The LSST Camera science sensor array will incorporate 189 large format Charge Coupled Device (CCD) image sensors.
Each CCD will include over 16 million pixels and will be divided into 16 equally sized segments and each segment will
be read through a separate output amplifier.
The science goals of the project require CCD sensors with state of the art performance in many aspects. The broad
survey wavelength coverage requires fully depleted, 100 micrometer thick, high resistivity, bulk silicon as the imager
substrate. Image quality requirements place strict limits on the image degradation that may be caused by sensor effects:
optical, electronic, and mechanical.
In this paper we discuss the design of the prototype sensors, the hardware and software that has been used to perform
electro-optic testing of the sensors, and a selection of the results of the testing to date. The architectural features that lead
to internal electrostatic fields, the various effects on charge collection and transport that are caused by them, including
charge diffusion and redistribution, effects on delivered PSF, and potential impacts on delivered science data quality are
The Large Synoptic Survey Telescope instrument include four guiding and wavefront sensing subsystems called corner
raft subsystems, in addition to the main science array of 189 4K x 4K CCDs. These four subsystems are placed at the
four corners of the instrumented field of view. Each wavefront/guiding subsystem comprises a pair of 4K x 4K guide
sensors, capable of producing 9 frames/second, and a pair of offset 2K x 4K wavefront curvature sensors from which the
images are read out at the cadence of the main camera system, providing 15 sec integrations. These four
guider/wavefront corner rafts are mechanically and electrically isolated from the science sensor rafts and can be installed
or removed independently from any other focal plane subsystem. We present the implementation of this LSST
subsystem detailing both hardware and software development and status.
The design of the Large Synoptic Survey Telescope (LSST) requires a camera system of unprecedented size and complexity. Achieving the science goals of the LSST project, through design, fabrication, integration, and operation, requires a thorough understanding of the camera performance. Essential to this effort is the camera modeling which defines the effects of a large number of potential mechanical, optical, electronic or sensor variations which can only be captured with sophisticated instrument modeling that incorporates all of the crucial parameters. This paper presents the ongoing development of LSST camera instrument modeling and details the parametric issues and attendant analysis involved with this modeling.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, telescope design feeding a camera system that
includes a set of broad-band filters and three refractive corrector lenses to produce a flat field at the focal plane with a
wide field of view. Optical design of the camera lenses and filters is integrated in with the optical design of telescope
mirrors to optimize performance. We discuss the rationale for the LSST camera optics design, describe the methodology
for fabricating, coating, mounting and testing the lenses and filters, and present the results of detailed analyses
demonstrating that the camera optics will meet their performance goals.
The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nanosatellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. We first give an overview of the STARE program. The details of the optical imaging payload for the STARE pathfinder CubeSats are then described, followed by a description of the track detection algorithm that will be used on the images it acquires. Finally, simulation results that highlight the effectiveness of the mission are presented.
The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information
needed to help satellite operators avoid collisions in space by using a network of nano-satellites to determine
more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program,
two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed
and deployed to demonstrate the main elements of the STARE concept. In this paper, we first give an overview
of the STARE program. We then describe the details of the optical imaging payload for the STARE pathfinder
CubeSats, including the optical design and the sensor characterization. Finally, we discuss the track detection
algorithm that will be used on the images acquired by the payload.
The Large Synoptic Survey Telescope (LSST) is a large aperture, wide-field facility designed to provide deep images of
half the sky every few nights. There is only a single instrument on the telescope, a 9.6 square degree visible-band
camera, which is mounted close to the secondary mirror, and points down toward the tertiary. The requirements of the
LSST camera present substantial technical design challenges. To cover the entire 0.35 to 1 μm visible band, the camera
incorporates an array of 189 over-depleted bulk silicon CCDs with 10 μm pixels. The CCDs are assembled into 3 x 3
"rafts", which are then mounted to a silicon carbide grid to achieve a total focal plane flatness of 15 μm p-v. The CCDs
have 16 amplifiers per chip, enabling the entire 3.2 Gigapixel image to be read out in 2 seconds. Unlike previous
astronomical cameras, a vast majority of the focal plane electronics are housed in the cryostat, which uses a mixed
refrigerant Joule-Thompson system to maintain a -100ºC sensor temperature. The shutter mechanism uses a 3 blade
stack design and a hall-effect sensor to achieve high resolution and uniformity. There are 5 filters stored in a carousel
around the cryostat and the auto changer requires a dual guide system to control its position due to severe space
constraints. This paper presents an overview of the current state of the camera design and development plan.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design,
with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3
lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square
degree field and ultraviolet to near infrared wavelengths.
We describe the image quality error budget analysis methodology which includes effects from optical and
optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature
gradients, gravity, pressure, stress, birefringence, and vibration.
