TPF-C Technology Plan - Exoplanet Exploration Program - NASA

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Chapter 3 3 Optics and Starlight Suppression Technology As a program matures, technology groupings grow to increasingly higher levels of integration. What began as individually identifiable component technologies naturally lead to subsystems and testbeds that are used to validate them. The development of TPF-C critical technologies can be understood in this framework. The bulk of the technology development effort has taken place at JPL. Unless otherwise noted, the component technologies and testbeds described below are JPL products. 3.1 Component Technologies 3.1.1 Apodizing Masks and Stops Objective The TPF coronagraph must suppress on-axis starlight, while passing light from off-axis planets that are many orders of magnitude dimmer. In order to meet the required contrast over the full bandwidth, the masks must be fabricated with extremely high optical density and controlled diffraction characteristics. This activity is aimed at developing the technology necessary to produce and test several types of high precision masks. Approach Several candidate technologies are being explored to demonstrate the feasibility of manufacturing various kinds of masks that would achieve the end goals for star light suppression. The two basic classes of masks are focal plane and pupil plane, as described previously in Section 1.6.3. Focal plane masks: Apodizing occulting masks to be placed at a focal plane require a very high dynamic range in optical density (OD from 0 to 8) and smooth variations within that range. Such masks are very difficult to both make and measure, and are not used in existing applications. There are two fundamental approaches to designing such masks: analog (i.e., gray scale) and binary (opaque and transparent). Several manufacturing techniques will be examined for each approach. JPL is leading the effort in developing the technology for occulting masks in association with industry resources for materials development, fabrication and characterization. 28
Optics and Starlight Suppression Technology Final performance of the masks will be evaluated in the HCIT at JPL. This activity will demonstrate that hardware can be manufactured to meet optical requirements of the coronagraph in space environment. Pupil plane masks: A second approach for coronagraphy is to employ masks at a pupil plane that apodize the pupil so as to suppress and diffract away unwanted star light, thereby providing the required contrast between star and planet lights at the image. Several theoretical designs have been proposed for such masks with varying through-put efficiencies and system complexities, primarily at universities under JPL subcontract. Experimental demonstrations are aimed at discriminating between technologies to allow selection of those with the best system performance. To support and complement experimental work, teams at JPL (Hoppe et al.), Princeton (Kasdin et al.), UC Berkeley (Neureuther et al.), Ball Aerospace (Lieber et al.), and GSFC (Lyon) focus on incorporation of experimental results into the optical system model and validation of those models. The goal is to develop an understanding of the limits of the scalar diffraction theory for this application and determine whether any design modifications are necessary to achieve the desired coronagraph performance. Progress to Date Focal plane gray scale masks: Significant progress has been made in the past year in fabricating and testing focal plane masks at JPL. The first approach uses HEBS glass manufactured by Canyon Materials, Inc., San Diego, CA, and further modified for JPL to meet TPF-C requirements. HEBS glass will darken to different levels of absorption of visible light when exposed to different electron beam levels. This makes it possible to create controlled optical density profiles in the glass with each mask design. Masks with linear 1-sinc 2 patterns have been written in such glass with a state-of-the-art electron beam exposure system at the Micro Devices Laboratory (MDL) at JPL. Tests with such masks during the past year in the HCIT have shown average contrast of 0.9 × 10 -9 in the dark field with 784 nm laser light 1 and more recently in the 5 × 10 -9 level with about 40 nm bandwidth around 785 nm. Figure 3-1 shows a mask and a picture showing the dark region in the image plane when such a mask is employed. Further experiments Figure 3-1. Mask (left) and image (right). The mask is included in the optical train of the HCIT where the corresponding image is recorded. 1 Trauger et al., “Coronagraph contrast demonstrations with the High Contrast Imaging Testbed,” Proc. SPIE V.5487, i.3, pp. 1330–36 (2004) 29
Page 1 and 2: JPL Publication 05-8 Technology Pla
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Chapter 4 giving confidence that fl
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Chapter 4 surface polish is nonethe
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Chapter 5 TPF-C is planning a suite
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Chapter 5 engineering judgment (i.e
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Chapter 5 categories, in reality ea
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Chapter 5 Table 5-3. Validation of
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Chapter 5 5.6.1 Modeling Methodolog
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Chapter 5 strength of computer simu
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Chapter 6 6 Instrument Technology a
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Chapter 6 Figure 6-1. Detailed conc
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Chapter 6 The first method is self-
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Chapter 6 super computers and is us
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Chapter 7 7 Plan for Technology Dev
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Chapter 7 Figure 7-1. TPF-C Technol
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Chapter 7 Improvements to the DM ov
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Chapter 7 7.3 Error Budgets 7.3.1 D
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Chapter 7 7.4 Optics and Starlight
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Chapter 7 7.4.2 Apodizing Masks and
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Chapter 7 7.4.4 Wavefront Sensing a
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Chapter 7 7.4.6 Transmissive Optics
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Chapter 7 7.4.8 Scatterometer Scope
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Chapter 7 7.5 Structural, Thermal,
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Chapter 7 7.5.3 Precision Structura
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Chapter 7 model of TPF-C and should
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Chapter 7 7.5.6 Secondary Mirror To
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Chapter 7 7.5.8 Sub-scale EM Sunshi
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Chapter 7 7.6 Integrated Modeling a
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Chapter 7 7.7.3 Advanced Concepts:
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Chapter 8 134
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Appendices Appendix B: TPF-C Detail
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Appendices Appendix D: TPF-C Techno
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Appendices Appendix F: Acronym List
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Appendices RWA SAO SBIR SIM SM SMFA
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TPF-C Technology Plan - Exoplanet Exploration Program - NASA

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