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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

The Maturing of High Contrast Imaging and Starlight Suppression Techniques for Future NASA Exoplanet Characterization Missions

Over 3000 exoplanets and hundreds of exoplanetary systems have been detected to date and we are now rapidly moving toward an era where the focus is shifting from detection to direct imaging and spectroscopic characterization of these new worlds and their atmospheres. NASA is currently studying several exoplanet characterization mission concepts for the 2020 Decadal Survey ranging from probe class to flagships. Detailed and comprehensive exoplanet characterization, particularly of exo-Earths, leading to assessment of habitability, or indeed detection of life, will require significant advances beyond the current state-of-the-art in high contrast imaging and starlight suppression techniques which utilize specially shaped precision optical elements to block the light from the parent star while controlling scattering and diffraction thus revealing and enabling spectroscopic study of the orbiting exoplanets in reflected light. In this paper we describe the two primary high contrast starlight suppression techniques currently being pursued by NASA: 1) coronagraphs (including several design variations) and 2) free-flying starshades. These techniques are rapidly moving from the technology development phase to the design and engineering phase and we discuss the prospects and projected performance for future exoplanet characterization missions utilizing these techniques coupled with large aperture telescopes in space.

high contrast↗
NASA NTRS2011

Advancing Technology for Starlight Suppression via an External Occulter

External occulters provide the starlight suppression needed for detecting and characterizing exoplanets with a much simpler telescope and instrument than is required for the equivalent performing coronagraph. In this paper we describe progress on our Technology Development for Exoplanet Missions project to design, manufacture, and measure a prototype occulter petal. We focus on the key requirement of manufacturing a precision petal while controlling its shape within precise tolerances. The required tolerances are established by modeling the effect that various mechanical and thermal errors have on scatter in the telescope image plane and by suballocating the allowable contrast degradation between these error sources. We discuss the deployable starshade design, representative error budget, thermal analysis, and prototype manufacturing. We also present our meteorology system and methodology for verifying that the petal shape meets the contrast requirement. Finally, we summarize the progress to date building the prototype petal.

high-contrast imaging↗
NASA NTRS2018

Apodized Pupil Lyot Coronagraphs Designs for Future Segmented Space Telescopes

A coronagraphic starlight suppression system situated on a future flagship space observatory offers a promising avenue to image Earth-like exoplanets and search for biomarkers in their atmospheric spectra. One NASA mission concept that could serve as the platform to realize this scientific breakthrough is the Large UV/Optical/IR Surveyor (LUVOIR). Such a mission would also address a broad range of topics in astrophysics with a multi-wavelength suite of instruments. The apodized pupil Lyot coronagraph (APLC) is one of several coronagraph design families that the community is assessing as part of NASAs Exoplanet Exploration Program Segmented aperture coronagraph design and analysis (SCDA) team. The APLC is a Lyot-style coronagraph that suppresses starlight through a series of amplitude operations on the on-axis eld. Given a suite of seven plausible segmented telescope apertures, we have developed an object-oriented software toolkit to automate the exploration of thousands of APLC design parameter combinations. This has enabled us to empirically establish relationships between planet throughput and telescope aperture geometry, inner working angle, bandwidth, and contrast level.In parallel with the parameter space exploration, we have investigated several strategies to improve the robust-ness of APLC designs to fabrication and alignment errors. We also investigate the combination of APLC withwavefront control or complex focal plane masks to improve inner working angle and throughput. Preliminaryscientic yield evaluations based on design reference mission simulations indicate the APLC is a very competitiveconcept for surveying the local exoEarth population with a mission like LUVOIR.

coronagraphic starlight suppression system↗
NASA NTRS2006

A Nulling Coronagraph for TPF-C

The nulling coronagraph is one of 5 instrument concepts selected by NASA for study for potential use in the TPF-C mission. This concept for extreme starlight suppression has two major components, a nulling interferometer to suppress the starlight to ~10(sup -10) per airy spot within 2 (lamda)/D of the star, and a calibration interferometer to measure the residual scattered starlight. The ability to work at 2 (lamda)/D dramatically improves the science throughput of a space based coronagraph like TPF-C. The calibration interferometer is an equally important part of the starlight suppression system. It measures the measures the wavefront of the scattered starlight with very high SNR, to 0.05nm in less than 5 minutes on a 5mag star. In addition, the post coronagraph wavefront sensor will be used to measure the residual scattered light after the coronagraph and subtract it in post processing to 1~2x10(sup -11) to enable detection of an Earthlike planet with a SNR of 5~10.

