In-flight validation of End-Of-Life optimized Triple Junction solar cells onboard ASTROBIO cubesat

Small satellites are known to provide low-cost access to space, enabling fast and cheap validation of new technologies for space missions. ASTROBIO is a 3U CubeSat (size 100x100x300 mm3), that was injected into an orbit crossing several times a day the cloud of radiation known as the Van Allen Belts. As a result, the solar panels are exposed to an enhanced dose rate and undergo in a few days the same degradation that would be observed after several years of space flight in Low Earth Orbit. We used this unique opportunity to validate the new End-Of-Life optimized Triple Junction solar cells (CTJ-EOL) produced in Italy by CESI. The spacecraft solar panel comprises two types of solar cells produced by the same manufacturer: the well-established CTJ-30 and the new CTJ-EOL. Their performance was separately monitored and the related telemetries were downloaded for off-line elaboration. This manuscript reports and analyses the telemetries received by our Ground Station and by the networked stations distributed all over the globe. Data analysis clearly and unequivocally demonstrated the superior ruggedness of the End-Of-Life optimized devices: in the first week, the CTJ-30 performance dropped like it would be expected along a 10-years+ mission in the most-commonly-used orbits, whereas degradation of the CTJ-EOL was barely detectable. The results also show that in-orbit testing can provide unique information about the operation of solar cells in the intended operational environment as well as an easy verification of the device's functionality, useful to complement standard characterization procedures for radiation hardness involving costly and time-consuming laboratory tests under particle beams.