Further author information send correspondence to Jeremy Kasdin, E-mail:
<EMAIL_ADDRESS>
# The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI)
Technology Demonstration

N. Jeremy Kasdin  University of San Francisco,College of Arts and Sciences,
2130 Fulton St., San Francisco, CA, USA, 94117  Vanessa P. Bailey  Jet
Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Dr,
Pasadena, CA, USA, 91109  Bertrand Mennesson  Jet Propulsion Laboratory -
California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, USA,
91109  Robert T. Zellem  Jet Propulsion Laboratory - California Institute of
Technology, 4800 Oak Grove Dr, Pasadena, CA, USA, 91109  Marie Ygouf  Jet
Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Dr,
Pasadena, CA, USA, 91109  Jason Rhodes  Jet Propulsion Laboratory - California
Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, USA, 91109  Thomas
Luchik  Jet Propulsion Laboratory - California Institute of Technology, 4800
Oak Grove Dr, Pasadena, CA, USA, 91109  Feng Zhao  Jet Propulsion Laboratory -
California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, USA,
91109  A J Eldorado Riggs  Jet Propulsion Laboratory - California Institute of
Technology, 4800 Oak Grove Dr, Pasadena, CA, USA, 91109  Byoung-Joon Seo  Jet
Propulsion Laboratory - California Institute of Technology, 4800 Oak Grove Dr,
Pasadena, CA, USA, 91109  John Krist  Jet Propulsion Laboratory - California
Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, USA, 91109  Brian
Kern  Jet Propulsion Laboratory - California Institute of Technology, 4800 Oak
Grove Dr, Pasadena, CA, USA, 91109  Hong Tang  Jet Propulsion Laboratory -
California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, USA,
91109  Bijan Nemati  University of Alabama in Huntsville, 301 Sparkman Drive,
Huntsville, AL, USA, 35899  Tyler D. Groff  NASA Goddard Space Flight Center,
8800 Greenbelt Rd, Greenbelt, MD, USA, 20771  Neil Zimmerman  NASA Goddard
Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, USA, 20771  Bruce
Macintosh  Stanford University, Stanford, CA, USA, 94305  Margaret Turnbull
The SETI Institute, 189 Bernardo Ave, Suite 200, Mountain View, CA, USA, 94043
John Debes  Space Telescope Science Institute, 3700 San Martin Dr., Baltimore,
MD,USA, 21218  Ewan S. Douglas  Steward Observatory, 933 North Cherry Avenue,
Tucson, AZ, USA, 85721-0065  Roxana E. Lupu  BAER Institute/NASA Ames Research
Center, Moffett Field, CA, USA, 94035

###### Abstract

The Coronagraph Instrument (CGI) on the Nancy Grace Roman Space Telescope will
demonstrate the high-contrast technology necessary for visible-light exoplanet
imaging and spectroscopy from space via direct imaging of Jupiter-size planets
and debris disks. This in-space experience is a critical step toward future,
larger missions targeted at direct imaging of Earth-like planets in the
habitable zones of nearby stars. This paper presents an overview of the
current instrument design and requirements, highlighting the critical
hardware, algorithms, and operations being demonstrated. We also describe
several exoplanet and circumstellar disk science cases enabled by these
capabilities. A competitively selected Community Participation Program team
will be an integral part of the technology demonstration and could perform
additional CGI observations beyond the initial tech demo if the instrument
performance warrants it.

###### keywords:

High-contrast imaging, Coronagraphy, Roman, CGI

##  1 Introduction

This paper gives a brief overview of the Coronagraph Instrument on the Nancy
Grace Roman Space Telescope. The Roman Space Telescope (formerly called
WFIRST) is NASA’s next flagship observatory, planned for launch in 2025,
employing a 2.4 meter diameter telescope and two instruments: a Wide-Field
Instrument (WFI) for cosmology and dark energy and the Coronagraph Instrument
(CGI) technology demonstrator for performing high-contrast imaging. This paper
introduces the goals, design, and progress of CGI. There are several more
detailed talks on various aspects of the instrument in this and other sessions
of the conference that will be referenced throughout.

##  2 CGI Technology Demonstration

The CGI instrument, whose schematic is shown in Figure 1, is scheduled for its
Critical Design Review (CDR) in April 2020. More details on the overall
optical layout are in the papers by Poberezhskiy [1] and Tang[2], and many
specifications, such as filter and detector parameters, are publicly
available.111https://roman.ipac.caltech.edu/sims/Param_db.html Currently, CGI
is on schedule to meet the 2025 launch of Roman. The primary purpose of CGI is
to demonstrate the essential technologies necessary for high-contrast imaging
that will be needed in future missions targeted at finding and characterizing
Earth-like planets in the habitable zone of nearby stars[3] (such as the
HabEx[4] and LUVOIR[5] mission studies).

As such, CGI has five primary technology demonstration objectives. CGI will be
the first coronagraphic instrument in space with active wavefront control, an
important milestone in the evolution of high-contrast imaging and an essential
precursor technology for all future large telescopes. It will demonstrate and
make flight-ready key hardware elements associated with advanced coronagraphy
and active wavefront control as well as the algorithms for sensing, control,
and data processing and analysis. One of the most important things that will
be learned from flying CGI is how the coronagraph interacts with the
observatory as a whole and with the spacecraft control systems in particular,
thus dramatically reducing the risk of future missions. Finally, CGI will
pioneer new advanced data processing techniques for extracting planets from
noisy, photon-counting images, a key advancement for future missions.

