Abstract:
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.
