# Section 4.14: Phase 5B - Mars Development

Mars has been the leading location in popular culture for future colonization. This is because the natural environment is the most Earth-like by a number of measures. Numerous fictional works have described the possibilities, with varying amounts of realism. The Library of Congress lists 450 works primarily about Mars as an astronomical object, 73 as an objective of space flight, and numerous other non-fiction works reference it, such as those on planetary science. As of 2017, 25 successful Missions have flown past or arrived at Mars, along with a number of failed attempts. Eight of these are operational, and seven more are in various stages of development. Human missions are a goal for NASA, and colonization is the stated goal of the private company SpaceX.

However, most of this attention and work has focused on Mars alone, to the exclusion of the resources and development of the rest of the Solar System. The program we describe in this book is more inclusive. It treats Mars as one place among many to develop. This is partly because other places have different material and energy resources, and their local environments are more suited to some purposes than others. It is also because people are different, and don't all want to live or work in the same kinds of places.

As in previous phases, we would bring starter sets of equipment to the Mars region. They use local resources to bootstrap their own expansion and begin development. This adds Mars to the growing network of developed regions. By the time Mars development is started, this approach would have been used seven times on Earth and in previous space locations, and should be well understood. Leveraging equipment and resources from earlier phases, plus from Mars itself, should enable large scale development of Mars at low cost. This is in comparison to "Flags and Footprints" type programs like Apollo. They leave no lasting infrastructure or economic activity, and so each mission requires everything come from Earth at the same cost. The return-to-cost ratio for our approach is should be much higher, and may even be economically self-supporting.

We begin concept exploration for this phase by describing the characteristics of the region and a survey to identify possible future activities. We then look at motivations, economics, and technology, and combine all the information to identify a development approach and sequence, and link them to the other program phases. As an output we identify necessary R&D for this phase, and feed it back to Phase 0N - R&D for Mars Development.

## Mars Region FeaturesEdit

The Mars region is embedded in the Inner Interplanetary region, which extends from near the Sun to a distance of 1.8 AU, and encompasses the regions around the four inner planets. This region includes the planet, two small moons, and orbits within 340,000 km (100 radii) of Mars' center. The Martian moons Phobos and Deimos have orbit radii of 9,376 and 23,460 km respectively, placing them well within the region. Their orbits are nearly circular and equatorial to Mars.

The Sun is 3,098,000 times Mars' mass, and at the edge of the region averages 670 times the distance. Therefore the Sun's gravity is 6.9 times stronger than the planet's at this distance. However, orbital stability depends on the cube root of the mass ratio, because it is the difference in solar attraction on the planet vs. on points along orbits which disturbs them. So orbits within 1,084,000 km of Mars are at least theoretically stable. We set the region boundary somewhat arbitrarily at about one-third of this, where objects are within 1% of escape energy.

Figure 4.14-1 - Topographic map of Mars.

The horizontal surface area of Mars is 144.8 million km2, which by coincidence is 97% of Earth's land area, or nearly equal. Elevations relative to a reference height range from -8.2 km in the Hellas Basin to +21.2 km on Olympus Mons (Figure 4.14-1). See USGS Topographic Map of Mars, 2013 for a more detailed version. The Martian day length is 24h 40m, slightly longer than Earth, and the Martian year is 1.88 Earth years. The planet is tilted 25.2 degrees to the orbit plane, resulting in seasonal changes similar to Earth's from a geographic standpoint, but larger in amplitude due to an orbit which varies from 1.381 to 1.666 AU from the Sun. Both moon's rotations are synchronous with their orbits, keeping the same side facing the planet. Their day lengths are equal to their orbit periods of 7.65 and 30.31 hours.

### Environment ParametersEdit

Temperature - The Climate of Mars has important similarities to Earth's, including polar ice caps, seasons, and weather patterns. Due to greater average distance from the Sun, surface temperatures vary from 120 to 293K (-153 to 20C), between the poles and noontime at the Equator. Average temperatures decrease by about 1-2K/km of elevation. Typical day-night variation is 70K/C because the thin atmosphere does not have much thermal mass. This variation is reduced to about 10 degrees during dust storms. The surface is mostly covered in sand and dust, which moderates variations towards the mean annual temperature as depths reach 1 meter. Subsurface geothermal gradients are poorly known, due to a lack of direct measurements. Models based on indirect estimates indicate they may be +6-10K/km of depth, with the lower values in ice-saturated ground.

