156 research outputs found
Advancing spaceborne tools for the characterization of planetary ionospheres and circumstellar environments
This work explores remote sensing of planetary atmospheres and their circumstellar surroundings. The terrestrial ionosphere is a highly variable space plasma embedded in the thermosphere. Generated by solar radiation and predominantly composed of oxygen ions at high altitudes, the ionosphere is dynamically and chemically coupled to the neutral atmosphere. Variations in ionospheric plasma density impact radio astronomy and communications. Inverting observations of 83.4 nm photons resonantly scattered by singly ionized oxygen holds promise for remotely sensing the ionospheric plasma density. This hypothesis was tested by comparing 83.4 nm limb profiles recorded by the Remote Atmospheric and Ionospheric Detection System aboard the International Space Station to a forward model driven by coincident plasma densities measured independently via ground-based incoherent scatter radar. A comparison study of two separate radar overflights with different limb profile morphologies found agreement between the forward model and measured limb profiles. A new implementation of Chapman parameter retrieval via Markov chain Monte Carlo techniques quantifies the precision of the plasma densities inferred from 83.4 nm emission profiles. This first study demonstrates the utility of 83.4 nm emission for ionospheric remote sensing.
Future visible and ultraviolet spectroscopy will characterize the composition of exoplanet atmospheres; therefore, the second study advances technologies for the direct imaging and spectroscopy of exoplanets. Such spectroscopy requires the development of new technologies to separate relatively dim exoplanet light from parent star light. High-contrast observations at short wavelengths require spaceborne telescopes to circumvent atmospheric aberrations. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) team designed a suborbital sounding rocket payload to demonstrate visible light high-contrast imaging with a visible nulling coronagraph. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space.
These two studies advance our ``close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system
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.Comment: 13 pages, 9 figures, submitted to SPIE Astronomical Telescopes &
Instrumentation 202
Compact Three Mirror Anastigmat Space Telescope Design using 6.5m Monolithic Primary Mirror
The utilization of a 6.5m monolithic primary mirror in a compact three-mirror
anastigmat (TMA) telescope design offers unprecedented capabilities to
accommodate various next generation science instruments. This design enables
the rapid and efficient development of a large aperture telescope without
segmented mirrors while maintaining a compact overall form factor. With its
exceptional photon collection area and diffraction-limited resolving power, the
TMA design is ideally suited for both the ground and space active/adaptive
optics concepts, which require the capture of natural guide stars within the
field of view for wavefront measurement to correct for misalignments and shape
deformation caused by thermal gradients. The wide field of view requirement is
based on a statistical analysis of bright natural guide stars available during
observation. The primary mirror clear aperture, compactness requirement, and
detector pixel sizes led to the choice of TMA over simpler two-mirror solutions
like Ritchey-Chretien (RC) telescopes, and the TMA design offers superior
diffraction-limited performance across the entire field of view. The standard
conic surfaces applied to all three mirrors (M1, M2, and M3) simplify the
optical fabrication, testing, and alignment process. Additionally, the TMA
design is more tolerant than RC telescopes. Stray light control is critical for
UV science instrumentation, and the field stop and Lyot stop are conveniently
located in the TMA design for this purpose.Comment: Presented at SPIE, Optics+Photonics 2023, Astronomical Optics:
Design, Manufacture, and Test of Space and Ground Systems IV in San Diego,
CA, US
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]Comment: 16 pages, 4 figure
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.Comment: Submitted to A
Hybrid propagation physics for the design and modeling of astronomical observatories: a coronagraphic example
For diffraction-limited optical systems an accurate physical optics model is
necessary to properly evaluate instrument performance. Astronomical
observatories outfitted with coronagraphs for direct exoplanet imaging require
physical optics models to simulate the effects of misalignment and diffraction.
Accurate knowledge of the observatory's PSF is integral for the design of
high-contrast imaging instruments and simulation of astrophysical observations.
