**2. The Mars atmosphere**

The Martian atmosphere is mainly composed of CO2 (95.3%), with small amounts of Nitrogen and other gases. Typical surface atmosphere conditions are a pressure of 700 Pa [5] and a surface temperature variable in the range from 145 to 245 K [6]. The atmosphere density *ρ* can be calculated considering the perfect gases law as follows:

$$
\rho\_{\text{Mars}} = \frac{P}{R\_{\text{g}}T} = \frac{700}{188.918 \times 195} = 0.019 \text{ kg/}m^3 \tag{1}
$$

where *Rg* is the constant of CO2 gas taken as *RCO2* = 188.918 J/kg�K, and *T* is the mean temperature in Kelvin degrees. The result indicates that the Mars atmosphere density is very low compared with the Earth atmosphere *(ρEarth = 65ρMars*). When the density of a flow is very low, as is this case, usually, the hypothesis of continuum media is investigated by means of the nondimensional Knudsen number (*Kn*), given by,

$$Kn = \frac{\lambda}{L} \tag{2}$$

*Re* <sup>¼</sup> *VL ν*

where *V* is the flow velocity, *L* a typical length, and *ν* the kinematic viscosity

Additionally, Reynolds number is a fundamental parameter that satisfies the dynamic similarity, which is necessary to maintain the similarity between both aerodynamic flows, in Mars and in Earth. The Reynolds ratio is given by

> <sup>¼</sup> *VEarthLEarth VMarsLMars*

Thereby, when a wind is blowing, in both planets, with the same velocity *V* over

the same object with a characteristic length *L*, different Reynolds numbers are obtained, and the Reynolds ratio only depends on the physical atmosphere properties, such as kinematic viscosity, which is related to thermodynamics conditions (*P* and *T*) so that, in this case, the Reynolds similarity law is conversely proportional to

> <sup>¼</sup> *<sup>ν</sup>Mars νEarth*

Consequently, the Reynolds number in Earth is approximately 35 times higher than these to be expected in Mars surface, when Earth conditions corresponds to standard atmospheric conditions; therefore, Reynolds in Earth only can be equal when using same gas and same thermodynamics conditions as those present in Mars. But, if we are trying to simulate the problem by wind tunnel testing in Earth atmospheric conditions, flow velocity and length in Earth will be reduced in the same quantity of kinematic viscosity ratio, in order to verify the same Reynolds number in both planets. Because velocity can be slightly reduced, but length can be modified in a large range, this way will be followed by wind tunnel testing. For example, an experiment of the same velocity requires a subscaled model of 1/35th scale, while a reduction to 1/2 of flow velocity requires a reduction of approximately

Mars 2020 rover is a nuclear-powered ground vehicle that transports a set of scientific instruments dedicated to investigate the Martian surface. The rover is

*νMars νEarth*

*Re Earth Re Mars*

> *Re Earth Re Mars*

1/18th in all dimensions of the rover model to be tested in Earth.

the corresponding kinematic viscosity coefficient

*Typical atmosphere flow conditions in Mars compared with Earth.*

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

coefficient of the fluid.

**Table 1.**

**3. The Mars 2020 rover**

**71**

(4)

*:* (5)

¼ 35*:*4*:* (6)

where *λ* is the mean free path, related with the averaged distance between nearest molecules of the gas, and *L* is a characteristic length scale of the fluidic system or process under study. Although the mean free path depends on the temperature and pressure conditions, a typical value for Mars atmosphere is of order of 10 μm. On the other hand, the typical length of the process can be taken as the characteristic length of rover vehicle (*L* � 1.7 m). When analyzing the local flow over rover wind sensors, the boom diameter (*L* � 0.05 m) must be taken, resulting in last case, a Knudsen number of order of 2 � <sup>10</sup>�<sup>4</sup> < < 0.1, [7] and consequently, the gas of Mars atmosphere can be considered as a continuous media.

