2021

An Open-Source Gaussian Beamlet Decomposition Tool for Modeling Astronomical Telescopes

In the pursuit of directly imaging exoplanets, the high-contrast imaging community has developed a multitude of tools to simulate the performance of coronagraphs on segmented-aperture telescopes. As the scale of the telescope increases and science cases move toward shorter wavelengths, the required physical optics propagation to optimize high-contrast imaging instruments becomes computationally prohibitive. Gaussian Beamlet Decomposition (GBD) is an alternative method of physical optics propagation that decomposes an arbitrary wavefront into paraxial rays. These rays can be propagated expeditiously using ABCD matrices, and converted into their corresponding Gaussian beamlets to accurately model physical optics phenomena without the need of diffraction integrals. The GBD technique has seen recent development and implementation in commercial software (e.g. FRED, CODE V, ASAP) but appears to lack an open-source platform. We present a new GBD tool developed in Python to model physical optics phenomena, with the goal of alleviating the computational burden for modeling complex apertures, many-element systems, and introducing the capacity to model misalignment errors. This study demonstrates the synergy of the geometrical and physical regimes of optics utilized by the GBD technique, and is motivated by the need for advancing open-source physical optics propagators for segmented-aperture telescope coronagraph design and analysis. This work illustrates GBD with Poisson's spot calculations and show significant runtime advantage of GBD over Fresnel propagators for many-element systems.

astro-ph.IM↗

arXiv2021

Faster imaging simulation through complex systems: a coronagraphic example

End-to-end simulation of the influence of the optical train on the observed scene is important across optics and is particularly important for predicting the science yield of astronomical telescopes. As a consequence of their goal of suppressing starlight, coronagraphic instruments for high-contrast imaging have particularly complex field-dependent point-spread-functions (PSFs). The Roman Coronagraph Instrument (CGI), Hybrid Lyot Coronagraph (HLC) is one example. The purpose of the HLC is to image exoplanets and exozodiacal dust in order to understand dynamics of solar systems. This paper details how images of exoplanets and exozodiacal dust are simulated using some of the most recent PSFs generated for the CGI HLC imaging mode. First, PSFs are generated using physical optics propagation techniques. Then, the angular offset of pixels in image scenes, such as exozodiacal dust models, are used to create a library of interpolated PSFs using interpolation and rotation techniques, such that the interpolated PSFs correspond to angular offsets of the pixels. This means interpolation needs only be done once and an image can then be simulated by multiplying the vector array of the model astrophysical scene by the matrix array of the interpolated PSF data. This substantially reduces the time required to generate image simulations by reducing the process to matrix multiplication, allowing for faster scene analysis. We will detail the steps required to generate coronagraphic scenes, quantify the speed-up of our matrix approach versus other implementations, and provide example code for users who wish to simulate their own scenes using publicly available HLC PSFs.

astro-ph.IM↗

arXiv2021

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) Technology Demonstration

The Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope will demonstrate the high-contrast technology necessary for visible-light exoplanet imaging and spectroscopy from space via direct imaging of Jupiter-size planets and debris disks. This in-space experience is a critical step toward future, larger missions targeted at direct imaging of Earth-like planets in the habitable zones of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical hardware, algorithms, and operations being demonstrated. We also describe several exoplanet and circumstellar disk science cases enabled by these capabilities. A competitively selected Community Participation Program team will be an integral part of the technology demonstration and could perform additional CGI observations beyond the initial tech demo if the instrument performance warrants it.

astro-ph.IM↗

arXiv2020

A review of simulation and performance modeling for the Roman coronagraph instrument

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will be capable of characterizing exoplanets in reflected light and will demonstrate space technologies essential for future missions to take spectra of Earthlike exoplanets. As the mission and instrument move into the final stages of design, simulation tools spanning from depth of search calculators to detailed diffraction models have been created by a variety of teams. We summarize these efforts, with a particular focus on publicly available datasets and software tools. These include speckle and point-spread-function models, signal-to-noise calculators, and science product simulations (e.g. predicted observations of debris disks and exoplanet spectra). This review is intended to serve as a reference to facilitate engagement with the technical and science capabilities of the CGI instrument.

