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Radio Wave Propagation for Communication on and

around Mars Part I: Propagation Through Mars Environment

1. Introduction 1.1 Mars Environment 1.2 Wave Propagation Parameters

2 Mars ionosphere and its Effects on Propagation (Plasma and Magnetic Field) 2.1 Introduction 2.2 Formation of Martian Ionosphere 2.3 Dayside Mars Ionospheric Structure 2.4 Nightside Martian Ionosphere 2.5 Ionospheric Effects on Wave Propagation 2.6 Recommendation

3. Mars Atmosphere and its Effects on Propagation 3.1 Introduction 3.2 Tropospheric Effects 3.3 Cloud Effects 3.4 Atmospheric Aerosols Effects 3.5 Recommendation

4. Mars Atmospheric Gaseous Attenuation 4.1 Introduction 4.2 Martian Gaseous Composition and Comparison with Earth Atmosphere

4.3 Martian Atmospheric Absorption Effects on Microwaves 4.4 Recommendation

5. Mars Dust Storms and their Effects on Propagation 5.1 Introduction 5.2 Local Dust Storms 5.3 Global Dust Storms 5.4 Radio Wave Attenuation though Dust Storms 5.5 Recommendation

6. Mars Geomorphology Effect 6.1 Introduction 6.2 Mars Polar Ice Caps 6.3 Mars Grand Canyons "Valles Marineris" 6.4 Recommendation

7. Propagation Issue for Communication between Earth and Mars 7.1 Free Space Spread Loss on Signals 7.2 Total Propagation Losses between Mars and Earth 7.3 Recommendation

8. Summary (Final Recommendations and Suggestions) 9. Glossary

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Mars Orbit

The Martian climate and surface features are significantly influenced by the shape of the Martian orbit. The eccentricity of Mars' orbit is 0.093,

in contrast to the near-circular Earth orbit (0.017). The high eccentricity

affects Mars in a number of ways.

When Mars is at its perihelion (closest point to the sun), the southern

Martian hemisphere tilts toward the sun. Thus, the southern hemisphere has

a relatively hot and short summer.

When 'Mars is at its aphelion (farthest point from the sun), the

northern Martian hemisphere tilts toward the sun. Thus, the northern

hemisphere has a relatively cold and long summer.

These differences have generated profound effects on Martian

atmospheric circulation patterns, surface geomorphologic change,

duststorm and polar ice cap formation, etc.

I I

S u n () Mars

Fundamental Theory For Radio Wave Propagation

For the low frequency waves, the refractive index of a medium

containing free electrons, with a superimposed steady magnetic field,

is given by the Appletion-Hartree fonnula.

2 X 12 =1-

1-iZ-

Thus, the refractive index is mainly function of electron density and

background magnetic field.

For the high frequency waves (> 1 GHz), the radiometeorology has

some effects on the wave propagation. These effects mainly take

place in the lower atmospheric portion: the troposphere.

N = (TZ - 1) X lo6 (N unit) (2)

5 pwv T T2 (3) P

N = 77.6- + 3.73 X 10 -

Thus, the tropospheric radio refractivity is a function of atmospheric

pressure, P (mb), absolute temperature, T (K), and water vapor

pressure, P,, (mb).

Martian Ionospheric Model

The Martian dayside ionosphere is generated through the photo-ionization

of its upper atmosphere. The top height of ionosphere (ionopause) is

dependent on solar wind pressure. A comet-like structure with low electron

density can extend several thousand kilometers at nightside. The Martian

dayside ionosphere may be described using a simple Chapman layer model.

The Martian dayside ionosphere has stable peak height and peak density. Its

peak height is between 120 and 130 km.

N(h)=Nrnexp{0 .5[1- (h-hrn) /H-exp(- (h-h , ) lH)]} (4)

where N , = No (COS X ) k ( 5 )

and h, = !Q + Hln sec x (6)

Measurement

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Table 3. Martian Ionospheric Peak Electron Densities and Critical Frequencies

Ionospheric Mars I Earth Condition no(m-’> no (cm-’) fo (MHz) no (cm”) fo (MHz)

Dayside Solar Max. 2 . 5 ~ 1 0 ~ ’ 2.5~10’ 4.5 2.0xOb 12.7

Solar Min. 1 .Ox 10’ ’ 1 .ox 10’ 2.9 5.0~10’ 6.3 Nightside* Solar Min. 5 .Ox 10’ 5.0~10’ 0.6 2.0x10’ 4.0