Figure 1:  CAD diagram of the CGI instrument entering CDR.

##  3 Wavefront Sensing and Control for High Contrast

The heart of the CGI technology demonstration is the active wavefront sensing
and control system. Figure 2 shows the architecture of the CGI sensing and
control. This figure illustrates how all the elements must work together as a
system. Low-order optical errors and fast variations (such as tip/tilt due to
spacecraft pointing) are controlled by the Low-Order Wavefront Sensing and
Control (LOWFS/C) loop, where aberrations and motion are measured using a
Zernike wavefront sensor that uses starlight rejected by the coronagraph masks
[6, 7, 8]. The LOWFS/C loop operates with control bandwidths of $\sim$20 Hz
and $\sim$2 mHz, for tip/tilt and Z4-Z11, respectively. CGI’s high-contrast
performance is only guaranteed for stars of Vmag$\leq$5, as LOWFS SNR begins
to degrade below this cutoff, particularly for the fast tip/tilt loop. Note
that the feed-forward portion of the LOWFS/C tip/tilt loop described in Shi[6]
will not be implemented in flight. Expected tip/tilt performance is better
than 1 mas RMS. The High-Order Wavefront Sensing and Control (HOWFS/C) loop
uses multiple measurements at the final imaging camera with probe signals from
the two deformable mirrors (DMs) for estimation[9, 10]. While the nominal
control approach uses the Electric Field Conjugation algorithm[11] to
determine the DM settings, the software is being configured to allow testing
of various types of control approaches. After CGI’s preliminary design review
(PDR), the decision was made to perform the slow, high-order control loop via
telemetry and commands from the ground (Ground In The Loop, or GITL).

Also shown in Figure 2 and described in Table 1 are the three primary modes of
CGI: a short-wavelength mode with 10% bandwidth222Bandwidth is the region
where average transmission $>90\%$ centered at 575 nm (Band 1) for imaging and
polarimetry from 3-9 $\lambda$/D using the Hybrid Lyot Coronagraph (HLC); a
medium-wavelength, 15% band centered at 730 nm (Band 3) for spectroscopy in a
“bowtie” shaped field of view from 3-9 $\lambda$/D using the Shaped Pupil
Coronagraph (SPC); and a 10%, wide-field, long-wavelength band centered at 825
nm (Band 4) for imaging and polarimetry from 6–20 $\lambda$/D using a second
Shaped Pupil Coronagraph. A fourth 15% spectroscopy band (Band 2) centered at
660 nm is installed on CGI, but will not be tested on the ground, due to
schedule constraints.

| $\lambda_{0}$ | FWHM | IWA | OWA | Angular | Polarimetry
---|---|---|---|---|---|---
Name | [nm] | [nm] | [$\lambda/D$] | [$\lambda/D$] | Coverage [∘] | Compatible?
Band 1 imaging | 575 | 70 | 3 | 9 | 360 | yes
Band 2 spectroscopy* | 660 | 112 | 3 | 9 | 2$\times$65 | no
Band 3 spectroscopy | 730 | 122 | 3 | 9 | 2$\times$65 | no
Band 4 imaging | 825 | 94 | 6 | 20 | 360 | yes
Table 1: CGI observing modes. Note that Band 2 spectroscopy hardware will be installed, but will not be tested on the ground; hence, it is not an officially supported observing mode. Figure 2:  The CGI optical train and wavefront sensing and control architecture. The LOWFS/C loop operates with control bandwidths of $\sim$20 Hz and $\sim$2 mHz, for tip/tilt and Z4-Z11, respectively. HOWFS/C is not conducted continuously, but rather on the order of once per day, with processing offloaded to the ground. |  |
---|---|---
|  |
Figure 3:  New coronagraph technology elements being demonstrated on CGI.
Clockwise from upper left: Wavefront sensing and control optical layout, AOX
Corp. 48x48 actuator Electrostrictive PMN (lead magnesium niobate) DM,
Teledyne 1k x 1k EMCCD, Hybrid Lyot image plane mask, Black Silicon reflctive
shaped pupils.

Successfully implementing the WFSC system above relies on several technology
advances, all considered enabling for future high-contrast imaging
missions[3]. The key ones are shown in Figure 3. These include the algorithms
and optical configuration needed for the wavefront sensing and control, which
has been shown in the lab to be able to correct phase errors to better than 1
nm[1, 10]; new, large format deformable mirrors produced by AOA Xinetics,
which have reached TRL 6 in the laboratory; masks and stops associated with
the two types of coronagraphs being demonstrated on CGI, the Shaped Pupil Lyot
Coronagraph (SPC[12, 13]) and the Hybrid Lyot Coronagraph (HLC[14, 15]) (all
flight designs are completed and the flight masks are in production[16]);
extremely low-noise, electron-multiplying CCD detectors operated in photon-
counting mode, necessary because of the very high magnitude of companion
planets[17, 18, 19]; and the Zernike wavefront sensor used in the low-order
control loop, which has also been successfully demonstrated in the lab.[1, 7,
6] All of these elements have passed all design milestones and flight article
production has begun.

