Lunar Surface Reactor General 1 Extraterrestrial Environments The Martian and lunar environments are quite different from the Earth and from each other in many respects such as reduced atmospheric pressure weaker gravitational pull surface elemental composition and the wide and often unpredictable temperature shifts In order to allow for appropriate and effective design adaptations and innovations these differences must be taken into account This section provides a brief description and listing of some important physical properties of the Martian and lunar environments The properties described and tabulated below will serve as a standard reference and will be useful for determining the appropriate materials and designs for the core power conversion unit shielding and radiator 1 1 The Moon Since the actual geological and weather conditions vary across the lunar surface accurate values can only be determined once a landing site is determined However until that location is known it is instructive to consider the average values for these factors It is also important to note that while the lunar poles are the most likely future mission sites many of the below values were obtained from the early lunar missions that landed predominately in the equatorial regions In the polar region the sun continuously occupies a low position on the horizon and surface temperatures are more moderate and less variable generally working to our advantage In this design while we anticipate going to the poles we have designed the reactor to be robust and work anywhere on the lunar surface 1 1 1 Lunar Atmosphere and Gravity The moon has almost no atmosphere With an atmospheric pressure of 10 8 Pa very little convection can occur on the lunar surface which has direct implications for material options radiator and shielding systems Yet with an atmosphere composed almost entirely of inert noble gases such as helium neon and argon minimal corrosion is expected Hydrogen represents a major exception but at a concentration of roughly 35 000 particles per cubic centimeter hydrogen can be disregarded as a threat to material stability 1 Gravity on the Moon is roughly one ninth of that on the Earth See tables 1 and 2 below for data on composition and properties of the lunar atmosphere Gas H2 He 4 1 Particles m3 35 000 40 000 Radiator Ne 20 Ne 22 Ar 36 Ar 40 CO2 H3N CH4 40 000 5 000 2 000 30 000 1 000 1 000 1 000 Table 1 Composition of Lunar Atmosphere Property surface Value Units Thermal Conductivity Effectively zero W m K Pressure 3 x 10 10 Pa Density 2 x 1011 particles m3 Gravity 1 62 m s2 Table 2 1 1 2 Average Properties of Lunar Atmosphere Lunar Geology Much of the moon s cratered surface is composed of igneous rock not unlike that found near volcanoes on Earth 2 See tables 3 and 4 below for data on composition and properties of the lunar soil Compound SiO2 TiO2 Al2O3 FeO MgO CaO Na2O Page 2 Weight Percent 47 3 1 6 17 8 10 5 9 6 11 4 0 7 Radiator K2O MnO Cr2O3 0 6 0 1 0 2 Table 3 Composition of Lunar Soil Property Value Units Thermal Conductivity 10 3 W m K Albedo 0 11 Table 4 Properties of Lunar Soil 1 1 3 Lunar Meteorological Properties Temperature variations on the moon are extreme when compared with the Earth The lunar day is equivalent to 28 5 Earth days and all parts of the lunar surface excepting the polar regions spend half this time in the sun With virtually nonexistent atmospheric convection and limited surface conductivity the side of the moon exposed to the sun heats to over 373K When the sun sets however temperatures drop below 160K Owing to the low surface conductivity shadowed regions on the sunny side will also fall to the night temperature resulting in large temperature gradients Table 5 displays some of the lunar meteorological properties Property Value Units Temperature 100 to 400 K Blackbody Temperature 274 5 K Solar Radiation 1367 6 W m2 Table 5 Lunar Meteorological Properties 1 2 Mars Page 3 Radiator The Martian environment differs greatly from the moon since Mars has a more significant atmosphere different elemental composition and is farther from the sun Again because the actual properties that will be encountered on Mars are highly variable based on location and season average values are given below Values obtained from the Viking I mission are also given for comparison Once likely landing sites are identified more specific values can be obtained 1 2 1 Martian Atmosphere and Gravity The Martian atmosphere consists of 95 carbon dioxide with the other 5 consisting of nitrogen argon and trace amounts of oxygen and carbon monoxide Unlike the inert lunar environment the Martian atmosphere is potentially corrosive especially to potential reactor core materials Atmospheric pressure ranges from 600 800 Pa on Mars considerably thinner than the Earth s by about 1 150 3 though many orders of magnitude thicker than the Moon s The surface gravity of Mars is about one third of that of Earth s See tables 6 9 below for data on composition and properties of the Martian atmosphere Gas CO2 N2 Ar O2 CO H2O NO Ne HD O Kr Xe Volume Percent 95 32 2 7 1 6 13 08 210 ppm 100 ppm 2 5 ppm 0 85 ppm 0 3 ppm 0 08 ppm Table 6 Composition of Martian Atmosphere 2 Page 4 Property surface Value Units Thermal Conductivity 3 0 012 W m K Pressure 2 600 to 800 Pa Radiator 3 Density 2 0 020 kg m Gravity 3 69 m s2 Table 7 Properties of Martian Atmosphere Page 5 Radiator Gas CO2 N2 Ar O2 CO H2 O Ne Kr Xe Volume Percent 95 32 2 7 1 6 0 13 0 07 0 03 2 5 ppm 0 3 ppm 0 08 ppm Table 8 Composition of Martian Atmosphere as measured during the Viking I mission 1 Property surface Value Units Pressure 800 Pa Density 0 0166 kg m3 Table 9 Properties of Martian Atmosphere as measured during the Viking I mission 1 1 2 2 Martian Geology The Martian crust and soil is rich in metal oxides such as silicon dioxide ferrous oxide and magnesium oxide The terrain is much less severe on Mars Flat plains cover approximately 60 of the Martian surface the remainder being valleys and canyons that were carved in theory from past rivers Furthermore a prominent topographic feature of the Martian landscape is a small chain of volcanoes located in the northern hemisphere These volcanoes can reach elevations of up to 25km with diameters in excess of 500km 3 See tables 10 13 below for data on composition and properties of the Martian soil Page 6 Radiator Compound SiO2 Other FeO Al2O3 MgO Na2O Weight Percent 40 20 15 10 10 5 Table 10 Composition of Martian Soil 2