The Full-sun Ultraviolet Rocket SpecTrograph (FURST) is a sounding rocket designed to acquire the first full-disk integrated high resolution vacuum ultraviolet (VUV) spectra of the Sun. The data enable analysis of the Sun comparable to stellar spectra measured by astronomical instruments such as those on board the Hubble Space Telescope. The mission is jointly operated by teams at Montana State University (MSU), developing the instrument, and Marshall Space Flight Center (MSFC), developing the camera and calibration systems, and is scheduled to launch from White Sands Missile Range, New Mexico, in 2022. This mission requires the development of a pre-and post-launch calibration plan for absolute radiometric and wavelength calibration to reliably generate Hubble analogue spectra. Absolute radiometric calibration, though initially planned to be performed at the National Institute for Standards and Technology (NIST) calibration facilities, is now planned to be completed with a portable VUV calibration system provided by MSFC, due to instrument incompatibilities with NIST infrastructure. The portable calibration system is developed to provide absolute wavelength calibration and track changes in calibration over the duration of the mission. The portable calibration system is composed mainly of a VUV collimator equipped with an extreme ultraviolet line source and calibrated photodiodes. The calibration system is developed to accommodate both repeatable wavelength and radiometric testing of the FURST instrument at various test sites before and after launch. Presented here are the requirements, design, and implementation of this portable calibration system with a focus on those features most significant to radiometric measurements.

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We present a model for atmospheric absorption of solar ultraviolet (UV) radiation. The initial motivation for this work is to predict this effect and correct it in Sounding Rocket (SR) experiments. In particular, the Full-sun Ultraviolet Rocket Spectrograph (FURST) is anticipated to launch in mid-2023. FURST has the potential to observe UV absorption while imaging solar spectra between 120-181 nm, at a resolution of ℛ > 2 ⋅ 10 4 ( Δ V < ± 15 km / s ) , and at altitudes of between ≈ 110-255 km. This model uses estimates for density and temperature, as well as laboratory measurements of the absorption cross-section, to predict the UV absorption of solar radiation at high altitudes. Refraction correction is discussed and partially implemented but is negligible for the results presented. Absorption by molecular Oxygen is the primary driver within the UV spectral range of our interest. The model is built with a wide range of applications in mind. The primary result is a method for inversion of the absorption cross-section from images obtained during an instrument flight, even if atmospheric observations were not initially intended. The potential to obtain measurements of atmospheric properties is an exciting prospect, especially since sounding rockets are the only method currently available for probing this altitude in-situ. Simulation of noisy spectral images along the FURST flight profile is performed using data from the High-Resolution Telescope and Spectrograph (HRTS) SR and the FISM2 model for comparison. Analysis of these simulated signals allows us to capture the Signal-to-Noise Ratio (SNR) of FURST and the capability to measure atmospheric absorption properties as a function of altitude. Based on the prevalence of distinct spectral features, our calculations demonstrate that atmospheric absorption may be used to perform wavelength calibration from in-flight data.