Temperatures in orbit and on the moons will depend mainly on percentage exposure to direct sunlight. This is lower for low orbits, which spend more time in the planet's shadow. The moons keep one face towards Mars and their shapes are irregular. So available sunlight, and thus temperature, will vary by particular surface site. Mars serves as a secondary infrared source which fills just under 50% of the view in low orbits, and only 0.00275% at the edge of the region. Black surfaces in full sunlight will have equilibrium temperatures of 302-332K (29-59C) depending on where Mars is in its orbit. Actual hardware temperatures in orbit will depend on their solar exposure durations and angles, albedos, emissivities, and thermal properties.

Atmosphere and Water - Mars has an Atmosphere which is 96% CO2, a bit under 2% each Argon and Nitrogen, and an assortment of trace gases. It extends about 200 km vertically to the point the exosphere merges with space vacuum. Surface pressure varies from 30 Pascals at the top of Olympus Mons to 1155 Pascals in the Hellas Planitia basin. For comparison, the highest value is 1.14% of sea-level pressure on Earth. Pressure decreases exponentially with elevation, with a scale height of about 11 km per factor of e change vs. a 636 Pascal reference value at zero elevation. The pressure varies by 30% annually with distance from the Sun, as some of the CO2 freezes and evaporates at the poles. The moons are too small to retain any atmosphere. Mars has remnant magnetic fields in some areas, which are about 100 times lower strength than Earth's, but no core-driven global field. Therefore it does not have a strong magnetosphere. The interplanetary solar wind dominates most of the region's space environment. The area immediately "upwind" of the planet creates a bow shock and magnetic pile-up of ions, and a rarefied downstream wake and tail, through which some ionosphere material leaks.

Mars has significant amounts of water in the soil as hydrated minerals and permafrost, and frozen in thick dusty ice caps. The ice caps contain about 1.75 million km3 of ice, and total Water on Mars may be 5 million km3. Water content in top meter of ground is generally high above 65 degrees latitude, but is still a few percent even at lower latitudes. Water content at depth on the planet and for the moons are poorly known. Pressure and temperature at the surface of Mars is nearly always below the Triple Point of water. So it is rarely liquid there, although it may be at depths where both are higher.

Figure 4.14-2 - Surface of Gale Crater as seen by Curiosity Rover.

Ground Loads - Mars' surface generally consists of variable amounts of sand, dust, and exposed rock, ranging from sand dunes to solid outcrops (Figure 4.14-2). Surface strength in places is low enough to have trapped a rover, but in others hard and sharp enough to have punctured metal wheels. Soil conditions are due to a combination of impact cratering, vulcanism, and more atmosphere and water early in the planet's history. As a result, suitability for construction and transport will be variable by site and need local investigation. The limits of overlying rock strength would be reached about 16 km in depth, but reduced from fracturing and water/ice fraction. Support structures would be needed for mining or drilling below these limits, and for surface excavation which exceeds the local angle of repose for loose material.

Gravity Level - Mars surface gravity varies from 3.683 to 3.743 m/s2, a 1.6% variation, with a reference value of 3.711, or 37.85% of Earth's. Lower values are due to equatorial location and extremely tall volcanoes, while higher values are at lower altitudes in the north polar region and Hellas Basin. Free fall conditions in orbit produce no effective acceleration. Structural support needed against gravity is therefore significantly lower than on Earth. Gravity levels needed for long-term human, plant, and animal health are unknown, but may be higher than Mars surface values and are definitely more than free-fall zero gravity. In both cases artificial gravity can be generated by rotation, in which case significant structural loads will be imposed on equipment.

