http://hdl.handle.net/2248/5068 2026-10-29T21:49:20Z http://hdl.handle.net/2248/9069 Reflectivity degradation study of 0.7-m Growth India Telescope (GIT), Hanle Remya, B.S. The reflectivity of the optical components of the 0.7-m GROWTH India Telescope (GIT) at the Indian Astronomical Observatory (IAO), Hanle, was measured using a CT7 reflectometer at seven discrete wavelengths ranging from 365 to 970 nm. The measurements were carried out to assess the present condition of the reflective coatings and establish baseline data for future monitoring. The primary mirror was measured at four accessible positions and showed an average reflectivity of approximately 78%, with a scattering loss of around 18.2%. The reflectivity varied with wavelength, ranging from 72.7% at 464 nm to 82.4% at 624 nm. Measurements of the secondary mirror at two positions yielded an average reflectivity of approximately 90.2%, with a scattering loss of about 2%. The results indicate comparatively higher dust accumulation and lower reflectivity for the primary mirror. The measurements provide baseline data for future assessment of coating degradation and optical performance through periodic monitoring under the environmental conditions of the Hanle site. Restricted Access; Supervised by S.Sriram 2026-10-14T00:00:00Z http://hdl.handle.net/2248/9068 Reflectivity degradation study of 2m Himalayan Chandra Telescope mirror Remya, B.S. The reflectivity degradation study of the optical components of the 2-m Himalayan Chandra Telescope (HCT) at the Indian Astronomical Observatory (IAO), Hanle, was carried out using a CT7 reflectometer. The measurements were performed at seven discrete wavelengths ranging from 365 nm to 970 nm. Reflectivity measurements of the HCT primary mirror were carried out at eight predefined positions, both before and after optical cleaning, to assess the effect of cleaning on the mirror reflectivity. Before cleaning, the primary mirror exhibited an average reflectivity of 74.8%, with scattering loss of 22.01%. Following optical cleaning using distilled water and Labolene solution, the average reflectivity increased to 84.9%, while the scattering loss decreased to 8.9%, corresponding to an improvement in average reflectivity of approximately 13.5%. Reflectivity measurements were also carried out for the secondary and tertiary mirrors, with average reflectivities of approximately 89.1% and 87%, respectively. A 30-mm-diameter bare-aluminium-coated S3 coupon installed on the elevation side member of the HCT was also characterized. Its reflectivity was measured at Bengaluru and Hanle prior to installation to establish baseline data for future coating degradation studies. In addition, visual inspection of the primary mirror revealed numerous pinholes, scratches, stains, and patch-like cosmetic defects across its surface, which were documented as part of the assessment of the mirror coating condition. The measurements presented in this report establish baseline reflectivity data for the HCT optical components and the S3 aluminium-coated coupon. Periodic measurements at six-month intervals, using the same measurement positions and wavelengths, are planned to monitor long term reflectivity degradation under the environmental conditions of the Hanle site. Restricted Access; Supervised by S.Sriram 2026-10-14T00:00:00Z http://hdl.handle.net/2248/9067 Reflectivity degradation study of mirror coupons at NLST site Merak Remya, B.S. The reflectivity degradation study of mirror coatings at the proposed National Large Solar Telescope (NLST) site at Merak, Ladakh, was initiated to assess the performance of different optical coating configurations under the site-specific environmental conditions. The study was carried out using a CT7 reflectometer, which measures specular reflectivity at seven discrete wavelengths ranging from 365 to 970 nm. Four mirror samples, namely M1, H1, S1, and S2, were characterized prior to installation and again at the Merak site to establish baseline reflectivity data. At Merak, the mean reflectivity values of M1 and H1 were measured as 86.5% and 89.1%, respectively, while the bare-aluminium-coated coupons S1 and S2 exhibited mean reflectivities of 89.2% and 88.9%, respectively. The corresponding scattering losses (due to any dust, pinhole effect, or any other contamination that leads to scattering effect) were estimated to be approximately 1.3% for M1, 0.4% for H1, and 0.9% for both S1 and S2. Following these baseline measurements, the mirrors were installed on the dome surface for environmental exposure and long-term monitoring. S1 was placed in an exposed location, whereas S2 was retained in a protected environment to serve as a reference coupon. This arrangement will facilitate the identification of changes specifically associated with environmental exposure. The measurements and installation carried out during this study establish the baseline required for subsequent monitoring of coating performance. Periodic measurements at the same locations and wavelengths will enable the assessment of reflectivity degradation and provide information on the long-term behaviour and suitability of the different mirror coating configurations under the environmental conditions prevailing at Merak. Restricted Access; Supervised by S.Sriram 2026-10-14T00:00:00Z http://hdl.handle.net/2248/8951 Design and implementation of an upgraded electrical control system for the Vainu Bappu Telescope hydraulic platform Dhanalal, K; Ramachandran, A; Kesavan, K; Satheesh Kumar, N; Veerpandiyan, M; Pandiyarajan, B; Naveen Kumar, R; Arjunan, M.S This paper details the design, fabrication, and performance evaluation of a newly implemented hydraulic control system for the 2.3m Vainu Bappu Telescope (VBT) Cassegrain platform. The hydraulic platform is a critical infrastructure component used for instrument integration, maintenance during focal-mode transitions (Prime to Cassegrain), and providing observer access to the Cassegrain focus. The system architecture integrates 20 HP induction motors coupled with high-pressure oil pumps, a centralized reservoir, and solenoid-actuated control valves. Central to the upgrade is a custom engineered control panel featuring robust safety interlock logic to govern the vertical displacement of the platform. Following an expedited four-day fabrication and verification phase in October 2023, the system was commissioned and integrated into the VBT hydraulic pump room. Operational data collected from October 2023 through February 2026 demonstrates high system availability and reliability. The platform has supported critical telescope operations, including mirror re-aluminization and frequent instrument swaps, without functional failure. This longitudinal performance validates the control logic and hardware selection for heavy-duty astronomical support systems. Restricted Access 2026-06-12T00:00:00Z