Solar Probe Plus Array Reliability

The Solar Probe Plus will follow a trajectory passing the sun in the closest orbit at approximately 9.86 solar radii. During this mission the probe will encounter a high irradiance high temperature (HIHT) environment, making it necessary for a more intricate solar array configuration. This requires the standard Failure Modes Effects and array reliability calculations to be modified. Failure modes include solder deterioration, VDA Kapton evaporation, solar cell material deterioration, coverglass to cell adhesive degradation, and also typical interconnect and wire failures. Using statistics suited for two different types of strings, the reliability of the solar array is calculated when the probe is at aphelion and perihelion. The array contains not only two different types of strings, but also cell sizes and panel sections, making the true reliability more complex. Through statistical analysis of individual components reliabilities, the reliability of the complete array with no, one and two string failures is calculated to be 89.55%, 5.22%, 0.13% respectively during perihelion mode and 80.17%, 13.64%, and 1.09% during aphelion mode. In result, the probe has a reliability of 94.89% with at most two string failures during perihelion mode and 94.91% during aphelion mode. After calculating the number of exposure hours per particular string exposed it was visible that the most inboard string, No. 22, experiences 39,994.875 exposure hours with strings No. 9 through No. 1 experiencing the full exposure time of the planned mission, 61,370.766 hours. With this, the reliability of 42 double-interconnected strings is 99.9% but with the inclusion of the two single-interconnected strings, this goes down to 94.9%. Due to the Solar Space Probe having a much different solar array configuration than that of most space systems it necessitates different statistical computation, in this case producing a unique reliability over the course of its 7-year mission.