NASA’s next flagship mission, the Nancy Grace Roman Space Telescope, is a 2.4-meter observatory set to launch no later than May 2027. Roman features two instruments: the Wide Field Imager and the Coronagraph Instrument. The Roman Coronagraph is a Technology Demonstration that will push the current capabilities of direct imaging to smaller contrast ratios (∼10−9) and inner-working angles (3 λ/D). In order to achieve this high precision, Roman Coronagraph data must be calibrated to remove as many potential sources of error as possible. Here we present a detailed overview of the current plans for the Nancy Grace Roman Space Telescope Coronagraph Instrument Observation Calibration Plan, including identifying potential sources of error and how they will be mitigated via on-sky calibrations.
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.
Princeton University is upgrading our space occulter testbed. In particular, we are lengthening it to ~76m to achieve flightlike Fresnel numbers. This much longer testbed required an all-new enclosure design. In this design, we prioritized modularity and the use of commercial off-the-shelf (COTS) and semi-COTS components. Several of the technical challenges encountered included an unexpected slow beam drift and black paint selection. Herein we describe the design and construction of this long-travel laser enclosure.
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.
Optical devices with features exhibiting ultra low reflectivity on the order of 10-7 specular reflectance in the visible spectrum are required for coronagraph instruments and some spectrometers employed in space research. 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. Particularly, devices with very high (>0.9) and very low reflectivity (<10-7) on adjacent areas have been fabricated and characterized. Significantly increased surface area due to the long needle like nano structures also provides some unique applications in other technology areas. We present some of the approaches, challenges and achieved results in producing and characterizing such devices currently employed in laboratory testbeds and instruments.
One of the two primary architectures being tested for the WFIRST-AFTA coronagraph instrument is the shaped pupil coronagraph, which uses a binary aperture in a pupil plane to create localized regions of high contrast in a subsequent focal plane. The aperture shapes are determined by optimization, and can be designed to work in the presence of secondary obscurations and spiders - an important consideration for coronagraphy with WFIRST-AFTA. We present the current performance of the shaped pupil testbed, including the results of AFTA Milestone 2, in which ≈ 6 × 10-9 contrast was achieved in three independent runs starting from a neutral setting.
Star light suppression technologies to find and characterize faint exoplanets include internal coronagraph instruments as well as external star shade occulters. Currently, the NASA WFIRST-AFTA mission study includes an internal coronagraph instrument to find and characterize exoplanets. Various types of masks could be employed to suppress the host star light 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, ultra-low reflectivity regions, uniformity, wave front quality, achromaticity, etc. 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 (HCIT) at JPL and from the High Contrast Imaging Lab (HCIL) at Princeton University. We also present briefly the technologies applied to fabricate laboratory scale star shade masks.
NASA’s WFIRST-AFTA mission concept includes the first high-contrast stellar coronagraph in space. This coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. In this paper we present the plan for maturing coronagraph technology to TRL5 in 2014-2016, and the results achieved in the first 6 months of the technology development work. The specific areas that are discussed include coronagraph testbed demonstrations in static and simulated dynamic environment, design and fabrication of occulting masks and apodizers used for starlight suppression, low-order wavefront sensing and control subsystem, deformable mirrors, ultra-low-noise spectrograph detector, and data post-processing.
The SIM-Planetquest (Space Interferometry Mission), currently under development at the Jet Propulsion Laboratory,
consists of two 6-meter baseline interferometers on a flexible truss. SIM's science goals require 1μas accuracy in its
astrometric measurements[1]. To achieve this level of accuracy for detecting planets SIM built the Spectrum Calibration
Development Unit (SCDU) testbed. The testbed requires a white light point source with broadband spectrum. Before
each long test the spectrum on the camera must be calibrated. To achieve this task a laser light visible to camera was
coupled to the white light source. The light system needed pointing stability of better than 4 micro-radians and a
minimum optical power level at the fringe tracking camera. Due to stability requirement of the experiment, the setup,
including the point source is in a vacuum chamber. To get a broadband spectrum point source inside the vacuum
chamber white light from a multimode fiber was combined with laser light in free space to a photonics crystal fiber
(PCF). The output is a single mode, broadband, and Gaussian beam. This paper explains the details of such a design and
shows some of the results.
SCDU (Spectral Calibration Development Unit) is a vacuum test bed that was built and operated for the SIM-Planetquest
Mission and has successfully demonstrated the calibration of spectral instrument error to an accuracy of
better than 20 picometers. This performance is consistent with the 1 micro-arc second goal of SIM. The calibration
procedure demonstrated in the test bed is traceable to the SIM flight instrument. This article is a review of all aspects of
the design and operation of the hardware as well as the methodology for spectral calibration. Spectral calibration to
better than 20 picometers and implications for flight are discussed.
The Space Interferometry Mission (SIM) requires the control of the optical path of each interferometer with picometer
accuracy. Laser metrology gauges are used to measure the path lengths to the fiducial corner cubes at the siderostats.
Due to the geometry of SIM a single corner cube does not have sufficient acceptance angle to work with all the gauges.
Therefore SIM employs a double corner cube. Current fabrication methods are in fact not capable of producing such a
double corner cube with vertices having sufficient commonality. The plan for SIM is to measure the non-commonalty of
the vertices and correct for the error in orbit. SIM requires that the non-common vertex error (NCVE) of the double
corner cube to be less than 6 μm. The required accuracy for the knowledge of the NCVE is less than 1 μm. This paper
explains a method of measuring non-common vertices of a brassboard double corner cube with sub-micron accuracy.
The results of such a measurement will be presented.
Kite is a system level testbed for the External Metrology System of the Space Interferometry Mission (SIM). The External Metrology System is used to track the fiducials that are located at the centers of the interferometer's siderostats. The relative changes in their positions needs to be tracked to an accuracy of tens of picometers in order to correct for thermal deformations and attitude changes of the spacecraft. Because of the need for such high precision measurements, the Kite testbed was build to test both the metrology gauges and our ability to optically model the system at these levels. The Kite testbed is a redundant metrology truss, in which 6 lengths are measured, but only 5 are needed to define the system. The RMS error between the redundant measurements needs to be less than 140pm for the SIM Wide-Angle observing scenario and less than 8 pm for the Narrow-Angle observing scenario. With our current testbed layout, we have achieved an RMS of 85 pm in the Wide-Angle case, meeting the goal. For the Narrow-Angle case, we have reached 5.8 pm, but only for on-axis observations. We describe the testbed improvements that have been made since our initial results, and outline the future Kite changes that will add further effects that SIM faces in order to make the testbed more representative of SIM.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.