Following the results of Starshade Milestone 1 in which we demonstrated broadband contrast better than 10−10, we have performed model validation experiments to show that diffraction models accurately predict the contrast due to perturbations representing the building blocks of the instrument error budget. The perturbations include the displacement of petal edge segments, sinusoidal petal edge shape deformations, global petal position errors, and random petal radial placement errors. We also show that the model accurately predicts the combined effects of two errors. The experiments result in a measured Model Uncertainty Factor (MUF) that is then applied to the starshade instrument contrast error budget.

Starshades are a leading technology to enable the detection and spectroscopic characterization of Earth-like exoplanets. We report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80-m long enclosure testing 1/1000'th scale starshades at a flight-like Fresnel number. We demonstrate 10(-)(10) contrast at the starshade's geometric inner working angle (IWA) across 10% of the visible spectrum, with an average contrast at the IWA of 2 x 10(-)(10) and contrast floor of 2 x 10(-11). In addition to these high-contrast demonstrations, we validate diffraction models to better than 35% accuracy through tests of intentionally flawed starshades. Overall, this suite of experiments reveals a deviation from scalar diffraction theory due to light propagating through narrow gaps between the starshade petals. We provide a model that accurately captures this effect at contrast levels below 10(-)(10). The results of these experiments demonstrate that there are no optical impediments to building a starshade that provides sufficient contrast to detect Earth-like exoplanets. This work also sets an upper limit on the effect of unknowns in the diffraction model used to predict starshade performance and set tolerances on the starshade manufacture. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Critical starshade technologies are currently being advanced through the S5 Project and at the Princeton starshade testbed. We report on the status of Milestone 2 of the S5 Project, optical model validation. We present results from optical experiments of starshades with intentional perturbations built into their design. These perturbations are representative of the type of perturbations possible in a flight design and serve as points of validation for diffraction models and error budgets. We show experimental results for two perturbed shapes, a mask with all petals shifted radially outward by 5 mu m and a mask with shallow sine waves built into two petals. We compare these data to outputs of the optical model and demonstrate better than 25% agreement. We also present images taken in crossed polarized light and use those data to constrain physical parameters of the optical edge. Bringing in previously obtained results for other perturbed shapes, we show an agreement between experiment and model of better than 25% and argue that this satisfies the Milestone 2 criteria.

Starshades are a leading technology to detect and characterize Earth-like exoplanets. In this paper we report on optical experiments of sub-scale starshades that advance critical starlight suppression technologies in preparation for the next generation of space telescopes. These experiments were conducted at the Princeton starshade testbed, an 80 m long enclosure testing 1/1000th scale starshades at a flight-like Fresnel number. In this paper we summarize recent updates made to the starshade testbed and optical model. We present results from recent experiments testing two starshade masks with intentional perturbations built into their shape. One of the perturbed masks has three petals that are shifted radially outward by 7-11 microns and the other mask has two petals shifted radially outward plus two petal edge segments displaced from their nominal position. We show the model agrees with experiment to better than 25% accuracy. These results are placed into context with previous experiments on perturbed shapes and progress made towards satisfying a critical milestone in advancing starshade technology to TRL 5.

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Starshade starlight suppression technology is being advanced through sub-scale starshade demonstrations at the Princeton Starshade Testbed and we present here the successful completion of a technology milestone focused on the demonstration of high contrast at flight-required levels. We demonstrate 10 contrast at the inner working angle of a starshade with a flight-like Fresnel number at multiple wavelengths spanning a 10% bandpass. We show that while contrast at the inner working angle is limited by the presence of non-scalar diffraction as light propagates through narrow slits between the starshade petals, high contrast is still achieved over most of the image. Successful completion of this milestone verifies we can design a starshade capable of producing scientifically useful contrast levels.

Direct imaging of an Earth-like exoplanet requires starlight suppression with a contrast ratio on the order of 1×10-10 at small angular separations of 100 milliarcseconds or less in visible light. To aid the technology development to reach this capability and enable future exoplanet missions, we built a high contrast coronagraph testbed, titled the Decadal Survey Testbed (DST). As of early 2019, the testbed has repeatedly demonstrated a monochromatic contrast floor about 1×10-10, and broadband performance at 550 nm with 10% color band- width <4×10-10 . The testbed has also demonstrated open-loop contrast drift rates of around 10-10/hour, temperature drift stabilities of <10 milliKelvins/day, passive pointing stability of around 0.1 λ/D per day on the occulting mask, and rms pointing jitter around 0.005 λ/D. This paper focusses primarily on the testbed hardware description, and a companion paper by Seo et al. details the experimental results.

