The PICTURE-C balloon mission launched on its second flight from Fort Sumner, NM on September 28, 2022. During this flight, PICTURE-C, which consists of a 60 cm off-axis telescope feeding a vector vortex coronagraph, demonstrated the first high-contrast dark hole from an observatory in a near-space environment. The coronagraph achieved a modest broadband (20%) contrast ratio of 5 x 10-6 , with performance limited by dynamic pointing transients. The low-order wavefront control system achieved optical pointing stabilization of one milliarcseconds RMS for intervals of up to 30 seconds between these transients. This paper will summarize the second flight results and present the development path for PICTURE-D, the next generation direct imaging balloon mission.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE C) is a high-altitude balloon-borne observatory that used a vector vortex coronagraph to image dust and debris disks around nearby stars, as well as develop and test technology necessary for direct imaging of exoplanets from a flight platform. The balloon flight environment presents several challenges: an ambient pressure and temperature of approximately 4 Torr and 220-240 K, combined with significant and varying solar irradiance, lead to time-dependent and anisotropic thermal deformation of the optics and their supporting structure. In order to characterize how these effects limit the ultimate performance of the mission, we present a finite-element model of the flight instrument, implemented in Thermal Desktop, which takes into account the interactions with the environment. We present the comparison of this thermal model with flight data.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission is designed to directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a 60 cm diameter off-axis telescope and a vector vortex coronagraph. During its second flight from Fort Sumner, New Mexico, on September 28, 2022, PICTURE-C successfully used its high and low-order wavefront control systems to perform focal plane wavefront correction for the first time on an observatory in a near-space environment. The coronagraph achieved a modest broadband (20%) contrast of 5 × 10 − 6, with performance limited by dynamic pointing transients. The low-order wavefront control system achieved optical pointing stabilization of 1 milliarcseconds (mas) root mean squared (RMS) over 30 second timescales.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The first flight of PICTURE-C launched from the NASA Columbia Scientific Balloon Facility (CSBF) in Ft. Sumner, NM on September 28, 2019. This flight successfully demonstrated many key technologies for exoplanetary direct imaging missions and all hardware components for the second, sciencefocused flight of PICTURE-C, which had been scheduled for the fall of 2021, but was delayed due to inclement weather until 2022. We present laboratory demonstrations of the flight 2 coronagraph, which uses a high-order 952 actuator MEMS deformable mirror to create a high-contrast dark zone at the 10-7 level. The performance of the low-order and high-order wavefront control systems is demonstrated and compared with model predictions.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment Coronagraph (PICTURE C) is a high-altitude balloon-borne observatory that uses a vector vortex coronagraph to image debris disks and exo-zodiacal dust around nearby stars. The engineering flight of PICTURE-C launched in September of 2019, successfully demonstrated several key technologies needed for the upcoming science flight, currently scheduled for September of 2022. The flight environment presents several challenges in thermal and mechanical effects. Low ambient pressure and temperature, approximately 4 Torr and 240 K respectively, combined with significant and varying solar irradiance, lead to time-dependent and anisotropic thermal deformation of the optics and their supporting structure. A constantly swaying observatory in a 1g environment, and the mechanical strains of a pointing system keeping the instrument on target lead to both a sag and flexing of the support structure. In order to characterize how these effects limit the ultimate performance of the mission, we present a finite-element model of the flight instrument, implemented in COMSOL, which takes into account the interactions with the environment. We present the comparison of this thermal model with the temperature data available from flight 1.