(a) Hybrid Lyot

(b) “Bowtie” Shaped Pupil Coronaraph

(c) “Wide” Shaped Pupil

Figure 4:  Demonstrations of high contrast in the three coronagraph modes in
the JPL High Contrast Imaging Testbed with high-order and low-order wavefront
control. (a) The Band 1 Hybrid Lyot Coronagraph in 10% band around 550 nm in a
3-9 $\lambda$/D annulus with a mean contrast of $1.6\times 10^{-9}$. (b) The
Band 3 “Bowtie” Shaped Pupil Coronagraph in a 15% band around 730 nm from 3-9
$\lambda$/D in two $65^{\circ}$ sections, with a mean contrast of $4.8\times
10^{-9}$ . (c) The Band 4 “Wide field” Shaped Pupil Coronagraph in a 10% band
around 825 nm from 6.5-20 $\lambda$/D with a mean contrast of $4.3\times
10^{-9}$.

All three modes for CGI have been tested with flight-like masks, deformable
mirrors and both high-order and low-order control in the High-Contrast Imaging
Testbed at JPL[20, 21, 22, 23]. As Figure 4 shows, all three have achieved
contrasts below $10^{-8}$ and reaching close to $10^{-9}$. These tests are
significant milestones toward CDR in April 2020 and give confidence in the
performance predictions of CGI[9, 24]. More detail can be found in the paper
by Zhou.[10]

##  4 Spectroscopy and Polarization

(a) Alignment of slit with the planet.

(b) Dispersed image after post-processing

(c) Extracted spectrum.

Figure 5: Simulating the spectrum extraction of a planet around 47 UMa with
the slit spectrograph mode of CGI (Band 3). In this illustration we
represented the planet source with a Jupiter-like spectral profile, scaled up
in intensity to a flux ratio of $5\times 10^{-8}$.

While the original plan for CGI called for an integral field spectrograph
(IFS) that would provide a full 3D data cube, cost and schedule constraints
forced a descoping of the IFS. CGI is instead equipped with a slit
spectrograph, as shown in Figure 5. The spectrograph will be used in Band 3
with the “bowtie” shaped pupil coronagraph. After detection of a planet in
Band 1 HLC imaging (and photometric measurements taken), CGI will be
reconfigured for Band 3 spectroscopy; the slit will be aligned with the planet
as shown in Figure 5(a), which is a simulated spectral image of a $5\times
10^{-8}$ flux ratio Jupiter-like planet around 47 UMa. The planet image is
then dispersed across a 15% band using an Amici prism with an R of 50 at the
center of the band, as shown in Figure 5(b) (a schematic of the Amici prism is
shown in Figure 6). Figure 5(c) shows a simulated, post-processed spectrum,
clearly indicating the capability to measure a deep methane band. The
spectrometer is equipped with a second prism for spectroscopy in the untested
Band 2 as well, should observation time be available. More detail on
spectrometer progress can be found in the paper by Groff.[25]

Figure 6: Diagram of the Amici prism used for spectral dispersion.

In addition to taking spectra, CGI will measure the linear polarization
fraction (LPF), and hence the phase scattering function, of extended objects
with an uncertainty on the LPF of better than 3% (rmse) per spatial resolution
element. It will conduct these measurements in CGI bands 1 and 4, which are
again centered at 575 and 825 nm, respectively. Polarimetric measurements will
be conducted using two Wollaston prisms contributed by JAXA, the Japanese
space agency, shown in Figure 7(b). They are mounted in the polarization
module shown in Figure 7(a). Each Wollaston prism produces two orthogonally
polarized images at a time ($0^{\circ}/90^{\circ}$ or
$45^{\circ}/135^{\circ}$), for a total of four images, as shown in Figure
7(c). The two Wollastons cannot be used simultaneously, so two sets of
observations are needed to collect all four images.

(a) Assembled Prism Module

(b) JAXA Polarization Module

(c) Two Pairs of Orthogonally Polarized Images

Figure 7: The Wollaston Prism assembly and sample performance. Only one
Wollaston can be used at a time; each produces one pair of images
($0^{\circ}/90^{\circ}$ or $45^{\circ}/135^{\circ}$).

In order to make such measurements, all instrumental polarization effects
affecting the overall optical system will be calibrated through observations
of (un)polarized standards. It is expected that after this calibration,
residual polarization measurement errors will be dominated by detector
effects, such as flat-fielding errors. Calibrated polarized images of point-
like targets will also be used to validate polarization models that predict
different dark hole depths in polarized vs. unpolarized light. These
polarization measurements will both provide new and important science, as well
as demonstrate for the first time high-contrast polarization capability.

##  5 Operations and Image Post-Processing

Figure 8: Example observing scenario with $\pm 13$ degree roll every 2 hours
and slewing to the reference star every 10 hours.