Dayside TEC 2 . 0 ~ 1 0 ’ ~ m ” 2 . 0 ~ 1 0 ’ ~ cm-L I I I I I

* There is no nightside ionospheric data available during solar maximum

Table 4. Usable Critical Frequencies and Hop Distances for Various Launch Angles

Launch Angle eo (P 15” 30” 45” w 75”

Maximum Usable Frequency 4.0 4.14 4.62 5.66 8.0 15.5

(MHz) One Hop Distance (km) 0 67.0 144.3 250.0 433.0 933.0

Table 5. Effects of Total Electron Contents (TEC=2x10 16 /m 2 ) of the Mars Ionosphere on Wave Characters (one-way path)

Faraday Rotation

Q=(2.36x104/f2)B,.TEC

Range Delay

AR=(40.3/f2)TEC

Phase Advance

AQ=(8.44xlO7/f)TEC

Time Delay

At=( 1.34x107/f2)TEC

100 MHz 500”

80 m

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270 ns

500 MHz 20”

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1 GHz I 5GHz

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16.9 rad 3.4 rad

2.7 ns 0.108 ns

10 GHz 0.05”

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1.69 rad

0.027 ns

Recommendation

The Martian ionosphere may play an important role in the future Mars

ground-to-ground communication. The Martian ionospheric critical

frequency is - 4.0 MHz for vertical incidence. The frequency is high

enough to carry the information. The stable condition in the dayside

ionosphere is favorable to oblique incident communication using the

ionosphere as a reflector for Martian surface-to-surface communication.

Using Mars' ionosphere we can also perform trans-horizon (or beyond line

of sight) communication for future Martian colonies, rover, vehicles and

robots released. from 'Mars landers. However, because of low usable

frequency and very unstable condition, the nightside ionosphere has some

limitations in being used for global communication.

.... "".-..-." .".

Mars Atmosphere and its Effects on ,Propagation

Martian Tropospheric Structure

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1 0-1 1 oo l o 1 MGSRST 1 7 A p lgad Pressure, millibars

Atmospheric Pressure Profile

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Atmospheric Temperature Profile

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Source: NASA

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Surface Atmospheric Composition and Gaseous Attenuation

Surface Pressure: -6.1 mb (variable)

Surface Density: -0.020 kg/m’

Scale height: -1 1.1 km

Average temperature: -2 10 K

Diurnal temperature range: 184 K to 242 K

Mean molecular weight: 43.34 g/mole

Atmospheric composition (by volume):

Major: Carbon Dioxide (C02) - 95.32% ; Nitrogen (N2) - 2.7%

Argon (Ar) - 1.6%; Oxygen (02) - 0.13%; Carbon Monoxide (CO) - 0.08%

Minor (ppm): Water vapor (H20) - -150-300 (variable);

Nitrogen Oxide (NO) - 100; Neon (Ne) - 2.5;

Hydrogen-Deuterium-Oxygen (HDO) - 0.85; Krypton (Kr) -

0.3; Xenon (Xe) - 0.08, Ozone (0,) - 0.04 - 0.2.

Gas Thermal Dynamic Equations

pi = nikgT, P = NkBT, P = C p i i

Table 7. Surface Atmospheric Parameters at Mars and Earth

P, T, tem- M , mean p , mass N , number V,,,, mole volume

Mars 6.1 210 43.34 g/mole 0.021 2 . 8 5 ~ 1 0 ' ~ 2 . 1 ~ 1 0 ~ Earth 1013 300 28.61 g/mole 1.29 2 . 7 ~ 1 0 ' ~ 22

Planets pressure perature molecule (mb) ( O K ) density . density -1 weight (kglm ) (m - ) (m3/kmo1e)

Table 8. A Comparison of the Top Six Atmospheric Compositions on Mar - Earth

(1013ml

fraction P i 9

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H, scale height (km)

-1 1.1 -9.5

; and Earth Ground

ppm: part per million.

