Initial Results From an In-Orbit High-Voltage Experimental Platform: HORYU-IV

HORYU-IV is a nanosatellite developed to conduct experiments on electrostatic discharges (ESDs) in real space environments. Testing in space is very important to confirm ground testing results, because it is difficult to fully simulate the comprehensive environment of space on the ground, to evaluate the effects of such things as satellite movements, plasma conditions, sunlight, and chamber walls. Conventionally, occurrence counters have been used for such in-orbit experiments to find threshold voltages. However, they cannot provide detailed information for example magnitudes and the location of each ESD. We became highly aware of this limitation through our HORYU-II experience (which only had an occurrence counter) and we designed HORYU-IV in order to overcome this limited data issue. The main challenge with HORYU-IV is the carrying of standard laboratory equipment, such as oscilloscopes and event-capture cameras, which have never been successfully used in space before. Such measurement instruments, with solar array sample coupons and a high-voltage source, were launched on this satellite and have successfully provided current waveforms and images of spark of light from ESDs from space. This experimental method has been commonly used in ground-based spacecraft charging experiments, but has never been used in orbit. Hence, our satellite became the world's first operational platform equipped with an oscilloscope and event-capture camera for high-voltage experiments in space. Three different shapes of current waveforms were observed, and the arcing locations from images captured in orbit were identified. We have proved the concept of the remote laboratory in orbit. The observed discharge conditions will be replicated on the ground and the feedback will improve the ground testing methodology.