Ground calibration of visible emission line coronagraph on board Aditya-L1 mission

Abstract

Visible emission line coronagraph (VELC) is the prime payload on board India’s first space solar observatory Aditya-L1. VELC is a unique payload with simultaneous observational capabilities in imaging, spectroscopy, and spectro polarimetry modes. VELC is capable of achieving high spatial, spectral, and temporal resolution closer to the solar limb 1.05 R ⊙ compared to the existing space and ground-based solar coronagraphs. VELC consists of a total of 44 optical elements in 18 groups, which are custom designed and developed to meet the desired performance requirements. In addition, it consists of four mechanisms out of which two are multioperational with expected life cycle of million operations. Four detectors (three sCMOS and one InGaAs) are used to record the data. The performance of the payload depends on the performance of individual element, subsystems, and the system level performance of all the elements (such as optics, mechanism, and detectors) together. To ensure the desired performance levels are achieved, each element/subsystem should be tested prior to integrating them together. Evaluation of performance of the integrated system is essential to validate the payload capabilities to meet the proposed science goals. This paper summarizes the calibration tests carried out on the integrated system and compares the results obtained with respect to the design requirements to meet the proposed science goals.