Very precise on-ground characterization and calibration of TESS CCD detectors will significantly assist in the analysis of the science data from the mission. An accurate optical test bench with very high photometric stability has been developed to perform precise measurements of the absolute quantum efficiency. The setup consists of a vacuum dewar with a single MIT Lincoln Lab CCID-80 device mounted on a cold plate with the calibrated reference photodiode mounted next to the CCD. A very stable laser-driven light source is integrated with a closed-loop intensity stabilization unit to control variations of the light source down to a few parts-per-million when averaged over 60 s. Light from the stabilization unit enters a 20 inch integrating sphere. The output light from the sphere produces near-uniform illumination on the cold CCD and on the calibrated reference photodiode inside the dewar. The ratio of the CCD and photodiode signals provides the absolute quantum efficiency measurement. The design, key features, error analysis, and results from the test campaign are presented.
The Transiting Exoplanet Survey Satellite, a NASA Explorer-class mission in development, will discover planets around
nearby stars, most notably Earth-like planets with potential for follow up characterization. The all-sky survey requires a
suite of four wide field-of-view cameras with sensitivity across a broad spectrum. Deep depletion CCDs with a silicon
layer of 100 μm thickness serve as the camera detectors, providing enhanced performance in the red wavelengths for
sensitivity to cooler stars. The performance of the camera is critical for the mission objectives, with both the optical
system and the CCD detectors contributing to the realized image quality. Expectations for image quality are studied
using a combination of optical ray tracing in Zemax and simulations in Matlab to account for the interaction of the
incoming photons with the 100 μm silicon layer. The simulations include a probabilistic model to determine the depth of
travel in the silicon before the photons are converted to photo-electrons, and a Monte Carlo approach to charge diffusion.
The charge diffusion model varies with the remaining depth for the photo-electron to traverse and the strength of the
intermediate electric field. The simulations are compared with laboratory measurements acquired by an engineering unit
camera with the TESS optical design and deep depletion CCDs. In this paper we describe the performance simulations
and the corresponding measurements taken with the engineering unit camera, and discuss where the models agree well in
predicted trends and where there are differences compared to observations.
The Transiting Exoplanet Survey Satellite (TESS) is an Explorer-class mission dedicated to finding planets
around bright, nearby stars so that more detailed follow-up studies can be done. TESS is due to launch in
2017 and careful characterization of the detectors will need to be completed on ground before then to
ensure that the cameras will be within their photometric requirement of 60ppm/hr. TESS will fly MITLincoln
Laboratories CCID-80s as the main scientific detector for its four cameras. They are 100μm deep
depletion devices which have low dark current noise levels and can operate at low light levels at room
temperature. They also each have a frame store region, which reduces smearing during readout and allows
for near continuous integration. This paper describes the hardware and methodology that were developed
for testing and characterizing individual CCID-80s. A dark system with no stimuli was used to measure the
dark current. Fe55 and Cd109 X-ray sources were used to establish gain at low signal levels and its
temperature dependence. An LED system that generates a programmable series of pulses was used in
conjunction with an integrating sphere to measure pixel response non-uniformity (PRNU) and gain at
higher signal levels. The same LED system was used with a pinhole system to evaluate the linearity and
charge conservation capability of the CCID-80s.
During 2014 and 2015, NASA's Neutron star Interior Composition Explorer (NICER) mission proceeded success- fully through Phase C, Design and Development. An X-ray (0.2-12 keV) astrophysics payload destined for the International Space Station, NICER is manifested for launch in early 2017 on the Commercial Resupply Services SpaceX-11 flight. Its scientific objectives are to investigate the internal structure, dynamics, and energetics of neutron stars, the densest objects in the universe. During Phase C, flight components including optics, detectors, the optical bench, pointing actuators, electronics, and others were subjected to environmental testing and integrated to form the flight payload. A custom-built facility was used to co-align and integrate the X-ray "con- centrator" optics and silicon-drift detectors. Ground calibration provided robust performance measures of the optical (at NASA's Goddard Space Flight Center) and detector (at the Massachusetts Institute of Technology) subsystems, while comprehensive functional tests prior to payload-level environmental testing met all instrument performance requirements. We describe here the implementation of NICER's major subsystems, summarize their performance and calibration, and outline the component-level testing that was successfully applied.
An instrument called Neutron Star Interior Composition ExploreR (NICER) will be placed on-board the Inter- national Space Station in 2017. It is designed to detect soft X-ray emission from compact sources and to provide both spectral and high resolution timing information about the incoming ux. The focal plane is populated with 56 customized Silicon Drift Detectors. The paper describes the detector system architecture, the electronics and presents the results of the laboratory testing of both ight and engineering units, as well as some of the calibration results obtained with synchrotron radiation in the laboratory of PTB at BESSY II.
