Speaker
Description
Electrostatic discharges (ESDs) are a known cause of satellite anomalies, particularly during disturbances in the radiation belts. While design guidelines to evaluate and mitigate ESD and electromagnetic coupling (EMC) risks have traditionally focused on large platforms, there is now a need to tailor these guidelines to the unique characteristics of smaller platforms, such as CubeSats.
This work consisted in assembling, testing and modelling the instruments of the Charging on Cubesat (CROCUS mission). The Sensing Impulses and Mitigation on CubeSat payload (CubeSIM) is designed to monitor charging events responsible for ESDs and to detect the occurrence of ESDs induced by the so-called inverted potential gradient situation with a negatively charged spacecraft and covering insulators positively charged with respect to the spacecraft frame. Additional instrumentation allows to artificially charge the spacecraft. It is composed of deployed elements biased to a positive high voltage to collect cold plasma electrons and force the spacecraft to charge even more negatively. This additional instrumentation is referred as active instrumentation in this work because it actively influences the charge of the spacecraft. It is operated during quiet periods of time in the absence of charging conditions. In the sun-synchronous Low Earth orbit (LEO) chosen for the mission, the active mode will be used in the sunlight portion of the orbit because the photoemission very significantly reduces the probability to trigger ESDs naturally. In the night sector and especially in the auroral zone, the focus will be put on the passive detection mode.
An engineering model of CubeSIM has been manufactured and mounted on a CubeSat structure equipped with electrical ground support equipment (EGSE) composed of a battery and a power board. The EGSE is completed with a set of three oscilloscope boards measuring the transient currents detected by current probes. The CubeSat mockup is mechanically maintained in the middle of an ionospheric plasma chamber with insulating wires. The system is thus electrically floating with respect to ground, which significantly adds to the representativity of the test with respect to flight conditions, especially regarding the blow-off and flash-over currents.
We will report the results of the tests performed in secondary vacuum under electron, VUV and plasma conditions. ESDs characteristics measured by the EGSE are used to update the specification of the CubeSIM payload. In addition, numerical simulations are used to predict power consumption during the active mode operations as a function of plasma conditions. They suggest that deploying antennas is more appropriate than deploying panels as initially anticipated. A description of the current status of the project, currently in phase C, will be presented.
