BILSAT-1: power system sizing and design

BILSAT-1 is a 129 kg enhanced microsatellite developed by SSTL with TUBITAK-BILTEN engineers as part of a technology transfer programme. The main objective of the mission is remote sensing. The multispectral imager of the satellite has a 26-meter ground sampling distance at 686 km altitude giving a swath width of 55 km and the panchromatic imager of the satellite with 12-meter ground sampling distance gives a 25 km swath width. The satellite has off-axis pointing capability, provided by the ADCS systems, which (amongst other benefits) reduces the revisit time for any given point on the Earth. The advanced and capable Attitude Determination and Control System including star cameras, sun sensors and rate gyros provide accurate and precise attitude information allowing a very high degree of attitude knowledge. Tetrahedral mounted four reaction wheels on board will make the satellite extremely agile, allowing fast slew maneuvers about its roll and pitch axes. On board the satellite there are additional Turkish payloads, including a Digital Signal Processing payload (GEZGIN), and a low-resolution multi spectral camera (COBAN), and SSTL developed payloads: Dual Control Moment Gyros. Due to the large number of subsystems and payloads, the SSTL enhanced microsatellite power system platform is extended to house more than 50 electronic switches to control subsystem and payload operations. Because of the power generation limitations, payload operations are scheduled in order to keep the battery depth of discharge (DoD) at the design level of 15% (which is dictated by the 5+10 years of extended design lifetime of the satellite), although analyses show that the DoD could reach 20% for some particular orbits where intensive operations are required. Several analyses have been done to increase the orbit average power generation and some structural modifications have been made based on the SSTL enhanced microsatellite platform, such as canting the solar panels to maintain energy balance.