Radiation Level - Radiation levels were measured by the Mars Science Laboratory/Curiosity Rover mission at 0.64 ± 0.12 mSv/day on the surface and 1.84 ± 0.30 mSv/day in orbit (Hassler et. al., 2013). These are 1.5 and 4.5 times higher than crew on the International Space Station get, and up to 200 times the US annual average from all sources. These levels are unacceptably high for long-term occupation of the region. The simplest near-term solution is bulk shielding of a meter or more, using material from the surface or the moons. Long-term solutions include increasing atmospheric mass and an artificial magnetosphere.

Communication and Travel Times - Ping time to the Mars region from Earth varies from 6 to 45 minutes, depending on relative orbital position and need for a relay satellite to avoid the Sun. Travel times from Earth vary according to the relative positions of Mars and Earth, and the propulsion method chosen. When aligned, minimum energy transfer orbits typically take 8 months one way.

Mars's orbit around the Sun is 9.3% eccentric, and varies from 1.38 to 1.67 AU in distance. This makes reaching it from other orbits a somewhat variable proposition. Orbit velocity at the region boundary is 355 m/s at this distance and the period is 70 days. Escape only requires adding 147 m/s so travel to and from the Inner Interplanetary region is easy at this distance.

Stay Time -

Transport Energy - The planet's mass is 10.7% of Earth's, and mean radius is 53.2% of ours. This results in an escape velocity from the surface of 5,027 m/s.

### Available ResourcesEdit

Figure 4.14-3 - Geologic map of Mars.

Energy Supply - Because of the eccentricity of it's orbit solar flux varies from 494 to 716 W/m^2, or 36 to 52.5% of the Earth's value. Orbital locations can differ by 0.33% from the planet, due to added or reduced solar distance. Global dust storms, which occur with irregular frequency, can block as much as 99% of sunlight on time scales of a month. At other times residual dust reduces illumination at the surface by typically 20-40% relative to orbit. Atmospheric gases have little effect because of the low density. Possible solutions for surface power during dust storms include large amounts of thermal energy storage using local rock, nuclear power to provide at least minimal capacity, or beamed power from orbit. Martian basalts may contain 5 ppm of Thorium and Uranium. If geologic processes have created concentrated deposits, they may be useful for local energy supply, however this is speculative at this time.

Materials Supply - Mars is a differentiated terrestrial planet, and has a varied geology as a result of internal melting and vulcanism, impacts, and much higher levels of water and atmospheric pressure earlier in it's history (Figure 4.14-3 and see USGS Map 3292, 2014 for a more detailed version). [Add more about elements & minerals].

Phobos and Deimos average 22.2 and 12.6 km in diameter, but are irregular in shape. They have a combined mass of 12,800 billion tons, or two centuries of Earth's total mining output, so represent a significant material resource in convenient orbits. Their composition is uncertain based on current visible, and near and thermal infrared spectra. They resemble both those of outer-belt asteroids and some Mars surface minerals, but are not a match to either. One possibility is they accreted from orbital debris after a large surface impact, of which there is much evidence on the surface, and later accumulated asteroid material from direct impact. Resolving this question and determining their composition requires closer observation or a dedicated mission.

The Mars Trojans in particular, and Inner Interplanetary Asteroids in general may be useful sources of raw materials. The latter group include the inner part of the Asteroid Belt, which Mars' orbit skims, and other asteroids orbiting somewhat closer to the Sun. Because of their large number, and the ability to use Mars for gravity assists, there should be some in particularly easy orbits to reach. These asteroids can provide more varied source materials than the two moons alone.

## Development ProjectsEdit

The next step in our concept exploration is to combine the above information into a general approach for Mars development, and identify specific near- and long-term projects to implement. We can provide early concepts for these projects, which will gives a sense of their scale and main features. However, this is merely a starting point, and does not exclude alternate ideas. It also does not yet include optimization and integration of the projects to each other and to projects in other phases of the program.

