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Completed TRL 8 (started at 8, targeting 8)
The Fast Neutron Spectrometer (FNS), formerly known as the Advanced Neutron Spectrometer, was developed, built, and operated by Marshall Space Flight Center (MSFC). From 2016 to 2018, it conducted a technology demonstration on the International Space Station (ISS) as an intravehicular neutron environment monitor, with sustained operations until 2023. After its return to MSFC, the FNS flight unit was evaluated and found to be in good operational condition. At the conclusion of the FNS project, the detector was then relocated to Johnson Space Center (JSC) to begin transition of future FNS operations under JSC personnel.
The FNS Reflight Assessment Campaign aims to 1) establish the necessary engineering and scientific expertise at JSC to operate the FNS, and 2) reassess the flight unit to ensure it meets all previous performance metrics and did not degrade during its ISS deployment. There are a number of measurable performance metrics that can be used to fully determine that the FNS did not incur degradation during flight. Degradation of the Photomultiplier Tube (PMT) and Scintillator interface, degradation of the PMT gain stages or high voltage supplies would result in loss of signal gain and resultant shift in signatures, and decreased signal-to-noise performance. These metrics can be measured on the ground at a high precision neutron metrology facility, and would manifest as a reduction in energy dependent neutron detection efficiency. A key component of the FNS reflight campaign will be a measurement of mono-energetic neutrons at Physikalisch-Technische Bundesanstalt (PTB) in Germany. Measurements conducted at that facility will provide data for one-to-one comparisons with the FNS’s performance pre-flight. Once it has been confirmed that the FNS is performing within the necessary performance target, the team will transition to preparing the unit for a reflight opportunity.
Typical development of high performance neutron spectrometers require long development times (5+ years) and significant cost ($10+ million), as was the case for FNS and the related ISS-RAD instrument (also operated by JSC personnel). As the only fast neutron spectrometer currently available with TRL8 flight readiness with the potential for reflight, it is imperative that NASA maintains the ability to evaluate and operate the FNS for future missions to retain the significant investment in developing the technology. Maintaining fast neutron measurement capabilities is critical to understanding the harmful effects of chronic radiation exposure on astronauts, including the excess relative risk of cancer and death; neutron radiation contributes an estimated 15-30% of the total effective dose an astronaut is expected to receive over their career, depending on vehicle configuration and environment (LEO, lunar orbit, lunar surface, etc.).
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