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Direct detection, also known as direct imaging, is a method for discovering and characterizing the atmospheres of planets at intermediate and wide separations. It is the only means of obtaining spectra of non-transiting exoplanets. Characterizing the atmospheres of planets in the <5 AU regime, where RV surveys have revealed an abundance of other worlds, requires a 30-m-class aperture in combination with an advanced adaptive optics system, coronagraph, and suite of spectrometers and imagers - this concept underlies planned instruments for both TMT (the Planetary Systems Imager, or PSI) and the GMT (GMagAO-X). These instruments could provide astrometry, photometry, and spectroscopy of an unprecedented sample of rocky planets, ice giants, and gas giants. For the first time habitable zone exoplanets will become accessible to direct imaging, and these instruments have the potential to detect and characterize the innermost regions of nearby M-dwarf planetary systems in reflected light. High-resolution spectroscopy will not only illuminate the physics and chemistry of exo-atmospheres, but may also probe rocky, temperate worlds for signs of life in the form of atmospheric biomarkers (combinations of water, oxygen and other molecular species). By completing the census of non-transiting worlds at a range of separations from their host stars, these instruments will provide the final pieces to the puzzle of planetary demographics. This whitepaper explores the science goals of direct imaging on 30-m telescopes and the technology development needed to achieve them., Comment: (March 2018) Submitted to the Exoplanet Science Strategy committee of the NAS

An analytic approximation for the critical clearing time (CCT) metric is derived from direct methods for power system stability. The formula has been designed to incorporate as many features of transient stability analysis as possible such as different fault locations and different post-fault network states. The purpose of this metric is to analyse trends in stability (in terms of CCT) of power systems under the variation of a system parameter. We demonstrate the performance of this metric to measure stability trends on an aggregated power network, the so-called two machine infinite bus network, by varying load parameters in the full bus admittance matrix using numerical continuation. Our metric is compared to two other expressions for the CCT which incorporate additional non-linearities present in the model., Comment: 11 pages

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The development of compact, high performance Deformable Mirrors (DMs) is one of the most important techno-logical challenges for high-contrast imaging on space missions. Microscale Inc. has fabricated and characterized piezoelectric stack actuator deformable mirrors (PZT-DMs) and Application-Speci c Integrated Circuit (ASIC) drivers for direct integration. The DM-ASIC system is designed to eliminate almost all cables, enabling a very compact optical system with low mass and low power consumption. We report on the optical tests used to evaluate the performance of the DM and ASIC units. We also compare the results to the requirements for space-based high-contrast imaging of exoplanets. .

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The Laser Communication Relay Demonstration is NASA’s multi-year demonstration of laser communication to a geosynchronous satellite. We are currently assembling the optical system for the first of the two baseline ground stations. The optical system consists of an adaptive optics system, the transmit system and a camera for target acquisition. The adaptive optics system is responsible for compensating the downlink beam for atmospheric turbulence and coupling it into the modem’s single mode fiber. The adaptive optics system is a woofer/tweeter design, with one deformable mirror correcting for low spatial frequencies with large amplitude and a second deformable mirror correcting for high spatial frequencies with small amplitude. The system uses a Shack-Hartmann wavefront sensor. The transmit system relays four beacon beams and one communication laser to the telescope for propagation to the space terminal. Both the uplink and downlink beams are centered at 1.55 microns. We present an overview of the design of the system as well as performance predictions including time series of coupling efficiency and expected uplink beam quality.

NASA's LCRD mission will lay the foundation for future laser communication systems. We show the design of the Table Mountain ground station's AO system and time series of predicted coupling efficiency.