Terrestrial Planet Finder Coronagraph (TPF-C)↗
NASA NTRS2012

Integrated Optics Achromatic Nuller for Stellar Interferometry

This innovation will replace a beam combiner, a phase shifter, and a mode conditioner, thus simplifying the system design and alignment, and saving weight and space in future missions. This nuller is a dielectric-waveguide-based, four-port asymmetric coupler. Its nulling performance is based on the mode-sorting property of adiabatic asymmetric couplers that are intrinsically achromatic. This nuller has been designed, and its performance modeled, in the 6.5-micrometer to 9.25-micrometer spectral interval (36% bandwidth). The calculated suppression of starlight for this 15-cm-long device is 10(exp -5) or better through the whole bandwidth. This is enough to satisfy requirements of a flagship exoplanet-characterization mission. Nulling interferometry is an approach to starlight suppression that will allow the detection and spectral characterization of Earth-like exoplanets. Nulling interferometers separate the light originating from a dim planet from the bright starlight by placing the star at the bottom of a deep, destructive interference fringe, where the starlight is effectively cancelled, or nulled, thus allowing the faint off-axis light to be much more easily seen. This process is referred to as nulling of the starlight. Achromatic nulling technology is a critical component that provides the starlight suppression in interferometer-based observatories. Previously considered space-based interferometers are aimed at approximately 6-to-20-micrometer spectral range. While containing the spectral features of many gases that are considered to be signatures of life, it also offers better planet-to-star brightness ratio than shorter wavelengths. In the Integrated Optics Achromatic Nuller (IOAN) device, the two beams from the interferometer's collecting telescopes pass through the same focusing optic and are incident on the input of the nuller.

Ksendzov, Alexander↗
NASA NTRS2014

The Advanced Technology Large-Aperture Space Telescope (ATLAST) Technology Roadmap

We present the key technologies and capabilities that will enable a future, large-aperture ultravioletopticalinfrared (UVOIR) space observatory. These include starlight suppression systems, vibration isolation and control systems, lightweight mirror segments, detector systems, and mirror coatings. These capabilities will provide major advances over current and near-future observatories for sensitivity, angular resolution, and starlight suppression. The goals adopted in our study for the starlight suppression system are 10-10 contrast with an inner working angle of 40 milliarcsec and broad bandpass. We estimate that a vibration and isolation control system that achieves a total system vibration isolation of 140 dB for a vibration-isolated mass of 5000 kg is required to achieve the high wavefront error stability needed for exoplanet coronagraphy. Technology challenges for lightweight mirror segments include diffraction-limited optical quality and high wavefront error stability as well as low cost, low mass, and rapid fabrication. Key challenges for the detector systems include visible-blind, high quantum efficiency UV arrays, photon counting visible and NIR arrays for coronagraphic spectroscopy and starlight wavefront sensing and control, and detectors with deep full wells with low persistence and radiation tolerance to enable transit imaging and spectroscopy at all wavelengths. Finally, mirror coatings with high reflectivity ( 90), high uniformity ( 1) and low polarization ( 1) that are scalable to large diameter mirror substrates will be essential for ensuring that both high throughput UV observations and high contrast observations can be performed by the same observatory.

