Design of The 3U Figure 2. LituanicaSAT-2 system block diagram. collecting electrical power (see Figure 3). The following chapters discuss the implementation aspects of each subsystem. ON BOARD CONTROL (OBC) SUBSYSTEM The on board computer is implemented as STMicroelectronics microcontroller with ARM 32-bit Cortex™-M4 core operating on a frequency up to 168 MHz. There are two redundant NOR flash memory chips for payload and housekeeping data storage connected via SPI bus. OBC has different interfaces for communication with other subsystems and on board or external devices: Serial Peripheral Interface (SPI), CAN, Universal Serial Bus (USB), UART and Inter-Integrated Circuit (I2C) bus. 36 The OBC is responsible for system level services such as mission planning, telemetry logging, power management, and payload control. It also provides power and data interfaces to science unit and propulsion payloads. Additionally, OBC performs automatic or manual thermal control management of the propulsion unit propellant tanks to keep the temperature of the monopropellant within an acceptable range. This is done using 5W kapton resistance heaters attached to each tank. ELECTRICAL POWER SUPPLY (EPS) SUBSYSTEM The EPS subsystem consists of 8 solar arrays connected to PCDU "GomSpace P31u". IEEE A&E SYSTEMS MAGAZINE JUNE 2017