While achieving high-contrast has been demonstrated by simulation and
laboratory experiments, long-term stability of the system still needs to be
managed. Because of potential drifts in the DM and optics, the dark hole needs
to be periodically reset. Additionally, reference images from a bright star
are needed to perform PSF subtraction to reveal the planets (known as
Reference Differential Imaging, or RDI). Also, in addition to RDI, Angular
Differential Imaging (ADI) is planned to be performed as well. Hence, the
example operational scenario shown Figure 8. Every two hours the spacecraft
will be rolled by ± 13 degrees and every 10 hours it will be slewed to a
reference star to recreate the dark hole and take reference PSFs. These times
are subject to change as more is learned about the stability of the system and
as dark hole touch-up cadence is adjusted to match ground station availability
in the new HOWFS GITL paradigm.

Figure 9: Demonstrating Classical ADI and RDI PSF subtraction on noiseless and
noisy simulated data with MUF and with planets (flux ratios of $1\times
10^{-8}$ and $3\times 10^{-9}$ at $3.5\lambda/D$ and $4.5\lambda/D$
respectively) from Observing Scenario 9 with the Band 1 HLC.

A critical step in image processing is “post-processing”—the PSF subtraction
process to remove the residual speckles in the high-contrast images. Extensive
effort has been put into developing and analyzing this approach on simulated
datasets. Simulated images are produced based on the current end-to-end opto-
mechanical simulation of the spacecraft and instrument for a realistic target-
reference Observing Sequence (OS)[26, 27]. Since before PDR, a sequence of
detailed simulations using Structural, Thermal, Optical (STOP) modeling of the
observatory, jitter modeling of the Attitude and Translational Control System
(ATC), and internal modeling of the CGI coronagraph and wavefront control have
been performed, including model uncertainty factors (MUFs), each building on
the last by adding more detail. These end-to-end models produce simulated
final images with planets injected including both roll and chopping to the
reference star. These images are used by the team to test post-processing
algorithms for detecting planets and to determine the ultimate performance of
CGI.[28] Images are also made publicly available to allow the community to
test alternative approaches.333CGI simulations available at:
https://roman.ipac.caltech.edu/sims/Coronagraph_public_images.html Shown in
Figure 9 are the results of the latest round of tests comparing RDI and ADI
approaches on both noiseless and noisy images from the OS9 release.

##  6 Science

Figure 10: CGI’s capability for detecting planets at $5\sigma$ as a function
of planet-to-star flux ratio and separation from the parent star. CGI provides
a 100 to 1000 times improvement over existing and planned facilities.

The final result of both modeling and experiments is rolled up into the chart
in Figure 10.444plot data is publicly available
https://github.com/nasavbailey/DI-flux-ratio-plot This chart shows the
predicted capability of CGI in its three bands compared to current ground and
space coronagraphs. Also shown is the current CGI threshold requirement of
$10^{-7}$ contrast, the value indicating a successful technology
demonstration. CGI will perform anywhere from 100 to 1000 times better than
any current facility. Current modeling predictions show that CGI performs
significantly better than requirements in all bands. If CGI successfully meets
these predictions, significant exoplanet and disk science will be possible,
including, as shown, visible light imaging of known young, self-luminous, hot
gas-giants and the first reflected light images of Jupiter analogs, including
current nearby RV targets.

(a) Self-Luminous Jupiters

(b) Reflected Light Jupiters

(c) Circumstellar Disks

Figure 11: Three sample science cases for CGI after the technology
demonstration phase. (a) Spectra of young, hot, self-luminous Jupiters to
determine atmospheric properties. [29] (b) Atmospheric properties of mature
Jupiter-analogues in reflected light to determine their albedo. (figure
courtesy of Roxana Lupu - NASA Ames) (c) Photometric characterization of all
three types of circumstellar disks: proplanetary (young; TW Hydra), debris
(mature; dashed curves), and exozodi (solid red lines). Roman/CGI’s HLC (shown
lower left) will provide higher precision observations of these objects than
those currently capable with Hubble’s STIS and ACS (shown upper right).
(figure courtesy of John Debes - STScI.)

While CGI is designated as a technology demonstrator, the team is confident
that its performance will exceed requirements, allowing us to perform new and
exciting exoplanet science both during and after the initial technology
demonstration phase. As shown in Figures 11 and 12, there is a robust set of
science possible by observing young, self-luminous, gas giants[29] as well as
direct imaging of mature Jupiter analogs in visible, reflected
light.555Predicted flux ratios for RV planets are publicly available via the
Imaging Mission Database[30, 31, 32]: https://plandb.sioslab.com/ Multiple
observations will also allow orbit determination of imaged planets. CGI will
also be capable of direct imaging and polarization measurements of
circumstellar disks, particularly debris disks, as well as potentially
characterizing protoplanetary disks and taking the first visible-light image
of an exozodi disk.

Current ground-based observations are exclusively limited to observing young,
hot super-Jupiters in the infra-red relatively far from their host star.
Roman/CGI will take visible-light images and spectra of these planets,
enabling the distinction between clear and cloudy atmospheres and further
constraining their properties and formation mechanisms[29]. Shown in Figure
11(a) is the planet to star contrast as a function of wavelength for the
young, self-luminous giant planet HR 8799e assuming an equilibrium temperature
of 1150 K, a cloudy atmosphere, and a mass of 9.2 Jupiter masses. The CGI
passbands are also shown. While infrared wavelengths already favor a cloudy
rather than a clear atmosphere for HR 8799e, adding optical coverage with CGI
should improve our understanding of the cloud properties beyond just stating
that they are there (e.g. rule out/favor some chemical compositions, provide
more information on particle sizes). Optical coverage with CGI should tighten
constraints on other planet properties as well (e.g., planetary metallicity).