Telescope↗
NASA NTRS2015

A Future Large-Aperture UVOIR Space Observatory: Key Technologies and Capabilities

We present the key technologies and capabilities that will enable a future, large-aperture ultravioletopticalinfrared (UVOIR) space observatory. These include starlight suppression systems, vibration isolation and control systems, lightweight mirror segments, detector systems, and mirror coatings. These capabilities will provide major advances over current and near-future observatories for sensitivity, angular resolution, and starlight suppression. The goals adopted in our study for the starlight suppression system are 10-10 contrast with an inner working angle of 20 milliarcsec and broad bandpass. We estimate that a vibration and isolation control system that achieves a total system vibration isolation of 140 dB for a vibration-isolated mass of 5000 kg is required to achieve the high wavefront error stability needed for exoplanet coronagraphy. Technology challenges for lightweight mirror segments include diffraction-limited optical quality and high wavefront error stability as well as low cost, low mass, and rapid fabrication. Key challenges for the detector systems include visible-blind, high quantum efficiency UV arrays, photon counting visible and NIR arrays for coronagraphic spectroscopy and starlight wavefront sensing and control, and detectors with deep full wells with low persistence and radiation tolerance to enable transit imaging and spectroscopy at all wavelengths. Finally, mirror coatings with high reflectivity ( 90), high uniformity ( 1) and low polarization ( 1) that are scalable to large diameter mirror substrates will be essential for ensuring that both high throughput UV observations and high contrast observations can be performed by the same observatory.

Instrument↗
NASA NTRS2009

Visible Nulling Coronagraph Testbed Results

The Extrasolar Planetary Imaging Coronagraph (EPIC) is a NASA Astrophysics Strategic Mission Concept study and a proposed NASA Discovery mission to image and characterize extrasolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC would provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, determine orbital inclinations and masses, characterize the atmospheres around A and F stars, observed the inner spatial structure and colors of inner Spitzer selected debris disks. EPIC would be launched to heliocentric Earth trailing drift-away orbit, with a 5-year mission lifetime. The starlight suppression approach consists of a visible nulling coronagraph (VNC) that enables starlight suppression in broadband light from 480-960 nm. To demonstrate the VNC approach and advance it's technology readiness we have developed a laboratory VNC and have demonstrated white light nulling. We will discuss our ongoing VNC work and show the latest results from the VNC testbed.

Lyon, Richard G.↗
NASA NTRS2005

The Visible Nulling Coronagraph--Architecture Definition and Technology Development

This paper describes the advantages of visible direct detection and spectroscopy of Earth-like extrasolar planets using a nulling coronagraph instrument behind a moderately sized single aperture space telescope. Our concept synthesizes a nulling interferometer by shearing the telescope pupil, with the resultant producing a deep null. We describe nulling configurations that also include methods to mitigate stellar leakage, such as spatial filtering by a coherent array of single mode fibers, and post-starlight suppression wavefront sensing and control. With diffraction limited telescope optics and similar quality components in the optical train (lambda/20), suppression of the starlight to 1e-10 is readily achievable. We describe key features of the architecture and analysis, present latest results of laboratory measurements demonstrating achievable null depth and component development, and discuss future key technical milestones.

nulling interferometer↗
NASA NTRS2008

Extrasolar Planetary Imaging Coronagraph: Visible Nulling Coronagraph Testbed Results

The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Discovery mission to image and characterize extrasolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will provide insights into the physical nature of a variety of planets in other solar systems complimenting radial velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets identified by radial velocity surveys, determine orbital inclinations and masses, characterize the atmospheres around A and F stars, observed the inner spatial structure and colors of inner Spitzer selected debris disks. EPIC would be launched to heliocentric Earth trailing drift-away orbit, with a 3-year mission lifetime ( 5 year goal) and will revisit planets at least three times at intervals of 9 months. The starlight suppression approach consists of a visible nulling coronagraph (VNC) that enables high order starlight suppression in broadband light. To demonstrate the VNC approach and advance it's technology readiness the NASA Goddard Space Flight Center and Lockheed-Martin have developed a laboratory VNC and have demonstrated white light nulling. We will discuss our ongoing VNC work and show the latest results from the VNC testbed,

