Humidity calibration of relative humidity devices in Martian conditions

Finnish Meteorological Institute (FMI) has developed relative humidity measurement devices for past and future Mars lander missions: REMS-H for Curiosity, MEDA HS for Mars 2020 and METEO-H for ExoMars 2020. The sensors used in these devices are HUMICAP® capacitive thin-film polymer sensors by Vaisala Inc. New calibration measurements are performed with ground reference models of these devices in the Mars Simulation Facility (MSF) and Planetary Analog Simulation Laboratory (PASLAB) at the German Aerospace Center (DLR) in spring 2020. The preliminary results will be given at the EGU 2020. Calibration of relative humidity devices requires in minimum two humidity points over the expected operational temperature and pressure range of the device. With two-point calibration the relative humidity devices can be used for scientific measurements with satisfactory quality but the uncertainty is notable. Stable humidity conditions between dry and saturation humidity in Martian conditions can be achieved reliably in very few laboratories in the whole world and humidity measurements in Martian conditions have been previously performed for the same devices in FMI laboratory and in Michigan Mars Environmental Chamber (MMEC) at the University of Michigan. The new measurement campaign will consist of stable humidity point measurements in multiple temperatures between +10°C to -70°C in CO2 gas and Martian pressure of approximately 7 hPa. The measurements are performed simultaneously for multiple devices in a small pressure vessel with continuous humidified carbon dioxide flow. The new measurement campaign will improve the characterization of the existing relative humidity devices in Mars lander missions and define in more detail the measurement uncertainties

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

MEDA HS is the relative humidity sensor on the Mars 2020 Perseverance rover provided by theFinnish Meteorological Institute (FMI). The sensor is a part of Mars Environmental DynamicAnalyzer (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-Hon board Curiosity.Calibration of relative humidity (RH) instruments for Mars missions is challenging due to the rangeof RH (from 0 to close to 100%) and temperature conditions (from about -90 ºC to + 22 ºC) thatneed to be simulated in the lab. Thermal gradients in different parts of the system need to be wellknown and controlled to ensure reliable reference RH readings. For MEDA HS the calibration testshave been performed for different models of MEDA HS in three Martian humidity simulatorlaboratories: 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 inlow 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 datatransferred from an identical ground reference model which has gone through rigorous testingalso after the flight model delivery. During the test campaign at DLR PASLAB that started inAutumn 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 surfaceatmospheric 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 presentedtogether with first results expected from the surface of Mars by the Perseverance rover

The MetNet vehicle : a lander to deploy environmental stations for local and global investigations of Mars

Investigations of global and related local phenomena on Mars such as atmospheric circulation patterns, boundary layer phenomena, water, dust and climatological cycles and investigations of the planetary interior would benefit from simultaneous, distributed in situ measurements. Practically, such an observation network would require low-mass landers, with a high packing density, so a large number of landers could be delivered to Mars with the minimum number of launchers. The Mars Network Lander (MetNet Lander; MNL), a small semi-hard lander/penetrator design with a payload mass fraction of approximately 17 %, has been developed, tested and prototyped. The MNL features an innovative Entry, Descent and Landing System (EDLS) that is based on inflatable structures. The EDLS is capable of decelerating the lander from interplanetary transfer trajectories down to a surface impact speed of 50-70 ms(-1) with a deceleration of <500 g for <20 ms. The total mass of the prototype design is approximate to 24 kg, with approximate to 4 kg of mass available for the payload. The EDLS is designed to orient the penetrator for a vertical impact. As the payload bay will be embedded in the surface materials, the bay's temperature excursions will be much less than if it were fully exposed on the Martian surface, allowing a reduction in the amount of thermal insulation and savings on mass. The MNL is well suited for delivering meteorological and atmospheric instruments to the Martian surface. The payload concept also enables the use of other environmental instruments. The small size and low mass of a MNL makes it ideally suited for piggy-backing on larger spacecraft. MNLs are designed primarily for use as surface networks but could also be used as pathfinders for high-value landed missions.Peer reviewe

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with -1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.Peer reviewe

Coulomb drag propulsion experiments of ESTCube-2 and FORESAIL-1

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with - 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.</p

