# Space Transport and Engineering Methods/Environment Ranges

    This study is preliminary as of Nov 2012

## Introduction

This design study is part of the Human Expansion (HE) program conceptual design. One of the HE program goals is to expand civilization into more difficult locations, while at the same time improving levels of technology and quality of life. The goal in this study is to establish location parameter ranges for where people live now, and then from that derive what difficult and extreme ranges would be for future locations. We set the middle 90% of where people live now as the existing range for each parameter, with 5% living at each extreme. The middle 90% is described as Temperate, and levels more than 10 and 20% beyond the Temperate range we call Difficult and Extreme respectively.
The study will be performed in two parts. The first part will make make initial estimates so that other parts of the HE program design can start to use the information. The second part will survey where people live in more detail and generate improved values. The HE program as a whole is using the start of 2013 as a baseline to reference against. The US Census Bureau projects population at the start of 2013 to be 7,062 million, thus 5% is 353 million. The more detailed population analysis will draw from world statistical data.

## Initial Estimates

Seven environment parameters and four time and distance parameters were chosen in the HE Requirements Analysis to determine what makes a difficult or extreme location. In the list of the parameters that follows, we first define what the parameter is, then discuss how we make our estimate for the 90% Temperate Range. We also discuss what the practical limits on Earth are for the Extreme ranges. Once the practical limits on Earth are reached, or they exceed what is found in space, more difficult locations in space are used.

### Environment Temperature

Definition - On Earth, this is the winter daily air temperature lows, and summer daily highs in Kelvin and (Celsius). For space locations this is the equilibrium temperature of a 50% gray body with one side facing the Sun and the opposite side facing away.
Estimate - On inspection of a world map, many more people live in far north locations than far south. Northern Europe, Russia, parts of Tibet, Northern China, and Canada may supply 350 million cold climate residents. Many people live in equatorial/hot climates, but the extremes are seen in dry climates where water vapor does not moderate daily temperature ranges. We make a rough estimate of 260 K (-13 C) as average January daily lows and 310 K (37 C) as average July daily highs as the limits of the Temperate range.
Limits - Ten percent, or 25-30K, beyond the temperate limits is a significant range for human climate, so Earth locations are likely to to have only one or two very cold and no hot difficult surface climates. Deep underground might reach extreme hot levels in certain locations.

### Water Supply

Definition - This is fresh water supply from rain and snow fall, flows from rivers and ice, and air moisture in meters depth/location area/year. Since the density of fresh water is 1 ton/m$^3$, this is equivalent to tons/m$^2$. Salt water does not count as fresh water supply, although evaporation does. Underground aquifers that represents flows from rain or water transport count, but not amounts merely drawn from storage, since that is not sustainable. Many people live near rivers, which supply high fresh water flows. We count available river flow distributed over the local land area, so a high range location above that may be difficult to find. Dry locations with low water flow are common.
Estimate - We use values of 0.25 and 2.5 meters on Earth as the Temperate range based on rainfall definitions of desert and wet climates. This needs more support from climate data.
Limits - On Earth, the lowest rainfall location, the Atacama Desert receives an average of 0.001 meters of rainfall/year. We can get an upper estimate by assuming the Amazon River flow of 200,000 cubic meters/second is allocated to the nearest 10% of the drainage basin to the main river and tributaries. Given a total area of 7 million km$^2$, that gives a water supply of 9 meters per year. The highest rainfall locations give about 11 meters/year. So we will adopt 10 meters/year as the extreme upper value. Space locations would range from essentially zero in the inner Solar System, to moderate when significant numbers of ice or hydrated bodies pass within reach, to very high for ice-covered satellites or bodies.