Lyon, Richard G.↗
NASA NTRS1991

Hubble Extra Solar Planet Interferometer

This paper describes a proposed third-generation Hubble instrument for extra-solar planet detection, the Hubble Extra-Solar Planet Interferometer (HESPI). This instrument would be able to achieve starlight cancellation at the 10 exp 6 to 10 exp 8 level, given a stellar wavefront with phase errors comparable to the present Hubble telescope wavefront. At 10 exp 6 starlight cancellation, HESPI would be able to detect a Jupiter-like planet next to a star at a distance of about 10 parsec, for which there are about 400 candidate stars. This paper describes a novel approach for starlight suppression, using a combination of active control and single-mode spatial filters, to achieve starlight suppression far below the classical limit set by scattering due to microsurface imperfections. In preliminary lab experiments, suppression by a factor of 40 below the classical scatter limit due to optical wavefront errors has been demonstrated.

Shao, M.↗
NASA NTRS2015

Scaling Relation for Occulter Manufacturing Errors

An external occulter is a spacecraft own along the line-of-sight of a space telescope to suppress starlight and enable high-contrast direct imaging of exoplanets. The shape of an external occulter must be specially designed to optimally suppress starlight and deviations from the ideal shape due to manufacturing errors can result loss of suppression in the shadow. Due to the long separation distances and large dimensions involved for a space occulter, laboratory testing is conducted with scaled versions of occulters etched on silicon wafers. Using numerical simulations for a flight Fresnel occulter design, we show how the suppression performance of an occulter mask scales with the available propagation distance for expected random manufacturing defects along the edge of the occulter petal. We derive an analytical model for predicting performance due to such manufacturing defects across the petal edges of an occulter mask and compare this with the numerical simulations. We discuss the scaling of an extended occulter test-bed.

Sirbu, Dan↗
NASA NTRS2011

Technology for Future Exoplanet Missions

A central theme in NASA's and ESA's vision for future missions is the search for habitable worlds and life beyond our Solar System. This presentation will review the current state of the art in planet-finding technology, with an emphasis on methods of starlight suppression. At optical wavelengths, Earth-like planets are about 10 billion times fainter than their host stars. Starlight suppression is therefore necessary to enable measurements of biosignatures in the atmospheres of faint Earth-like planets. Mission concepts based on coronagraph, starshade, and interferometers will be described along with their science objectives and technology requirements.

interferometer↗
NASA NTRS2017

Shaped Pupil Coronagraphy for WFIRST: High-Contrast Broadband Testbed Demonstration

The Shaped Pupil Coronagraph (SPC) is one of the two operating modes of the WFIRST (Wide-Field InfraRed Survey Telescope) coronagraph instrument. The SPC provides starlight suppression in a pair of wedge-shaped regions over an 18 percent bandpass, and is well suited for spectroscopy of known exoplanets. To demonstrate this starlight suppression in the presence of expected on-orbit input wavefront disturbances, we have recently built a dynamic testbed at JPL (Jet Propulsion Lab.) analogous to the WFIRST fight instrument architecture, with both Hybrid Lyot Coronagraph (HLC) and SPC architectures and a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to apply, sense, and correct dynamic wavefront disturbances. We present our best up-to-date results of the static SPC mode demonstration from the testbed, along with model comparisons and performance under realistic dynamical conditions. HLC results will be reported separately.

Cady, Eric↗
NASA NTRS1994

Extrasolar planet detection

This paper discusses the concept of extrasolar planet detection using a large-aperture infared imaging telescope. Coronagraphic stellar apodization techniques are less efficient at infrared wavelengths compared to the visible, as a result of practical limitations on aperture dimensions, thus necessitating additional starlight suppression to make planet detection feasible in this spectral domain. We have been investigating the use of rotational shearing interferometry to provide up to three orders of magnitude of starlight suppression over broad spectral bandwidths. We present a theoretical analysis of the system performance requirements needed to make this a viable instrument for planet detection, including specifications on the interferometer design and telescope aperture characteristics. The concept of using rotational shearing interferometry as a wavefront error detector, thus providing a signal that can be used to adaptively correct the wavefront, will be discussed. We also present the status of laboratory studies of on-axis source suppression using a recently constructed rotational shearing interferometer that currently operates in the visible.

Korechoff, R. P.↗