Robust diffraction-limited near-infrared-to-near-ultraviolet wide-field imaging from stratospheric balloon-borne platforms—Super-pressure Balloon-borne Imaging Telescope performance

Abstract

At a fraction the total cost of an equivalent orbital mission, scientific balloon-borne platforms, operating above 99.7% of the Earth's atmosphere, offer attractive, competitive, and effective observational capabilities -namely space-like resolution, transmission, and backgrounds -that are well suited for modern astronomy and cosmology. SUPERBIT is a diffraction-limited, wide-field, 0.5 m telescope capable of exploiting these observing conditions in order to provide exquisite imaging throughout the near-IR to near-UV. It utilizes a robust active stabilization system that has consistently demonstrated a 1σ sky-fixed pointing stability at 48 milliarcseconds over multiple 1 hour observations at float. This is achieved by actively tracking compound pendulations via a three-axis gimballed platform, which provides sky-fixed telescope stability at < 500 milliarcseconds and corrects for field rotation, while employing high-bandwidth tip/tilt optics to remove residual disturbances across the science imaging focal plane. SUPERBIT's performance during the 2019 commissioning flight benefited from a customized high-fidelity science-capable telescope designed with exceptional thermo-and opto-mechanical stability as well as tightly constrained static and dynamic coupling between high-rate sensors and telescope optics. At the currently demonstrated level of flight performance, SUPERBIT capabilities now surpass the science requirements for a wide variety of experiments in cosmology, astrophysics and stellar dynamics.

Weak Lensing in the Blue: A Counter-intuitive Strategy for Stratospheric Observations

“…In this analysis we consider one set of system optics, with two different configurations of detector throughput and optical transmission. Our optics model matches the SUPERBIT telescope (Romualdez et al 2020): a diffraction-limited 500 mm diameter telescope with 38% of the collecting area obscured by a secondary mirror, and a focal plane Gaussian jitter with σ = 0.05′′. The first configuration of detector throughput (SUPERBIT configuration) comprises the nominal SUPERBIT science detector: the Sony IMX455 CMOS camera, with dark current of 0.002 e s −1 pixel −1 , read noise of 1.5 e pixel −1 , and sensitivity in the 300-900 nm range measured and presented in Gill et al (2022).…”

“…where n is the total number of stacked exposures, t is the duration of a single exposure in seconds,  p is the fraction of the source intensity that lands inside p = 3 × 3 = 9 pixels on the focal plane, N s is the total number of electrons per second from the observed source, N b is the number of electrons per second per pixel from the sky background, N d is the dark current in electrons per pixel, and N r is the read noise in electrons per pixel. We determined {N s , N b , N d , N r } in previous sections, and the duration of each exposure is dictated by SUPERBIT ' s pointing and tracking specifications to be t = 300 s (see Romualdez et al 2020). The number of such exposures, n, will be our independent variable.…”

Modeling and stability of balloon-borne gondolas with coupled pendulum-torsion dynamics

“…For many applications, the pointing requirements become more and more challenging. Current architectures are able to provide telescope stability under the arc-second [3,4], and current developments aim at further improving line of sight precision to the milli-arcsecond by using fast-steering or deformable mirrors [5,6]. Thus, an accurate dynamic modeling of ballon-borne flight chains and the development of specific control algorithms are necessary.…”

Optical Night Sky Brightness Measurements from the Stratosphere

“…The CCD was upgraded to one with improved quantum efficiency, 6576 (Horizonal)×4384 (Vertical) pixels with a 5.5 μm×5.5 μm pixel size, and a 0 206 pixel −1 plate scale. We refer the reader to Romualdez et al (2020) for further details on the SuperBIT 2019 commissioning flight.…”