### Atmosphere Pressure

Definition - The average location gas pressure in kPa.
Estimate - On Earth nearly everyone lives in a fairly narrow range of pressures. We will assume for now the nominal range is from 80 to 100 kPa (sea level to 2000 m altitude).
Limits - On Earth the lowest surface pressure is presumed to be at the highest point, Mt. Everest, at +8,850 m elevation. The highest pressure is presumed to be at the bottom of the LaRonde Gold mine in Quebec, which reaches 3 km below a surface elevation of 300 m, for a net height of -2,700 m. The pressure range is thus from 31.5 to 138 kPa. To go beyond these limits would require artificial structures, or ambient pressure underwater locations. In space, local pressure can range from complete vacuum to many times Earth values on Venus or the Gas Giants.

### Ground Pressure

Definition - On bodies with gravity this is the foundation design load in MPa or exterior water or rock pressure for below surface locations. In both cases this amounts to a boundary pressure on location structures. Low range would be surface water structures or swamps, and high range would be tall buildings or below surface locations.
Estimate - We make a rough estimate of the Temperate range by referring to allowable soil bearing pressures from soft clay up to hard bedrock. Dropping extreme values, these give a range from to 0.25 to 2.0 MPa.
Limits - For low range limit, we can assume a shallow boat or raft foundation with a depth of 1 meter or less. This gives a load of 0.01 MPa. For high range limits, assuming a floor + dead load of 1000 kg/m$^2$ per floor, a 100 story skyscraper might impose a bearing pressure of 1 MPa on the foundation base. Practical limits on tall construction have more to do with economics than with structural materials, so taller buildings are possible.
Since the depths of the ocean and deep underground can reach very extreme pressures and temperatures, we set a practical limit based on the energy to reach Earth orbit (31.3 MJ/kg) compared to the column of mass which must be displaced to access such deep locations. For a 1 kg volume of ocean, which has a mass of ~1 kg, displacing a column 800 m high requires raising 8000 kg x 400 m avg height x 9.8 m/s$^2$ = 31.3 MJ. For continental crust, which has a density of 2.7kg/liter, a 1 kg volume then is 7.2 x 7.2 cm. Each meter of rock above this area then is then 13.925 kg. A column 675 m deep then masses 9400 kg, and raising it an average of 337.5 m also yields 31.3 MJ/kg. Therefore we will consider the practical limits to be ocean depths to 800 meters and continental depths to 675 m, after which we start including space locations. Other parameters may drive us to space before depth does. The corresponding water and rock pressures are 8 and 18 MPa respectively.

### Energy Supply

Definition - Flux from natural sources in W/m$^2$. On Earth this will mostly be from solar and wind, with water flow and geothermal in some locations.
Estimate - On Earth, average solar flux ranges from 100 to 300 W/m$^2$ after accounting for night, clouds, and sun angle. Wind power in the US ranges from below 100 to over 1000 W/m$^2$. Hydroelectric, tidal and sea currents, and geothermal are localized, so we will ignore them for this first estimate. Combining wind and solar we get a rough estimate of 150 to 900 W/m$^2$ as the temperate range. In space, solar flux is 1366 W/m$^2$ at the Earth's distance, times the percentage time in sunlight.
Limits - Any significant water or ground depth will have near zero energy supply. Peak Earth values might be at high altitudes where a combination of high winds and increased sunlight would supply high power levels. In space, peak energy level will vary dramatically with distance from the Sun.

### Gravity Level

Definition - Local gravity level in meters/s$^2$. Space locations near large objects still has a gravity level, even though orbits may create free-fall conditions with low relative forces between system elements.
Estimate - The Earth's surface, where almost everyone lives, is entirely within 10% of the 9.80665 m/s$^2$ standard value.
Limits - Values more than 10% outside the Temperate range require extremely tall structures ( > 320 km tall ), or orbital locations. Thus this parameter is effectively fixed for Earth locations. Solar system locations can range from zero to about 200 m/s$^2$ very close to the Sun.