### General ApproachEdit

Mars' surface area is nearly equal to all the land on Earth, and the orbital region has a cross section of 363 billion km2, or 712 times the Earth's total surface area. Like the Lunar region, the Mars region is far too large to develop all at once, or by a single project or organization. Our general approach is then to identify a number of smaller tasks and projects. These can be put in a logical sequence, with later projects building on earlier ones, and be carried out by individual organizations or groups of them. These tasks and projects would interact with each other when they exist at the same time, with other program phases which operate in parallel, and with the rest of civilization.

The various activities can be grouped by start time into preparation, orbital development, and surface development. Mars activities are less far along than those in Earth orbits or for the Moon, so most of the current and near-term work is preparatory, such as scientific exploration. We note these in the next section. Long-term projects are listed in the following section. They are not yet organized into an integrated sequence, so we group them by primary function (production, habitation, transport, and services) and location (the orbital region or on the planet surface). Within each group they are placed in approximate time order. We expect many of these projects and activities to overlap in time, rather than be a strict sequence of one following another.

Preparation - Planning and designing future Mars projects requires understanding the local features of the region in general, and specific operating sites. Preparation for Mars development therefore involves tasks like exploration, surveys, prospecting, and site investigation. Scientific investigation of Mars began as soon as large telescopes allowed seeing more than a point of light in the sky. It accelerated in the mid-20th century when rocketry enabled sending instruments to the planet and communicating data back to Earth. We have not yet brought back samples from the planet, although over 100 Martian Meteorites have been identified that came to Earth.

Orbital Development - Orbital development leads work on the surface because it is easier to reach from previous regions, and because of the existing material resources at Phobos and Deimos. Sites on the moons may need physical preparation, such as providing anchorage due to the low gravity or shifting surface material to provide radiation shielding. Their low escape velocities, 11.4 and 5.6 m/s, mean that loose material is easily lost and would become an orbital debris hazard. Therefore covers may be needed over active work areas. Open orbits elsewhere in the region don't need preparation, but also lack raw materials, so they must be imported.

Surface Development -

## Early DevelopmentEdit

### Phobos and DeimosEdit

Conveniently Mars already has two fairly large asteroids in orbit (Phobos and Deimos), giving us a ready supply of materials. Phobos alone has a mass of about 10,000 gigatons, which is more than we would need for a very long time. The first step in development is to set up a base of operations on one of them. This would do mining, processing, and construction of habitats. The composition of the Martian moons is not entirely clear yet[1], but they appear to be similar to CM type Chondrite asteroids and meteorites. If any particular materials are not found in these satellites, they can be fetched from Near Mars Objects, otherwise known as the Main Asteroid Belt, which starts just outside Mars' orbit. The velocity to reach them from the Martian satellites is fairly low.

Chondrites are known to contain a large amount of carbon, so the main goal of the Phobos base would be to provide cable and other materials for a Mars Skyhook. Secondary goals are to provide fuel for landers and human control of surface operations before humans can be supported on the surface. The short distance of the Mars satellites relative to Earth allow for real-time control.

### Mars SkyhooksEdit

There are two sizes of Martian Skyhooks that make sense to look at. One set is capable of reaching from low Mars orbit (LMO) to Phobos orbit, and whatever suborbital velocity to Mars that produces. The other set would be capable of doing a full velocity transfer to the Martian surface. The first could grow into the second over time, but we will look at them as specific design points.

#### LMO to Phobos SkyhooksEdit

Orbit Mechanics - The product of a planet's mass M and the universal gravitational constant G is called the Standard Gravitational Parameter or ${\displaystyle \mu }$ . For Mars the value is ${\displaystyle \mu }$  = GM = 42.837 x 10^12. This value is useful for calculating circular orbit velocities by the formula

${\displaystyle v_{o}\approx {\sqrt {\frac {GM}{r}}}}$

Knowing the average radius of Phobos from the center of Mars is 9,377 km, putting that into the formula in meters (9,377,000 since we must use all SI units and not multiples thereof), we can determine the orbit velocity of Phobos is 2137 m/s. Since Mars has an equatorial radius of 3,396 km, then Phobos is 5,981 km from the surface. For elliptical transfer orbits, where r is the current radius from the body center, and a is the semi-major axis, or half the long axis of the ellipse, the velocity is

