During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu’s immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission’s safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu’s surface to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6 degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with evolutionary implications.

/pdf/the-operational-environment-and-rotational-acceleration-of-25pb0r9b60.pdf

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for an 8- to 16-m ultraviolet optical near Infrared space observatory for launch in the 2025 to 2030 era. ATLAST will allow astronomers to answer fundamental questions at the forefront of modern astrophysics, including: Is there life elsewhere in the Galaxy? We present a range of science drivers and the resulting performance requirements for ATLAST (8- to 16-marcsec angular resolution, diffraction limited imaging at 0.5 micron wavelength, minimum collecting area of 45 sq m, high sensitivity to light wavelengths from 0.1 to 2.4 micron, high stability in wavefront sensing and control). We also discuss the priorities for technology development needed to enable the construction of ATLAST for a cost that is comparable to that of current generation observatory-class space missions.

Advanced Technology Large-Aperture Space Telescope: science drivers and technology developments

Roughness measurement of metals using a modified binary speckle image and adaptive optics

We report on the development of high actuator count, 
micro-electromechanical (MEMS) deformable mirrors designed
for high order wavefront correction in ground and space-based astronomical adaptive optics instruments. The design of
these polysilicon, surface-micromachined MEMS deformable mirrors builds on technology that has been used
extensively to correct for ocular aberrations in retinal imaging systems and for compensation of atmospheric turbulence
in free-space laser communication. These light-weight, low power deformable mirrors have an active aperture of up to
25.2mm consisting of a thin silicon membrane mirror supported by an array of 140 to 4092 electrostatic actuators which
exhibit no hysteresis and have sub-nanometer repeatability making them well suited for open-loop control applications
such as Multi-Object Adaptive Optics (MOAO). The continuous membrane deformable mirrors, coated with a highly
reflective metal film, are capable of up to 6μm of stroke, have a surface finish of <10nm RMS with a fill factor of 99.8%.
Presented in this paper are device characteristics and performance test results, as well as reliability test data and device
lifetime predictions that show that trillions of actuator cycles can be achieved without failures.

/pdf/mems-deformable-mirrors-for-astronomical-adaptive-optics-mhclw9chjm.pdf

MEMS deformable mirrors for astronomical adaptive optics

RAVEN will be a Multi-Object Adaptive Optics (MOAO) technology and science demonstrator on the Subaru telescope. The baseline design calls for three natural guide star (NGS) wavefront sensors (WFS) and two science pickoff arms that will patrol a ∼2' diameter field of regard (FOR). Sky coverage is an important consideration, because RAVEN is both a technical and science demonstrator. Early-stage simulation of RAVEN's performance is critical in establishing that the key science requirement can be met. That is, 30% of the energy of an unresolved point- spread function (PSF) be ensquared within a 140 mas slit using existing WFS camera and deformable mirror (DM) technology. The system was simulated with two independent modeling tools, MAOS and OOMAO, which were in excellent agreement. It was established that RAVEN will be an order 10 × 10 adaptive optics (AO) system by examining the tradeoffs between performance, sky coverage, and WFS field of view. The 30% ensquared-energy (EE) requirement will be met with three NGSs and will exceed 40% if the Subaru Laser Guide Star (LGS) is used on- axis (assuming median image quality). This is also true for NGSs as faint as mR ¼ 14:5.

https://iopscience.iop.org/article/10.1086/665924/pdf

Performance Modeling for the RAVEN Multi-Object Adaptive Optics Demonstrator

We present first results from the Multi-Conjugate and Multi-Object Adaptive Optics (MCAO and MOAO) testbed, at the UCO/Lick Laboratory for Adaptive Optics (LAO) facility at U.C. Santa Cruz. This testbed is constructed to simulate a 30-m telescope executing MCAO and/or open loop MOAO atmospheric compensation and imaging over 5 arcminutes. It is capable of performing Shack-Hartmann wavefront sensing on up to 8 natural or laser guide stars and 2-3 additional tip/tilt stars. In this paper, we demonstrate improved on-axis correction relative to ground layer adaptive optics (~ 15% Strehl relative to ~ 12%) with a simulated 28-m aperture at a D/r 0 corresponding to a science wavelength of 2.6 microns using three laser guide stars on a simulated 41 arcsec radius with a central science object and one deformable mirror at the ground layer.

First results from the UCSC Laboratory for Adaptive Optics multi-conjugate and multi-object adaptive optics testbed

Pyramid wavefront sensors offer an alternative to traditional Hartmann sensing for wavefront measurement in astronomical 
adaptive optics systems. The Pyramid sensor has been described as a slope sensor with potential sensitivity 
gains over the Shack Hartmann sensor, but in actuality seems to exhibit traits of both a slope sensor and a direct phase 
sensor. The original configuration, utilizing glass pyramids and modulation techniques, is difficult to implement. We 
present results of laboratory experiments using a Pyramid sensor that utilizes a micro-optic lenslet array in place of a 
glass pyramid, and does not require modulation. A group of four lenslets forms both the pyramid knife-edge and the 
pupil reimaging functions. The lenslet array is fabricated using a technique that pays careful attention to the quality of 
the edges and corners of the lenslets. The devices we have tested show less than 1 micron edge and corner imperfections, 
making them some of the sharpest edges available. We finish by comparing our results to theoretical wave optic 
predictions which clearly show the dual nature of the sensor.

Pyramid wavefront sensing: theory and component technology development at LAO

We investigate the non-modulating pyramid wave-front sensor's (P-WFS) implementation in the context of Lick
Observatory's Villages visible light AO system on the Nickel 1-meter telescope. A complete adaptive optics correction,
using a non-modulated P-WFS in slope sensing mode as a boot-strap to a regime in which the P-WFS can act as a direct
phase sensor is explored. An iterative approach to reconstructing the wave-front phase, given the pyramid wave-front
sensor's non-linear signal, is developed. Using Monte Carlo simulations, the iterative reconstruction method's photon
noise propagation behavior is compared to both the pyramid sensor used in slope-sensing mode, and the traditional
Shack Hartmann sensor's theoretical performance limits. We determine that bootstrapping using the P-WFS as a slope
sensor does not offer enough correction to bring the phase residuals into a regime in which the iterative algorithm can
provide much improvement in phase measurement. It is found that both the iterative phase reconstructor and the slope
reconstruction methods offer an advantage in noise propagation over Shack Hartmann sensors.

Implementation of the pyramid wavefront sensor as a direct phase detector for large amplitude aberrations

Status of The Catalina Sky Survey for Near Earth Asteroids

Status of The Catalina Sky Survey

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