### Radiation Dose

Definition - Human radiation exposure in an unprotected state from background radiation, in milliSievert/year. It should be noted that in many locations humans cannot survive in an unprotected state, but for consistency the exposure level is measured that way. In addition to background radiation, humans also get significant exposure from medical and other human-made sources, but that is not location-specific, so is not counted as part of this location parameter.
Estimate - Most of the Earth's population lives in a relatively low radiation environment, but higher altitudes or high natural radioactivity areas exist. Data derived from a UN report indicate the typical range is from 1-13 mSv/yr.
Limits - The city of Ramsar in northern Iran has background levels up to 135 mSv/yr due to underground concentrations of Uranium and mobile decay products. Low Earth Orbit locations range from 80-160 mSv/yr, and locations above this can reach much higher levels from trapped particle belts and Solar particle events.

### Ping Time

Definition - Minimum round trip communication delay to next nearest 5% of human population, in seconds. Depending on location, this may be by wired or wireless methods.
Estimate - In theory all of the Earth is within 0.13 second ping time from any other point, but actual communications systems in place increase this value. We assume at least voice/cellphone bandwidth for communications. There are now more fixed and mobile telephone connections than there are people, so again, in theory, everyone has access to one. From Slovakia, around 5% of the world population is within about 600 km. Theoretical ping time is then 8 milliseconds (ms). The distance from Tahiti to major population centers is roughly 6600 km. Therefore best case ping time is 44 ms. Given actual routing, and fiber-optic speeds, this is likely to be more like 100 ms.
Limits - The worst case on Earth is no worse than locations like Tahiti, which require submarine cable, or satellite relay through the Iridium network. Thus the limits for Earth are the same as for the Temperate range. Space locations can range to 45,000 seconds from Earth to the Kuiper Belt.

### Travel Time

Definition - Maximum one way normal travel time for humans, in hours or days, from the nearest 5% of human population.
Estimate - In dense areas such as Europe the maximum direct distance to reach 5% of the world's population is about 600 km. Allowing for actual highway routing and travel speed, we can estimate 8 hours to reach any point in that radius. Ninety percent of the world's land area can be reached within 48 hours according to the EU Joint Research Centre map of accessibility.
Limits - The same accessibility map places parts of the Tibetan plateau at 20 days travel to a city of any size. Point Nemo, the farthest point in the world from land, is about 4000 km by sea from the nearest airports. Therefore it is about 10 days travel by chartered ship. Current travel time to space is measured in months to years, mostly because trips carrying humans are rare. The actual transit time from the launch site is 2-3 days

### Stay Time

Definition - Average per person stay time per location, in years. People are assumed to stay in the same location if they live and sleep in the same place on a regular basis.
Estimate - In the US, in 2010-2011, 3.9% of the population moved to a different county in one year. We will take a county to represent a "location". Therefore the average stay time is 25 years. We assume there are significant parts of the world where the average person does not move far from their place of birth, thus the average stay time in one location is their life expectancy of about 70 years.
Limits - The fastest growing counties in the US in 2011 had a growth rate of 10%, and thus an average stay time of 7 years if both growth and normal mobility are counted. Stay times in space are currently much shorter than this because there are no permanent residents, and time is limited by zero gravity and radiation exposure. We invert the time scale for space, and set a minimum stay time of 10% of Earth, or 0.7 years, as the initial range. At the other extreme, stay times are bounded by life expectancy, so are no higher than 70 years.

### Transport Energy

Definition - Maximum total energy to reach a location from nearest 5% of population, by most efficient method, in MJ/kg. Includes kinetic, potential, and friction energy cost.
Estimate - For Earth, since most of the surface is near the same potential, this is mostly frictional losses for rail or ocean shipping. Rail transport consumes 330 BTU/ton-mile, or 216 J/kg-km. Assuming a total transport distance of 1000 km for dense areas, including partial road travel from nearest rail point, we get about 0.215 MJ/kg. Ships consume 375 J/kg-km. Eastern Australia is about 6000 km by ship from the nearest 5% of the worlds population, giving 2.25 MJ/kg.
Limits - Assuming a mule pulling a cart equal to its body mass for 20 days to reach inaccessible areas in Tibet, we get 1.8 MJ/kg transport energy. If we then add another 2000 km by rail to reach 5% of the world's population, this adds another 0.43 MJ/kg, for a total of 2.23 MJ/kg. Assuming transport distance of 7000 km from population centers to Tahiti, this gives 2.6 MJ/kg, which is the higher value. Low Earth orbit requires 31 MJ/kg, so there is a large step function from Earth to space locations.

