ASHI: The All Sky Heliospheric Imager: August 22 – 26, 2022, NASA Balloon Flight and Image Data Reduction Analysis

Abstract We have conceived, designed, and evaluated components for an All Sky Heliospheric Imager (ASHI), suitable for flight on future space missions both in Earth orbit and in deep space. ASHI was tested in the summer of 2022 on a NASA-sponsored topside balloon flight; in this paper, we highlight the images taken and the current state of the data reduction from this instrument’s successful overnight flight. The data reduction involves the removal of starlight, zodiacal light, and atmospheric glow to enable the measurements of the outward flow of heliospheric structures. A key photometric specification for ASHI is better than 0.05% differential photometry in one-degree sky bins at 90° elongation. The ASHI balloon flight exceeded expectations and reached to a background white light level of small-scale solar wind structure variations beyond ∼ 60° from the Sun considerably lower than this. Used as a simple, light weight (∼ 8 kg) and relatively inexpensive spaceflight instrument, ASHI has the principal objective of providing a minute-by-minute and day-by-day near real time acquisition of precision Thomson-scattering photometric maps of the inner heliosphere over nearly a hemisphere of sky starting a few degrees from the Sun. This has large potential benefits for improving space-weather nowcast and forecast capabilities of small heliospheric structures.