Design of The 3U Four monopole antennas are connected to each splitter output to assemble a complete system. Each antenna deploys 90 deg to the longitudinal axes on each side of the satellite. The view of the antenna radiation characteristics can be seen in Figure 6. The antenna array is circular polarized when seen from top (left hand) and bottom (right hand) transitioning to linear polarization (horizontal/ vertical) in the antenna plane. The highest gain (2.03 dBi) is along the long (Z) axis of the CubeSat with lower gains (-1.9 to -0.2 dBi) along the X and Y axes. ATTITUDE DETERMINATION AND CONTROL (ADCS) SUBSYSTEM ADCS Requirements for QB50 Mission The main QB50 system requirement for attitude control is that the long axis of the CubeSat (Z axis) must be aligned with the velocity vector in such a way as to point the experiment package in the direction of motion. The attitude shall be controlled such that there is less than 10 degrees between the long axis of the CubeSat and the velocity vector (3-sigma, 95% confidence), down to 250 km altitude. However there is no mission level requirement for roll angle. Furthermore a specific requirement is set for the ability to recover from tip-off rates of up to 50 deg/s within 3 days after satellite deployment at nominal conditions and a recommendation to be able to recover from tip-off rates of up to 90 deg/s in off-nominal situation. The other important system requirement for QB50 satellites that is related to ADCS design as a major constraint is that of the orbital lifetime. Initially it was required that the CubeSats would be designed to have an in-orbit lifetime of 3 months. Later in the project this requirement was changed to 6 months [5]. ADCS Design Philosophy The initial ADCS design concept for LituanicaSAT-2 was based on 3-axis stabilized momentum bias type attitude control and determination system, consisting of a miniature reac- Figure 5. UHF radio system block diagram. Figure 6. Antenna model with 3D radiation pattern (left) and radiation patterns in xy (center) and xz planes (right). 38 IEEE A&E SYSTEMS MAGAZINE JUNE 2017