The state of the art is to model the misalignment, ray aberration, and
diffraction across multiple software packages, which complicates the design
process. Gaussian Beamlet Decomposition (GBD) is a ray-based method of
diffraction calculation that has been widely implemented in commercial optical
design software. By performing the coherent calculation with data from the ray
model of the observatory, the ray aberration errors can be fed directly into
the physical optics model of the coronagraph, enabling a more integrated model
of the observatory. We develop a formal algorithm for the transfer-matrix
method of GBD, and evaluate it against analytical results and a traditional
physical optics model to assess the suitability of GBD for high-contrast
imaging simulations. Our GBD simulations of the observatory PSF, when compared
to the analytical Airy function, have a sum-normalized RMS difference of
~10^-6. These fields are then propagated through a Fraunhofer model of a
exoplanet imaging coronagraph where the mean residual numerical contrast is
4x10^-11, with a maximum near the inner working angle at 5x10^-9. These results
show considerable promise for the future development of GBD as a viable
propagation technique in high-contrast imaging. We developed this algorithm in
an open-source software package and outlined a path for its continued
development to increase the fidelity and flexibility of diffraction simulations
using GBD.Comment: 58 pages, 15 figures, preprint version for article in press. Accepted
to SPIE's Journal of Astronomical Telescopes, Instruments, and Systems on
October 23 202
Microfabricated pinholes for high contrast imaging testbeds
In order to reach contrast ratios of and beyond, coronagraph
testbeds need source optics that reliably emulate nearly-point-like starlight,
with microfabricated pinholes being a compelling solution. To verify, a
physical optics model of the Space Coronagraph Optical Bench (SCoOB) source
optics, including a finite-difference time-domain (FDTD) pinhole simulation,
was created. The results of the FDTD simulation show waveguide-like behavior of
pinholes. We designed and fabricated microfabricated pinholes for SCoOB made
from an aluminum overcoated silicon nitride film overhanging a silicon wafer
substrate, and report characterization of the completed pinholes.Comment: Submitted to SPIE Optical Engineering + Applications (OP23O
Approaches to developing tolerance and error budget for active three mirror anastigmat space telescopes
The size of the optics used in observatories is often limited by fabrication,
metrology, and handling technology, but having a large primary mirror provides
significant benefits for scientific research. The evolution of rocket launch
options enables heavy payload carrying on orbit and outstretching the
telescope's form-factor choices. Moreover, cost per launch is lower than the
traditional flight method, which is obviously advantageous for various novel
space observatory concepts. The University of Arizona has successfully
fabricated many large-scale primary optics for ground-based observatories
including the Large Binocular Telescope (LBT, 8.4 meter diameter two primary
mirrors), Large Synoptic Survey Telescope (now renamed to Vera C. Rubin
Observatory, 8.4 meter diameter monolithic primary and tertiary mirror), and
the Giant Magellan Telescope (GMT, 8.4 meter diameter primary mirror seven
segments). Launching a monolithic primary mirror into space could bypass many
of the difficulties encountered during the assembly and deployment of the
segmented primary mirrors. However, it might bring up unprecedented challenges
and hurdles, also. We explore and foresee the expected challenges and evaluate
them. To estimate the tolerance and optical error budget of a large optical
system in space such as three mirror anastigmat telescope, we have developed a
methodology that considers various errors from design, fabrication, assembly,
and environmental factors.Comment: 6 pages, presented August 2023 at SPIE Optics+Photonics, San Diego,
CA, US
Focus diverse phase retrieval testbed development of continuous wavefront sensing for space telescope applications
Continuous wavefront sensing on future space telescopes allows relaxation of
stability requirements while still allowing on-orbit diffraction-limited
optical performance. We consider the suitability of phase retrieval to
continuously reconstruct the phase of a wavefront from on-orbit irradiance
measurements or point spread function (PSF) images. As phase retrieval
algorithms do not require reference optics or complicated calibrations, it is a
preferable technique for space observatories, such as the Hubble Space
Telescope or the James Webb Space Telescope. To increase the robustness and
dynamic range of the phase retrieval algorithm, multiple PSF images with known
amount of defocus can be utilized. In this study, we describe a recently
constructed testbed including a 97 actuator deformable mirror, changeable
entrance pupil stops, and a light source. The aligned system wavefront error is
below ~30nm. We applied various methods to generate a known wavefront error,
such as defocus and/or other aberrations, and found the accuracy and precision
of the root mean squared error of the reconstructed wavefronts to be less than
~10nm and ~2nm, respectively. Further, we discuss the signal-to-noise ratios
required for continuous dynamic wavefront sensing. We also simulate the case of
spacecraft drifting and verify the performance of the phase retrieval algorithm
for continuous wavefront sensing in the presence of realistic disturbances
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