# Development of a Novel Deployable Solar Panel and Mechanism for 6U CubeSat of STEP Cube Lab-II
## 2 The STEP Cube Lab-II CubeSat's Overview
### Design of Solar Panel Module with the Accommodation of Solar Cell  
A deployable solar panel based on a PCB substrate using multilayered thin stiffeners attached using double-sided viscoelastic tapes is proposed for STEP Cube Lab-II CubeSat as a novel design approach to ensure structural protection of solar cells by suppressing the transmitted vibration loads on a panel in a launch environment. The holding and releasing action of the solar panel is accomplished using an optimized version of the pogo pin-based burn wire cutting release mechanism. The solar panel deployment is set to occur within 1 h of the orbital injection of STEP Cube Lab-II from the P-POD. The passive torsional force of the torsional hinges deploys and latches the panel at its projected position. Twenty AZUR space 30% efficiency triple-junction GaAs solar cells (3G30C) [9] can be mounted on the front surface of the proposed solar panel because this design strategy does not reduce the available area for solar cell accommodation. Thus, the power generation of the proposed solar panel is maximized compared to the same solar panel area by employing the aforementioned design strategies to ensure the structural safety of solar cells.  
The energy balance analysis (EBA) of the CubeSat is performed to verify whether the power generation from the proposed solar cell composition is well adjusted with power consumption by the subsystems and payloads in mission scenarios, power storage for system operation in eclipse, and battery health over the mission life [21]. Table 2 shows the results of the EBA in the multi-band still imaging and IR video operation modes of earth observation. The earth observation period of the multi-band still imaging and IR video operation mode of the CubeSat is the most power-consuming phase relative to the other operating modes that were determined by the power on/off status of the hardware in operational modes. The total power consumption by the CubeSat subsystems and payloads in multi-band still imaging and IR video operation mode with a contingency margin of 10 percent is 18.38 W, which was calculated using the operating voltage and current information provided in each component's datasheet. CubeSat's power analysis was performed using the FreeFlyer software in accordance with the orbital information mentioned in Table 1. The AZUR space 30% efficiency triple-junction GaAs solar cell (3G30C) was considered in the analysis. The analysis result shows that the average power  
Figure 2: STEP Cube Lab-II’s mechanical configurations: (**a**) solar panel stowed and (**b**) solar panel deployed.  
generation in an orbit in the worst-case scenario would be 33.29 W. The EBA result indicates that the power margin of the satellite in an orbit is 2.25 Wh, which is 5.63% of the generated power in a daylight period. Furthermore, the maximum depth of discharge (DoD) of the battery in an orbit with a battery pack capacity of 77 Wh is 13.41%, which is within the maximum 20% system requirement. The results show that the CubeSat will have a sufficient power margin and good battery health over the mission life period in the proposed composition of solar cells with the satellite's sun-pointing attitude. The system requirement of battery DoD% less than 20 cannot be guaranteed with only body-mounted solar cells, which justifies the choice of deployable solar panels for STEP Cube Lab-II to accomplish mission objectives over the 1-year mission operation lifetime.  
Table 3 summarizes the detailed mass budget of the solar panel module proposed in this study. The total mass of the proposed solar panel module is 306.5 g, which is comparatively lighter than that of the commercially available deployable solar panel for 6U CubeSat and those developed in an academic environment. For instance, the mass of the proposed solar panel module is lower by a factor of 2.04, compared to the 6U CubeSat's solar panel module stiffened by applying additional high-pressure laminated G10 material [8].