Evaluation of UV optics for Triple Tiny Ionospheric Photometers on CubeSat missions

摘要

We have developed the Triple Tiny Ionospheric Photometer (Tri-TIP) as a CubeSat-compatible 1U sensor to obtain high-sensitivity measurements of the far-ultraviolet (FUV) OI 1356 A airglow for remote sensing of ionospheric density. The Tri-TIP concept evolved from heritage sensors flown on the COSMIC/FORMOSAT-3 (CF3) constellation, and more recently as part of the GPS and Radio Occultation and UV Photometry - Colocated (GROUP-C) experiment on the International Space Station. The concept for all of these sensors is to isolate this emission using heated strontium-fluoride filters to eliminate shorter wavelength emissions such as O I 1304 A and H I 1216 A and cesium iodide photocathodes to reduce sensitivity longward of ～1800 A. There are no other spectral features in this FUV portion of the airglow spectrum at night. However, the nadir-viewing sensors on CF3 observed significant long-wavelength emissions from city lights and moonlit clouds that contaminated the data. The GROUP-C instrument included a sapphire filter that could be alternated with the strontium fluoride to measure and remove this spectral "red leak'" from the observations. The Tri-TIP design pairs a heated strontium fluoride filter in line with a sapphire beam splitter that feeds the UV (with spectral leak) and long-wavelength (spectral leak only) signals to two matched photomultiplier tubes (PMTs). A third PMT monitors the signal contribution from high-energy particles and dark current. We present the results from laboratory tests of these components that ensure the high-sensitivity performance of this new optical configuration for ionospheric remote sensing and imaging from a CubeSat platform.