Large-format infrared detectors are at the heart of major ground and space-based astronomical instruments, and the HgCdTe HxRG is the most widely used. The Near Infrared Spectrometer and Photometer (NISP) of the ESA’s Euclid mission launched in July 2023 hosts 16 H2RG detectors in the focal plane. Their performance relies heavily on the effect of image persistence, which results in residual images that can remain in the detector for a long time contaminating any subsequent observations. Deriving a precise model of image persistence is challenging due to the sensitivity of this effect to observation history going back hours or even days. Nevertheless, persistence removal is a critical part of image processing because it limits the accuracy of the derived cosmological parameters. We will present the empirical model of image persistence derived from ground characterization data, adapted to the Euclid observation sequence and compared with the data obtained during the in-orbit calibrations of the satellite.
Launched successfully on July 1st, 2023, Euclid, the M2 mission of the ESA cosmic vision program, aims mainly at understanding the origin of the accelerated expansion of the Universe. Along with a visible imager VIS, it is equipped with the NISP instrument, a Near Infrared Spectrometer and Photometer, bespoke tailored to perform a 3D mapping of the observable Universe. It operates in the near-infrared spectral range, from 900 nm to 2000 nm with 2 observing modes: as a spectrometer, the NISP instrument will permit measuring millions of galaxy spectroscopic redshifts over the 6.5 years lifetime of the Euclid mission; as a photometer, it will obtain photometric redshifts of billions of galaxies. This paper provides a description of the NISP instrument, its scientific objectives, and offers an assessment of its current performance in flight.
Euclid, the M2 mission of the ESA’s Cosmic Vision 2015-2025 program, aims to explore the Dark Universe by conducting a survey of approximately 14 000 deg2 and creating a 3D map of the observable Universe of around 1.5 billion galaxies up to redshift z ∼ 2. This mission uses two main cosmological probes: weak gravitational lensing and galaxy clustering, leveraging the high-resolution imaging capabilities of the Visual Imaging (VIS) instrument and the photometric and spectroscopic measurements of the Near Infrared Spectrometer and Photometer (NISP) instrument. This paper details some of the activities performed during the commissioning phase of the NISP instrument, following the launch of Euclid on July 1, 2023. In particular, we focus on the calibration of the NISP detectors’ baseline and on the performance of a parameter provided by the onboard data processing (called NISP Quality Factor, QF) in detecting the variability of the flux of cosmic rays hitting the NISP detectors. The NISP focal plane hosts sixteen Teledyne HAWAII-2RG (H2RG) detectors. The calibration of these detectors includes the baseline optimization, which optimizes the dynamic range and stability of the signal acquisition. Additionally, this paper investigates the impact of Solar proton flux on the NISP QF, particularly during periods of high Solar activity. Applying a selection criterion on the QF (called NISP QF Proxy), the excess counts are used to monitor the amount of charged particles hitting the NISP detectors. A good correlation was found between the Solar proton flux component above 30 MeV and the NISP QF Proxy, revealing that NISP detectors are not subject to the lower energy components, which are absorbed by the shielding provided by the spacecraft.
Euclid is a European Space Agency (ESA) wide-field space mission dedicated to the high-precision study of dark energy and dark matter. In July 2023 a Space X Falcon 9 launch vehicle put the spacecraft in its target orbit, located 1.5 million kilometers away from Earth, for a nominal lifetime of 6.5 years. The survey will be realized through a wide field telescope and two instruments: a visible imager (VIS) and a Near Infrared Spectrometer and Photometer (NISP). NISP is a state-of-the-art instrument composed of many subsystems, including an optomechanical assembly, cryogenic mechanisms, and active thermal control. The Instrument Control Unit (ICU) is interfaced with the SpaceCraft and manages the commanding and housekeeping production while the high-performance Data Processing Unit manages more than 200 Gbit of compressed data acquired daily during the nominal survey. To achieve the demanding performance necessary to meet the mission’s scientific goals, NISP requires periodic in-flight calibrations, instrument parameters monitoring, and careful control of systematic effects. The high stability required implies that operations are coordinated and synchronized with high precision between the two instruments and the platform. Careful planning of commanding sequences, lookahead, and forecasting instrument monitoring is needed, with greater complexity than previous survey missions. Furthermore, NISP is operated in different environments and configurations during development, verification, commissioning, and nominal operations. This paper presents an overview of the NISP instrument operations at the beginning of routine observations. The necessary tools, workflows, and organizational structures are described. Finally, we show examples of how instrument monitoring was implemented in flight during the crucial commissioning phase, the effect of intense Solar activity on the transmission of onboard data, and how IOT successfully addressed this issue.
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