From Event: SPIE Optical Engineering + Applications, 2017
The detectors of the Sentinel 4 multi spectral imager are operated in flight at 215K while the analog electronics is operated at ambient temperature. The detector is cooled by means of a radiator. For thermal reasons no active component has been allowed in the cooled area closest to the detector as the passive radiator is restricted in its size. For thermal decoupling of detector and electronics a long distance between detector and electronics is considered ideal as thermal conductivity decreases with the length of the connection. In contradiction a short connection between detector and electronics is ideal for the electronic signals. Only a short connection ensures the signal integrity of both the weak detector output signal but similarly also the clock signals for driving the detector. From a mechanical and thermal point of view the connection requires a certain minimum length. The selected solution serves all these needs but had to approach the limits of what is electrically, mechanically and thermally feasible. In addition, shielding from internal (self distortion) and external distorting signals has to be realized for the connection between FEE(Front End Electronics) and detectors. At the time of the design of the flex it was not defined whether the mechanical structure between FEE and FPA (Focal Plane Assembly) would act as a shielding structure. The physical separation between CCD detector and the Front-end Electronics, the adverse EMI environment in which the instrument will be operated in (the location of the instrument on the satellite is in vicinity to a down-link K-band communication antenna of the S/C) require at least the video output signals to be shielded. Both detectors (a NIR and a UVVIS detector) are sensitive to contamination and difficult to be cleaned in case of any contamination. This brings up extreme cleanliness requirements for the detector in manufacturing and assembly. Effectively the detector has to be kept in an ISO 5 environment and additionally humidity has to be avoided - which does not comply with the usual clean-room atmosphere. This paper describes how in Sentinel 4 the given challenges have been overcome, how the limited load drive capability of the detector component has been considered on a flex length of about 20 cm (7.87 in) and how EMC shielding of the highly sensitive analog signals of the detector has been realized. Also covered are design/manufacturing aspects and a glance on testing results is provided
M. Hermsen, R. Hohn, M. Skegg, C. Woffinden, and R. Reulke, "Realization of the electrical Sentinel 4 detector integration," Proc. SPIE 10402, Earth Observing Systems XXII, 1040219 (Presented at SPIE Optical Engineering + Applications: August 08, 2017; Published: 5 September 2017); https://doi.org/10.1117/12.2274392.
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