Thesis Defense Presented By Akshata Krishnamurthy: January 6, 2020

Monday January 6, 2020 2:00 pm
Marlar Lounge 37-252

“Instrument Systematics Calibration and Performance Validation for High Precision Photometry Missions

Committee: Prof. Jeff Hoffman (Chair), Prof. Sara Seager (Research Advisor, MIT EAPS),
Dr. George Ricker (MIT Kavli), Dr. Rebecca Masterson

Exoplanet detection using planetary transits requires very high precision photometry. The systematic noise requirement on photometry missions is limited to tens of parts per million over few hour timescales. On-orbit calibration techniques are time consuming, rely on the availability of the space telescope and utilize valuable time that would otherwise be dedicated to science operations. On the other hand, laboratory studies could overcome these challenges, but require simulating on-orbit conditions and very high photometric stability of the light source to obtain precise measurements. While large space telescopes have longer test campaigns that can accommodate extensive camera testing, CubeSat-based missions are often both time and budget-constrained. Hence, performing extensive tests during Verification and Validation may not be feasible for small satellite missions. The thesis research addresses the challenges for both large space telescopes and CubeSat-based missions through the development of a generalized framework to characterize and calibrate systematic noise and develop techniques to improve photometric performance. Two applications namely the Transiting Exoplanet Survey Satellite (TESS) and Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) are presented.

TESS is a NASA Astrophysics Explorer mission that was successfully launched on April 18, 2018, with a primary goal to discover more than a thousand planets that are smaller in size than Neptune, orbiting bright dwarf stars. TESS employs four wide-field optical charge-coupled device (CCD) cameras with a band-pass of 650 nm – 1050 nm to detect temporary drops in brightness of stars due to planetary transits. The present work establishes the noise floor for TESS by evaluating hundreds of very bright stars over multiple sectors of observation. We also develop methods to improve the photometric performance for outliers that do not conform to the noise floor. In addition, laboratory techniques are developed to very precisely characterize key detector properties such as absolute quantum efficiency and charge blooming.

The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) is a 6U CubeSat that was started at MIT, built and operated by the Jet Propulsion Laboratory (JPL). ASTERIA was deployed from the International Space Station into a low-earth orbit in November 2017 and is still operational as of Fall 2019. The primary goal of ASTERIA was to demonstrate two key technologies: arcsecond-level pointing control and highly stable temperature control, both of which are necessary to perform high precision photometric observations and detect transiting exoplanets. ASTERIA successfully demonstrated pointing stability of 0.5 arcsecond root mean square (RMS) and thermal stability of  0.01K, both over 20-minutes. ASTERIA employs the scientific-grade complementary metal-oxide semiconductor (sCMOS) array detectors that are now becoming more widespread for science applications and are under active consideration for future JPL projects. Due to ASTERIA’s mission status as a technology demonstration, characterization of the detectors and validation of the photometric performance was not performed before launch. The present work outlines performance metrics for key science target observations and provides a framework to assess the photometric performance of ASTERIA. We also present in-flight calibration techniques and ground characterization tests of the camera assembly to characterize and remove significant noise sources such as fixed pattern noise and temperature variations, in addition to developing an optimal systematics correction framework to improve photometric performance.

The results from the research will inform error budgeting, and verification and validation test campaigns for upcoming astrophysics missions such as SPARCS, a JPL CubeSat mission to demonstrate UV photometry, and provide guidelines for early phase noise budgeting and detector selection for future exoplanet discovery missions including the ASTERIA constellation, Large UV/Optical/Infrared Surveyor (LUVOIR), and Habitable Exoplanet Imager (HabEx).

Best of luck to Akshata!


Monday, January 6, 2020 @ 2:00pm (Marlar Lounge, 37-252)


Event Contact

Debbie Meinbresse