Roman/CGI will also take the first visible-light images and spectra of cool,
true Jupiter analogs (old and cold Jupiter-mass planets orbiting several AU
from their stars), thus coarsely probing the metallicity and cloud properties
of Jupiter analogues, as illustrated in Figure 11(b). Shown as solid lines are
3 models: M1—a Jupiter-like planet model with a $\sim$4.5$\times$ Solar
metallicity; M3—a 6.6$\times$ Jupiter model ($\sim$30$\times$ Solar
Metallicity); and M4—a cloud-free Jupiter-like model. Simulated CGI
observations for model M1 are shown as datapoints for Bands 1 (photometry;
red) and 3 (spectroscopy; black). CGI could loosely constrain metallicity
(solar vs. enriched) for the cloudy planets, providing information important
to formation modeling and as precursors to future missions both by
demonstrating high-contrast spectroscopy and highlighting potential targets.

CGI can probe the formation and evolution of extrasolar systems by observing
all three types of circumstellar disks at lower density and in regions closer
to the star than currently possible from the ground, as shown in Figure 11(c).
Imaging of debris disks provides information on the remains of planet
formation as well as colliding or evaporating asteroids and comets.
Polarimetric observations complement integrated light imaging to constrain
grain properties. Roman/CGI could also provide the first close-in, visible-
light images of exozodiacal dust clouds produced by collisions of asteroids
and comets. These clouds can potentially obscure small Earth-like planets; CGI
images will provide crucial information for future mission planning. If CGI
WFS/C is able to perform well on fainter target stars, it could observe
protoplanetary and transition disk systems, providing information on newly-
forming planetary systems. Figure 11(c) shows predicted CGI disk imaging
performance in the context of HST detection limits and surface brightness
profiles of previously-resolved disks and exozodi predictions. Surface
brightness units are flux ratio per resolution element.

Figure 12: Simulated, post-processed CGI HLC images of a multiplanetary system
observed at two epochs separated by two years, displayed in units of
integrated photoelectrons. The blue, dashed ellipses illustrate the projected
orbits of the two planets detected as point sources. These simulations were
produced using “OS6” integrated models that include the effects of time-
varying spacecraft pointing jitter, low-order aberrations, and speckle noise.
Similar multi-epoch data sets were simulated for a community data challenge
organized by one of the science teams, which probed strategies for retrieving
planet orbits and masses[33].

CGI will also measure the orbital solution of planets that have been
previously detected via the radial velocity method, allowing the direct
measurement of a planet’s orbital inclination, providing a crucial constraint
on m*sin(i), and allowing us to directly measure the planet’s mass. (See
Figure 12.)

##  7 Timeline

CGI is on track to meet its schedule targets. Great progress has been made
since entering Phase C last February with almost all engineering units
procured and many flight units in manufacture. The team anticipates a
successful CDR this coming April and delivery of the completed instrument to
the Goddard Space Flight Center for integration and test in 2023. After launch
in late 2025, CGI will enter a commissioning phase during the first 90 days,
followed by its 3 month technology demonstration phase spread across the first
1.5 years of the mission. Upon completion of the technology demonstration
phase, if deemed successful, and if additional funding is made available, CGI
could potentially be available for science- and technology-driven observations
using somewhere between 10% and 25% of the remaining Roman mission time.

A competitively selected Community Participation Program is planned to be an
integral part of the technology demonstration and could lead additional CGI
observations beyond the initial tech demo if the instrument performance
warrants it. The Community Participation Program will be the mechanism through
which members of the community engage in both the technology demonstration
phase and potential science phase. Details of the program are still being
worked out and a call for applications is expected sometime in 2021.

##  8 Summary

In Summary, the CGI instrument on the Roman space telescope is on schedule for
CDR in April 2020 and launch in 2025 and is exceeding its performance
requirements. Upon launch and commencement of operation, it will be the first
actively controlled, high-contrast coronagraph in space. Its combination of
multiple technologies (including three different coronagraphs) and modes of
operation while raising the TRL (technology-readiness level) of critical
hardware, such as deformable mirrors, low-noise, photon-counting detectors,
coronagraph masks, and other elements will make CGI a critical technology
demonstration for future missions, paving the way for direct imaging of Earth-
like planets in the habitable zone of nearby stars. If successful, CGI will
also provide breakthrough science, including spectroscopy of known RV and
self-luminous planets, imaging and photometry of reflected light planets, and
characterization of zodiacal dust and debris disks.

##  9 Acknowledgements

Part of the work described here was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under contract with the
National Aeronautics and Space Administration. Copyright 2020. All rights
reserved. Work also supported by a grant from NASA Goddard Space Flight
Center, Award #NNG16PJ29C. This research has made use of the Imaging Mission
Database, which is operated by the Space Imaging and Optical Systems Lab at
Cornell University. The database includes content from the NASA Exoplanet
Archive, which is operated by the California Institute of Technology, under
contract with the National Aeronautics and Space Administration under the
Exoplanet Exploration Program, and from the SIMBAD database, operated at CDS,
Strasbourg, France.