astro-ph.EP↗

arXiv2020

Modeling light-controlled actuation of flexible magnetic composite structures using the finite element method (FEM)

Photoactive materials hold great promise for a variety of applications. We present a finite element model of light-controlled flexible magnetic composite structure composed of 33.3% Chromium dioxide (CrO2) and 66.7% Polydimethylsiloxane (PDMS) by weight. The structure has a dimension of 8 mm x 2 mm x 100 um and has been previously experimentally studied. Due to the low Curie temperature, the structure acts as an actuator, shows significant deflection under the external magnetic field and relaxation due to laser heating. Thermal and magnetic deflection analysis has been performed using the FEM model. The simulation results show a maximum structural deflection of 6.08 mm (76% of the length of the structure) when subjected to 30 mT magnetic flux density and 160 mW laser power at 303 K (room temperature). We will present the results of the simulation model and comparison to experimental data reproducing the previously observed motion of the (CrO2+PDMS). This model will enable future fracture and fatigue analysis as well as extension to new photoactive geometries.

physics.app-ph↗

arXiv2020

Implementing multi-wavelength fringe tracking for the Large Binocular Telescope Interferometer's phase sensor, PHASECam

PHASECam is the fringe tracker for the Large Binocular Telescope Interferometer (LBTI). It is a near-infrared camera which is used to measure both tip/tilt and fringe phase variations between the two adaptive optics (AO) corrected apertures of the Large Binocular Telescope (LBT). Tip/tilt and phase sensing are currently performed in the $H$ (1.65 $μ$m) and $K$ (2.2 $μ$m) bands at 1 kHz, but only the $K$-band phase telemetry is used to send corrections to the system in order to maintain fringe coherence and visibility. However, due to the cyclic nature of the fringe phase, only the phase, modulo 360 deg, can be measured. PHASECam's phase unwrapping algorithm, which attempts to mitigate this issue, occasionally fails in the case of fast, large phase variations or low signal-to-noise ratio. This can cause a fringe jump, in which case the OPD correction will be incorrect by a wavelength. This can currently be manually corrected by the operator. However, as the LBTI commissions further modes which require robust, active phase control and for which fringe jumps are harder to detect, including multi-axial (Fizeau) interferometry and dual-aperture non-redundant aperture masking interferometry, a more reliable and automated solution is desired. We present a multi-wavelength method of fringe jump capture and correction which involves direct comparison between the $K$-band and $H$-band phase telemetry. We demonstrate the method utilizing archival PHASECam telemetry, showing it provides a robust, reliable way of detecting fringe jumps which can potentially recover a significant fraction of the data lost to them.

astro-ph.IM↗

arXiv2019

CubeSats for Astronomy and Astrophysics

CubeSats have the potential to expand astrophysical discovery space, complementing ground-based electromagnetic and gravitational-wave observatories. The CubeSat design specifications help streamline delivery of instrument payloads to space. CubeSat planners have more options for tailoring orbits to fit observational needs and may have more flexibility in rapidly rescheduling observations to respond to transients. With over 1000 CubeSats launched, there has been a corresponding increase in the availability and performance of commercial-off-the-shelf (COTS) components compatible with the CubeSat standards, from solar panels and power systems to reaction wheels for three axis stabilization and precision attitude control. Commercially available components can reduce cost CubeSat missions, allowing more resources to be directed toward scientific instrument payload development and technology demonstrations.

