65 research outputs found
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
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
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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Global Existence and Energy Decay Rates for a Kirchhoff-Type Wave Equation with Nonlinear Dissipation
The first objective of this paper is to prove the existence and uniqueness of global solutions for
a Kirchhoff-type wave equation with
nonlinear dissipation of the form Kuⁿ + (|¹/²|²) + (')=0 under suitable
assumptions on , , (⋅), and (⋅). Next, we under some growth conditions on the nonlinear
dissipation . Lastly, numerical simulations in order to
verify the analytical results are given
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
Analysis of active optics correction for a large honeycomb mirror
In the development of space-based large telescope systems, having the
capability to perform active optics correction allows correcting wavefront
aberrations caused by thermal perturbations so as to achieve
diffraction-limited performance with relaxed stability requirements. We present
a method of active optics correction used for current ground-based telescopes
and simulate its effectiveness for a large honeycomb primary mirror in space.
We use a finite-element model of the telescope to predict misalignments of the
optics and primary mirror surface errors due to thermal gradients. These
predicted surface error data are plugged into a Zemax ray trace analysis to
produce wavefront error maps at the image plane. For our analysis, we assume
that tilt, focus and coma in the wavefront error are corrected by adjusting the
pointing of the telescope and moving the secondary mirror. Remaining mid- to
high-order errors are corrected through physically bending the primary mirror
with actuators. The influences of individual actuators are combined to form
bending modes that increase in stiffness from low-order to high-order
correction. The number of modes used is a variable that determines the accuracy
of correction and magnitude of forces. We explore the degree of correction that
can be made within limits on actuator force capacity and stress in the mirror.
While remaining within these physical limits, we are able to demonstrate sub-25
nm RMS surface error over 30 hours of simulated data. The results from this
simulation will be part of an end-to-end simulation of telescope optical
performance that includes dynamic perturbations, wavefront sensing, and active
control of alignment and mirror shape with realistic actuator performance.Comment: 8 pages, 6 figures, presented at SPIE Optics + Photonics 202
Polarimetric modeling and assessment of science cases for Giant Magellan Telescope-Polarimeter (GMT-Pol)
Polarization observations through the next-generation large telescopes will
be invaluable for exploring the magnetic fields and composition of jets in AGN,
multi-messenger transients follow-up, and understanding interstellar dust and
magnetic fields. The 25m Giant Magellan Telescope (GMT) is one of the
next-generation large telescopes and is expected to have its first light in
2029. The telescope consists of a primary mirror and an adaptive secondary
mirror comprising seven circular segments. The telescope supports instruments
at both Nasmyth as well as Gregorian focus. However, none of the first or
second-generation instruments on GMT has the polarimetric capability. This
paper presents a detailed polarimetric modeling of the GMT for both Gregorian
and folded ports for astronomical B-K filter bands and a field of view of 5 arc
minutes. At 500nm, The instrumental polarization is 0.1% and 3% for the
Gregorian and folded port, respectively. The linear to circular crosstalk is
0.1% and 30% for the Gregorian and folded ports, respectively. The Gregorian
focus gives the GMT a significant competitive advantage over TMT and ELT for
sensitive polarimetry, as these telescopes support instruments only on the
Nasmyth platform. We also discuss a list of polarimetric science cases and
assess science case requirements vs. the modeling results. Finally, we discuss
the possible routes for polarimetry with GMT and show the preliminary optical
design of the GMT polarimeter.Comment: 13 pages, 5 figures,SPIE Optics + Photonics 2023 conference
proceeding, Paper no 12690-2
Generalized large optics fabrication multiplexing
High precision astronomical optics are manufactured through deterministic computer controlled optical surfacing processes, such as subaperture small tool polishing, magnetorheological finishing, bonnet tool polishing, and ion beam figuring. Due to the small tool size and the corresponding tool influence function, large optics fabrication is a highly time-consuming process. The framework of multiplexed figuring runs for the simultaneous use of two or more tools is presented. This multiplexing process increases the manufacturing efficiency and reduces the overall cost using parallelized subaperture tools
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