## References

  * [1] Poberezhskiy, I., Luchik, T., Zhao, F., Frerking, M., Bailey, V., Basinger, S., Cady, E., Colavita, M., Creager, B., Fathpour, N., Goullioud, R., Groff, T., Morriesy, P., Kempenaar, J., Kern, B., Krist, J., Mok, F., Muliere, D., Nemati, B., Riggs, A. J., Seo, G.-J., Shi, F., Steeves, J., Shreckengost, B., and Tang, H., “CGI engineering design and operational concept,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11443(195) (2020).
  * [2] Tang, H., Rodgers, M., Creager, B., Krist, J., McGuire, J., Patterson, K., Rud, M., Shi, F., and Zhao, F., “The WFIRST coronagraph instrument phase B optical design,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 11117, 111170C (Sept. 2019).
  * [3] Mennesson, B., Juanola-Parramon, R., Nemati, B., Ruane, G., Bailey, V. P., Bolcar, M., Martin, S., Zimmerman, N., Stark, C., Pueyo, L., Benford, D., Cady, E., Crill, B., Douglas, E., Gaudi, B. S., Kasdin, J., Kern, B., Krist, J., Kruk, J., Luchik, T., Macintosh, B., Mandell, A., Mawet, D., McEnery, J., Meshkat, T., Poberezhskiy, I., Rhodes, J., Riggs, A. J., Turnbull, M., Roberge, A., Shi, F., Siegler, N., Stapelfeldt, K., Ygouf, M., Zellem, R., and Zhao, F., “Paving the Way to Future Missions: the Roman Space Telescope Coronagraph Technology Demonstration,” arXiv e-prints , arXiv:2008.05624 (Aug. 2020).
  * [4] Gaudi, B. S., Seager, S., Mennesson, B., Kiessling, A., Warfield, K., Cahoy, K., Clarke, J. T., Domagal-Goldman, S., Feinberg, L., Guyon, O., Kasdin, J., Mawet, D., Plavchan, P., Robinson, T., Rogers, L., Scowen, P., Somerville, R., Stapelfeldt, K., Stark, C., Stern, D., Turnbull, M., Amini, R., Kuan, G., Martin, S., Morgan, R., Redding, D., Stahl, H. P., Webb, R., Alvarez-Salazar, O., Arnold, W. L., Arya, M., Balasubramanian, B., Baysinger, M., Bell, R., Below, C., Benson, J., Blais, L., Booth, J., Bourgeois, R., Bradford, C., Brewer, A., Brooks, T., Cady, E., Caldwell, M., Calvet, R., Carr, S., Chan, D., Cormarkovic, V., Coste, K., Cox, C., Danner, R., Davis, J., Dewell, L., Dorsett, L., Dunn, D., East, M., Effinger, M., Eng, R., Freebury, G., Garcia, J., Gaskin, J., Greene, S., Hennessy, J., Hilgemann, E., Hood, B., Holota, W., Howe, S., Huang, P., Hull, T., Hunt, R., Hurd, K., Johnson, S., Kissil, A., Knight, B., Kolenz, D., Kraus, O., Krist, J., Li, M., Lisman, D., Mandic, M., Mann, J., Marchen, L., Marrese-Reading, C., McCready, J., McGown, J., Missun, J., Miyaguchi, A., Moore, B., Nemati, B., Nikzad, S., Nissen, J., Novicki, M., Perrine, T., Pineda, C., Polanco, O., Putnam, D., Qureshi, A., Richards, M., Eldorado Riggs, A. J., Rodgers, M., Rud, M., Saini, N., Scalisi, D., Scharf, D., Schulz, K., Serabyn, G., Sigrist, N., Sikkia, G., Singleton, A., Shaklan, S., Smith, S., Southerd, B., Stahl, M., Steeves, J., Sturges, B., Sullivan, C., Tang, H., Taras, N., Tesch, J., Therrell, M., Tseng, H., Valente, M., Van Buren, D., Villalvazo, J., Warwick, S., Webb, D., Westerhoff, T., Wofford, R., Wu, G., Woo, J., Wood, M., Ziemer, J., Arney, G., Anderson, J., Maíz-Apellániz, J., Bartlett, J., Belikov, R., Bendek, E., Cenko, B., Douglas, E., Dulz, S., Evans, C., Faramaz, V., Feng, Y. K., Ferguson, H., Follette, K., Ford, S., García, M., Geha, M., Gelino, D., Götberg, Y., Hildebrandt, S., Hu, R., Jahnke, K., Kennedy, G., Kreidberg, L., Isella, A., Lopez, E., Marchis, F., Macri, L., Marley, M., Matzko, W., Mazoyer, J., McCandliss, S., Meshkat, T., Mordasini, C., Morris, P., Nielsen, E., Newman, P., Petigura, E., Postman, M., Reines, A., Roberge, A., Roederer, I., Ruane, G., Schwieterman, E., Sirbu, D., Spalding, C., Teplitz, H., Tumlinson, J., Turner, N., Werk, J., Wofford, A., Wyatt, M., Young, A., and Zellem, R., “The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report,” arXiv e-prints , arXiv:2001.06683 (Jan. 2020).
  * [5] The LUVOIR Team, “The LUVOIR Mission Concept Study Final Report,” arXiv e-prints , arXiv:1912.06219 (Dec. 2019).
  * [6] Shi, F., Seo, B.-J., Cady, E., Kern, B., Lam, R., Marx, D., Patterson, K., Mejia Prada, C., Shaw, J., Shelton, C., Shields, J., Tang, H., and Truong, T., “WFIRST low order wavefront sensing and control dynamic testbed performance under the flight like photon flux,” in [Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave ], Lystrup, M., MacEwen, H. A., Fazio, G. G., Batalha, N., Siegler, N., and Tong, E. C., eds., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10698, 106982O (July 2018).
