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.
The Advanced Baseline Imager (ABI) is the next-generation imaging sensor for the National Oceanic and Atmospheric Administration’s (NOAA’s) operational meteorological satellites in geostationary orbit. One pathway for traceability to reference standards of the visible and near-infrared radiometric response for ABI is to a 1.65 m diameter integrating sphere source standard of spectral radiance. This source illuminates the full entrance pupil via the ABI Earth-view port, thus determining the absolute spectral radiance responsivity in the visible and shortwave infrared. The spectral radiance values of the large sphere are assigned by Exelis using a double monochromator and a 15.24 cm diameter integrating sphere source standard that is calibrated by NIST. As part of the ABI program, Exelis was required by NASA to have the spectral radiance values assigned by Exelis to the large sphere be validated by NIST. Here we report the results of that activity, which took place in April, 2013. During the week of April 8, Exelis calibrated the 1.65 m diameter sphere at all 24 levels that correspond to the ABI calibration protocol. During the week of April 15, the NIST validation exercise for five selected levels took place. NIST deployed a portable spectral radiance source, a filter radiometer restricted to the visible and near-infrared, and two spectroradiometers that covered from 350 nm to 2500 nm. The NIST sphere source served as the validation standard. The comparison results, which are reported at the ABI bands, agreed to within the combined uncertainties. We describe the methodology, results, and uncertainty estimates related to this effort.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.