High contrast imaging and characterization of faint exoplanets require a coronagraph instrument to efficiently suppress the host star light to 10(-9) level contrast over a broad spectral bandwidth. The NASA WFIRST mission plan includes a coronagraph instrument to demonstrate the technology needed to image and characterize exoplanets. Lyot coronagraph masks designed to serve at the focal plane followed by a Lyot stop will be key elements in the WFIRST coronagraph and in future advanced missions such as LUVOIR (Bolcar (2019) and HabEx (Morgan 2019, Martin 2019)). Shaped pupil masks designed to work in reflective geometry are also employed in the WFIRST Coronagraph. High-contrast performance reaching much better than 10(-9) contrast requires very tight design, fabrication tolerances, and material properties to meet a wide range of specifications, including precise shapes, micron-scale island features, ultra-low reflectivity regions, uniformity, wavefront quality, etc. In this paper, we present all the critical analytical and measured properties of materials and designs in relation to the results from our coronagraph testbeds.

COMPOSITIONAL MAPPING TO UNDERSTAND EUROPA. Diana L Blaney1, , Charles Hibbitts2, Robert O Green1 Roger Nelson Clark3, James B Dalton4, Ashley Gerard Davies5, Yves Langevin6, Jonathan I Lunine7, Matthew Hedman8, Thomas B McCord9, Scott L Murchie10, Chris Paranicas11, Frank P Seelos IV12, Jason M Soderblom13 Serina Diniega1, Morgan Cable1, David Thompson1, Carl Bruce1, Andrew Santo2, R. Redick1, Daniel Hahn2, Holly Bender1, Byron Van Gorp1, Jose Rodriguez1, Peter Sullivan1, Timothy Neville1, Sarah Lundeen1, Matt Bowers2, K. Ryan2, John Hayes2, Brian Bryce2, Ramsey Hourani2, E. Zarate1, Lori B. Moore1, Kirsten Maynard1, Ian M McKinley1, Dean Johnson1, Patricia Aubuchon1, Janan Fedosi1, Rami Wehbe1, Robert Calvet1, Pantazis Mouroulis1, V. White1, D. Wilson1. (1)Jet Propulsion Laboratory, Pasadena, CA, United States, (2)JHU-APL, Laurel, MD, United States, (3)Planetary Science Institute Tucson, Tucson, AZ, United States, (4)Self Employed, United States, (5)JPL, Pasadena, CA, United States, (6)CNRS, Paris Cedex 16, France, (7)Cornell University, Department of Astronomy, Ithaca, NY, United States, (8)University of Idaho, Physics, Moscow, ID, United States, (9)Bear Fight Institute, Winthrop, WA, United States, (10)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (11)Applied Physics Lab, Laurel, MD, United States, (12)JHU APL, Laurel, MD, United States, (13)MIT, Cambridge, MA, United States.

BACKGROUND:Images of the patella are invaluable for demonstrating fractures, acute injuries, and degenerative pathology of the patellar region. However, quality images of the patella can be difficult to acquire because of the distal femur obscuration. This article presents a method of imaging the patella, using film-screen radiography, computed radiography, or digital radiography that virtually eliminates the problem associated with distal femur obscuration and describes 7 radiography cases that demonstrate the clinical utility of the method.DISCUSSION:The described method of imaging the patella is simple, reproducible, and uses 2 projections-the posterolateral axial oblique and the posteromedial axial oblique-which help eliminate distal femur obscuration.CONCLUSION:The presented method demonstrates the base, body, apical, lateral, and medial borders of the patella without significant distal femur obscuration. In addition, radiologists and orthopedic surgeons express positive impressions of the resulting images' diagnostic usefulness.

To maintain the required performance of WFIRST Coronagraph in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C uses a Zernike wavefront sensor (ZWFS) with the phase shifting disk combined with the starlight rejecting occulting mask. For wavefront error corrections, WFIRST LOWFS/C uses a fast steering mirror (FSM) for line-of-sight (LoS) correction, a focusing mirror for focus drift correction, and one of the two deformable mirrors (DM) for other low order wavefront error (WFE) correction. As a part of technology development and demonstration for WFIRST Coronagraph, a dedicated Occulting Mask Coronagraph (OMC) testbed has been built and commissioned. With its configuration similar to the WFIRST flight coronagraph instrument the OMC testbed consists of two coronagraph modes, Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC), a low order wavefront sensor (LOWFS), and an optical telescope assembly (OTA) simulator which can generate realistic LoS drift and jitter as well as low order wavefront error that would be induced by the WFIRST telescope’s vibration and thermal changes. In this paper, we will introduce the concept of WFIRST LOWFS/C, describe the OMC testbed, and present the testbed results of LOWFS sensor performance. We will also present our recent results from the dynamic coronagraph tests in which we have demonstrated of using LOWFS/C to maintain the coronagraph contrast with the presence of WFIRST-like line-of-sight and low order wavefront disturbances.