The vector vortex coronagraph (VVC) is a leading choice for future space-based exoplanet direct imaging missions due to its simplicity and high throughput. The construction of the VVC as an azimuthally rotating half-wave plate implies a differential influence on the two orthogonal circular polarization states of incident starlight - particularly on the mapping of deformable mirror (DM) actuators to the final image plane. Traditional electric field conjugation (EFC) coupled with the VVC is capable of digging a high-contrast dark zone in one circular polarization, but the dark zone is not preserved in the orthogonal state. This paper presents an extension to the traditional EFC algorithm to find DM actuator solutions that produce a dark zone simultaneously in both circular polarizations. This dual-polarization EFC can be used in conjunction with low-leakage VVC architectures to perform high-contrast polarimetric measurements using a single coronagraph.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The first flight of PICTURE-C launched from the NASA Columbia Scientific Balloon Facility in Ft. Sumner, NM on September 28, 2019 and ew for a total of 20 hours, with 16 hours at float altitude above 110,000 ft. This flight successfully demonstrated many key technologies for exoplanetary direct imaging missions and all hardware components for the second, science-focused flight of PICTURE-C scheduled for the fall of 2021. These technologies include a vector vortex coronagraph, high and low-order deformable mirrors and a high speed low-order wavefront control system. The experiment also demonstrated a 60 cm off-axis telescope with a hexapod-actuated secondary mirror that aligned itself automatically during flight. This paper details the flight performance of PICTURE-C, focusing on the operation of the low-order wavefront control system and the influence of high-frequency structural vibrations. We present new structural modifications that have been made to reduce these vibrations and laboratory demonstrations of the flight 2 coronagraph, which uses a high-order 952 actuator MEMS deformable mirror to create a high-contrast dark zone.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment-Coronagraph (PICTURE-C) experiment is a balloon-borne observatory for high-contrast imaging of debris disks and exoplanets around nearby stars. This experiment will use a 10,000-pixel Microwave Kinetic Inductance Detector (MKID) instrument as its science camera. The PICTURE-C MKID Camera is an integral field spectrograph (IFS) with a bandpass of λ = 540 − 660 nm that sits behind a modest adaptive optics system and coronagraph which promise to achieve contrast ratios down to 10-7 from 1.7 to 10 λ/D (0.35” to 2.1”). The MKIDs are photon counting detectors promising a resolution R up to 20 for the PICTURE-C mission. The ability to count photons with microsecond time resolution will allow the MKID camera to double as a Focal Plane Wavefront Sensor (FPWFS), helping to discriminate between speckles and circumstellar objects in real time and in post-processing. The intrinsic spectral resolution of the detectors will allow for further characterization of the debris disks and exoplanets around the stars targeted during its flight. The visible light observations taken with this instrument will complement infrared observations taken from the ground and serve to demonstrate MKIDs utility in a space-like environment. For this poster, we will introduce and discuss the PICTURE-C MKID Camera.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) is a direct imaging experiment designed to observe exozodiacal dust and debris disks that orbit nearby stars from a high-altitude balloon platform. The experiment consists of a vector vortex coronagraph and a multi stage adaptive optics system with multiple wavefront sensors and two deformable mirrors. This paper details the hardware and software implementation of one of the DM interfaces used in the PICTURE-C low-order wavefront control system. We discuss the algorithm used to drive a commercial o_-the-shelf DM with an actuation resolution of 14-bits to meet the PICTURE-C requirement of 16-bits. The algorithm utilizes fast temporal dithering in the form of pulse density modulation to reduce the quantization error of the DM actuation. The described DM control mechanism can operate at a framerate of ~500 Hz with an equivalent actuation resolution of 16-bits with minimal computational load on the deployed processor.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. PICTURE-C employs both image-plane wavefront sensing for high-order wave- front control and a reflective Lyot-stop sensor for low-order wavefront control. Since both of these systems lie downstream from the coronagraph's deformable mirror, and since both must run simultaneously, they must be calibrated as to not interfere with each other. The deformable mirror probe patterns required for image-plane sensing appear as wavefront errors to the low-order sensor. This paper presents simulations of low and high-order wavefront sensing for PICTURE-C and calibration techniques for decoupling the two sensors.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The first flight of PICTURE-C was recently rescheduled by NASA for September, 2019. This paper describes preparations for the first flight of PICTURE-C, including the final mission design, flight integration process and observation plan. Laboratory measurements of the low-order wavefront control system and coronagraph performance are also presented.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. One of the many starlight leakage sources that can degrade the performance of the coronagraph is polarization aberration induced by the reflective optical coatings. A polarization ray trace of the PICTURE-C telescope and coronagraph is combined with a physical optics wavefront propagation simulation to quantify the expected amount of coronagraph leakage due to polarization aberration. The simulations show the leakage is below the budgeted contrast of 1 × 10 − 8.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. Four leakage sources owing to the optical fabrication tolerances and optical coatings are: electric field conjugation (EFC) residuals, beam walk on the secondary and tertiary mirrors, optical surface scattering, and polarization aberration. Simulations and analysis of these four leakage sources for the PICTUREC optical design are presented here.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around three nearby stars from a high-altitude balloon using a vector vortex coronagraph. We present experimental results of the PICTURE-C low-order wavefront control (LOWFC) system utilizing a Shack-Hartmann (SH) sensor in an instrument testbed. The SH sensor drives both the alignment of the telescope secondary mirror using a 6-axis Hexapod and a surface parallel array deformable mirror to remove residual low-order aberrations. The sensor design and actuator calibration methods are discussed and the preliminary LOWFC closed-loop performance is shown to stabilize a reference wavefront to an RMS error of 0.30 ± 0.29 nm.