${\displaystyle v^{2}=\mu \left({\frac {2}{r}}-{\frac {1}{a}}\right)}$

If we want to transfer from Phobos to 400 km above the Mars surface ( r = 3796 km ), then the velocities at the high and low points of the transfer orbit, and at the low orbit can be calculate as follows:

• Transfer High point: r = 9,377,000 m ; a = half of high + low altitudes = 6,586,000 m ; from formula ${\displaystyle v^{2}=}$  2,632,300 m^2/s^2, and so v = 1622 m/s.
• Transfer Low point: r = 3,796,000 m ; a is the same as previous = 6,586,000 m ; therefore ${\displaystyle v^{2}=}$  = 16,065,000 m^2/s^2 and v = 4008 m/s.
• 400 km Circular: r = a = 3,796,000 m ; v = 3,359 m/s.

The velocity difference from Phobos to the transfer orbit is 515 m/s, and from the transfer orbit to 400 km circular is 649 m/s. These velocities are relatively small compared to the Lunar or Earth orbit Skyhooks we have looked at previously, so they would be relatively low mass ratio. Assuming the tips are at 1 gravity, the Phobos Skyhook would have a radius of 26.5 km, and the LMO one would be 42 km. Phobos is tidally locked to Mars, always keeping one face to the planet, but it is not locked in rotation about the Mars-pointing axis, and tidal variations from the sun and slight orbit eccentricity cause it to wobble. Thus the Phobos Skyhook should probably not be attached to Phobos directly, but placed nearby.

Both Skyhooks will have low mass ratios because of their low tip velocities. Therefore they would shift their own orbits by a large amount when transferring cargo. The solution is to anchor both of them with a sufficient amount of ballast mass from Phobos at their center points. The LMO Skyhook can drop cargo at 3,359 - 649 = 2,710 m/s. Mars' equatorial rotation is 241 m/s, so the relative velocity to the surface will be 2,469 m/s. To reach Mars escape from Phobos requires adding 884 m/s. Since our Phobos Skyhook can add 514 m/s, that leaves 370 m/s to be done by other means.

A "Flags and Footprints" type mission would require no propulsion in theory to land on Mars, if it uses all aerodynamic braking. It would need 5 km/s of propulsion to reach Mars escape velocity on the return trip. With a base at Phobos and the transfer Skyhooks, no propulsion is needed is needed to land either. The LMO Skyhook drops the vehicle about 20% below orbit velocity and re-entry will be automatic. The return propulsion would require about half as much velocity to reach orbit - 2.47 km/s. With a permanent habitat at Phobos, there is no need to escape from Mars, but if you choose to do so, it would require 2.84 km/s. Assuming a chemical rocket for both with an exhaust velocity of 3,500 m/s, the mass ratio will be 4.17 without the Skyhooks, giving a cargo of 14% if the vehicle hardware is 10%. With the Skyhooks, the mass ratio is 2.02, and landed cargo is 39.4%. So the Skyhooks allow 2.8 times as much payload per trip.

#### LMO to Surface SkyhookEdit

A full orbit to ground Skyhook will likely not make economic sense until traffic grows to a higher level, but let us take a look at a possible design. Start by assuming a 1000 km high orbit. That will have a radius from the center of Mars of 4,396,000 m. From the above formula we calculate the orbit velocity is 3122 m/s. Subtracting 241 m/s for the rotation of Mars gives a relative velocity of 2881 m/s. If the tip is at 1 gravity centrifugal acceleration, then the Skyhook radius will be 846 km, and the tip will become motionless when the Skyhook is vertical 154 km above Mars mean surface level. That should be high enough to avoid significant atmosphere friction. The Mars Global Surveyor spacecraft used a no-drag holding orbit at around 175 km lowest point, and active aerobraking between 120 and 135 km. It did so when moving between circular and escape orbit velocities of 3,500 to 5,000 m/s. So the Skyhook with near zero velocity at the lowest point should not see much drag.