On the other hand, the dynamic viscosity (*μ*) in standard Mars conditions can be computed following the Sutherland law [8]:

$$
\mu(T) = \mu\_0 \left(\frac{T}{T\_0}\right)^{3/2} \left(\frac{T\_0 + \mathcal{S}}{T + \mathcal{S}}\right) \tag{3}
$$

where *T0* = 273 K, *S* = 222 K, and *μ<sup>0</sup>* is the dynamic viscosity at *T0*, taken as *<sup>μ</sup>*<sup>0</sup> = 1.37 � <sup>10</sup>�<sup>5</sup> <sup>N</sup>�s/m2 . Computation of Eq. (3) gives a dynamic viscosity coefficient value *<sup>μ</sup>* <sup>¼</sup> <sup>9</sup>*:*<sup>817</sup> � <sup>10</sup>�6N � <sup>s</sup>*=m*<sup>2</sup> when temperature is 195 K.

Finally, kinematic viscosity coefficient (*ν*) is given by the ratio of the dynamic viscosity to gas density (*<sup>ν</sup> <sup>=</sup> <sup>μ</sup>/ρ*) resulting a value of 5.167 � <sup>10</sup>�<sup>4</sup> m2 /s. **Table 1** shows the main Mars atmosphere parameters compared with Earth values, including the Mars gravity being 3.7 m/s2 .

From the aerodynamics point of view, the most important parameter to evaluate incompressible flows is the Reynolds number (*Re*), which is a dimensionless parameter defined as the ratio of inertial forces (� *<sup>ρ</sup>V*<sup>2</sup> *L*) to viscous forces (� *<sup>μ</sup>V=L*<sup>2</sup> ) and also indicates how turbulent the flow is. The expression of Reynolds number is as follows:

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*


**Table 1.**

hand, quality measurements of the wind in Mars could provide a better understanding of the geophysical phenomena occurring in Mars such as dust devils, carving intracrater layered deposits, and changes on dunes or any other eolian

The Martian atmosphere is mainly composed of CO2 (95.3%), with small amounts of Nitrogen and other gases. Typical surface atmosphere conditions are a pressure of 700 Pa [5] and a surface temperature variable in the range from 145 to 245 K [6]. The atmosphere density *ρ* can be calculated considering the perfect gases law as follows:

where *Rg* is the constant of CO2 gas taken as *RCO2* = 188.918 J/kg�K, and *T* is the mean temperature in Kelvin degrees. The result indicates that the Mars atmosphere density is very low compared with the Earth atmosphere *(ρEarth = 65ρMars*). When the density of a flow is very low, as is this case, usually, the hypothesis of continuum media is investigated by means of the nondimensional Knudsen number (*Kn*),

*Kn* <sup>¼</sup> *<sup>λ</sup>*

where *λ* is the mean free path, related with the averaged distance between nearest molecules of the gas, and *L* is a characteristic length scale of the fluidic system or process under study. Although the mean free path depends on the temperature and pressure conditions, a typical value for Mars atmosphere is of order of 10 μm. On the other hand, the typical length of the process can be taken as the characteristic length of rover vehicle (*L* � 1.7 m). When analyzing the local flow over rover wind sensors, the boom diameter (*L* � 0.05 m) must be taken, resulting in last case, a Knudsen number of order of 2 � <sup>10</sup>�<sup>4</sup> < < 0.1, [7] and consequently,

On the other hand, the dynamic viscosity (*μ*) in standard Mars conditions can be

<sup>3</sup>*=*<sup>2</sup> *<sup>T</sup>*<sup>0</sup> <sup>þ</sup> *<sup>S</sup>*

*T* þ *S* 

. Computation of Eq. (3) gives a dynamic viscosity

*T T*<sup>0</sup>

where *T0* = 273 K, *S* = 222 K, and *μ<sup>0</sup>* is the dynamic viscosity at *T0*, taken as

Finally, kinematic viscosity coefficient (*ν*) is given by the ratio of the dynamic

From the aerodynamics point of view, the most important parameter to evaluate

) and also indicates how turbulent the flow is. The expression of Reynolds

shows the main Mars atmosphere parameters compared with Earth values, includ-

the gas of Mars atmosphere can be considered as a continuous media.

