Development of the Wind and Air Temperature Sensor of the ExoMars 2022 HABIT Instrument

• This work presents the development, validation and calibration of the air temperature sensors (ATS) and the air and wind retrieval method of the HABIT (HabitAbility: Brines, Irradiation and Temperature) instrument. HABIT is one of the two European  payloads of the ESA/Roscosmos ExoMars 2022 mission that will land at Oxia Planum (18.20° N, 335.45° E), on Mars.One of the main novelties of this Ph.D. thesis is to use the thin fins that work as ATS on HABIT as a wind sensor for the planetary boundary layer of Mars. The thesis is based on the study and modelling of heat transfer along three rods when exposed to forced convection in a gaseous fluid, and that is tested: (1) through computational fluid dynamic simulations, which provided inputs to the early design of the HABIT structure; (2) under laboratory conditions, with the use of a specifically designed prototype and a cooling fan; and (3) within a subsonic wind tunnel facility under terrestrial conditions.A preliminary validation of the wind speed retrieval approach is first performed using temperature measurements from Mars provided by the Rover Environmental Monitoring Station (REMS) instrument, on board the NASA Curiosity rover of the Mars Science Laboratory (MSL) mission. The method is based on modelling forced convection of the ATS of REMS when assumed as thin rods immersed in the extreme low-pressure and high-radiating atmospheric conditions of the Martian thermal boundary layer, at a height of ∼ 1.5 m from the surface. Assuming the previously reported REMS wind sensor (WS) retrieval errors of 20% for the wind speed, ±30° for the horizontal “front” wind directions, and ±45° for the horizontal “rear” wind directions, agreement with the WS values of up to 77% of the acquisition time, on average, for wind speeds and coincidence between 60% and 80% of the time for wind directions is reported for some sols. These promising results are limited to only evening extended acquisitions from 18:00 to 21:00 local mean solar time (LMST) and orientations within the validity region of the retrieval. That is, the method was only considered valid over a narrow angle range of 13° to 107° in azimuth angle. In addition to this, the results of this first study suggested a new optimal orientation when using the ATS for wind speed and direction retrievals of +60° clockwise with respect to the forward direction of the Curiosity rover.The wind retrieval model is also validated and calibrated with the HABIT engineering and qualification model (EQM) in the Aarhus Wind Tunnel Simulator (AWTS) of the Aarhus University, Denmark. The AWTS is designed to reproduce typical winds on the surface of Mars. The data acquired during the wind tunnel campaign were used to validate the forced convective and radiative heat transfer model for each of the three ATS. The campaign investigated winds in steady CO2 flows at a pressure of 9.9 mbar, an ambient temperature of 25°C, and for horizontal free-stream velocities between 0.8 and 12 m/s. Several relationships between the Nusselt number and the Reynolds and Prandtl numbers reported in the literature were evaluated in the tunnel to model forced convection through the ATS rods. Where needed, corrections to account for radiative heat transfer within the AWTS were implemented to correct for experimental artefacts. The tests demonstrated that this retrieval method can be used to derive wind speed for frontal winds on Mars in the range of 0 to 10 m/s, with an error of ±0.3 m/s, using the cooling profile of the ATS rod 3, and for lateral winds in the range of 0 to 6 m/s, with an error of ±0.3 m/s, using the ATS rod 2 cooling profile.The thesis also includes the calibration of the HABIT ATS flight model (FM) in the clean room of Omnisys Instruments AB, and the retrieval model that will be used in operations during the ExoMars 2022 mission and for archiving in the Planetary Science Archive (PSA) of the European Space Agency (ESA).Finally, the wind retrieval method developed in this thesis can be applied not only to the future analysis of HABIT data at Oxia Planum, but also to re-analyse the ATS data of REMS at Gale crater, and for future comparative analysis with the HABIT/ExoMars 2022, the Temperature and Wind Sensors for InSight (TWINS)/InSight, and the Mars Environmental Dynamics Analyzer (MEDA)/Mars 2020 rover instruments.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Rymd- och flygteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Aerospace Engineering (hsv//eng)

Nyckelord

Mars

Atmosphere

Heat transfer

Forced convection

Wind

Space instrumentation

Exploration

Atmospheric science

Atmosfärsvetenskap

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