Pavonis Mons is a 14 km tall mountain on the Martian Equator. So a vehicle wanting to reach the Skyhook from there would need to climb 140 km vertically. This requires a vertical velocity of 1,020 m/s plus about 12% gravity loss for a total velocity of 1145 m/s. This might be reduced if the Skyhook reached a lower altitude, but drag must be carefully looked at so the Skyhook is not in danger of de-orbiting itself. Without a Skyhook we found in the previous section we needed 5.4 units of fuel for each unit of payload returned from Mars surface to Mars escape. Escape velocity is 1.41 times circular orbit velocity, and this Skyhook has a release velocity of 1.92 times orbit velocity at the highest point, so well above escape velocity. Thus with this system the mass ratio becomes 1.387, and fuel used is 28% of takeoff mass, or 45% of cargo mass. Therefore it uses 12 times less fuel than without a Skyhook.

An alternate approach that eliminates launch fuel use entirely is to build an 8.67 km tall tower with an electromagnetic or gas accelerator that operates at 6 gravities (60 m/s2). This results in 1020 m/s vertical muzzle velocity.

The working length we previously used for Carbon fiber is 126.4 g-km. Acceleration in the Skyhook varies smoothly from 0 at the center to 1.0 gravities at the tip. With an average of 0.5 gravities times a radius of 846 km the requirement is 423 g-km. Therefore the mass ratio of the cable is 28.4 times its load per arm, or 56.8 for both arms. That is heavy enough that it may not need ballast mass at the center to keep from shifting its orbit too much in operation. It will still need propulsion to maintain orbit when traffic going up and down are not in balance. Since the Skyhook saves 4.95 units of fuel on the Martian surface for each unit of return cargo, in theory it pays for itself in fuel savings in under 12 flights. In practice it will take a detailed design to find out what the system mass and payback times in terms of mass and cost will be.

### Mars Surface SystemsEdit

#### ConstructionEdit

Earth-moving equipment will be needed for a number of purposes. The Mars surface is not protected from radiation like the Earth is, so long term habitats would need to be protected by a layer of soil. Landing areas will need to be flattened, and protective berms built around them so exhaust plumes don't sandblast nearby equipment. Once cargoes are delivered to the surface, they will need to be moved, lifted, and assembled, so devices to do those tasks will be needed. Most of the site preparation will likely be done by remote controlled machines.

#### Power SupplyEdit

Solar panels are a viable power supply on the Martian surface. It is rarely cloudy, aside from dust storms, and the atmosphere is thin, which partially compensates for the greater distance from the Sun. When larger amounts of power are needed, then radio-isotope or reactor devices can be added.

#### On-Site Propellant ManufactureEdit

Producing propellant on the surface of Mars has been studied extensively, since it lowers the mass brought from Earth for a "Flags and Footprints" mission. If we already have a robust orbital mining and processing capability and Skyhooks in place to deliver cargo, there may not be much benefit in early production of fuel locally vs delivery. The economics of doing so will need to be examined. For portable power, such as in moving vehicles, and for rocket propellant to reach a Skyhook on a return mission, an Oxygen/Methane fuel mix is a reasonable combination. Once sufficient need for fuel exists, producing it locally will make more sense

#### Linear AcceleratorEdit

Pavonis Mons, which is located on the Martian Equator, has a slope about 175 km long, which rises about 6.5 km. If large amounts of cargo need to be delivered from Mars, a gas or electromagnetic accelerator can be used here. If the full slope is used, orbital velocity can be reached with human-tolerable accelerations (3.6 gravities). This would not be an early system, since sufficient traffic is needed to justify such a large installation. Another option is a centrifugal catapult on top of the mountain for early cargo launch.

It is quite feasible to build a rotating space elevator (Rotovator) in orbit, coupled to a linear accelerator on Pavonis Mons ( http://upload.wikimedia.org/wikipedia/commons/1/12/Pavonis_mons_topo.jpg ). You have 60-120 km of ramp space, and no atmosphere to speak of, so at 3 g's and 60 km you can reach half of Mars orbit velocity, and the Rotovator provide the rest.