astro-ph.IM↗

arXiv2019

Cold Debris Disks as Strategic Targets for the 2020s

Cold debris disks (T$<$200 K) are analogues to the dust in the Solar System's Kuiper belt--dust generated from the evaporation and collision of minor bodies perturbed by planets, our Sun, and the local interstellar medium. Scattered light from debris disks acts as both a signpost for unseen planets as well as a source of contamination for directly imaging terrestrial planets, but many details of these disks are poorly understood. We lay out a critical observational path for the study of nearby debris disks that focuses on defining an empirical relationship between scattered light and thermal emission from a disk, probing the dynamics and properties of debris disks, and directly determining the influence of planets on disks. We endorse the findings and recommendations published in the National Academy reports on Exoplanet Science Strategy and Astrobiology Strategy for the Search for Life in the Universe. This white paper extends and complements the material presented therein with a focus on debris disks around nearby stars. Separate complementary papers are being submitted regarding the inner warm regions of debris disks (Mennesson et al.), the modeling of debris disk evolution (Gaspar et al.), studies of dust properties (Chen et al.), and thermal emission from disks (Su et al.).

astro-ph.IM↗

arXiv2018

Laser Guide Star for Large Segmented-Aperture Space Telescopes, Part I: Implications for Terrestrial Exoplanet Detection and Observatory Stability

Precision wavefront control on future segmented-aperture space telescopes presents significant challenges, particularly in the context of high-contrast exoplanet direct imaging. We present a new wavefront control architecture that translates the ground-based artificial guide star concept to space with a laser source aboard a second spacecraft, formation flying within the telescope field-of-view. We describe the motivating problem of mirror segment motion and develop wavefront sensing requirements as a function of guide star magnitude and segment motion power spectrum. Several sample cases with different values for transmitter power, pointing jitter, and wavelength are presented to illustrate the advantages and challenges of having a non-stellar-magnitude noise limited wavefront sensor for space telescopes. These notional designs allow increased control authority, potentially relaxing spacecraft stability requirements by two orders of magnitude, and increasing terrestrial exoplanet discovery space by allowing high-contrast observations of stars of arbitrary brightness.

astro-ph.IM↗

arXiv2018

WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach

The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey Telescope (WFIRST) will demonstrate technologies and methods for high-contrast direct imaging and spectroscopy of exoplanet systems in reflected light, including polarimetry of circumstellar disks. The WFIRST management and CGI engineering and science investigation teams have developed requirements for the instrument, motivated by the objectives and technology development needs of potential future flagship exoplanet characterization missions such as the NASA Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR). The requirements have been refined to support recommendations from the WFIRST Independent External Technical/Management/Cost Review (WIETR) that the WFIRST CGI be classified as a technology demonstration instrument instead of a science instrument. This paper provides a description of how the CGI requirements flow from the top of the overall WFIRST mission structure through the Level 2 requirements, where the focus here is on capturing the detailed context and rationales for the CGI Level 2 requirements. The WFIRST requirements flow starts with the top Program Level Requirements Appendix (PLRA), which contains both high-level mission objectives as well as the CGI-specific baseline technical and data requirements (BTR and BDR, respectively)... We also present the process and collaborative tools used in the L2 requirements development and management, including the collection and organization of science inputs, an open-source approach to managing the requirements database, and automating documentation. The tools created for the CGI L2 requirements have the potential to improve the design and planning of other projects, streamlining requirement management and maintenance. [Abstract Abbreviated]

astro-ph.IM↗

arXiv2018

The Deformable Mirror Demonstration Mission (DeMi) CubeSat: optomechanical design validation and laboratory calibration

Coronagraphs on future space telescopes will require precise wavefront correction to detect Earth-like exoplanets near their host stars. High-actuator count microelectromechanical system (MEMS) deformable mirrors provide wavefront control with low size, weight, and power. The Deformable Mirror Demonstration Mission (DeMi) payload will demonstrate a 140 actuator MEMS deformable mirror (DM) with \SI{5.5}{\micro\meter} maximum stroke. We present the flight optomechanical design, lab tests of the flight wavefront sensor and wavefront reconstructor, and simulations of closed-loop control of wavefront aberrations. We also present the compact flight DM controller, capable of driving up to 192 actuator channels at 0-250V with 14-bit resolution. Two embedded Raspberry Pi 3 compute modules are used for task management and wavefront reconstruction. The spacecraft is a 6U CubeSat (30 cm x 20 cm x 10 cm) and launch is planned for 2019.