  * [7] Shi, F., Balasubramanian, K., Hein, R., Lam, R., Moore, D., Moore, J., Patterson, K., Poberezhskiy, I., Shields, J., Sidick, E., Tang, H., Truong, T., Wallace, J. K., Wang, X., and Wilson, D., “Low-order wavefront sensing and control for WFIRST-AFTA coronagraph,” Journal of Astronomical Telescopes, Instruments, and Systems 2, 011021 (Jan. 2016).
  * [8] Sidick, E. and Riggs, A. J. E., “Optimization of Lyot coronagraph focal plane masks for improved low-order wavefront sensing,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 11117, 111170G (Sept. 2019).
  * [9] Zhou, H., Krist, J. E., Kern, B. D., Seo, B.-J., Cady, E., Nemati, B., Moody, D., Riggs, A. J. E., Marx, D. S., Wilson, D., Balasubramanian, K., Poberezhskiy, I. Y., and Basinger, S. A., “WFIRST Phase B HLC occulter mask baselining and testbed WFC performance validation,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 11117, 111170H (Sept. 2019).
  * [10] Zhou, H., Krist, J., Seo, B.-J., Kern, B., Cady, E., and Poberezhskiy, I., “CGI wfc modeling and testbed validation,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11443(196) (2020).
  * [11] Give’on, A., Kern, B. D., Shaklan, S., Moody, D. C., and Pueyo, L., “Electric field conjugation-a broadband wavefront correction algorithm for high-contrast imaging systems,” in [Bulletin of the American Astronomical Society ], 39, 975 (2007).
  * [12] Zimmerman, N. T., Eldorado Riggs, A. J., Jeremy Kasdin, N., Carlotti, A., and Vanderbei, R. J., “Shaped pupil Lyot coronagraphs: high-contrast solutions for restricted focal planes,” Journal of Astronomical Telescopes, Instruments, and Systems 2, 011012 (Jan. 2016).
  * [13] Eldorado Riggs, A. J., Zimmerman, N. T., Nemati, B., and Krist, J., “Shaped pupil coronagraph design improvements for the WFIRST coronagraph instrument,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10400, 104000O (Sept. 2017).
  * [14] Seo, B.-J., Gordon, B., Kern, B., Kuhnert, A., Moody, D., Muller, R., Poberezhskiy, I., Trauger, J., and Wilson, D., “Hybrid Lyot coronagraph for wide-field infrared survey telescope-astrophysics focused telescope assets: occulter fabrication and high contrast narrowband testbed demonstration,” Journal of Astronomical Telescopes, Instruments, and Systems 2, 011019 (Jan. 2016).
  * [15] Trauger, J., Moody, D., Krist, J., and Gordon, B., “Hybrid Lyot coronagraph for WFIRST-AFTA: coronagraph design and performance metrics,” Journal of Astronomical Telescopes, Instruments, and Systems 2, 011013 (Jan. 2016).
  * [16] Balasubramanian, K., Seo, B.-J., Patterson, K., Mejia Prada, C., Riggs, A. J. E., Zhou, H., Moody, D., Cady, E., White, V., Yee, K., Muller, R., Echternach, P., Greer, F., and Wilson, D., “Critical characteristics of coronagraph masks influencing high contrast performance,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 11117, 111171H (Sept. 2019).
  * [17] Bush, N., Morrissey, P., Hoenk, M., and Kyne, G., “Controlling EMCCD charge handling capacity through customized clocking,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11454(143) (2020).
  * [18] Effinger, R., Nemati, B., Rizzo, M., Morrissey, P., Harding, L., Bottom, M., Pontrelli, D., Demers, R., Bush, N., Hall, D., Clarke, A., and Holland, A., “WFIRST coronagraph detector trap modeling results and improvements,” in [High Energy, Optical, and Infrared Detectors for Astronomy VIII ], Holland, A. D. and Beletic, J., eds., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10709, 1070917 (July 2018).
  * [19] Harding, L. K., Demers, R. T., Hoenk, M., Peddada, P., Nemati, B., Cherng, M., Michaels, D., Neat, L. S., Loc, A., Bush, N., Hall, D., Murray, N., Gow, J., Burgon, R., Holland, A., Reinheimer, A., Jorden, P. R., and Jordan, D., “Technology advancement of the CCD201-20 EMCCD for the WFIRST coronagraph instrument: sensor characterization and radiation damage,” Journal of Astronomical Telescopes, Instruments, and Systems 2, 011007 (Jan. 2016).
  * [20] Seo, B.-J., Cady, E., Gordon, B., Kern, B., Lam, R., Marx, D., Moody, D., Muller, R., Patterson, K., Poberezhskiy, I., Mejia Prada, C., Sidick, E., Shi, F., Trauger, J., and Wilson, D., “Hybrid Lyot coronagraph for WFIRST: high-contrast broadband testbed demonstration,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10400, 104000F (Sept. 2017).
