We present the results of the JUpiter ICy moons Explorer ultraviolet spectrograph (JUICE-UVS) near-earth commissioning performed between June 14th and 25th 2023. JUICE-UVS is a modest power (9 W), compact ultraviolet spectrograph that is the fifth in a series of six such spectrographs designed and built by Southwest Research Institute for ESA and NASA missions. JUICE-UVS includes several innovations in detector, electronics, optics, and software. These innovations include an atomic-layer deposition (ALD) coating on the detector microchannel plates to minimize gain sag as photons are detected during the mission, electronic components able to withstand the harsh Jovian radiation environment, low-scatter optics to minimize the “wings” of the detected interplanetary Lyman-alpha emission, and a programmable histogram data collection mode that maximizes science return while minimizing stored and telemetered data volume. JUICE-UVS also features a high-spatial resolution observation mode, where a small (1/4 the width of nominal) aperture swings into place at the aperture stop and sharpens the instrument focus. Near-earth commissioning activities included measurements of detector dark noise, optimizing detector HV level via observations of the interplanetary Lyman-alpha, and a “sky-spin” observation over the JUICE-UVS 7.5°-long slit while the spacecraft rolled about the high-gain antenna (a “great circle” swath 7.5° wide). Dark rates matched those measured on the ground (approximately 5 Hz/cm2). HV levels were nominal for the operational temperature (approximately 0°C). Observations with the high-spatial resolution aperture confirmed the sharpened focus when compared to nominal observations. The “sky-spin” observation passed through the galactic plane, allowing for the identification of many known UV-bright stars. These stars provide a rough estimate of instrument effective area that will be refined after JUICE passes >2 AU from the sun, enabling 3-axis stabilized pointed observations.
We describe the post-delivery performance testing of the JUpiter ICy moons Explorer Ultraviolet Spectrograph (JUICE-UVS). JUICE-UVS is a modest power (8 W) ultraviolet imaging spectrograph that is the fifth in a series of Alice/UVS instruments built by Southwest Research Institute (SwRI). JUICE-UVS covers a 50-204 nm bandpass with 0.4 nm spectral resolution over a 7.5° field of view with better than 0.3° spatial resolution. JUICE-UVS will explore the Galilean satellites, examine the dynamics of Jupiter’s upper atmosphere from pole to equator, and investigate the Jupiter-Io connection through observations of the Io torus. JUICE-UVS underwent an extensive ground testing campaign at strategic points during the JUICE integration-and-testing over the course of four years and four countries on three continents. High voltage operations were enabled via the usage of specially designed Optical Ground Support Equipment (OGSE) that attached to the spacecraft for key tests. All performance requirements continue to be met, and there is no observable performance degradation after all spacecraft environmental testing and transport activities. In particular, the microchannel plate detector has similar sensitivity and dark rates as measured during pre-delivery testing. Testing of optical witness samples removed during key tests indicates the instrument optical throughput is unchanged. In-flight calibrations planned for shortly after launch will further confirm the performance of JUICE-UVS.
We describe the radiometric performance and ground calibration results of the Europa Clipper Ultraviolet Spectrograph (Europa-UVS). Europa-UVS is a modest power (~8 W) ultraviolet spectrograph that is the sixth in a series of Alice/UVS instruments built by SwRI. Europa-UVS covers a 55-206 nm bandpass with approximately 0.6 nm spectral resolution over a 7.5° field of view with better than 0.25° spatial resolution on-axis. Europa-UVS also features three different observing modes to allow higher-than-normal spatial resolution observing as well as solar occultations of Europa. Both the high spatial resolution and solar occultation observations have reduced sensitivity when compared with nominal observations. Europa-UVS meets all performance requirements with margin, and is the first planetary UV spectrograph to feature a microchannel plate detector with curved borosilicate microchannel plates (expected to be less sensitive to gamma rays than traditional plates). Europa-UVS, like its predecessor JUICE-UVS, incorporates both timetagged pixel list and histogram observing with programmable acquisitions to maximize science return while minimizing data storage and downlink. Europa-UVS will search near Europa for water vapor plumes, examine the composition and structure of Europa’s atmosphere and surface, and characterize Europa's aurora.
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