## Long Term DevelopmentEdit

Often the phrase "Terraforming Mars" has been used in the past. This is not a good phrase because it means "Make Mars like Earth". Because of orbit and mass differences, we cannot make Mars just like Earth, nor do I think that should be the goal. I prefer the word "humanize", meaning making it more suitable for humans. It may also mean modifying humans to better suit the Mars environment (like the lower gravity). Large scale changes to Mars should be delayed till after we have a firm idea if there is any native life on the planet, and even then done with due consideration and forethought. They should also be delayed until there are enough people on Mars to justify the large-scale projects. So what follows is more to answer what is possible from a technical point of view, and less to say "I urge you to do all these".

### MagnetosphereEdit

Mars lacks a strong magnetosphere - a magnetic field around the planet that traps and diverts charged particles from space. The Earth has one due to the magnetic field generated by our planet's core. A strong magnetosphere protects the atmosphere from being slowly stripped off as solar wind and other particles hit the upper atmosphere. Short of stirring up the planet's core, there may be some other ways to generate a field. The practicality of any of them is yet to be determined:

• Run one or more superconducting cables around lines of latitude, which, like any current-carrying wires, will generate a field
• Place some number of iron-nickel asteroids in Mars orbit and magnetize them, and point their fields in the same direction.
• Mars is red because there is a lot of iron oxide on it's surface. Extract the iron, and magnetize it. You might be able to use the iron for other purposes at the same time as it being a magnet.

Magnets to make the magnetic field have fewer ways to break than superconductors, but if the superconductors work 99% of the time the other 1% doesn't make much difference to long term atmosphere loss. Some leakage of the atmosphere will still happen because Mars is a smaller planet than the Earth, so it is easier for atoms to escape.

### GreenhousesEdit

If you want to eliminate leakage, and bring up the pressure to breathable levels without importing a planet's worth of atmosphere, you can use greenhouse domes. If you really need the space, you can extend the domes to cover the entire planet bit by bit. To create Earth sea level pressure on Mars, a pressure balanced dome would consist of 10 meter thick quartz, glass, or equivalent, which you extract from Mars surface material. Lighter domes tend to float up, as the internal pressure is higher than the surrounding air. In that case they need to be tied down so they don't float away. A very large or planetary dome doesn't need much to hold it up, just some towers or cables to keep it from moving sideways.

You can design the clear material like armored glass to be resist damage, and ten meters of anything is pretty hard to break. But anything can be broken, so a lot of thought needs to go into how to deal with damage. As a greenhouse, you can take advantage of the "greenhouse effect", which is the trapping of infrared heat radiated back from the ground. You can specifically select the glass type or add coatings to trap infrared. You also want to block Solar UV radiation, which is not blocked by the Martian atmosphere. On Earth the greenhouse effect is a problem, since we don't want the planet warmer than it already is. On Mars it's a solution, since it's too cold for us there at the moment.

### Full AtmosphereEdit

If you find living under a dome objectionable, you would need to provide a full atmosphere at a breathable level. That is a very big job because planets are large. On Mars you need to provide 25 tons of atmosphere for each and every square meter of the planet, or 3.6 million billion tons total. That's to provide one Earth atmosphere pressure. If you are satisfied with less oxygen (similar to mountains on Earth), and a different mix for the rest of the air, you can get by with somewhat less. Despite it's distance, the easiest place to get enough nitrogen might be the Kuiper belt, which is outside Neptune's orbit and which Pluto is a part of. You could use a "reverse gravity assist" from Neptune to drop the material into the inner solar system. Nitrogen is rather scarce in the inner solar system, and getting it from anyplace with a deep gravity well (like Earth) takes a lot of work. Some of the outer moons might have enough ammonia (NH3).

## [Text to be merged]Edit

The combined systems discussed in the previous sections are a different route to getting to Mars. They build capabilities step by step, each one preparing for the next, and generally using machines to prepare the way for humans. In this section we will discuss the last steps to get to Mars, building on the prior technology from our combined system. Mars is the most nearly Earth-like planet we know of, so we will also mention some ideas for long term development. They would get done, if ever, much later, when Mars and the Solar System are more fully developed.