# UVSQ-SAT, a Pathfinder CubeSat Mission for Observing Essential Climate Variables
## 3 Materials and Methods
### The Ground Segment: The UHF/VHF Station  
The UVSQ/LATMOS ground station (Figure 5) was implemented using the hardware components recommended by the INSPIRE program [45].  
The antenna rig consisted of two circularly polarized Yagi antennas and two rotators, which made it possible to change the elevation and azimuth angles. The antennas were frequency centered on the VHF band (for uplink from ground to space) and UHF band (for downlink from space to ground). The antenna rig is located on the roof of the Observatoire de Versailles Saint-Quentin-en-Yvelines (OVSQ) building, which offers a clear full sky for satellite visibility.  
The TS2000 radio was used to transmit RF signals, and a RTL software-defined radio (SDR) was used to receive RF signals. The hardware (i.e., rotators and radio) was controlled through SatPC32 and SDR-Sharp software. Based on the Two Line Elements (TLE), the SatPC32 program allows automatic tracking of the satellite and compensation of the Doppler shift in the radio signal. On the RF transmit line, modulation and AX.25 encapsulation were performed by hardware (i.e., TS2000),  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Requirements** \\ \hline DEVINS signal range & 0 to 2.1 Wm\({}^{-2}\) (200–242 nm band) \\  & Target value: \(\sim\)1.4 Wm\({}^{-2}\) \\ Central wavelength & 220 \(\pm\) 5 nm \\ Full width at half maximum & 20 \(\pm\) 2 nm \\ Rejection & 10\({}^{-4}\) in the 250–3000 nm band \\ DEVINS resolution & 18 bits (\(\sim\)0.03 nA) \\ DEVINS noise detection & \(<\)30 nA \\ DEVINS time response & \(<\)20 ms \\ \hline Acquisition integration time & Better than 10 s \\ \hline \hline \end{tabular}
\end{table}
Table 6: DEVINS photodiodes’ technical requirements.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Requirements** \\ \hline TW signal range & Accelerometer: \(\pm\)2 g \\  & Gyroscope: \(\pm\)250 deg \\  & Compass: \(\pm\)4912 uT \\ TW resolution & 16 bits \\ TW noise detection & Accelerometer: 230 \(\mathrm{\SIUnitSymbolMicro g}/\sqrt{\mathrm{Hz}}\) \\  & Gyroscope: 0.015 deg/s/\(\sqrt{\mathrm{Hz}}\) \\ DEVINS time response & \(<\)20 ms \\ \hline Acquisition integration time & 10 s \\ \hline \hline \end{tabular}
\end{table}
Table 7: TW sensor technical requirements.  
whereas de-modulation and AX.25 de-encapsulation were done by software on the RF receiver line (i.e., RTL-SDR). A custom application was employed to write and read the Consultative Committee for Space Data Systems packet utilization standard (CCSDS PUS) protocol, as well as provide a Graphical User Interface (GUI) to the ground station operator.  
Since the UVSQ-SAT CubeSat will use satellite amateur radio frequency bands (i.e., VHF 145.830 MHz and UHF 437.020 MHz), an international frequency coordination is under preparation for being submitted to the International Amateur Radio Union. This will ensure that frequencies are not used by other satellites during the UVSQ-SAT mission, and it will act as an engagement with the amateur radio community. The preparation of the frequency coordination was done with the help of the local Radio-Club (F6 KRK) and the AMSAT-Francophone (amateur radio satellite national organization). Thanks to this cooperation, UVSQ-SAT will be able to transmit periodical beacon data, which will be recorded over the world by amateur radio stations.