# INSPIRE-SAT 7, a Second CubeSat to Measure the Earth's Energy Budget and to Probe the Ionosphere
## 3 Description of the INSPIRE-SAT 7 Mission and Mission Operations
### The Space Segment
#### 3.2.3 The CUIONO1 Payload  
The INSPIRE-SAT 7 mission develops an innovative approach based on one ground-based HF transmitter and one HF receiver onboard a CubeSat to probe the ionosphere. The signal will be transmitted from an HF antenna located in France and received by the INSPIRE-SAT 7 CubeSat (Figure 4). For this first mission, there will be no synchronization between the transmitter and the receiver. Hence, only the addition of three or four pure continuous sinusoidal signals will be transmitted and the amplitude attenuation due to the path through the ionosphere will be measured. Taking into account the evolution of cutoff frequencies with the incidence angle, the transmitted frequency will be set between 8 MHz and 20 MHz. The CUIONO1 payload consists of one antenna (\(98\times 98\times 7\) mm, 100 g, 40 mW and 2000 mW during deployment) and one Software Defined Radio (SDR) electronic board (\(89.3\times 93.3\times 13.6\) mm, 137 g, 1400 mW OAP), which will receive, digitize and process the HF signal. The antenna is below the \(+Z\) face of the CubeSat solar panel (not shown in Figure 1). \begin{table}
\begin{tabular}{l l l l l l l} \hline
**Sensor** & **N** & **Aperture** & \(\lambda\) & **P** & **Range** & **Resolution** & **Noise** \\ \hline TSIS & 4 & \(\mathcal{O}\)1 mm & 0–1100 nm & \(\sim\)0.21 AW\({}^{-1}\) & [0... 250 nA] & \(9.5\times 10^{-4}\) nA/bit & \(<\)0.1 nA rms \\ UVS\({}_{NG}\) & 4 & \(500\times 800\) μm & 215 nm & \(\sim\)0.01 AW\({}^{-1}\) & [0... 250 nA] & \(9.5\times 10^{-4}\) nA/bit & \(<\)0.1 nA rms \\ UVS\({}_{2}\) & 3 & \(\mathcal{O}\)3 mm & 308 nm & \(\sim\)0.14 AW\({}^{-1}\) & [0... 3000 nA] & \(11.4\) pA/bit & \(<\)0.1 nA rms \\ UVS\({}_{3}\) & 3 & \(\mathcal{O}\)3 mm & 340 nm & \(\sim\)0.15 AW\({}^{-1}\) & [0... 3000 nA] & \(11.4\) pA/bit & \(<\)0.1 nA rms \\ \hline \end{tabular}
\end{table} 
Table 4: UVS and TSIS sensors technical requirements with their photoresponsivity (P). Figure 3: Design of the TSIS and standard UVS sensors (UVS\({}_{2}\) and UVS\({}_{3}\)). For HF frequency, a matched broadband antenna should be several meters long. However, we preferred to use an unmatched but flight proven VHF antenna. This antenna has an efficiency of \(-40\) to \(-20\) dB according the received frequency between 8 MHz and 20 MHz. The integration time will be adjusted to compensate the attenuation due to the antenna. As the wave polarization will rotate during the ionosphere crossing, two cross dipole antenna are required. These antennas should be preferably orientated in a plane perpendicular to the line joining the transmitter and the satellite. Small antennas have smooth patterns and do not require an accurate knowledge of the satellite orientation. The SDR electronic board  
The CUIONO1 payload is based on the TOTEM SDR electronic unit developed by the Spanish company Alen Space. The analogic front-end and the ADC has been modified to receive the HF signals. Due to the selection of an unmatched antenna, the noise factor is determined by the low noise factor of the first amplifier (LNA) and not by the background noise that is often the case for HF frequencies. The integration time (\(T_{i}\)) must maximized to improve the signal to noise ratio (SNR). However, to avoid a Doppler frequency migration greater than the Doppler bin, \(T_{i}\) must meet the relation: \(T_{i}<\sqrt{\lambda/\gamma}\) where \(\lambda\) is the wavelength and \(\gamma\) the radial acceleration. \(\gamma\) is maximum when the satellite passes to zenith. For a 500 km altitude satellite \(\gamma<\)160 m\(\cdot\)s\({}^{-2}\), which limit \(T_{i}\) to 306 ms for a 20 MHz signal. We selected \(T_{i}=300\) ms, which led led to a very comfortable SNR (assuming 43 dBm power emission and reasonable parameters for the link budget calculation). Nevertheless, the main issue in receiving the sounder signal could arise from parasite signals. To minimize the amount of transferred data, only the spectrum around the transmitted frequencies will be computed.