The LSST Telescope has critical requirements on tracking error to meet image quality specifications, and will require
closing a guiding loop, with the telescope servo control, to meet its mission. The guider subsystem consists of eight
guiding sensors located inside the science focal plane at the edge of the 3.5deg field of view. All eight sensors will be
read simultaneously at a high rate, and a centroid average will be fed to the telescope and rotator servo controls, for
tracking error correction. A detailed model was developed to estimate the sensors centroid noise and the resulting
telescope tracking error for a given frame rate and telescope servo control system.
The centroid noise depends on the photo-electron flux, seeing conditions, and guide sensor specifications. The model for
the photo-electron flux takes into consideration the guide star availability at different galactic latitudes, the atmospheric
extinction, the optical losses at different filter bands, the detector quantum efficiency, the integration time and the
number of stars sampled. A 7-layer atmospheric model was also developed to estimate the atmospheric decorrelation
between the different guide sensors due to the 3.5deg field of view, to predict both correlated and decorrelated
atmospheric tip/tilt components, and to determine the trade-offs of the guider servo loop.
The Large Synoptic Survey Telescope (LSST) is a proposed ground based telescope that will perform a comprehensive
astronomical survey by imaging the entire visible sky in a continuous series of short exposures. Four special purpose
rafts, mounted at the corners of the LSST science camera, contain wavefront sensors and guide sensors. Wavefront
measurements are accomplished using curvature sensing, in which the spatial intensity distribution of stars is measured
at equal distances on either side of focus by CCD detectors. The four Corner Rafts also each hold two guide sensors. The
guide sensors monitor the locations of bright stars to provide feedback that controls and maintains the tracking of the
telescope during an exposure. The baseline sensor for the guider is a Hybrid Visible Silicon hybrid-CMOS detector. We
present here a conceptual mechanical and electrical design for the LSST Corner Rafts that meets the requirements
imposed by the camera structure, and the precision of both the wavefront reconstruction and the tracking. We find that a
single design can accommodate two guide sensors and one split-plane wavefront sensor integrated into the four corner
locations in the camera.
We obtained 960,200 22-by-22-pixel windowed images of a pinhole spot using the Teledyne H2RG CMOS detector
with un-cooled SIDECAR readout. We performed an analysis to determine the precision we might expect in the position
error signals to a telescope's guider system. We find that, under non-optimized operating conditions, the error in the
computed centroid is strongly dependent on the total counts in the point image only below a certain threshold,
approximately 50,000 photo-electrons. The LSST guider camera specification currently requires a 0.04 arcsecond error
at 10 Hertz. Given the performance measured here, this specification can be delivered with a single star at 14th to 18th
magnitude, depending on the passband.
The BioAerosol Mass Spectrometry (BAMS) system is a rapidly fieldable, fully autonomous instrument that can perform correlated measurements of multiple orthogonal properties of individual aerosol particles. The BAMS front end uses optical techniques to nondestructively measure a particle's aerodynamic diameter and fluorescence properties. Fluorescence can be excited at 266nm or 355nm and is detected in two broad wavelength bands. Individual particles with appropriate size and fluorescence properties can then be analyzed more thoroughly in a dual-polarity time-of-flight mass spectrometer. Over the course of two deployments to the San Francisco International Airport, more than 6.5 million individual aerosol particles were fully analyzed by the system. Analysis of the resulting data has provided a number of important insights relevant to rapid bioaerosol detection, which are described here.
The Bio-Aerosol Mass Spectrometry (BAMS) system is an instrument used for the real time detection and identification of biological aerosols. Particles are drawn from the atmosphere directly into vacuum and tracked as they scatter light from several continuous wave lasers. After tracking, the fluorescence of individual particles is excited by a pulsed 266nm or 355nm laser. Molecules from those particles with appropriate fluorescence properties are subsequently desorbed and ionized using a pulsed 266nm laser. Resulting ions are analyzed in a dual polarity mass spectrometer. During two field deployments at the San Francisco International Airport, millions of ambient particles were analyzed and a small but significant fraction were found to have fluorescent properties similar to Bacillus spores and vegetative cells. Further separation of non-biological background particles from potential biological particles was accomplished using laser desorption/ionization mass spectrometry. This has been shown to enable some level of species differentiation in specific cases, but the creation and observation of higher mass ions is needed to enable a higher level of specificity across more species. A soft ionization technique, matrix-assisted laser desorption/ionization (MALDI) is being investigated for this purpose. MALDI is particularly well suited for mass analysis of biomolecules since it allows for the generation of molecular ions from large mass compounds that would fragment under normal irradiation. Some of the initial results from a modified BAMS system utilizing this technique are described.