*μ*ð Þ¼ *T μ*<sup>0</sup>

coefficient value *<sup>μ</sup>* <sup>¼</sup> <sup>9</sup>*:*<sup>817</sup> � <sup>10</sup>�6N � <sup>s</sup>*=m*<sup>2</sup> when temperature is 195 K.

viscosity to gas density (*<sup>ν</sup> <sup>=</sup> <sup>μ</sup>/ρ*) resulting a value of 5.167 � <sup>10</sup>�<sup>4</sup> m2

.

parameter defined as the ratio of inertial forces (� *<sup>ρ</sup>V*<sup>2</sup>

incompressible flows is the Reynolds number (*Re*), which is a dimensionless

computed following the Sutherland law [8]:

*<sup>μ</sup>*<sup>0</sup> = 1.37 � <sup>10</sup>�<sup>5</sup> <sup>N</sup>�s/m2

(� *<sup>μ</sup>V=L*<sup>2</sup>

**70**

number is as follows:

ing the Mars gravity being 3.7 m/s2

<sup>188</sup>*:*<sup>918</sup> � <sup>195</sup> <sup>¼</sup> <sup>0</sup>*:*<sup>019</sup> *kg=m*<sup>3</sup> (1)

*<sup>L</sup>* (2)

(3)

/s. **Table 1**

*L*) to viscous forces

processes due to the wind-driven particle mobility.

*<sup>ρ</sup>Mars* <sup>¼</sup> *<sup>P</sup>*

*RgT* <sup>¼</sup> <sup>700</sup>

**2. The Mars atmosphere**

*Mars Exploration - A Step Forward*

given by,

*Typical atmosphere flow conditions in Mars compared with Earth.*

$$Re = \frac{\text{VL}}{\nu} \tag{4}$$

where *V* is the flow velocity, *L* a typical length, and *ν* the kinematic viscosity coefficient of the fluid.

Additionally, Reynolds number is a fundamental parameter that satisfies the dynamic similarity, which is necessary to maintain the similarity between both aerodynamic flows, in Mars and in Earth. The Reynolds ratio is given by

$$\frac{Re\_{Earth}}{Re\_{Mars}} = \frac{V\_{Earth} L\_{Earth}}{V\_{Mars} L\_{Mars}} \frac{\nu\_{Mars}}{\nu\_{Earth}}.\tag{5}$$

Thereby, when a wind is blowing, in both planets, with the same velocity *V* over the same object with a characteristic length *L*, different Reynolds numbers are obtained, and the Reynolds ratio only depends on the physical atmosphere properties, such as kinematic viscosity, which is related to thermodynamics conditions (*P* and *T*) so that, in this case, the Reynolds similarity law is conversely proportional to the corresponding kinematic viscosity coefficient

$$\frac{Re\_{Earth}}{Re\_{Mars}} = \frac{\nu\_{Mars}}{\nu\_{Earth}} = \text{35.4.}\tag{6}$$

Consequently, the Reynolds number in Earth is approximately 35 times higher than these to be expected in Mars surface, when Earth conditions corresponds to standard atmospheric conditions; therefore, Reynolds in Earth only can be equal when using same gas and same thermodynamics conditions as those present in Mars. But, if we are trying to simulate the problem by wind tunnel testing in Earth atmospheric conditions, flow velocity and length in Earth will be reduced in the same quantity of kinematic viscosity ratio, in order to verify the same Reynolds number in both planets. Because velocity can be slightly reduced, but length can be modified in a large range, this way will be followed by wind tunnel testing. For example, an experiment of the same velocity requires a subscaled model of 1/35th scale, while a reduction to 1/2 of flow velocity requires a reduction of approximately 1/18th in all dimensions of the rover model to be tested in Earth.

#### **3. The Mars 2020 rover**

Mars 2020 rover is a nuclear-powered ground vehicle that transports a set of scientific instruments dedicated to investigate the Martian surface. The rover is

where *E* is the energy of the wire, *Q* is the transferred heat to the flow, and *W* is the heating power, related with the electric intensity *I* and the resistance of the wire

On the other hand, the convicted heat is given by the Newton's cooling law as

where *h* is the thermal convection coefficient,*Tw* is the wire temperature,*T*<sup>∞</sup> is

Dimensional analysis indicates that thermal convection coefficient depends on

where *Nu* is the nondimensional Nusselt number that represents the convection

Assuming the orientation of the wire as constant, low airspeed, natural convection is neglectable, and Prandtl number as constant as usual in gases flows, the

This function was empirically determined by King, as the following potential

So that, the output signal measured between the ends of the wire is the square of

where coefficients *C1, D1*, and *n* must be experimentally determined by calibration. Concluding, the voltage *EW* is a measurement directly related with the flow

