Photometric stability and subpixel sensitivity of a back-illuminated CCD

Characterization of scientific-grade CCDs is extremely important if one hopes to attain very precise quantitative results. A number of characterization methods exist that yield accurate and fast properties in order to make simple measurements. As CCDs are pushed to the their operating limit, other, esoteric tests are required. In this situation, such tests become the determining factors for usability of CCDs. The research presented in this dissertation describes two such tests. This work first examines the ultimate signal-to-noise achievable with a back-illuminated CCD. The focus of this research is on the ability of the tested sensor to reach and continuously maintain a very high photometric precision over an extended period of time. This is important for the upcoming Kepler mission, to search for extra-solar Earth-size planets by looking for changes in relative brightness caused by transit of a planet. The results demonstrate that when the effects such as jitter and flat- field are calibrated out, the back-illuminated CCD is essentially a shot- noise- limited relative-photometric detector. Another effect that can provide further understanding of the limits of capabilities of CCDs is how each pixel responds to incident radiation. Therefore, the second half of the thesis is devoted to an experimental measurement of the subpixel spatial variations within the same back-illuminated CCD. The measurements are made using a stable broadband light source and two high-precision translation stages. The experimentally measured pixel response is examined for implications on precise photometric and astrometric measurements in astronomy

JWST Noise Floor II: Systematic Error Sources in JWST NIRCam Time Series

JWST holds great promise in characterizing atmospheres of transiting exoplanets, potentially providing insights into Earth-sized planets within the habitable zones of M dwarf host stars if photon-limited performance can be achieved. Here, we discuss the systematic error sources that are expected to be present in grism time series observations with the NIRCam instrument. We find that pointing jitter and high gain antenna moves on top of the detectors' subpixel crosshatch patterns will produce relatively small variations (less than 6 parts per million, ppm). The time-dependent aperture losses due to thermal instabilities in the optics can also be kept to below 2 ppm. To achieve these low noise sources, it is important to employ a sufficiently large (more than 1.1 arcseconds) extraction aperture. Persistence due to charge trapping will have a minor (less than 3 ppm) effect on time series 20 minutes into an exposure and is expected to play a much smaller role than it does for the HST WFC3 detectors. We expect temperature fluctuations to be less than 3 ppm. In total, our estimated noise floor from known systematic error sources is only 9 ppm per visit. We do however urge caution as unknown systematic error sources could be present in flight and will only be measurable on astrophysical sources like quiescent stars. We find that reciprocity failure may introduce a perennial instrument offset at the 40 ppm level, so corrections may be needed when stitching together a multi-instrument multi-observatory spectrum over wide wavelength ranges.Comment: Published in AJ, 25 page

Characterization of the MIC photon counting detector

A new photon counting detector, MIC, has been developed at UCL and is an enhanced performance version of the highly successful IPCS in use at a number of large ground based optical telescopes throughout the world. This detector is light weight, compact and has a low power consumption making it suitable for Space as well as ground based applications. In particular, a prototype version of the MIC detector, XMM-MIC, has been developed for the Optical Monitor (OM) that is to be included in the ESA 'Horizon 2000' X-Ray Multi-Mirror Mission (XMM). In this thesis details of the detector system are given along with the theory of operation. A description of those components which limit the detector performance in terms of resolution, image quality, dynamic range and detective quantum efficiency is presented. The performance is characterized both under laboratory and telescope conditions and compared against theoretical data. In addition, computer simulations have been used to compare the detector performance with other types of photon counting detector thus defining the scientific applications to which MIC can most usefully be put. Finally, future developments of the MIC detector are discussed in terms of both Space and ground based applications. Within the context of this thesis the author has been responsible for the theoretical modelling of a number of detector characteristics, analysis of data and its comparison with theoretical predictions. Computer models were also developed by the author in order to simulate the dynamic range performance of other types of photon counting detector. In addition the author has contributed towards the software development of the detector system and participated fully in all the observing and laboratory trials

Star Imager For Nanosatellite Applications

This research examines the feasibility of Commercial-off-the-shelf Complementary Metal-Oxide-Semiconductor image sensors for use on nanosatellites as a star imager. An emphasis is placed on method selection and implementation of the star imager algorithm: Centroiding, Identification and Attitude Determination. The star imager algorithm makes use of the Lost-in-Space condition to provide attitude knowledge for each image. Flat Field, Checker Board and Point Spread Function calibration methods were employed to characterize the star imager. Finally, feasibility testing of the star imager is accomplished through simulations and night sky images

Modeling Navigation System Performance of a Satellite-Observing Star Tracker Tightly Integrated with an Inertial Measurement Unit

