10/12/2022
By Lynne Schaufenbil
Abstract:
Quasi-static wavefront error drifts due to thermal and mechanical variations are a common issue for both stratospheric and space telescopes. Balloon-borne telescopes offer a unique compromise between ground and space telescopes in which atmospheric losses and costs are significantly reduced. They fly at altitudes ranging from 30 to 45 km in the stratosphere which provides a space-like environment but maintains gravity loading, as seen by ground-based instruments. The Super-pressure Balloon-borne Imaging Telescope (SuperBIT) is a 0.5m optical to near-UV telescope which aims to map dark matter in galaxy clusters using weak lensing. SuperBIT has performed four overnight test flights and will be completing a 30-day science flight out of Wanaka, NZ in 2023. Both SuperBIT and its successor, GigaBIT (1.3m optical-NUV telescope) will eventually be available to the community as balloon-based observatories. Since these instruments perform weak lensing measurements, they are very sensitive to varying aberrations both across the field of view and over time at the nanometer level. On the other hand, space-based coronagraphic instruments have a very small field of view but are sensitive to time-varying aberrations at the picometer level when imaging Earth-like exoplanets. Due to the limited number of photons, directly imaging planets requires long integration times. The wavefront must be stable on the same time scale, which is often difficult in space due to time-varying wavefront errors from thermal gradients and other mechanical instabilities. A photon-efficient dark zone maintenance (DZM) algorithm has been developed that corrects for quasi-static wavefront error drifts and allows simultaneous estimation and control while using only science images. This algorithm has been tested on the High-contrast imager for Complex Aperture Telescopes (HiCAT) at the Space Telescope Science Institute (STScI) as well as the In Air Coronagraph Testbed (IACT) at JPL. Each deformable mirror (DM) actuator performs random walk drift, and this drift is corrected for using DZM. Laboratory results show DZM can maintain contrasts of 2.5e-8 using either a monochromatic source or broadband source (10% band centered at 635nm with 3 sub-bands).
Introduction:
Susan is a fifth-year graduate student in the William Jones Laboratory and the High Contrast Imaging Laboratory at Princeton University. She completed a BEng in mechanical engineering at the Memorial University of Newfoundland and a MSc in aerospace engineering at the University of Toronto. As part of the William Jones Laboratory, Susan works on the optical and thermal systems for the Super-pressure Balloon-borne Imaging Telescope which studies galaxy-galaxy weak-lensing. Susan also works on developing and implementing novel focal plane wavefront estimation and control algorithms for exoplanet direct imaging adaptive optics systems as part of the High Contrast Imaging Laboratory. Susan is a frequent collaborator with the Russell B. Makidon Optics Laboratory at the Space Telescope Science Institute where she works on the High-contrast imager for Complex Aperture Telescopes testbed.
If you are interested in attending, please contact Lynne_Schaufenbil@uml.edu.