Onboard Dynamic Image Exposure Control for the Star-Planet Activity Research CubeSat (SPARCS)

TL;DR

SPARCS is a CubeSat designed to monitor M dwarf star activity in ultraviolet wavelengths, using onboard real-time image processing to dynamically optimize exposure settings during flaring events.

Contribution

This paper introduces a novel onboard autonomous exposure control algorithm for UV detectors, enhancing real-time star activity monitoring in CubeSat missions.

Findings

Algorithm responds robustly to flaring and quiescent states

Simulations confirm effective exposure adjustments

Potential for application in future transient astrophysics observatories

Abstract

The Star-Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under development to monitor the flaring and chromospheric activity of M dwarfs at near-ultraviolet (NUV) and far-ultraviolet (FUV) wavelengths. The spacecraft hosts two UV-optimized delta-doped charge-coupled devices fed by a 9-cm telescope and a dichroic beam splitter. A dedicated science payload processor performs near real-time onboard science image processing to dynamically change detector integration times and gains to reduce the occurrence of pixel saturation during strong M dwarf flaring events and provide adequate flare light curve structure resolution while enabling the detection of low-amplitude rotational modulation. The processor independently controls the NUV and FUV detectors. For each detector, it derives control updates from the most recent completed exposure and applies them to the next exposure. The detection of a flare event in the NUV channel resets the exposure in the FUV channel with new exposure parameters. Implementation testing of the control algorithm using simulated light curves and full-frame images demonstrates a robust response to the quiescent and flaring levels expected for the stars to be monitored by the mission. The SPARCS onboard autonomous exposure control algorithm is adaptable for operation in future point source-targeting space-based and ground-based observatories geared towards the monitoring of extreme transient astrophysics phenomena.