## Detailed Estimates
### Atmospheric Temperature

We selected the seasonal daily highs and lows for this parameter as the "normal extremes" that people are adapted to, even though particular days can exceed this range. We start from the hot and cold ends of where people live, and count until we reach 5% in each. We count by countries when they are small and consist of one climate region, or by sections when they are large. If the population is concentrated in one part, we use climate data for that area.
Coldest Populate Areas
The following table of cold locations starts at the poles and highest elevations and works down until we reach 353 million population.
    Country, RegionPopulation (million)Average Winter Lows C (K)Notes (subtotals) Russia, Sakha and Chukotka1.0-41 (232)at Yakutsk Canada, 3 North Territories0.1-37 (236)at Pond Inlet, Nunavut Russia, Tuva0.3-35 (238)at Kyzyl Russia, Zabaykalsky Krai1.1-32 (241)at Chita Russia, Yamalo-Nenets0.5-30 (243)at Salekhard Russia, Buryatia1.0-28 (245)at Ulan-Ude Russia, Amur Oblast0.9-27 (246)at Blagoveshchensk (4.9m) Russia, Khabarovsk Krai1.4-24 (249)at Khabarovsk city Russia, Kemerovo Oblast2.9-23 (250)at Kemerovo city Russia, Khakassia0.5-23 (250)at Abakan Russia, Khanty-Mansi1.4-23 (250)at Surgut (6.2m) Russia, Irkutsk Oblast2.5-22 (251)at Irkutsk city Russia, Tyumen Oblast3.4-22 (251)at Tyumen city Russia, Komi1.0-21 (252)at Syktyvkar Russia, Omsk Oblast2.0-21 (252)at Omsk city Russia, Tomsk Oblast1.0-21 (252)at Tomsk city (9.9m) Russia, Altai Krai2.4-20 (253)at Barnaul Russia, Novosibirsk Oblast2.7-20 (253)at Novosibirsk city Russia, Altai Republic0.2-19 (254)at Gorno-Altaysk (5.3m) Russia, Krasnoyarsk Krai2.8-19 (254)at Krasnoyarsk city Russia, Magadan Oblast0.1-19 (254)at Magadan town Greenland0.1-18 (255)at Sisimiut Russia, Arkhangelsk Oblast1.3-16 (257)at Arkhengelsk city Russia, Perm Krai2.6-16 (257)at Perm city Russia, Sverdlovsk Oblast4.3-16 (257)at Yekaterinburg (11.2m) Russia, Kirov Oblast1.3-15 (258)at Kirov city Russia, Murmansk Oblast0.9-14 (259)at Murmansk city Russia, Vologda Oblast1.2-14 (259(at Vologda city Russia, Karelia0.7-13 (260)at Petrozavodsk (4.1m) Russia, Kamchatka Krai0.3-10 (263)at Petropavlovsk-Kamchatsky Russia, Pskov Oblast0.7-9 (264)at Pskov city Russia, Leningrad Oblast1.7-8 (265)at St. Petersburg Russia, St. Petersburg4.9-8 (265)City is Federal District Russia, Kaliningrad Oblast0.9-4 (269)at Kaliningrad Argentina, Tierra Del Fuego province0.1-2 (271)southernmost province Chile, Punta Arenas0.1-1 (272)Southernmost world city of any size (8.7m) Totals50.3-1 (272)Sum of above populations, and highest winter lows
Coldest Locations
These are locations where few or no people live, with extreme environment conditions:
    Country, RegionPopulation (million)Average Winter Lows C (K)Notes Antarctica, McMurdo Station0.0-32 (241)Largest populated location on the continent Antarctica, Vostok Station0.0-72 (201)Coldest place on Earth