Several wind sensors are described in the literature [8]. Some sensors based on flow dynamic pressure (Pitot-static probe, rotating sensors as cup and vane anemometers, etc.) were discarded to be used in Mars, mainly due to the very low density of Martian atmosphere, and others as Laser Doppler Anemometry (LDA) because they require an appropriate particle seeding of the flow. Finally, thermal anemometry was selected because it offers reliability in a wide range of temperature, simplicity and robustness, low power consumption, high resolution, and short time of response [4]. Moreover, this technology was used during the Viking mission, demonstrating their

*R* (8)

*dt* <sup>¼</sup> *h T*ð Þ *<sup>w</sup>* � *<sup>T</sup>*<sup>∞</sup> *Aw* (9)

*<sup>d</sup> Nu* (10)

*Nu* ¼ *Nu Re* ð Þ*:* (11)

*Nu* <sup>¼</sup> *<sup>C</sup>* <sup>þ</sup> *D Re <sup>n</sup>:* (12)

*<sup>R</sup>*<sup>2</sup> <sup>¼</sup> *<sup>C</sup>*<sup>1</sup> <sup>þ</sup> *<sup>D</sup>*1*U<sup>n</sup>* ð Þð Þ *Tw* � *<sup>T</sup>*<sup>∞</sup> (13)

*dW dt* <sup>¼</sup> *<sup>I</sup>* 2

*dQ*

the flow temperature, and *Aw* is the area of heat transfer for the wire.

heat transfer to the conduction heat transfer ratio.

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

Nusselt number is only a function of the Reynolds number *Re*

*<sup>W</sup>* related with wind velocity as follows:

measurement capabilities in the Martian atmosphere [10, 11].

*E*2 *<sup>W</sup>* ¼ *I* 2

the conductivity of fluid *k*, wire diameter *d*, and the Nusselt number so that

*<sup>h</sup>* <sup>¼</sup> *<sup>k</sup>*

*R*, given by

follows:

correlation:

voltage *E*<sup>2</sup>

velocity.

**73**

**5. Rover wind sensors**

**Figure 1.** *Scheme of the Mars rover vehicle.*

basically composed of a central box body with rectangular section supported by six wheels. A vertical mast supports the remote vision camera and MEDA environmental instruments and an articulated robotic arm is dedicated to get biologic and geologic samples from soil.

Electrical power for engineering systems and science payload of the rover is provided by the Multi-Mission Radioisotope Thermoelectric Generator (MMRGT). The MMRGT converts heat from the natural radioactive plutonium into electrical power [1]. MMRGT is a cylindrical box connected to heat dissipation fins and two heat exchanger plates [9]. **Figure 1** shows a general view of the Mars 2020 rover vehicle (robotic arm was not represented for a better vision of the rover devices).

MEDA wind sensors are located in both booms, around the Remote Sensing Mast (RSM) and oriented 120° from each other. Sensors are capable to measure wind speed up to 70 m/s, and they are located on the rover mast and affected by the rover presence. A correction of the wind data is necessary in order to obtain correct measurements by avoiding the flow perturbation produced by the rover.

#### **4. Thermal anemometry**

Thermal anemometry, usually named as hot wire (HW) technique, is a wellestablished measurement technique introduced in the first half of twentieth century from the study carried out by King after investigating the thin cylinders heat transfer. This technique has got a very high state of development, offering high quality in measuring flow velocities and especially for study of turbulent flows. Air flow velocity and fluctuations can be measured by HW based on the detection of rapid changes in the transferred heat from a tiny sensor (wire typically 5 μm in diameter) to the flow. This sensor is electrically heated so that the flow velocity is determined from the electric power necessary to maintain the temperature of wire at a constant value, by means of an electronic circuit that provides an automatic control loop of temperature. This type of HW is named as Constant Temperature Anemometer (CTA). When electric current crosses through the wire, its temperature is rising due to the heat produced by Joule effect. In a stationary situation, the heat produced is equilibrated by the refrigeration effect produced by the gas flow motion. The energy variation of the wire is given by the following expression:

$$\frac{dE}{dt} = \frac{dW}{dt} + \frac{dQ}{dt} \tag{7}$$

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

where *E* is the energy of the wire, *Q* is the transferred heat to the flow, and *W* is the heating power, related with the electric intensity *I* and the resistance of the wire *R*, given by

$$\frac{dW}{dt} = I^2 R \tag{8}$$

On the other hand, the convicted heat is given by the Newton's cooling law as follows:

$$\frac{dQ}{dt} = h(T\_w - T\_\infty)A\_w\tag{9}$$

where *h* is the thermal convection coefficient,*Tw* is the wire temperature,*T*<sup>∞</sup> is the flow temperature, and *Aw* is the area of heat transfer for the wire.

