## 2 Materials and Methods  
The wireless communication system developed in this work consists of a small single-chip wireless communication module and control microcomputer; i.e., the control IC. For the former, we used a module that is commercially available as a consumer electronic component: CC1120 (Texas Instruments). Figure 2 and Table 1 show the appearance and specifications of the wireless communication module, respectively. This low-cost and sub-1 GHz wireless communication module can be utilized in the industrial, scientific and medical (ISM), space reseach, and hann radio bands, and is designed for low-power wireless transceiver applications. In addition, because it is an all-in-one software-controlled IC, miniaturization is achieved by condensing the transmission and reception functions onto a single chip; this setup is in contrast to conventional space wireless devices in which the transmitter and receiver occupy two separate substrate sections [8]. In addition, because the transmission output, data rate, modulation method, and other values are software-adjustable, no hardware modification is required, and the system functions can respond flexibly to a given objective. A similar attempt was made in the Greek CubeSat project [14]. Figure 2: Compact single-chip wireless communication module. An Arduino UNO R3 (ARDUINO) microcomputer (Figure 3) was used as the control IC of the small single-chip wireless communication module. Table 2 lists the main specifications. The Arduino UNO R3 is open-source. Moreover, this microcomputer is based on the ATmega328P (Microchip Technology) microcontroller, which has many A/D I/O lines and an A/D converter, rendering it highly versatile. Abundant information on the Arduino integrated development environment is available online [15]. Importantly, as the Arduino UNO R3 can be used as a development environment, an experimental environment can be easily constructed. We fabricated a wireless communication system using the small single-chip wireless communication module and Arduino microcomputer described in the previous section. \begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Specification** \\ \hline Micoprocessor & ATmega328P \\ VCC* & 5 V \\ Input voltage & 7–12 V \\ I/O number & 14 \\ Analog input & 6 \\ Flash memory & 32 kB \\ SRAM & 2 kB \\ EERROM & 1 kB \\ Clock frequency & 16 MHz \\ A/D convertor & 10 bit \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Arduino UNO R3 specifications. Figure 3: Arduino UNO R3. Figure 4 shows a photograph of the fabricated wireless communication system. The Arduino microcomputer was used as the control IC to switch the transmission and reception modes of the wireless communication module and to set parameters, such as the frequency, modulation method, communication speed, and transmission power. We prepared two such communication systems, and verified that the transmission and reception between them was effective. We then conducted various space environment tests using one of these systems as a testbed. The effects of radiation on semiconductor devices can be roughly classified into total ionizing dozing effects and single-event effects (SEEs). In the former, the effects of charged particles accumulate in the semiconductor and change its characteristics over time; in the latter, the charged particle effects temporarily cause a single-event upset (SEU) in the memory or a single-event latch-up (SEL) in the switching device [16]. Because SEEs are a stochastic phenomenon, the SEE occurrence moment during an experiment cannot be predicted. Therefore, we conducted radiation testing under constant monitoring to investigate the effect of the radiation environment on the operation of the wireless communication system, and thus, evaluate its performance. Although constant monitoring is necessary for radiation tests on semiconductors, manual resets and reboots may damage the semiconductor [17; 18]; therefore, we applied an improved automated monitoring method developed in previous studies [19; 20].