This dissertation evaluates a navigation system using satellite observations from a star tracker tightly-integrated with an inertial measurement unit (IMU) and a barometric altimeter using an extended Kalman filter. The star tracker measurement accuracy of a satellite is derived. Several system configurations are simulated comparing the performance of the estimate with respect to system parameters of the IMU, and star tracker, as well as comparing performance when providing a remote sensor satellite ephemeris error correction. Experimental observations are used to evaluate the model performance. Additionally, power requirements were calculated for a satellite signal operating in imaging bands, such that a Low Earth Orbiting satellite constellation could be detected during the day. This type of signal would make it possible to operate the star tracker integrated navigation system in GPS-degraded environments with similar duration and comparable accuracy of GPS

Astrometry with the Wide-Field InfraRed Space Telescope

The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of delivering precise astrometry for faint sources over the enormous field of view of its main camera, the Wide-Field Imager (WFI). This unprecedented combination will be transformative for the many scientific questions that require precise positions, distances, and velocities of stars. We describe the expectations for the astrometric precision of the WFIRST WFI in different scenarios, illustrate how a broad range of science cases will see significant advances with such data, and identify aspects of WFIRST's design where small adjustments could greatly improve its power as an astrometric instrument.Comment: version accepted to JATI

Theoretical Limits of Lunar Vision Aided Navigation with Inertial Navigation System

The precision navigation capabilities of the Global Positioning System (GPS) are used extensively within US military operations. However, GPS is highly vulnerable to intentional and unintentional external interference. Therefore, a need exists to develop a non-GPS precision navigation method to operate in GPS degraded environments. This research effort presents the theoretical limits of a precision navigation method based on an inertial navigation system (INS) aided by angle measurements with respect to lunar surface features observed by a fixed camera. To accomplish this task, an extended Kalman filter (EKF) was implemented to estimate INS drift errors and bring in simulated lunar feature angle measurements to correct error estimates. The research scope focused solely on the feasibility of lunar vision aided navigation with INS where only measurement noise effects from a simulated CCD camera and barometer were considered. Various scenarios based on camera specifications, lunar feature quantity, INS grade, and lunar orbital parameters were conducted to observe the INS drift correction by lunar feature angle measurements. The resulting trade spaces presented by the scenarios showed theoretical substantial improvement in the navigation solution with respect to a stand alone INS

An Image Processing Pipeline for Autonomous Deep-Space Optical Navigation

A new era of space exploration and exploitation is fast approaching. A multitude of spacecraft will flow in the future decades under the propulsive momentum of the new space economy. Yet, the flourishing proliferation of deep-space assets will make it unsustainable to pilot them from ground with standard radiometric tracking. The adoption of autonomous navigation alternatives is crucial to overcoming these limitations. Among these, optical navigation is an affordable and fully ground-independent approach. Probes can triangulate their position by observing visible beacons, e.g., planets or asteroids, by acquiring their line-of-sight in deep space. To do so, developing efficient and robust image processing algorithms providing information to navigation filters is a necessary action. This paper proposes an innovative pipeline for unresolved beacon recognition and line-of-sight extraction from images for autonomous interplanetary navigation. The developed algorithm exploits the k-vector method for the non-stellar object identification and statistical likelihood to detect whether any beacon projection is visible in the image. Statistical results show that the accuracy in detecting the planet position projection is independent of the spacecraft position uncertainty. Whereas, the planet detection success rate is higher than 95% when the spacecraft position is known with a 3sigma accuracy up to 10^5 km.Comment: 26 pages, 7 figure

Design of a Programmable Star Tracker-Based Reference System For a Simulated Spacecraft

The main objective of this research effort is to achieve an accuracy level for the SimSat star tracker system comparable to what is reported in current literature by various star tracker manufacturers and researchers. Previous work has provided a spherical star dome that needs to be fully populated with light sources. Programmable organic light emitting diode (OLED) panels were chosen to populate the dome to allow high contrast ratios without backlighting and increase the number of star combinations able to be represented. Noise equivalent angles less than five arcseconds (1 delta ) are achieved about the boresight axis and less than half an arcsecond around the other axes. Absolute accuracy near the center of the star dome is tested to be less than 0.04 degree about each axis. Two different approaches to inertially cataloging the star eld are also investigated, externally referencing each panels coordinates using a coordinate measurement arm and utilizing the camera\u27s known position to catalog the panel\u27s location. The full population of the SimSat star dome and reprogrammable capability of the panels allows many future research endeavors related to star pattern recognition and attitude determination to be undertaken