Dimensional analysis indicates that thermal convection coefficient depends on the conductivity of fluid *k*, wire diameter *d*, and the Nusselt number so that

$$h = \frac{k}{d} \text{Nu}$$

where *Nu* is the nondimensional Nusselt number that represents the convection heat transfer to the conduction heat transfer ratio.

Assuming the orientation of the wire as constant, low airspeed, natural convection is neglectable, and Prandtl number as constant as usual in gases flows, the Nusselt number is only a function of the Reynolds number *Re*

$$\mathbf{N}u = \mathbf{N}u(\operatorname{Re}).\tag{11}$$

This function was empirically determined by King, as the following potential correlation:

$$\text{Nu} = \text{C} + D \,\text{Re}^n.\tag{12}$$

So that, the output signal measured between the ends of the wire is the square of voltage *E*<sup>2</sup> *<sup>W</sup>* related with wind velocity as follows:

$$E\_W^2 = I^2 R^2 = (\mathbf{C}\_1 + D\_1 U'')(T\_w - T\_\infty) \tag{13}$$

where coefficients *C1, D1*, and *n* must be experimentally determined by calibration. Concluding, the voltage *EW* is a measurement directly related with the flow velocity.

#### **5. Rover wind sensors**

Several wind sensors are described in the literature [8]. Some sensors based on flow dynamic pressure (Pitot-static probe, rotating sensors as cup and vane anemometers, etc.) were discarded to be used in Mars, mainly due to the very low density of Martian atmosphere, and others as Laser Doppler Anemometry (LDA) because they require an appropriate particle seeding of the flow. Finally, thermal anemometry was selected because it offers reliability in a wide range of temperature, simplicity and robustness, low power consumption, high resolution, and short time of response [4]. Moreover, this technology was used during the Viking mission, demonstrating their measurement capabilities in the Martian atmosphere [10, 11].

basically composed of a central box body with rectangular section supported by six wheels. A vertical mast supports the remote vision camera and MEDA environmental instruments and an articulated robotic arm is dedicated to get biologic and

Electrical power for engineering systems and science payload of the rover is provided by the Multi-Mission Radioisotope Thermoelectric Generator (MMRGT). The MMRGT converts heat from the natural radioactive plutonium into electrical power [1]. MMRGT is a cylindrical box connected to heat dissipation fins and two heat exchanger plates [9]. **Figure 1** shows a general view of the Mars 2020 rover vehicle (robotic arm was not represented for a better vision of the rover

MEDA wind sensors are located in both booms, around the Remote Sensing Mast (RSM) and oriented 120° from each other. Sensors are capable to measure wind speed up to 70 m/s, and they are located on the rover mast and affected by the rover presence. A correction of the wind data is necessary in order to obtain correct measurements by avoiding the flow perturbation produced by the rover.

Thermal anemometry, usually named as hot wire (HW) technique, is a wellestablished measurement technique introduced in the first half of twentieth century from the study carried out by King after investigating the thin cylinders heat transfer. This technique has got a very high state of development, offering high quality in measuring flow velocities and especially for study of turbulent flows. Air flow velocity and fluctuations can be measured by HW based on the detection of rapid changes in the transferred heat from a tiny sensor (wire typically 5 μm in diameter) to the flow. This sensor is electrically heated so that the flow velocity is determined from the electric power necessary to maintain the temperature of wire at a constant value, by means of an electronic circuit that provides an automatic control loop of temperature. This type of HW is named as Constant Temperature Anemometer (CTA). When electric current crosses through the wire, its temperature is rising due to the heat produced by Joule effect. In a stationary situation, the heat produced is equilibrated by the refrigeration effect produced by the gas flow motion. The energy variation of the wire is given by the following expression:

> *dE dt* <sup>¼</sup> *dW*

*dt* <sup>þ</sup> *dQ*

*dt* (7)

geologic samples from soil.

*Scheme of the Mars rover vehicle.*

*Mars Exploration - A Step Forward*

**4. Thermal anemometry**

devices).

