We describe the development of flight electron multiplying charge coupled devices (EMCCDs) for the photon-counting camera system of a coronagraph instrument (CGI) to be flown on the 2.4-m Nancy Grace Roman Space Telescope. Roman is a NASA flagship mission that will study dark energy and dark matter, and search for exoplanets with a planned launch in the mid-2020s. The CGI is intended to demonstrate technologies required for high-contrast imaging and spectroscopy of exoplanets, such as high-speed wavefront sensing and pointing control, adaptive optics with deformable mirrors, and ultralow noise signal detection with photon counting, visible-sensitive (350 to 950 nm) detectors. The camera system is at the heart of these demonstrations and is required to sense both faint and bright targets (10 − 4 − 107 counts-s − 1) adaptively at up to 1000 frames-s − 1 to provide the necessary feedback to the instrument control loops. The system includes two identical cameras, one to demonstrate faint light scientific capability, and the other to provide high-speed real-time sensing of instrument pointing disturbances. Our program at the Jet Propulsion Laboratory (Pasadena, California, United States) has evaluated the low-signal performance of radiation-damaged commercial EMCCD sensors and used those measurements as a basis for targeted radiation hardening modifications developed in partnership with the Open University (Milton Keynes, United Kingdom) and Teledyne-e2v (Chelmsford, United Kingdom). A pair of EMCCDs with test features was then developed and their low signal performance is reported here. The program has resulted in the development of a flight version of the EMCCD with low signal performance improved by more than a factor of three over the commercial one after exposure to 2.6 × 109 protons-cm − 2 (10 MeV equivalent). The flight EMCCD sensors are contributed by ESA through a contract with Teledyne-e2v (Chelmsford, United Kingdom). We will describe the program requirements, sensor design, test results and metrics used to evaluate photon counting performance.
UV-SCOPE is a mission concept to determine the causes of atmospheric mass loss in exoplanets, investigate the mechanisms driving aerosol formation in hot Jupiters, and study the influence of the stellar environment on atmospheric evolution and habitability. As part of these investigations, the mission will generate a broad-purpose legacy database of time-domain ultraviolet (UV) spectra for nearly 200 stars and planets. The observatory consists of a 60 cm, f/10 telescope paired to a long-slit spectrograph, yielding simultaneous, almost continuous coverage between 1203 Å and 4000 Å, with resolutions ranging from 6000 to 240. The efficient instrument provides throughputs < 4% (far-UV; FUV) and < 15% (near-UV; NUV), comparable to HST/COS and much better than HST/STIS, over the same spectral range. A key design feature is the LiF prism, which serves as a dispersive element and provides high throughput even after accounting for radiation degradation. The use of two delta-doped Electron-Multiplying CCD detectors with UV-optimized, single-layer anti-reflection coatings provides high quantum efficiency and low detector noise. From the Earth-Sun second Lagrangian point, UV-SCOPE will continuously observe planetary transits and stellar variability in the full FUV-to-NUV range, with negligible astrophysical background. All these features make UV-SCOPE the ideal instrument to study exoplanetary atmospheres and the impact of host stars on their planets. UV-SCOPE was proposed to NASA as a Medium Explorer (MidEx) mission for the 2021 Announcement of Opportunity. If approved, the observatory will be developed over a 5-year period. Its primary science mission takes 34 months to complete. The spacecraft carries enough fuel for 6 years of operations.
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