The quality of the Mars Phoenix pressure data

The Phoenix lander operated on the surface of Mars for circa 5 months in 2008. One of its scientific instruments is an atmospheric pressure sensor called MET-P. We perform a comprehensive study to identify all error sources affecting the data measured by MET-P and to generate methods for compensating these errors. Our results show that MET-P performed much better than was reported immediately after the mission (Taylor et al., 2010). The error limits of the original calibrated Phoenix pressure data currently available in NASA's Planetary Data System (Dickinson, 2008) are from −5.3 Pa to +3.5 Pa. Further, almost no temperature-dependent error exists in the original calibrated MET-P data. However, we identify a previously unknown error source, temperature hysteresis, which causes minor peaks in the measured pressure curve (<0.4 Pa). The electronic supplementary material of this article contains a version of the Phoenix pressure data generated by applying all the error compensations developed in this study (Online Resource 1). The study is based on the re-analysis of the original test data of MET-P, the analysis of the engineering data measured during the mission on Mars and during the interplanetary cruise, and laboratory tests with the Reference Model of the MET-P sensor. Temperature dependent errors are evaluated by comparing the readings of two sensor heads with different sensitivities, measuring the same quantity. The principle of this method is applicable also for other types of instruments.Peer reviewe

MEDA HS : Relative humidity sensor for the Mars 2020 Perseverance rover

The Finnish Meteorological Institute (FMI) provides a relative humidity measurement sensor (HS) for NASA’s Mars 2020 rover. The sensor is a part of the Mars Environmental Dynamic Analyzer (MEDA), a suite of environmental sensors provided by Spain’s Centro de Astrobiolog´ıa. The main scientific goal of the humidity sensor is to measure the relative humidity of the Martian atmosphere near the surface and to complement previous Mars mission atmospheric measurements for a better understanding of Martian atmospheric conditions and the hydrological cycle. Relative humidity has been measured from the surface of Mars previously by Phoenix and Curiosity. Compared to the relative humidity sensor on board Curiosity, the MEDA HS is based on a new version of the polymeric capacitive humidity sensor heads developed by Vaisala. Calibration of humidity devices for Mars conditions is challenging and new methods have been developed for MEDA HS. Calibration and test campaigns have been performed at the FMI, at University of Michigan and the German Aerospace Center (DLR) in Berlin to achieve the best possible calibration. The accuracy of HS and uncertainty of the calibration has been also analysed in detail with VTT Technical Research Centre of Finland. Assessment of sensor performance after landing on Mars confirms that the calibration has been successful, and the HS is delivering high quality data for the science community

Pressure observations by the Curiosity rover: Initial results

REMS-P, the pressure measurement subsystem of the Mars Science Laboratory (MSL) Rover Environmental Measurement Station (REMS), is performing accurate observations of the Martian atmospheric surface pressure. It has demonstrated high data quality and good temporal coverage, carrying out the first in situ pressure observations in the Martian equatorial regions. We describe the REMS-P initial results by MSL mission sol 100 including the instrument performance and data quality and illustrate some initial interpretations of the observed features. The observations show both expected and new phenomena at various spatial and temporal scales, e.g., the gradually increasing pressure due to the advancing Martian season signals from the diurnal tides as well as various local atmospheric phenomena and thermal vortices. Among the unexpected new phenomena discovered in the pressure data are a small regular pressure drop at every sol and pressure oscillations occurring in the early evening. We look forward to continued high-quality observations by REMS-P, extending the data set to reveal characteristics of seasonal variations and improved insights into regional and local phenomena.Peer reviewe

Curiosity's rover environmental monitoring station: Overview of the first 100 sols

In the first 100 Martian solar days (sols) of the Mars Science Laboratory mission, the Rover Environmental Monitoring Station (REMS) measured the seasonally evolving diurnal cycles of ultraviolet radiation, atmospheric pressure, air temperature, ground temperature, relative humidity, and wind within Gale Crater on Mars. As an introduction to several REMS‐based articles in this issue, we provide an overview of the design and performance of the REMS sensors and discuss our approach to mitigating some of the difficulties we encountered following landing, including the loss of one of the two wind sensors. We discuss the REMS data set in the context of other Mars Science Laboratory instruments and observations and describe how an enhanced observing strategy greatly increased the amount of REMS data returned in the first 100 sols, providing complete coverage of the diurnal cycle every 4 to 6 sols. Finally, we provide a brief overview of key science results from the first 100 sols. We found Gale to be very dry, never reaching saturation relative humidities, subject to larger diurnal surface pressure variations than seen by any previous lander on Mars, air temperatures consistent with model predictions and abundant short timescale variability, and surface temperatures responsive to changes in surface properties and suggestive of subsurface layering. Key Points Introduction to the REMS results on MSL mission Overiview of the sensor information Overview of operational constraintsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108302/1/jgre20265.pd