Calibration and first results of relative humidity sensor MEDA HS on board M2020 rover

MEDA HS is the relative humidity sensor on the Mars 2020 Perseverance rover provided by the Finnish Meteorological Institute (FMI). The sensor is a part of Mars Environmental Dynamic Analyzer (MEDA), a suite of environmental sensors provided by Centro de Astrobiología in Madrid, Spain. MEDA HS, along with METEO-H in ExoMars 2022 surface platform, is a successor of REMS-H on board Curiosity.

Calibration of relative humidity (RH) instruments for Mars missions is challenging due to the range of RH (from 0 to close to 100%) and temperature conditions (from about -90 ºC to + 22 ºC) that need to be simulated in the lab. Thermal gradients in different parts of the system need to be well known and controlled to ensure reliable reference RH readings. For MEDA HS the calibration tests have been performed for different models of MEDA HS in three Martian humidity simulator laboratories: FMI laboratory, Michigan Mars Environmental Chamber (MMEC) and DLR PASLAB (Planetary Analog Simulation Laboratory).

MEDA HS flight model was tested at FMI together with flight spare and ground reference models in low pressure dry CO₂ gas from +22ºC to -70ºC and in saturation conditions from -40ºC down to -70ºC. Further, the MEDA HS flight model final calibration is complemented by calibration data transferred from an identical ground reference model which has gone through rigorous testing also after the flight model delivery. During the test campaign at DLR PASLAB that started in Autumn 2020, MEDA HS has been calibrated over the full relative humidity scale between -70 to -40ºC in CO₂ in the pressure ranges from 5.5 to 9.5 hPa, representative of Martian surface atmospheric pressure. The results can be extrapolated to higher and lower temperatures.

In this presentation the final flight calibration and performance of the MEDA HS will be presented together with first results expected from the surface of Mars by the Perseverance rover.