Starshade rendezvous: exoplanet sensitivity and observing strategy

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Starshade in formation flight with a space telescope is a rapidly maturing technology that would enable imaging and spectral characterization of small planets orbiting nearby stars in the not-too-distant future. While performance models of starshade-assisted exoplanet imaging have been developed and used to design future missions, their results have not been verified from the analyses of synthetic images. Following a rich history of using community data challenges to evaluate image-processing capabilities in astronomy and exoplanet fields, the Starshade Technology Development to TRL5 (S5), a focused technology development activity managed by the NASA Exoplanet Exploration Program, is organizing and implementing a starshade exoplanet data challenge. The purpose of the data challenge is to validate the flow down of requirements from science to key instrument performance parameters and to quantify the required accuracy of noisy background calibration with synthetic images. This data challenge distinguishes itself from past efforts in the exoplanet field in that (1) it focuses on the detection and spectral characterization of small planets in the habitable zones of nearby stars, and (2) it develops synthetic images that simultaneously include multiple background noise terms-some observations specific to starshade-including residual starlight, solar glint, exozodiacal light, detector noise, as well as variability resulting from starshade's motion and telescope jitter. We provide an overview of the design and rationale of the data challenge. Working with data challenge participants, we expect to achieve improved understanding of the noise budget and background calibration in starshade-assisted exoplanet observations in the context of both starshade rendezvous with Roman and Habitable Exoplanet Observatory. This activity will thus help NASA prioritize further technology developments and prepare the science community for analyzing starshade exoplanet observations. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Section: Astrophysical and Observational Scenariosmentioning

confidence: 99%

Starshade exoplanet data challenge

Damiano

et al. 2021

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“…This is fully consistent with the search completeness estimate in which the overall habitable-zone characterization completeness is >25% for the nearest stars and ∼10% or less for the slightly farther stars. 66 In other words, a more favorable target for spectral characterization shown in this paper generally has more favorable search completeness. Interestingly, the nearest stars (procyon A, τ ceti, indi A, and sirius A, exhaustively) are truly the outstanding targets for both Starshade Rendezvous with Roman and HabEx for the highsearch completeness, relatively loose requirement of background calibration, and short integration time to characterize Earth-sized planets in their HZs.…”

Section: Implications On Mission Designsmentioning

confidence: 85%

“…We used the reference wavelength of 700 nm for the analyses presented in this work, and it provides a representation of the "green" band of Starshade Rendezvous with Roman (615 to 800 nm 66 ) and the UV-visible band of HabEx (0.3 to 1.0 μm 7 ). Roman may also have imaging and spectroscopy capabilities in the "blue" band (425 to 552 nm 6 ).…”

Section: Implications On Mission Designsmentioning

confidence: 99%

Overview and reassessment of noise budget of starshade exoplanet imaging

Lisman

Shaklan

et al. 2021

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High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA's Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. We reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light sources-including the leakage through micrometeoroid damage and the reflection of bright celestial bodies-indicate that sunlight scattered by the optical edge (i.e., the solar glint) is by far the dominant stray light. With telescope and observation parameters that approximately correspond to Starshade Rendezvous with Roman and Habitable Exoplanet Observatory (HabEx), we find that the dominating noise source is exozodiacal light for characterizing a temperate and Earth-sized planet around Sun-like and earlier stars and the solar glint for later-type stars. Further, reducing the brightness of solar glint by a factor of 10 with a coating would prevent it from becoming the dominant noise for both Roman and HabEx. With an instrument contrast of 10 −10 , the residual starlight is not a dominant noise, and increasing the contrast level by a factor 10 does not lead to any appreciable change in the expected science performance. If unbiased calibration of the background to the photon-noise limit can be achieved, Starshade Rendezvous with Roman could provide nearly photon-limited spectroscopy of temperate and Earth-sized planets of F, G, and K stars <4 parsecs away, and HabEx could extend this capability to many more stars <8 parsecs. Larger rocky planets around stars <8 parsecs would be within the reach of Roman. To achieve these capabilities, the exozodiacal light may need to be calibrated to a precision better than 2% and the solar glint to better than 5%. Our analysis shows that the expected temporal variability of the solar glint is unlikely to hinder the calibration, and the main challenge for background calibration likely comes from the unsmooth spatial distribution of exozodiacal dust in some stars. Taken together, these results validate the optical noise budget and technology milestones adopted by S5 against key science objectives and inform the priorities of future technology developments and science and industry community partnerships. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

“…In a space mission, out-of-band reflectivity is limited by dichroic filters in the cameras; we are only concerned about in-band performance. 4 The goal of this shotgun approach was to find a coating that best compensated for the combined diffraction and reflection from the terminal edge.…”

Section: Design Approachmentioning

confidence: 99%

“…1 The starshade's petals are designed to suppress the diffraction of starlight at the 10 −10 level, enabling the telescope to image exoplanets as close as tens of milliarcseconds from their parent stars. Several mission design concepts have been proposed, including the 26-m diameter Roman Space Telescope Starshade Rendezvous Mission (SRM) [2][3][4] and the 52-m diameter Habitable Exoplanet (HabEx) Observatory Starshade. 5,6 During observations, glint from the Sun appears along the starshade's specularly reflecting edges and is mainly concentrated in two bright lobes interior to the petal tips (Fig.…”

Section: Introductionmentioning

confidence: 99%

Antireflection coatings on starshade optical edges for solar glint suppression

McKeithen

Shaklan

Sheikh³

et al. 2021

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Starshades are designed to enable the direct observation of an exoplanet by blocking the light of the planet's star from reaching the telescope. As discussed in our companion paper [S. Shaklan et al., "Solar glint from uncoated starshade optical edges," J. Astron. Telesc. Instrum. Syst. 7(2), 021204 (2021)], diffraction and reflection of sunlight incident on the starshade's razor-sharp uncoated edges will appear as glint that may be brighter than the feeble light of the exoplanet. We report on the measurement and modeling of thin, conformal, multilayer antireflection coatings that reduce solar glint by more than an order of magnitude when applied to uncoated edges. We used the Lumerical finite-difference time-domain simulation software suite to determine the performance of coatings designed to work on a flat surface when applied to a sharp, curved edge. Laboratory measurements of coated edges, including a 50-cm long segment, confirm the glint reduction predicted by these models. We consider two coating approaches and compare their performance: a line-of-sight coating and a coating that uniformly covers the entire terminal edge. Starting with a wide range of coating designs emphasizing different angles of incidence and bandpass characteristics, we use Lumerical to account for edge diffraction and reflection, and we optimize the designs for the Starshade Rendezvous Mission and the HabEx mission concept.