A document describes solutions to problems of astrometry at the microarc-second (picoradian) level using a simple staring telescope. The problems include field-dependent beam-walk on the telescope’s mirrors, pixel position irregularity and distortion over time, non-flat intra-pixel quantum efficiency, and systematic errors inherent in the most common image centroiding algorithms (imperfect knowledge of the point spread function).
The problems are solved by using an architecture that is free of field-dependent beamwalk, using heterodyne (traveling) metrology fringes to calibrate the focal plane array’s inter-pixel distances and intra-pixel quantum efficiencies at the micro-pixel level, and using a low-error algorithm for determining image positions and displacements.
Precision astrometry is the most promising method of detecting Earth-like planets in the habitable zones of nearby stars. Precision photometry needed for weak-lensing-based investigations of dark energy is also helped by this technology.
This work was done by Michael Shao, Chengxing Zhai, Bijan Nemati, and Renaud Goullioud of Caltech for NASA’s Jet Propulsion Laboratory. NPO-48313
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Picoradian Staring Astrometry Using a Simple Staring Telescope
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Overview
The document presents a Technical Support Package for "Picoradian Staring Astrometry Using a Simple Staring Telescope," developed under NASA's Commercial Technology Program. It outlines advancements in astrometry, particularly focusing on high-precision measurements of celestial objects.
The core of the research involves the SIM Lite (Strometric Observatory) project, which aims to enhance the accuracy of astrometric measurements through innovative techniques. A significant aspect of this work is the exploration of micro-pixel centroid estimation, which is crucial for narrow-angle astrometry. The preliminary studies indicate that if images are sampled at or above the Nyquist rate, the systematic error in centroid displacement estimation can be minimized to a few micro-pixels, even in the presence of wavefront errors as small as λ/20.
The document highlights the use of laser fringes as a stable measurement tool, with a CCD (Charge-Coupled Device) serving as an intermediary for capturing data. The research demonstrates the feasibility of achieving high precision in centroid estimation, with initial lab results showing the capability to measure down to 30 micro-pixels after 200 seconds of exposure.
Additionally, the study reveals unexpected findings, such as a 4% shift in pixel locations for a specific E2V CCD39 model at the midpoint boundary, which could have implications for future astrometric measurements. The results underscore the importance of meticulous calibration and understanding of sensor behavior in high-precision applications.
The document also discusses future work, indicating that further funding is anticipated to complete the demonstration of these techniques. The research is conducted by Bijan Nema3 at the Jet Propulsion Laboratory, California Institute of Technology, and is presented at the SPIE conference in San Diego.
Overall, this Technical Support Package serves as a comprehensive overview of the ongoing efforts to refine astrometric techniques, emphasizing the potential for significant advancements in our ability to measure distances between stars and improve our understanding of the universe. The findings could have broader applications in various fields, including aerospace technology and scientific research.
