The Visible Emission Line Coronagraph (VELC), the primary payload of Aditya L1, which is the inaugural Indian space mission aimed at studying the Sun, is scheduled for launch on Saturday. Once it reaches its designated orbit, VELC will transmit a total of 1,440 images per day to the ground station for analysis. VELC, considered the largest and most technically demanding payload on Aditya-L1, underwent integration, testing, and calibration at the Indian Institute of Astrophysics’s (IIA) CREST (Centre for Research and Education in Science Technology) campus in Hoskote, in close collaboration with ISRO.
The launch of Aditya-L1 is scheduled for September 2 at 11:50 AM, utilizing the PSLV-C57 rocket. This mission carries seven payloads designed for solar study, with four focused on observing solar light and the remaining three measuring in-situ parameters of plasma and magnetic fields. Aditya-L1 will be positioned in a halo orbit around Lagrangian Point 1 (L1), which is 1.5 million kilometers from Earth, positioned in the direction of the Sun. This orbit allows it to continuously observe the Sun from a fixed relative position.
Dr. Muthu Priyal, the Project Scientist for Aditya L1 and the Operation Manager for VELC, explained that the imaging channel will provide one image per minute, resulting in approximately 1,440 images over a 24-hour period, which will be received at the ground station. IIA will host the VELC Payload Operations Centre (POC), responsible for receiving raw data from ISRO’s Indian Space Science Data Centre (ISSDC), processing it for scientific analysis, and returning it to ISSDC for dissemination.
Dr. Priyal also mentioned a unique software developed by IIA, designed to automatically detect coronal mass ejections and their timing, with this information made available to the scientific community within 24 hours. This data will include details on whether the ejection is directed towards Earth, its energy level, and the potential impact.
The VELC payload, weighing 190 kg, is expected to transmit images for the nominal five-year life of the satellite, but its operational duration may extend depending on fuel consumption and other factors. Out of the four channels, the continuum channel will independently send 1,440 images daily, while the other three spectroscopy channels will provide images based on observer preferences. The first images are expected to be accessible by the end of February.
Prof. Jagdev Singh explained that testing will begin after the satellite reaches orbit in mid-January, with instrument-by-instrument evaluation. The VELC’s shutter will be opened last to avoid potential contamination from other payloads.
VELC, being an internally occulted coronagraph, contains 40 optical elements such as mirrors and gratings meticulously aligned. It can capture images of the solar corona closer to the Sun’s disc than any other solar space observatory, thanks to its highly polished primary mirror by LEOS (Laboratory for Electro Optics Systems) of ISRO, which minimizes light scatter. This instrument can rapidly capture images of the corona with high spatial resolution in both white light and spectral lines.
The primary objectives of the Aditya-L1 mission are to gain insights into the origin, dynamics, and propagation of Coronal Mass Ejections and address the Coronal Heating Problem. IIA’s solar astronomy community is ready to calibrate and utilize data from VELC and other Aditya-L1 payloads in the coming months to address fundamental questions about solar astrophysics and its impact on daily life.
