The instrument control unit of the EChO space mission: electrical architecture and processing requirements

The Exoplanet Characterization Observatory (EChO) is conceived for the spectrophotometric study from space of the atmospheres of a selected target sample of transiting extra-solar planets. It has been designed to run as a candidate for the M3 launch opportunity of the ESA Cosmic Vision program and can be considered as the next step towards the fully characterization of a representative sample of the already discovered transiting exoplanets. The EChO payload is based on a single highly thermo-mechanical stabilized remote-sensing instrument hosting a dispersive spectrograph. It is able to perform time-resolved spectroscopy exploiting the temporal and spectral variations of the measured signal due to the primary and secondary occultations occurring between the exoplanet and its parent star. The adopted technique allows the extraction of the planet spectral signature and to probe the physical and chemical properties of its atmosphere. EChO is composed by four scientific modules, all suited on a common Instrument Optical Bench (IOB). Each module is operated by a unique control and processing electronics, the Instrument Control Unit (ICU), acting as interface between the payload and the spacecraft (S/C) Data Management Subsystem (DMS) and Power Control and Distribution Unit (PCDU). The main ICU tasks concern the instrument commanding, based on the received and interpreted TC and TM; instrument monitoring and control by means of the housekeeping (HK) data acquired from the focal plane units; synchronization of all the scientific payload activities; detectors readout and data acquisition, pre-processing, lossless compression and formatting before downloading the TM science data and HK to the spacecraft mass memory. As far as the software is concerned, these activities can be basically grouped and managed by the Instrument Control software and Data Processing software; both will constitute the On Board Software of the overall payload designed to address all the processing requirements as driven by the EChO science case [1, 2]. This paper is conceived as a memory for an EChO-like payload electrical architecture with processing capabilities mainly driven by the scientific requirements as defined and frozen at the end of both the Payload Assessment Phase and the M3 mission selection process, held by ESA at the beginning of February 2014.