## 4 Mission S-Net
### Fault Tolerant Satellite Bus TUBiX10  
The nanosatellite platform TU Berlin innovative neXt generation bus (TUBiX) 10 aims for a high integration level to obtain the maximum bus performance within the given form factor. The structure of the TUBiX10 is designed to specifically fit the dispenser SNL. The cube shaped structure, with 25 cm edge length, features four guiding rails parallel to the separation direction to avoid tilting during the ejection process (see Figure 8). A mechanical specification has been developed to adapt future TUBiX10-based satellites [23].  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Number of satellites & 4 \\ Orbit height & 580 km SSO \\ Launch date & 2019/02/01 \\ Design lifetime & 1 year \\ Platform & TUBiX10 \\ Mass & 8.8 kg per S/C \\ Volume & 25 \(\times\) 25 cm\({}^{3}\) \\ TM/TC & UHF, TX power: 5 W \\ Power & Battery: Li-ion 5 Ah \\  & Solar cells: GaAs 30\% \\ Attitude determination & \textless{}1 deg with MEMS array of sun sensor, gyro, magnetometer \\ Attitude control & \textless{}5 deg (3-axis) with 3\(\times\) reaction wheels, 3\(\times\) coils \\ Payload & SLINK: Stand transceiver for ISL, UL, and DL \\  & Laser reflector for high precision position measurement \\ Ground station & UHF: Berlin, Backrang (Germany) and Svalbard (Norway) \\  & S band: Berlin \\ \hline \hline \end{tabular}
\end{table}
Table 8: Overview of S-NET mission.  
The middle deck accommodates the battery and backplane, and additionally serves as a mounting interface for the electronics box, payload, reaction wheels, and communication modules. The side panels are also electrically and mechanically connected to the middle deck. Despite the fact that four satellites provide redundancy on a satellite level, the bus is designed to be single-failure tolerant on the subsystem level. Thus, the main subsystems OBC, EPS, PDH, and ADCS are fully redundant. Figure 9 shows an overview of the single-failure tolerant bus architecture.  
The power string, including the batteries, battery control, power switches, and DC/DC converters, is completely redundant. The six solar generators are connected in parallel. Each generator consists of eight solar cells and a diode for the prevention of current back-flow connected in series. Triple junction GaAs solar cells, with an efficiency of more than 30%, are used for energy generation. No sun pointing is required for a positive energy budget in nominal operation. The complete system allows for a peak power consumption of approximately 40 W, with 4.5 W on average. The maximum power generation, in the best case, is approximately 7 W.  
The Communication System (COM) consists of two UHF transceivers, which are operated in a hot redundant configuration and are permanently in RX mode attempting to decode ground commands using omni-directional antennas. The Terminal Node Controller (TNC) connects to the UHF transceiver  
Figure 8: View of the TUBix10 nano satellite bus.  
Figure 9: Redundancy and power distribution of space segment.  
and performs modulation/demodulation and coding/decoding. The main payload SLINK is not redundant and can be powered on for the duration of a satellite pass, either to perform ISL experiments or to transmit the experimental data to ground.