A root cause analysis of REXIS detection efficiency loss during phase E operations

Abstract

The Regolith X-ray Imaging Spectrometer (REXIS) is a student-built instrument flown on NASA's Origins, Spectral Interpretation, Resource Identification, Safety, Regolith Explorer (OSIRIS-REx) mission. During main science operations, the instrument experienced detector efficiency loss in the form of loss of iron calibration source counts, which greatly affected the science output. In this thesis, a root cause investigation is performed on the loss of iron counts, and an optical light leak onto the edge of the instrument's detectors is identified as the most likely cause. A CAST analysis is then performed to identify possible organizational and cultural causes of the design that allowed for an optical light leak, and recommendations for future similar instruments (low-cost, high-risk) are made.