**72**

**Figure 1.**

MEDA wind sensors are a new design based on the wind REMS sensor [2, 3] that was embarked on the Mars Science Laboratory (MSL) Curiosity rover [4] currently sending data from Mars atmosphere. The behavior of thermal wind sensors installed over the boom of the Mars rover is similar to hot wire, described in earlier paragraph. They are based on a group of four sensitive surface hot film sensors (named dices A, B, C, and D) installed in the same plane (see **Figure 2**). Sensors are refrigerated when the wind is blowing over each dice, and consequently, an electric power must be apply to keep temperature constant on the dice (constant operation reference temperature CTA). The value of electric power gives a measurement of the airspeed on each dice and the direction from blowing. Dices situated in front the flow are cooled more than those located in back positions, since the wind heats up as the first ones are cooled and heat is transferred to the airstream. A comparative analysis of the electric power required for each of the four dices will give us an indication of the angle of incidence of the air flow.

**6. Boom aerodynamics**

*Aerodynamics of Mars 2020 Rover Wind Sensors DOI: http://dx.doi.org/10.5772/intechopen.90912*

The rover wind sensors are installed on the boom surface. Booms are located in the vertical mast over the upper rover central box surface (see **Figures 1** and **2**). Two booms are at the same height and contained in the same horizontal plane, with an angular offset of 120°. The boom external geometry is similar to these of the Pitot-static tube. This is a classical instrument for measuring airspeed in aerodynamics and fluid mechanics that has proven its efficiency for more than a century. This tube has a hemispherical head followed by a cylindrical body with axisymmetric geometry so that the longitudinal flow is coming to the wind sensor without detachment. On the other hand, rover booms have a hemispherical head followed by a cylindrical body with polygonal faces where thermal sensors are installed (see **Figure 2**). In this section, a theoretical analysis of two simplified cases is presented:

When the wind is blowing in longitudinal axisymmetric direction, the head of the boom receives the flow without detachment. A first approximation to this kind of flow can be studied by considering the incompressible potential flow on the axisymmetric Rankine half-body of revolution. This flow is produced when a uniform stream of velocity *U*<sup>∞</sup> is flowing over a three-dimensional point source of strength *M* located at the origin. This situation is depicted in **Figure 4**, for a

A stagnation point denoted by P is produced by the upstream source point when both singularities are equal in velocity. The location of this point is calculated as

> ffiffiffiffiffiffiffiffiffiffi *M πU*<sup>∞</sup>

r

The velocity potential *Φ* corresponding to the superposition of a uniform stream

*<sup>Φ</sup>*ð Þ¼ x, r *<sup>U</sup>*∞*<sup>x</sup>* � *<sup>M</sup>*

<sup>4</sup>*πd*<sup>2</sup> , (14)

*:* (15)

<sup>4</sup>*π<sup>R</sup>* (16)

*<sup>U</sup>*<sup>∞</sup> <sup>¼</sup> *<sup>M</sup>*

*<sup>d</sup>* <sup>¼</sup> <sup>1</sup> 2

and a source located in the origin is given by the following expression:

longitudinal axisymmetric flow and cross flow over the boom.

**6.1 Longitudinal axisymmetric flow**

half-body of revolution with radius *a*.

and finally, the distance to point P is

where *<sup>R</sup>* <sup>¼</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffi

*Axial flow over wind sensor boom.*

*<sup>x</sup>*<sup>2</sup> <sup>þ</sup> *<sup>r</sup>*<sup>2</sup> <sup>p</sup> .

follows:

**Figure 4.**

**75**

Finally, a joint calibration of the four dices allows us to know the wind speed and the incidence angle over the sensor. A more detailed description is in Ref. [4].

**Figure 3** shows the set-up for functional tests of rover wind sensors. A simplified version of hot film sensor, similar to the real sensor was implemented over a flat plate. A specially designed bed fabrication in extruded polystyrene was used to support the plate with hot film sensors in order to perform the functional tests by wind tunnel testing to verify the wind endurance. During this test campaign, several values of airspeed were blown by wind tunnel and the air was flowing on the sensors refrigerating them. Readings of electric signals from dices electronic chip were acquired to verify the correct behavior of the wind sensors, and its integrity was verified when the flow was blowing over them. A laser Doppler anemometer was used as an airspeed standard.

**Figure 2.** *Rover wind sensor boom.*

**Figure 3.** *Mars rover wind sensors during functional tests.*
