Title:

3UCubed: Calibration of Ultraviolet Photomultiplier Tube

The 3UCubed project is a 3U CubeSat being developed by the University of New Hampshire, Sonoma State University, and Howard University as a part of NASA IMAP student collaboration. This project consists of a multidisciplinary team of undergraduate students from all three universities. The mission goal of 3UCubed is to understand how Earth's polar upper atmosphere (‘the thermosphere’ in the auroral and varying conditions associated with cusp regions) responds to particle precipitation and solar wind forcing and internal magnetospheric processes. The 3UCubed includes two instruments with rocket heritage, an Ultraviolet photomultiplier tube (UV-PMT) to measure neutral atomic oxygen emissions to characterize the most common neutral in Earth’s upper atmosphere, and an electron retarding potential analyzer (ERPA) to measure energetic precipitating electrons. In order to successfully analyze the data collected by the UV-PMT once launched into the orbit, the sensor response must be calibrated to accurately measure oxygen emissions. Here, we discuss the calibration of the UV-PMT instrument. The calibration will be performed in a lab at UNH where the UV-PMT and a NIST-calibrated photodiode are placed on a rotating table in the vacuum chamber to simulate the space environment. A UV light source with a known flux spectrum is directed toward the detectors through a baffle to reduce glare. The preliminary response of the UV light is measured with a calibrated photodiode for cross-calibration, followed by swapping the UV-PMT to measure response, ensuring light flux measured by the photodiode and PMT are the same. A current response from the detectors is converted to voltage and measured to calculate UV light flux. Neutral density filters are used to calibrate the instrument at varying UV light flux intensities. The calibration data will be used to analyze the data collected by the UV-PMT.

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