The Solar Ultra-Violet Imaging Telescope (SUIT) Onboard Intelligence for Flare Observations

Aditya-L1 is India’s first observatory-class solar space mission to study the Sun from the Lagrange L₁ point. The Solar Ultra-Violet Imaging Telescope (SUIT) is one of the payloads onboard Aditya-L1. SUIT is an off-axis Ritchey–Chrétien (RC) telescope, which images the Sun onto a 4k×4k CCD covering a field-of-view of 1.5 R_⊙ with a plate scale of \(0.7''\) pixel⁻¹. One of the primary objectives of SUIT is to study the early evolution of solar flares with high temporal cadence in the near-UV wavelengths (200 – 400 nm). The SUIT onboard intelligence was developed to achieve this objective. The complete intelligence algorithm is divided into several sub-modules, each working on a specific aspect of intelligence. These are: the HEL1OS flare-trigger module: generates flare trigger using HEL1OS hard X-ray data, the flare-localization module: locates the flare on the SUIT full-disc images, the Region of Interest (RoI) tracking module: accounts for the shift in RoI coordinates caused by rotation of the Sun, auto-exposure control module: adjusts the exposure time depending upon the flare intensity for better contrast. In this article, these onboard-intelligence modules are explained in detail. The working principles of these modules are tested using available data from various existing missions and also using synthetic data, and the obtained results are presented. The modules are implemented in hardware using an Actel RTAX 2000S FPGA and are tested using a laboratory setup. From the testing, it is found that flares are successfully localized in a mean time of 40 seconds from the GOES soft X-ray catalog start time. Also, a temporal cadence of under three seconds for a single-filter flare RoI image is achieved.