The Transiting Exoplanet Survey Satellite (TESS) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its 2-year mission, TESS will employ four wide-field optical charge-coupled device cameras to monitor at least 200,000 main-sequence dwarf stars with IC≈4−13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from 1 month to 1 year, depending mainly on the star’s ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10 to 100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every 4 months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.
The Transiting Exoplanet Survey Satellite (TESS ) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its two-year mission, TESS will employ four wide-field optical CCD cameras to monitor at least 200,000 main-sequence dwarf stars with IC (approximately less than) 13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from one month to one year, depending mainly on the star's ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10-100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations.
The OSIRIS-REx Mission was selected under the NASA New Frontiers program and is scheduled for launch in
September of 2016 for a rendezvous with, and collection of a sample from the surface of asteroid Bennu in 2019.
101955 Bennu (previously 1999 RQ36) is an Apollo (near-Earth) asteroid originally discovered by the LINEAR project in 1999 which has since been classified as a potentially hazardous near-Earth object. The REgolith X-Ray Imaging Spectrometer (REXIS) was proposed jointly by MIT and Harvard and was subsequently accepted as a student led instrument for the determination of the elemental composition of the asteroid's surface as well as the surface distribution of select elements through solar induced X-ray fluorescence. REXIS consists of a detector plane that contains 4 X-ray CCDs integrated into a wide field coded aperture telescope with a focal length of
20 em for the detection of regions with enhanced abundance in key elements at 50 m scales. Elemental surface distributions of approximately 50-200 m scales can be detected using the instrument as a simple collimator. An overview of the observation strategy of the REXIS instrument and expected performance are presented here.
We have studied timing properties of the Amptek Silcon Drift Detectors (SDD) using pulsed X-ray source
designed at NASA Goddard Space Flight Center. The proposed Neutron Star Interior Composition Explorer
(NICER) mission will use 56 of these detectors as X-ray sensors in an attached payload to the International
Space Station to study time variability of millisecond X-ray pulsars. Using a rastered pinhole we have measured
the delay times for single X-ray photons as a function of the impact position on the detector, as well as signal
rise time as a function of impact position. We find that the interdependence of these parameters allows us to
determine photon position on the detector by measuring the signal rise time, and, improve the accuracy of the
photon arrival time measurement.
Nanosatellites, i.e. spacecraft that weigh between 1 and 10 kg, are drawing increasing interest as platforms
for conducting on-orbit science. This trend is primarily driven by the ability to piggyback nanosatellites on
the launch of large spacecraft and hence achieve orbit at greatly reduced cost. The CubeSat platform is a
standardized nanosatellite configuration, consisting of one, two, or three 10 cm x 10 cm x 10 cm units (1, 2,
or 3 "U"s) arranged in a row. We present a CubeSat-based concept for the discovery of transiting exoplanets
around the nearest and brightest Sun-like stars. The spacecraft prototype - termed ExoplanetSat - is a 3U space
telescope capable of monitoring a single target star from low Earth orbit. Given the volume limitations of
the CubeSat form factor, designing a capable spacecraft requires overcoming significant challenges. This work
presents the initial satellite configuration along with several subsystem-specific solutions to the aforementioned
constraints. An optical design based on a modified commercial off-the-shelf camera lens is given. We also
describe a novel two-stage attitude control architecture that combines 3-axis reaction wheels for coarse pointing
with a piezoelectric translation stage at the focal plane for fine pointing. Modeling and simulation results are
used to demonstrate feasibility by quantifying ExoplanetSat pointing precision, signal-to-noise ratio, guide star
magnitude, and additional design parameters which determine system performance.
ExoplanetSat is a proposed three-unit CubeSat designed to detect down to Earth-sized exoplanets in an orbit
out to the habitable zone of Sun-like stars via the transit method. To achieve the required photometric precision
to make these measurements, the target star must remain within the same fraction of a pixel, which is equivalent
to controlling the pointing of the satellite to the arcsecond level. The satellite will use a two-stage control
system: coarse control will be performed by a set of reaction wheels, desaturated by magnetic torque coils, and
fine control will be performed by a piezoelectric translation stage. Since no satellite of this size has previously
demonstrated this high level of pointing precision, a simulation has been developed to prove the feasibility of
realizing such a system.
The current baseline simulation has demonstrated the ability to hold the target star to within 0.05 pixels
or 1.8 arcseconds (with an 85 mm lens and 15 μm pixels), in the presence of large reaction wheel disturbances
as well as external environmental disturbances. This meets the current requirement of holding the target star
to 0.14 pixels or 5.0 arcseconds. Other high-risk aspects of the design have been analyzed such as the effect of
changing the guide star centroiding error, changing the CMOS sampling frequency, and reaction wheel selection
on the slew performance of the satellite. While these results are promising as an initial feasibility analysis,
further model improvements and hardware-in-the-loop tests are currently underway.