astro-ph.IM↗

arXiv2018

Accelerated Modeling of Near and Far-Field Diffraction for Coronagraphic Optical Systems

Accurately predicting the performance of coronagraphs and tolerancing optical surfaces for high-contrast imaging requires a detailed accounting of diffraction effects. Unlike simple Fraunhofer diffraction modeling, near and far-field diffraction effects, such as the Talbot effect, are captured by plane-to-plane propagation using Fresnel and angular spectrum propagation. This approach requires a sequence of computationally intensive Fourier transforms and quadratic phase functions, which limit the design and aberration sensitivity parameter space which can be explored at high-fidelity in the course of coronagraph design. This study presents the results of optimizing the multi-surface propagation module of the open source Physical Optics Propagation in PYthon (POPPY) package. This optimization was performed by implementing and benchmarking Fourier transforms and array operations on graphics processing units, as well as optimizing multithreaded numerical calculations using the NumExpr python library where appropriate, to speed the end-to-end simulation of observatory and coronagraph optical systems. Using realistic systems, this study demonstrates a greater than five-fold decrease in wall-clock runtime over POPPY's previous implementation and describes opportunities for further improvements in diffraction modeling performance.

astro-ph.IM↗

arXiv2018

Wavefront Sensing in Space: Flight Demonstration II of the PICTURE Sounding Rocket Payload

A NASA sounding rocket for high-contrast imaging with a visible nulling coronagraph, the PICTURE payload, has made two suborbital attempts to observe the warm dust disk inferred around Epsilon Eridani. The first flight in 2011 demonstrated a 5 milliarcsecond fine pointing system in space. The reduced flight data from the second launch, on 25 November 2015, presented herein, demonstrate active sensing of wavefront phase in space. Despite several anomalies in flight, post-facto reduction phase stepping interferometer data provides insight into the wavefront sensing precision and the system stability for a portion of the pupil. These measurements show the actuation of a 32$\times$32-actuator microelectromechanical system deformable mirror. The wavefront sensor reached a median precision of 1.4 nanometers per pixel, with 95% of samples between 0.8 and 12.0 nanometers per pixel. The median system stability, including telescope and coronagraph wavefront errors other than tip, tilt, and piston, was 3.6 nanometers per pixel, with 95% of samples between 1.2 and 23.7 nanometers per pixel.

astro-ph.IM↗

arXiv2017

Wavefront Sensing in Space from the PICTURE-B Sounding Rocket

A NASA sounding rocket for high contrast imaging with a visible nulling coronagraph, the Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B) payload has made two suborbital attempts to observe the warm dust disk inferred around Epsilon Eridani. We present results from the November 2015 launch demonstrating active wavefront sensing in space with a piezoelectric mirror stage and a micromachine deformable mirror along with precision pointing and lightweight optics in space.

astro-ph.IM↗

arXiv2016

Evaluation of Ionospheric Densities Using Coincident OII 83.4 nm Airglow and the Millstone Hill Radar

We test the utility of the OII 83.4 nm emission feature as a measure of ionospheric parameters. Observed with the Remote Atmospheric and Ionospheric Detection System (RAIDS) Extreme Ultraviolet Spectrograph on the International Space Station (ISS), limb profiles of 83.4 nm emissions are compared to predicted dayglow emission profiles from a theoretical model incorporating ground-based electron density profiles measured by the Millstone Hill radar and parameterized by a best-fit Chapman-α function. Observations and models are compared for periods of conjunction between Millstone Hill and the RAIDS fields-of-view. These RAIDS observations show distinct differences in topside morphology between two days, 15 January and 10 March 2010, closely matching the forward model morphology and demonstrating that 83.4 nm emission is sensitive to changes in the ionospheric density profile from the 340 km altitude of the ISS during solar minimum. We find no significant difference between 83.4 nm emission profiles modeled assuming a constant scale height Chapman-α best-fit to the ISR measurements and those assuming varying scale height.

physics.space-ph↗