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The Ariel Instrument Control Unit

its role within the Payload and B1 Phase design


Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey mission (Tinetti 2019; Puig et al. 2018; Pascale et al. 2018), has been selected in March 2018 by ESA for the fourth medium-class mission (M4) launch opportunity of the Cosmic Vision Program, with an expected lift off in late 2028. It is the first mission dedicated to measuring the chemical composition and thermal structures of the atmospheres of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of our own Solar System. Its Payload (P/L) (Eccleston and Tinetti 2018; Eccleston et al. 2017; Middleton et al. 2019), has been designed to perform transit spectroscopy from space during primary and secondary planetary eclipses in order to achieve a large unbiased survey concerning the nature of exoplanets atmospheres and their interiors, to determine the key factors affecting the formation and evolution of planetary systems (Tinetti et al. 2017, 2018). Ariel will observe hundreds of warm and hot transiting gas giants, Neptunes and super-Earths around a wide range of host star types, targeting planets hotter than \(\sim \)600 K to take advantage of their well-mixed atmospheres. It will exploit primary and secondary transit spectroscopy in the 1.10 to 7.80 μm spectral range and broad-band photometry in the optical (0.50 - 0.80 μm) and Near IR (0.80 - 1.10 μm) . One of the two instruments of the Ariel Payload is the Fine Guidance System (FGS), including three photometric channels (two used for guiding as well as science) between 0.5-1.1 μm plus a low resolution NIR spectrometer for 1.1-1.95 μm range. Along with FGS an IR Spectrometer (AIRS) (Amiaux et al. 2017) is foreseen, providing low-resolution spectroscopy in two IR channels: Channel 0 (CH0) for the 1.95 − 3.90 μm band and Channel 1 (CH1) for the 3.90 − 7.80 μm range. Finally, an Active Cooler System (ACS) including a Ne Joule-Thomson cooler is adopted to provide active cooling capability to the AIRS detectors working at cryogenic temperatures. AIRS is located at the intermediate focal plane of the telescope and common optical system and it hosts two HgCdTe-based hybrid IR detectors and two cold front-end electronics (CFEE) for detectors control and readout. Each CFEE is driven by a Detector Control Unit (DCU) part of AIRS but hosted within and managed by the Instrument Control Unit (ICU) of the Payload (Focardi et al. 2018). ICU is a warm unit residing into the S/C Service Module (SVM) and it is based on a cold redundant configuration involving the Power Supply Unit (PSU) and the Commanding and Data Processing Unit (CDPU) boards; both DCUs are instead cross-strapped and can be managed by the nominal or the redundant (PSU+CDPU) chain. ICU is in charge of AIRS management, collecting scientific and housekeeping (HK) telemetries from the spectrometer and HK from the telescope (temperatures readings), the P/L Optical Bench (OB) and other Subsystems (SS), thanks to a warm slave unit (TCU, Telescope Control Unit) interfaced to the ICU. Science and HK telemetries are then forwarded to the S/C, for temporary storage, before sending them to Ground. Here we describe the status of the ICU design at the end of B1 Phase, prior to the Mission Adoption Review (MAR) by ESA, with some still open architectural choices to be addressed and finalised once selected the ICU industrial Prime contractor.

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  1. 1.

    Field Programmable Gate Array

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    Remote Memory Access Protocol

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    Latching Current Limiter

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    Real-Time Executive for Multiprocessor Systems

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    Advanced Microcontroller Bus Architecture

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    On-Board Data Handling

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    Consultative Committee for Space Data Systems / Packet Utilisation Standard

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    Fault Detection, Isolation and Recovery

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    Refer to the Metis coronagraph on-board Solar Orbiter and PLATO ICU compression algorithms

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    Hardware Description Language Finite State Machine

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    One Time Programmable

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    Indeed this value is a function of the SVM shielding material and here is reported only as a worst case for a SVM bench based on CRFP (no or only partial Al shielding)

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    Space AVionics Open Interface aRchitecture


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The authors would like to thank the UK Science and Technology Facilities Council (STFC), the Italian Space Agency (ASI) for the financial contribution to the Ariel project in the framework of the ASI/INAF agreement 2018.22.HH.0 (Accordo Attuativo della Convenzione Quadro), the French CNES (Centre National d’Etudes Spatiales) and OHB Italy for the support to the preliminary design of the ICU and DCU boards, for both AIRS and FGS instruments on-board Ariel.

Finally, a special thank to the Ariel Study Team of the European Space Agency, for the invaluable support provided to the Ariel Mission Consortium.

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Correspondence to M. Focardi.

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Focardi, M., Di Giorgio, A., Naponiello, L. et al. The Ariel Instrument Control Unit. Exp Astron (2021).

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  • Exoplanets atmospheres
  • Transit spectroscopy
  • Infrared spectrometer
  • Payload electronics
  • Instrument control unit
  • On-Board SW