We describe the IR focal plane unit of the MAJIS imaging spectrometer for the JUICE mission to the Jupiter Sys tem. Optical light from the telescope and spectrometer is focalized on the IR Focal plane unit which compris es a Teledyne Imaging Sensors H1RG detector overlain by a Viavi Solutions filter assembly. Both components are baffled and work at cryogenic temperatures. We describe the IR focal plane architecture, the measurement facilities and the main performance-critical specifications. The IR channel of MAJIS offers strong versatility with the capability to acquire high resolution spectra from the Jupiter atmosphere to organic matter on icy moon surfaces, over a wide spectral and dynamical range.
The JUICE (JUpiter ICy moons Explorer) mission by ESA aims to explore the emergence of habitable worlds around gas giants and the Jupiter system as an archetype of gas giants. MAJIS (Moons and Jupiter Imaging Spectrometer) is the visible to near-infrared imaging spectrometer onboard JUICE which will characterize the surfaces and exospheres of the icy moons and perform monitoring of the Jupiter atmosphere. The launch is scheduled for 2023 with the first MAJIS observations inside the Jovian system occurring more than 8 years later. The MAJIS optical head is equipped with two Teledyne H1RG detectors, one for each of the two spectrometer channels (VIS-NIR and IR). This paper describes the characterization of the VIS-NIR Focal Plane Unit. These detectors will be operated in a non-standard way, allowing near/full-frame retrieval over short integration times (<< 1 sec) while maintaining good noise performance. After a quick description of the characterization strategy that was designed to evaluate the performances of the VIS-NIR detector according to the MAJIS operational specifications, the paper will address the data analyses and the main results of the characterization campaign. The major performance parameters such as dark current, linearity, noise, quantum efficiency, and operability will be presented and compared with the requirements.
MAJIS is an imaging spectrometer operating in the visible and IR range which is part of the payload of the JUICE mission of ESA, dedicated to the study of the icy moons of Jupiter, Jupiter and the Jupiter environment, to be launched in April 2023. MAJIS implements two channels, one for the visible-near IR range (0.5 – 2.35 μm) and one for the IR range (2.25 – 5.52 μm). H1RG detectors from Teledyne where selected for these two channels. The specific constraints of MAJIS (very wide dynamic range, windowing, on-board de-spiking) required very significant adjustments to readout microcodes provided by Teledyne. The de-spiking approach implemented by MAJIS relies on on-board processing of series of consecutive sub-integrations5 . For reaching optimum performance, possible biases between successive CDS readouts of the same signal needed to be lower than the total noise. The first of the two detector readouts required for CDS had to be implemented very shortly after reset so as to benefit from the full well depth for dynamic range. This required coping with the reset anomaly which is specific to the HxRG family of detectors. The MAJIS team selected an approach based on drop frames and dark subtraction which minimized microcode adjustments so as to limit development and schedule risks. Detector characterization then instrument calibration showed that this approach was quite successful in terms of performances with no impact on the duty cycle for observations with short integration times.
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