The Europa Imaging System (EIS) combines a Narrow-Angle Camera (NAC) and a Wide-Angle Camera (WAC) to explore Jupiter’s Icy moon Europa. EIS is designed to address high-priority geology, composition, ice shell and ocean science objectives with the challenges of imaging in a wide range of scenarios spanning fast, low-altitude flybys with rapidly changing geometry and illumination to high-altitude imaging of faint scenes. Images for both EIS cameras are taken with a 10-μm pixel-pitch, 4096×2048 frontside illuminated CMOS image sensor. To perform color pushbroom imaging, the NAC and WAC both have six 32-row broadband stripe filters. The WAC is an F/5.75, 46-mm focal length, 8- lens refractive telescope with a 48° × 24° FOV and an IFOV of 218-μrad, achieving 11-m pixel scale from a 50-km altitude over a 44-km-wide swath. The along-track FOV provides 3-line (forward, nadir, and aft) pushbroom stereo swaths enabling digital topographic models with 32-m spatial scale and 4-m vertical precision. In order to perform over a 400- 1050 nm bandwidth in the extreme radiation environment surrounding Europa, the design contains 4 different materials: fused silica, CaF2, and two radiation resistant glasses. Each lens, except the exposed front surface of Lens 1 (L1), is coated with a proprietary antireflective (AR) coating, which has been tested for durability and performance in varying temperature and radiation environments. The 25-mm thick fused silica L1 plays dual roles in the WAC telescope design to also protect the CMOS sensor from the intense radiation of the Jovian environment. The optomechanical design maintained the optical alignment through thermal and vibration environmental testing. The WAC was delivered to NASA’s Jet Propulsion Laboratory (JPL) and integrated to the Europa Clipper spacecraft in summer 2022.
The Jupiter environment presents many unique challenges to the optomechanical design of the Europa Imaging System (EIS) Wide Angle Camera (WAC) for NASA’s Europa Clipper Mission. EIS is designed to address Europa Clipper’s highpriority geology, composition, ice shell and ocean science objectives. The WAC is an F/5.75, 46-mm focal length 8-lens refractive telescope with a 48° x 24° FOV and a 218-μrad IFOV, resulting in 11-m pixel scale from 50-km altitude over a 44-km-wide swath. The 4096 x 2048 x 10 μm sensor and 6-color stripe spectral filters enable two imaging modes, framing for global mapping and plume searches, and time delay integration for color imaging (400-1050 nm) with three-line stereo topography. This paper describes the design, material selection, integration, and testing of the EIS WAC to survive the Jovian environment leading up to Europa Clipper integration in Summer 2022.
The impact of gamma radiation on refractive index and transmission was analyzed for several glasses. The goal of the analysis is to quantify the optical performance impact of Jovian electron and proton radiation environments using gamma radiation as a proxy for the Europa Imaging System (EIS) Wide Angle Camera1 (WAC) refractive telescope. The testing was split into two sample sets. The first set of glasses tested are baselined in the current WAC design: BK7G18, Calcium Fluoride, Fused Silica, and LF5G15. Analysis demonstrates no significant change in the refractive index or transmission in BK7G18, Calcium Fluoride, Fused Silica, and LF5G15 when exposed to 1 Mrad of gamma radiation. The second set of glasses tested was two i-line and two radiation resistant glasses from Ohara. Analysis demonstrates no significant change in the refractive index in BAL35Y, PBL25Y, S-BAL25-R, and S-BSL7-R when exposed to 1 Mrad of gamma radiation. Significant loss in transmission was observed for the two i-line glasses (BAL35Y and PBL25Y) when exposed to 1 Mrad of gamma radiation.
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