Small Atmospheric Mars Payload Landed Experiment (SAMPLE): Concept and Modelling. Matthew Miersma1, John E. Moores2, Warren Soh3 and Carlos F. Lange1, 1University of Alberta, 2York University, 3Magellan Aerospace Winnipeg.

Introduction: To accurately model the Martian at-

mosphere and climate, it is important to have high qual-ity measurements of the near surface behavior of the at-mosphere. The atmosphere-surface interaction on Mars has been studied with meteorological stations, included on almost every landed mission from Viking 1 to In-Sight [1][2]. Since the meteorological instruments are part of the lander, interference from the rest of the lander can affect the quality of the measurements. The meas-urements are also constrained to the landing site or the changing position of the rover.

To address these issues, the Small Atmospheric Mars Payload Landed Experiment (SAMPLE) concept is proposed as shown in Figure 1. This consists of a small meteorological station, carried as a secondary payload on a future rover. By using the rover to deploy the station, the location and orientation of the station is precisely controlled. The station also includes a sonic anemometer to capture turbulent fluctuations [3].

Figure 1. SAMPLE concept design

SAMPLE Concept: Once deployed, SAMPLE would operate independent of the rover, communicating directly with a Mars orbiter.

Unlike past Martian weather instruments co-located on a lander or rover, the small station would have lim-ited instrument interference, since it is designed as an isolated meteorological station. This allows a priority to be given to the placement of the meteorological instru-ments, especially the anemometer.

The station is designed around a six element Cu-beSat frame with the anemometer attached to the top of an extended boom. Meteorological instruments for the station consist of a hygrometer, a dust sensor, and a

sonic anemometer, capable of capturing both wind speed and temperature measurements. A camera is also included to capture cloud movement.

Sonic Anemometer: The sonic anemometer fea-tured in the design would provide a significant improve-ment over previous anemometers. Those included with previous stations lack the precision and measurement frequency necessary to directly capture the turbulent fluctuations in the near surface atmosphere [3]. This measurement of the turbulent fluctuations is important for accurately modelling the interaction between the surface and the atmosphere.

The sonic anemometer shown in Figure 2, uses three pairs of transducers that measure the change in acoustic travel time along the line between the transducers. The precise high frequency measurements in three dimen-sions allow the anemometer to directly measure the tur-bulent fluctuations in the near surface atmosphere [3]. Since the anemometer measures the speed of sound, it can also provide high frequency measurements of the air temperature.

Figure 2. Sonic anemometer measurement lines

CFD Model: Computational fluid dynamics (CFD) simulations of the air flow around the station are used to guide the accommodation of the instruments, especially the sonic anemometer. First the orientation and interfer-ence of the anemometer is studied, then the convective flow around the station.

The simulations are performed using ANSYS CFX 19.1. Details of the simulation setup for the anemometer study are given in Table 1. Since the smallest scale of turbulence on Mars is significantly greater than on Earth [4], a laminar flow model is used. To capture the flow

Background Credit: NASA/JPL-Caltech

6249.pdfNinth International Conference on Mars 2019 (LPI Contrib. No. 2089)

around the station local refinement is used in the mesh. The mesh is also checked for grid independence.

Table 1. Simulation Settings

Setting Value Inlet Prescribed velocity profile Outlet Zero gradient Ground and Station No-slip wall Sides and Top Free-slip wall Turbulence Model Laminar Time Scheme Steady-state Advection Scheme Blended method Energy Isothermal Pressure 600 Pa Temperature 263 K Wind Speed* 3, 11, and 40 m/s Wind Direction 45˚ interval

*Wind speed at the height of the anemometer Anemometer Study: In order to evaluate the per-

formance of the sonic anemometer, the expected read-ings of the anemometer are calculated from the simula-tions. The speed ratio of the measurements is calculated by dividing the measurement by the free stream velocity so that the anemometer ideally has a speed ratio of one.

First the orientation of the anemometer is consid-ered. Two designs are compared, one with the anemom-eter directed horizontally and the other with the ane-mometer directed vertically. Streamlines are shown in Figure 3 for the two cases.

Figure 3. Streamlines for two anemometer orientations

When the anemometer is on the downwind side, the

supporting boom interferes with the horizontally ori-ented anemometer, resulting in a speed ratio 0.45 com-pared to 0.72 for the vertical orientation. Thus, the ver-tical orientation is preferred.

The performance of the anemometer is simulated for a range of wind speeds and directions to examine poten-tial interference. The resulting speed ratio is shown in Figure 4. When the wind is aligned with the anemome-ter arms the speed ratio decreases due to interference from the arms. The speed ratio also tends to decrease

with wind speed. This interference is small enough that it can be addressed in calibration.

Figure 4. Speed ratio versus wind direction

Hygrometer Study: For the hygrometer to give ac-curate readings, it is important that its temperature be kept close to that of the surrounding air. However, the station must be maintained at a high enough temperature to operate properly. While the hygrometer is insulated from the rest of the station, the air, heated by the station, can warm the hygrometer, especially at low wind speeds.

To determine the hygrometer temperature the con-vective flow around the station is simulated. Two poten-tial hygrometer locations are considered: one near the center of the station and one near the corner. A cold nighttime condition and a hot daytime condition are considered with a wind speed of 0.1 m/s. The cold night surface temperature is shown in Figure 5.

Figure 5. Hygrometer temperature for a cold night

For these conditions, the corner position consist-

ently provides a lower temperature than the central lo-cation and is the preferred position for the hygrometer.

Conclusion: The SAMPLE concept would provide important data to improve our understanding of the near surface atmosphere. It would also give much needed de-tails of turbulence that are important when modelling the Martian atmosphere. The CFD simulations of the station help guide the accommodation assessment of the instruments and can aid future calibration activities.

References: [1] Martinez G. M. et al. (2017) Space Sci. Rev., 212, 295-338, [2] Spiga A. et al. (2018) Space Sci. Rev., 214, 109, [3] Banfield D. et al. (2016) J. Acoust. Soc. Am., 140, 1420-1428, [4] Petrosyan A. et al. (2011) Rev. Geophys., 49, RG3005

6249.pdfNinth International Conference on Mars 2019 (LPI Contrib. No. 2089)