The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The PICTURE-C low-order wavefront control (LOWC) system will be used to correct time-varying low-order aberrations due to pointing jitter, gravity sag, thermal deformation, and the gondola pendulum motion. We present the hardware and software implementation of the low-order ShackHartmann and reflective Lyot stop sensors. Development of the high-speed image acquisition and processing system is discussed with the emphasis on the reduction of hardware and computational latencies through the use of a real-time operating system and optimized data handling. By characterizing all of the LOWC latencies, we describe techniques to achieve a framerate of 200 Hz with a mean latency of ∼378 μs
We describe the capabilities and performance of a terrestrial laser scanning instrument built for the purpose of recording and retrieving the three-dimensional structure of forest vegetation. The dual-wavelength Echidna® lidar characterizes the forest structure at an angular resolution as fine as 1 mrad while distinguishing between leaves and trunks by exploiting their differential reflectances at two wavelengths: 1 and 1.5 μm. The instrument records the full waveforms of return signals from 5 ns laser pulses at half-nanosecond time resolution; obtains ±117 deg zenith and 360 deg azimuth coverage out to a radius of more than 70 m; provides single-target range resolution of 4.8 and 2.3 cm for the 1 and 1.5 μm channels, respectively (1σ); and separates adjacent pulse returns in the same waveform at a distance of 52.0 and 63.8 cm apart for the 1 and 1.5 μm channels, respectively. The angular resolution is in part controlled by user-selectable divergence optics and is shown to be <2 mrad for the instrument’s standard resolution mode, while the signal-to-noise ratio is 10 at 70 m range for targets with leaf-like reflectance for both channels. The portability and target differentiation make the instrument an ideal ground-based lidar suited for vegetation sensing.
We describe a set of numerical approaches to modeling the performance of space flight high-contrast imaging payloads. Mission design for high-contrast imaging requires numerical wavefront error propagation to ensure accurate component specifications. For constructed instruments, wavelength and angle-dependent throughput and contrast models allow detailed simulations of science observations, allowing mission planners to select the most productive science targets. The PICTURE family of missions seek to quantify the optical brightness of scattered light from extrasolar debris disks via several high-contrast imaging techniques: sounding rocket (the Planet Imaging Concept Testbed Using a Rocket Experiment) and balloon flights of a visible nulling coronagraph, as well as a balloon flight of a vector vortex coronagraph (the Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph, PICTURE-C). The rocket mission employs an on-axis 0.5m Gregorian telescope, while the balloon flights will share an unobstructed off-axis 0.6m Gregorian. This work details the flexible approach to polychromatic, end-to-end physical optics simulations used for both the balloon vector vortex coronagraph and rocket visible nulling coronagraph missions. We show the preliminary PICTURE-C telescope and vector vortex coronagraph design will achieve 10-8 contrast without post-processing as limited by realistic optics, but not considering polarization or low-order errors. Simulated science observations of the predicted warm ring around Epsilon Eridani illustrate the performance of both missions.
The PICTURE-C mission will fly a 60 cm off-axis unobscured telescope and two high-contrast coronagraphs in successive high-altitude balloon flights with the goal of directly imaging and spectrally characterizing visible scattered light from exozodiacal dust in the interior 1-10 AU of nearby exoplanetary systems. The first flight in 2017 will use a 10-4 visible nulling coronagraph (previously flown on the PICTURE sounding rocket) and the second flight in 2019 will use a 10-7 vector vortex coronagraph. A low-order wavefront corrector (LOWC) will be used in both flights to remove time-varying aberrations from the coronagraph wavefront. The LOWC actuator is a 76-channel high-stroke deformable mirror packaged on top of a tip-tilt stage. This paper will detail the selection of a complementary high-speed, low-order wavefront sensor (LOWFS) for the mission. The relative performance and feasibility of several LOWFS designs will be compared including the Shack-Hartmann, Lyot LOWFS, and the curvature sensor. To test the different sensors, a model of the time-varying wavefront is constructed using measured pointing data and inertial dynamics models to simulate optical alignment perturbations and surface deformation in the balloon environment.
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