We demonstrate a flexible, electrostatic adhesive gripper designed to controllably grasp and manipulate soft goods in space. The 8-fingered gripper has 50 cm 2 of active electrodes operating at 3 kV. It generates electrostatic adhesion forces up to 3.5 N (0.70 kPa) on Ge-coated polyimide film and 1.2 N on MLI blanket, a film composite used for satellite thermal insulation. Extremely low-force gripper engagement (0.08 N) and release (0.04 N) of films is ideal for micro-gravity. Individual fingers generate shear adhesion forces up to 4.76 N (5.04 kPa) using electrostatic adhesive and 45.0 N (47.6 kPa) with a hybrid electrostatic / gecko adhesive. To simulate a satellite servicing task, the gripper was mounted on a 7-DoF robot arm and performed a supervised grasp, manipulate, and release sequence on a hanging, Al-coated PET film.

Optical devices with features exhibiting ultra low reflectivity on the order of 1e-7 specular reflectance and 0.1% hemispherical TIR in the visible spectrum enable unique applications in astronomical research and instruments such as coronagraphs and spectrometers. Nanofabrication technologies have been developed to produce such devices with various shapes and feature dimensions to meet these requirements. Infrared reflection is also suppressed significantly with chosen wafers and processes. Very low levels of specular and scattered light are achievable over a very broad spectral band. We present some of the approaches, challenges and achieved results in producing and characterizing such surfaces and devices currently employed in laboratory testbeds and instruments. The level of blackness achievable in relation to basic material properties such as conductivity and process variables are discussed in detail.

NASA WFIRST mission has planned to include a coronagraph instrument to find and characterize exoplanets. Masks are needed to suppress the host star light to better than 10-8 – 10-9 level contrast over a broad bandwidth to enable the coronagraph mission objectives. Such masks for high contrast coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultra-low reflectivity regions, uniformity, wave front quality, etc. We present the technologies employed at JPL to produce these pupil plane and image plane coronagraph masks, and lab-scale external occulter masks, highlighting accomplishments from the high contrast imaging testbed (HCIT) at JPL and from the high contrast imaging lab (HCIL) at Princeton University. Inherent systematic and random errors in fabrication and their impact on coronagraph performance are discussed with model predictions and measurements.

NASA WFIRST-AFTA mission study includes a coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host starlight to about 10-9 level contrast over a broad spectrum to enable the coronagraph mission objectives. Such masks for high-contrast internal coronagraphic imaging require various fabrication technologies to meet a wide range of specifications, including precise shapes, micron scale island features, ultralow reflectivity regions, uniformity, wave front quality, and achromaticity. We present the approaches employed at JPL to produce pupil plane and image plane coronagraph masks by combining electron beam, deep reactive ion etching, and black silicon technologies with illustrative examples of each, highlighting milestone accomplishments from the High Contrast Imaging Testbed at JPL and from the High Contrast Imaging Lab at Princeton University. (c) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Fabrication of 3-D microstructures is one of the most challenging aspects of silicon micromachining. In this paper, we present a novel microfabrication method using one single-step deep reactive ion etching process with gray-scale e-beam lithography mask that offers deeply etched (>350-mu m deep) dual-angle 3-D microneedles with control over the height and shape of the structures. Moreover, we found that the shape of the e-beam lithography patterns can determine the general configuration and features of the final etched microneedles, and that the etching process parameters have the most impact on the microneedles' shape, such as size and vertical base angle. Large arrays of 20 x 20 microneedles with height uniformity of better than 3% are fabricated. [2014-0209]

Silicon direct bonding offers flexibility in the design and development of Si optics by allowing manufacturers to combine subcomponents with a potentially lossless and mechanically stable interface. The bonding process presents challenges in meeting the requirements for optical performance because air gaps at the Si interface cause large Fresnel reflections. Even small (35 nm) gaps reduce transmission through a direct bonded Si compound optic by 4% at λ=1.25  μm at normal incidence. We describe a bond inspection method that makes use of precision slit spectroscopy to detect and measure gaps as small as 14 nm. Our method compares low-finesse Fabry-Perot models to high-precision measurements of transmission as a function of wavelength. We demonstrate the validity of the approach by measuring bond gaps of known depths produced by microlithography.

In December 2013, NASA announced the selection of the Occulting Mask Coronagraph (OMC) as the primary architecture for the WFIRST/AFTA coronagraph instrument. OMC is a point design that is convertible between Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC) modes of operation. NASA set the objective of maturing the WFIRST/AFTA coronagraph to Technology Readiness Level (TRL) 5 by 9/30/2016. To this end, a technology development plan was drafted and approved that defined 9 milestones in fiscal years 2014-2016 that marked significant accomplishments on the path toward reaching TRL-5. The first key milestone was worded as: