Since Venus is closer to the Sun than Earth, there is a higher solar irradiance at Venus [1]. On the planet's surface, the thick atmosphere negates this effect in terms of power, but for a satellite that is orbiting the planet, solar power is the natural choice for a power source. To use solar power, a solar cell oriented for space use had to be chosen to collect power, and a battery must be used to store energy so that the satellite has power during solar eclipses when Venus is between the satellite and the Sun. We chose to use a ZTG Photvolatic Cell - Advanced Triple Cell for Space Applications from Emcore and a Clyde Space Lithium Polymer Battery.

ZTG Photvolatic Cell - Advanced Triple Cell for Space Applications from Emcore features [2]:

• space qualified
• radiation resistant
• 0.92 absorptance for triple junctions [3]
• 29.5% peak solar cell efficiency
• 84 mg/cm^2

Clyde Space Lithium Polymer Battery features [4]:

• integrated battery heater
• 35000 cycle expected life
• 150 Wh/kg
• 80% depth of discharge

The solar cell area and battery size was calculated by summing the energy requirements of the satellite and dividing by the efficiency of the solar cell or multiplying by the relevant capacity. Table 1 shows relevant specifications and resulting solar area, solar weight, battery capacity, and battery weight.

Multiple environmental factors also had to be considered when calculating the required capacities of the solar cell array and battery. Solar cells are susceptible to radiation damage which causes the efficiency of the cells in a space environment to decrease with time. This effect is mitigated by glass coverings and other methods, but safety in power estimation means the efficiency of the cell used in calculations should be lowered to accurately represent its end of life efficiency. From Figure 2, the efficiency at a safe margin of 4 years is 24%. This efficiency was used in our calculations.

Another factor considered was the eclipse of the Sun by Venus. Since the orbit of the satellite is relatively low and only partially inclined, the satellite will be in direct sunlight only 60% of the time. The time out of the sun was taken into account by dividing the power requirements on the solar cell by 0.6.