  * [21] Seo, B.-J., Shi, F., Balasubramanian, B., Cady, E., Gordon, B., Kern, B., Lam, R., Marx, D., Moody, D., Muller, R., Patterson, K., Poberezhskiy, I., Mejia Prada, C., Riggs, A. J. E., Trauger, J., and Wilson, D., “Hybrid lyot coronagraph for WFIRST: high contrast testbed demonstration in flight-like low flux environment,” in [Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave ], Lystrup, M., MacEwen, H. A., Fazio, G. G., Batalha, N., Siegler, N., and Tong, E. C., eds., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10698, 106982P (Aug. 2018).
  * [22] Marx, D., Cady, E., Riggs, A. J. E., Prada, C., Kern, B., Seo, B.-J., and Shi, F., “Shaped pupil coronagraph: disk science mask experimental verification and testing,” in [Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave ], Lystrup, M., MacEwen, H. A., Fazio, G. G., Batalha, N., Siegler, N., and Tong, E. C., eds., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10698, 106981E (July 2018).
  * [23] Cady, E., Balasubramanian, K., Gersh-Range, J., Kasdin, J., Kern, B., Lam, R., Mejia Prada, C., Moody, D., Patterson, K., Poberezhskiy, I., Riggs, A. J. E., Seo, B.-J., Shi, F., Tang, H., Trauger, J., Zhou, H., and Zimmerman, N., “Shaped pupil coronagraphy for WFIRST: high-contrast broadband testbed demonstration,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10400, 104000E (Sept. 2017).
  * [24] Nemati, B., Krist, J. E., and Mennesson, B., “Sensitivity of the WFIRST coronagraph performance to key instrument parameters,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10400, 1040007 (Sept. 2017).
  * [25] Groff, T., Marx, D., Kern, B., Krist, J., Balasubramanian, B., Riggs, A. J. E., Seo, B.-J., Cady, E., Tang, H., Prada, C., Ruane, G., Shi, F., Noecker, C., and Crowther, B., “Roman space telescope CGI: Prism and polarizer characterization modes,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11443(153) (2020).
  * [26] Krist, J., Riggs, A. J., McGuire, J., Tang, H., Amiri, N., Gutt, G., Marchen, L., Marx, D., Nemati, B., Saini, N., Sidick, E., and Zhou, H., “WFIRST coronagraph optical modeling,” in [Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series ], Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10400, 1040004 (Sept. 2017).
  * [27] Krist, J., Effinger, R., Kern, B., Mandic, M., McGuire, J., Moody, D., Morrissey, P., Poberezhskiy, I., Riggs, A. J., Saini, N., Sidick, E., Tang, H., and Trauger, J., “WFIRST coronagraph flight performance modeling,” in [Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave ], Lystrup, M., MacEwen, H. A., Fazio, G. G., Batalha, N., Siegler, N., and Tong, E. C., eds., Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series 10698, 106982K (July 2018).
  * [28] Douglas, E., Ashcraft, J. A., Belikov, R., Debes, J., Kasdin, N. J., Kirst, J., Lacy, B. I., Milani, K., Nemati, B., Pogorelyuk, L., Riggs, A. J. E., Savransky, D., and Sirbu, D., “A review of simulation and performance modeling for the WFIRST coronagraph instrument,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11443(148) (2020).
  * [29] Lacy, B. and Burrows, A., “Prospects for Directly Imaging Young Giant Planets at Optical Wavelengths,” ApJ 892, 151 (Apr. 2020).
  * [30] Wenger, M., Ochsenbein, F., Egret, D., Dubois, P., Bonnarel, F., Borde, S., Genova, F., Jasniewicz, G., Laloë, S., Lesteven, S., and Monier, R., “The SIMBAD astronomical database. The CDS reference database for astronomical objects,” Astronomy & Astrophysics Supplement 143, 9–22 (Apr. 2000).
  * [31] Batalha, N. E., Smith, A. J. R. W., Lewis, N. K., Marley, M. S., Fortney, J. J., and Macintosh, B., “Color Classification of Extrasolar Giant Planets: Prospects and Cautions,” Astrophysical Journal 156, 158 (Oct. 2018).
  * [32] Turnbull, M. C., “ExoCat-1: The Nearby Stellar Systems Catalog for Exoplanet Imaging Missions,” arXiv e-prints , arXiv:1510.01731 (Oct. 2015).
  * [33] Girard, J. H., Bogat, E., Gonzalez-Quiles, J., Hildebrandt, S. R., Kane, S. R., Li, Z., Turnbull, M. C., Stark, C., Mandell, A., Meshkat, T., and Zimmerman, N. T., “The Roman Exoplanet Imaging Data Challenge: A Major Community Engagement Effort,” in [Proceedings of the SPIE Astronomical Telescopes and Instrumentation ], 11443(146) (2020).