The Laser Communication Relay Demonstration will feature a geostationary satellite communicating via optical links to multiple ground stations. The first ground station (GS-1) is the 1m OCTL telescope at Table Mountain in California. The optical link will utilize pulse position modulation (PPM) and differential phase shift keying (DPSK) protocols. The DPSK link necessitates that adaptive optics (AO) be used to relay the incoming beam into the single mode fiber that is the input of the modem. The GS-1 AO system will have two MEMS Deformable mirrors to achieve the needed actuator density and stroke limit. The AO system will sense the aberrations with a Shack-Hartmann wavefront sensor using the light from the communication link's 1.55 microns laser to close the loop. The system will operate day and night. The system's software will be based on heritage software from the Palm 3000 AO system, reducing risk and cost. The AO system is being designed to work at r(sub 0) greater than 3.3 cm (measured at 500 nm and zenith) and at elevations greater than 20deg above the horizon. In our worst case operating conditions we expect to achieve Strehl ratios of over 70% (at 1.55 microns), which should couple 57% of the light into the single mode DPSK fiber. This paper describes the conceptual design of the AO system, predicted performance and discusses some of the trades that were conducted during the design process.

The next generation of large ground based telescopes use segmented mirrors. Sensors mounted on the edge of the segments measure the relative heights of the segments. The segments are actively controlled in height by three actuators per segment, but lateral motion is only passively constrained. Thus there will be some small change in the gap and shear between segments as changing telescope orientation and temperature make small distortions in the telescope structure. These "in-plane" motions place an additional performance burden on the edge sensors, and on the precision with which they must be mounted relative to the optical surface. In addition, both the scaling and offset of sensor edge height readings also vary with changes in gap.

Zodiac II is a proposed balloon-borne science investigation of debris disks around nearby stars. Debris disks are analogs of the Asteroid Belt (mainly rocky) and Kuiper Belt (mainly icy) in our Solar System. Zodiac II will measure the size, shape, brightness, and color of a statistically significant sample of disks. These measurements will enable us to probe these fundamental questions: what do debris disks tell us about the evolution of planetary systems; how are debris disks produced; how are debris disks shaped by planets; what materials are debris disks made of; how much dust do debris disks make as they grind down; and how long do debris disks live? In addition, Zodiac II will observe hot, young exoplanets as targets of opportunity. The Zodiac II instrument is a 1.1-m diameter SiC (Silicone carbide) telescope and an imaging coronagraph on a gondola carried by a stratospheric balloon. Its data product is a set of images of each targeted debris disk in four broad visible-wavelength bands. Zodiac II will address its science questions by taking high-resolution, multi-wavelength images of the debris disks around tens of nearby stars. Mid-latitude flights are considered: overnight test flights in the US followed by half-global flights in the Southern Hemisphere. These longer flights are required to fully explore the set of known debris disks accessible only to Zodiac II. On these targets, it will be 100 times more sensitive than the Hubble Space Telescope's Advanced Camera for Surveys (HST/ACS); no existing telescope can match the Zodiac II contrast and resolution performance. A second objective of Zodiac II is to use the near-space environment to raise the Technology Readiness Level (TRL) of SiC mirrors, internal coronagraphs, deformable mirrors, and wavefront sensing and control, all potentially needed for a future space-based telescope for high-contrast exoplanet imaging.

The Thirty Meter Telescope primary mirror is composed of 492 segments that are controlled to high precision in the presence of wind and vibration disturbances, despite the interaction with structural dynamics. The higher bandwidth and larger number of segments compared with the Keck telescopes requires greater attention to modeling to ensure success. We focus here on the development and validation of a suite of quasi-static and dynamic modeling tools required to support the design process, including robustness verification, performance estimation, and requirements flowdown. Models are used to predict the dynamic response due to wind and vibration disturbances, estimate achievable bandwidth in the presence of control-structure-interaction (CSI) and uncertainty in the interaction matrix, and simulate and analyze control algorithms and strategies, e.g. for control of focus-mode, and sensor calibration. Representative results illustrate TMT performance scaling with parameters, but the emphasis is on the modeling framework itself.

The young open cluster Collinder 419 surrounds the massive O star, HD 193322, that is itself a remarkable multiple star system containing at least four components. Here we present a discussion of the cluster distance based upon new spectral classifications of the brighter members, UBV photometry, and an analysis of astrometric and photometric data from the third U. S. Naval Observatory CCD Astrograph Catalog and Two Micron All Sky Survey Catalog. We determine an average cluster reddening of E(B - V) = 0.37 +/-.05 mag and a cluster distance of 741 plus or minus 36 pc. The cluster probably contains some very young stars that may include a reddened M3 III star, IRAS 20161+4035.