Table 9. Ratios of Atmospheric Compositions between Earth and Mars

Surface ,300"K) pi , mass nipurnbe density density

0.8 1 . 1 ~ 1 0 ' ~ ( dm3) (cmm3)

986.9 2 . 1 ~ 1 0 ~ ~ 16.8 2 . 6 ~ 1 0 ' ~

283.7 5 . 7 ~ 1 0 ' ~

2.6x10-~ 5:6x1012 ~ 8.1 2 . 7 ~ 1 0 ' ~

Ratios (EarthMars) CO, N2 4 0' co H'O ,

(fraction by volume)

(fraction by weight)

(density)

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for j3, 6 . 4 ~ 1 0-4 44 0.88 244 3 . 9 ~ 1 0'4 50.4

for pi and ni 0.04 2704 54 1 . 4 ~ 1 0 ~ 0.024 3068 ~ ~ ~ ~~~ ~~~~~

,277

Atmospheric Absorption Attenuation by Wator Vapor and Oxygen at Earth and Mars Surface

. - 0 50 100 150 200 2 5 0 300 350

Frequency (GHz)

Martian Dust Storms and their Effects on Propagation

On Mars the threshold velocities are much larger than those on Earth

because of the thinner atmosphere, but depending on the surface pressure.

The optimum size for particle movement on Mars is near 0.1 mm, close to

the size for Earth. Threshold shear velocities (V,) required to move the

0.1-mm particles range from 1.4 d s e c . On Earth threshold velocities at

the optimum size are close to 0.2 d s e c .

Table 10. Martian Great Dust Storms

Year Observation L, Initial Location 1909 (Aug) Earth 191 1 (Nov) Earth 1922 Earth 192 1924 (Oct) Earth 1924 (Dec) Earth 237 Isidis Planita 1939 Earth Utopia 1941 (Nov) Earth South of Isidis 1943 Earth 3 10 Isidis 1956 Earth 250 Hellespontus 1958 Earth 3 10 Isidis 197 1 (July) Earth 213 Hellespontus 1971 (Sept) Earth, Mariner 9 260 Hellespontus 1973 Earth 300 Solis Planum 1977 (Feb) Vilung 205 Thaumasia 1977 (June) Viking 275 1979 Viking 225

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Martian dust storm types include: planet-encircling, i.e., those dust

storms that are believed to have encircled the planet at some latitude;

regional dust storms, clouds, and hazes with a spatial dimension greater

than 2000 km; local dust storms, clouds, and hazes with a spatial dimension

smaller than 2000 km.

Mars dust basically consists of basalt and montmorillonitic clay. Clear

atmosphere corresponds to a background aerosol of optical depth ranging

from 0.3 to 0.5, at a wavelength of 0.67mm, while during the most intense

portions of the global storms the opacity was found to increase to 4.0 - 5.0.

A local storm generally has a spatial extent of several hundred kilometers.

A great dust storm can have a size as big as the state of Texas, and even

cover half the planet. . '

Dust size distribution has been modeled using a modified gamma

function [Toon et al., 1977; Hunt, 19791:

Chu [1979] and Goldhirsh [1982] have summarized the studies of the

effects of Earth dust storms on radio wave propagation due to earth dust

storms. Microwave attenuation A(1) is

282

Smith and Flock [1986] have performed a first study of X and Ka band

wave propagation through Martian dust. Attenuation may be expressed as

When a distribution of particle size is available, we can use another type

of expression as [Goldhirsh, 19821:

Table 1 1. Dielectric Permittivity Index of Dust Particles Index 10 GHz 10 GHz 10 GHz S band 32 GHz 8.8 GHz Dust at Dust at

E Ghobrial Clay Sand Goldhirsh Clay* Clay* 2oPm* 2 pm* ( 1980) (1982)

E' ~ 4.56 7.42 3.35 .4.56 2.5 2.5 2.0 3.0 (+O. 1 1, (+1.73, (20.03) -0.24) - 1.22)

E" 2.5 1 1.119 0.042 0.25 1 0.06 0.02 0.4 0.1 (+0.074, (+0.597, (20.02) -0.066) -0.437)

* Smith and Flock [1986]

Table 12. A Comparison of Dust Storm Parameters between Earth and Mars

NT p Mean Size Maximum Visibility Path Attenuation Mass

m-3 g/m3 (pm) Size ( p - 4 (m) Length at 32 GHz Loading Earth 10' 2 . 6 ~ 1 0 ~ 30-40 80-300 5.1-3.8 l O k m 65 dB 40-60g/m3 Mars 3x107 3 . 0 ~ 1 0 ~ 1-10 20 184 lOkm 3 dB 0.4 g/m3

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