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Evan Bray

Publications and source records attributed to Evan Bray.

12 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Parabolic Deformable Mirror Project Development and Device Characterization

Existing state-of-the-art wavefront sensing and control setups for the imaging of exoplanets utilize two high-actuator count flat deformable mirrors (DMs) to control both phase and amplitude aberrations. One of the objectives of the Exoplanet Spectroscopy (ExoSpec) project at Goddard Space Flight Center (GSFC) is to improve upon this regime through the development of parabolic deformable mirrors (PDMs), which can address several of the key limitations in existing setups. Specifically, the need for flat DMs to be located in conjugate pupil planes drives unique packaging challenges that can be overcome by allowing the off-axis imaging elements to be controllable as well. In addition, simulations show that the use of deformable powered elements will increase the overall controllable bandwidth, up to 35% over 5-12 lambda/D. To pursue this effort, the ExoSpec group has begun testing a first-generation parabolic DM, which is already informing a second generation design. This paper will provide a comprehensive update on its characterization, including influence function measurements, linearity analysis, closed-loop wavefront control performance, and thermal stability assessment.

spectroscopy↗
NASA NTRSDate not supplied

Prism Assembly for Roman Space Telescope Wide Field Instrument Slit-less Spectroscopy

The Roman Space Telescope (RST) is a three mirror anastigmat design with a 2.4 m primary mirror. RST will be based in L2 orbit, from where it will provide science information on exoplanets and dark energy using the Coronagraph Instrument (CGI) and Wide Field Instrument (WFI). The WFI features a 300 megapixel near-infrared detector array which provides a field of view 100 times larger than that of Hubble Space Telescope. The Prism Assembly is a small add-on instrument to the Roman Space Telescope’s Wide Field Instrument (WFI), installed in a slot in WFI’s element wheel. The Prism assembly has a passband from 0.75 µm to 1.8 µm, enabling a survey of redshifts in the range 0.2 to 1.7 µm. It provides low resolution slit-less spectroscopy with a spectral resolution R > 70 for all wavelengths, and R < 170 for λ > 0.8 µm across the full field. The Prism Assembly has the potential to provide more supernova spectra than ground-based spectroscopy during the mission lifetime. Being a late add-on to the RST mission, the Prism Assembly has had restrictions on size, weight and geometry, and a challenging schedule, which has dictated much of the implementation. Despite these challenges, the Prism Assembly is a pocket-sized high-performance spectrographic element, implemented as a refractive, all-spherical optical design using only two elements, one S-TIH-1 glass and one CaF2. This presentation will give an overview of the Prism Assembly, from design and implementation, through alignment, test and calibration. (100 words): The Roman Space Telescope is a three mirror anastigmat design with a 2.4 m primary mirror, which will provide science information on dark energy and exoplanets. The Prism Assembly is a small add-on instrument to the telescope’s Wide Field Instrument, enabling low resolution slit-less spectroscopy with a spectral resolution 70 < R < 170 across the full field from λ= 0.75 µm to 1.8 µm. The Prism Assembly is a refractive, all-spherical optical design using a glass and a CaF2 element. This presentation will give an overview of the Prism Assembly, from design and implementation, through alignment, test and calibration.

Space Instrumentation↗
NASA NTRSDate not supplied

RST CGI: Final Verification and Calibration of Prism and Polarizer Flight Units

As part of its technology demonstration, the Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will demonstrate point source spectroscopy and polarization measurements of disks. The spectroscopy mode is a zero-deviation Amici prism and slit which is deployed to the planet position after an imaging detection. The Wollaston prism polarization optics allow for imaging two orthogonal polarization states simultaneously. The CGI spectral characterization modes, designed and built at Goddard Space Flight Center (GSFC), have a spectral resolution of R50 in two 15% bandpass centered at 660nm and 730nm. There are duplicate Wollaston prism channels, clocked 45 degrees with respect to one another to completely characterize the instrument polarization effects and recover the Stokes parameters of the targeted disk. The Wollaston design and optical elements are a contribution by the Japanese Aerospace Exploration Agency, with final alignment and testing being done at GSFC. The spectroscopy mode is optimized to target Methane absorption features around 730nm, keeping the spectral resolution as low as possible to improve the signal-to-noise ratio and hence reduce detection time. We highlight the requirements for these modes, the ground-to-orbit calibration process, and the operations required to use a deployable slit on a CGI point source in the presence of pointing error. We also provide further detail on the optomechanical design, testing results from the final as-built flight units, verification process, and performance of the as-built flight assemblies.

high contrast imaging↗
NASA NTRSDate not supplied

Verification and Calibration of Spectroscopy and Polarization modes for the Roman Coronagraph Instrument

As part of its technology demonstration, the Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will demonstrate point source spectroscopy and polarization measurements of disks. The spectroscopy mode is a zero-deviation Amici prism and slit to a confirmed planet after an imaging detection. The Wollaston prism polarization optics allow for imaging two orthogonal polarization states simultaneously. The CGI spectral characterization modes, designed and built at Goddard Space Flight Center (GSFC), have a spectral resolution of R50 in two 15% bandpass centered at 660nm and 730nm intended to capture key methane absorption features. There are duplicate Wollaston prism channels, clocked 45 degrees with respect to one another covering 10% bandpasses at 575 and 825nm, but the optics meet performance requirements across the full CGI bandpass. The Wollaston design and optical elements are a contribution by the Japanese Aerospace Exploration Agency, with final alignment and testing being done at GSFC. We highlight the requirements for these modes, the ground-to-orbit calibration process, and the operations required to use a deployable slit on a CGI point source in the presence of pointing error. We also provide further detail on the optomechanical design, testing results from the final as-built flight units, verification process, and performance of the as-built flight assemblies.

Tyler D. Groff↗
NASA NTRSDate not supplied

Spectral characterization of the Roman Space Telescope Grism and Prism assemblies

The Roman Space Telescope (RST) Wide Field Instrument (WFI) recently completed its thermal vacuum (TVAC) campaign in Boulder, CO. This campaign, which concludes multiple years of preparation, represented the last opportunity for characterization and verification of the Grism and Prism spectral properties before launch; currently scheduled for late-2026. To this end, a highly-automated series of measurements were performed to acquire images of calibration spectra at many field points. Features that were measured during these efforts include dispersion scale, blue/red bandpass edges, diffraction order radiometry, and ghost images. A summary of the techniques and results for several of these efforts is provided here.

Astronomy↗