Space Transport and Engineering Methods/Mars Development

Mars has been a 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.

&emsp;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.

&emsp;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" projects 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 should be much higher, and may even be economically self-supporting.

&emsp;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 set of projects by function, then link them to the other program phases. Projects for which we have additional details and calculations are then more fully described at the end of the section. As an output from this concept exploration, we identify what R&D will be needed for this phase, and feed it back to the preceding Phase 0N - R&D for Mars Development.

Mars Region Features
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.

&emsp;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.



&emsp;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. 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. The planet is tilted 25.2 degrees to the orbit plane, resulting in seasonal changes similar to Earth's from a geographic standpoint. They are larger in amplitude due to an orbit which varies from 1.381 to 1.666 AU from the Sun.

Environment Parameters
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 change by about 1-2 K/km of elevation. Typical day-night variation is 70 K because the thin atmosphere does not have much thermal mass. This variation is reduced to about 10 K 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 temperatures are poorly known, due to a lack of direct measurements. Models based on indirect data indicate they may increase 6-10 K/km of depth, with the lower values in ice-saturated ground.

&emsp;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 almost 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 302-332 K (29-59 C) depending on where Mars is in its orbit. Actual hardware temperatures in orbit will depend on their solar exposure times 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.

&emsp;The planet 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 planet creates a bow shock on the side facing the wind, a magnetic pile-up of ions, and a rarefied downstream wake and tail, through which some ionosphere material leaks.

&emsp;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 the 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 is 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 lower depths where conditions are suitable.



Ground Strength - Mars' surface generally consists of of a fine Soil containing sand and dust, with variable amounts larger rocks, and exposed bedrock (Figure 4.14-2). Surface strength in sandy areas is low enough to have trapped a rover, but in others is hard and sharp enough to have punctured metal wheels. Soil conditions come from a combination of impact cratering, volcanism, 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 by fracturing and water/ice fraction. Support structures would be needed for mining or drilling below these limits. Support structures are also needed 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 net gravity, and gravity on the Moons is negligible. 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 the levels in orbit. 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 &plusmn; 0.12 mSv/day on the surface and 1.84 &plusmn; 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 - Round-trip (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. As noted above, Mars's orbit has an eccentricity of 9.3%, so the maximum distance from the Sun is 20.6% more than the minimum. This makes reaching it from other regions a somewhat variable proposition. Orbit periods within the region range from 100 minutes at low altitude to 70 days at the region boundary. Minimum energy transfers between points will therefore take half these values. Actual travel times will depend on the methods used.

Stay Time - Average stay times affect transport and habitation needs. No one has traveled beyond the Moon yet, so there is no historical data for this parameter. Minimum energy trajectories between Earth and Mars impose transit + stay times of 1.5 to 3 years. However, these trajectories assume inefficient chemical rockets. Advances in technology and previous development of other regions of space should allow more options. So we will let future projects define this value based on internal needs until long=term occupation of the region establishes an average.

Transport Energy - Reaching the Mars region from Earth requires a theoretical velocity change of 11.8 km/s, and thus a theoretical kinetic energy of 69.6 MJ/kg. Actual energy required is generally much more due to inefficiency and overhead of the transport methods used. This is large compared to the 10-20 MJ/kg production energy of typical products. Therefore local production is favored where possible, and why we choose a bootstrap approach to developing Mars and other space regions. 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. Theoretical minimum energy to reach orbit is 5.5 MJ/kg and to the farthest point in the region is 12.5 MJ/kg. Efficient transport from the surface is therefore less energy than typical production energy, and it would be reasonable to supply materials to orbit from the surface.

&emsp;Delivery in the other direction can exploit friction with the atmosphere, and therefore require less energy. Large-scale infrastructure like a space elevator can use regenerative energy, where the energy of cargo being lowered can be used to raise cargo in the other direction. With balanced traffic, in theory this requires no net energy. In practice traffic is not likely to be perfectly balanced, and real systems have overhead and inefficiencies. Transport between points on the surface, between points in the orbital region, and between the region and other destinations besides Earth will have highly variable energy requirements. They depend on the transport methods used, the starting and end points, and for orbital travel, on the departure and arrival times.

Available Resources


Our approach in this program phase, as in other phases, is to bootstrap development of the Mars region using a starter set of equipment brought from elsewhere. That equipment uses local resources, where possible, to make more equipment, and then finished products to use locally or export elsewhere. When local resources or production capacity are inadequate, needed inputs are supplied from other regions. The percentage of imports should decrease over time as the region develops, and exports increase. With both imports and exports, Mars would be economically integrated with the rest of civilization and may become self-supporting. To follow this approach, we first need to understand what local energy and material resources are available.

Energy Resources
Solar Energy - This is likely to be the main energy source for the region. Incoming solar flux at Mars varies from 494 - 716 W/m2 (36 - 52.5% of Earth), with an average of 579.4 W/m2. The range is due to Mars' variation in orbital distance from the Sun. The orbital region around Mars can differ in flux by ±0.33% from the planet, due to added or reduced solar distance. The distribution in wavelengths is the same as at Earth. Total solar energy in the region averages 213 million TW, or about ten million times civilization's 2017 energy use. This energy is available 100% of the time in orbit around Mars, except when crossing the planet's shadow. Low equatorial orbits can be shadowed nearly 50% of the time, while circular orbits at the edge of the region are shadowed at most 0.23% of the time, and much less if inclined to Mars' orbit plane. In terms of what can be done with this much energy, it could theoretically be used to completely dismantle Mars and turn it into other products in less than 2000 years. There would be immense practical challenges in doing so, but it shows the available energy should be enough for any future projects in the region.

&emsp;Incoming energy to the planet averages 20,900 TW, or one thousand times Earth's 2017 energy use. Surface flux is reduced by a factor of 4 on average because a spherical planet has 4 times the surface area relative to the cross section which intercepts sunlight. The available amount varies by latitude, season, and time of day. It is further reduced by 20-40% at typical elevations from dust scattering and absorption in the atmosphere. Atmospheric gases have little effect because of their low density. Global Dust Storms average once per three Mars years, and regional ones annually. They can block as much as 99% of sunlight on time scales of a month.

Other Energy Sources - Orbital time in Mars' full shadow can be up to 3.8 hours, average nights on the surface are 12.3 hours, and locations above 65 degrees latitude experience long periods of seasonal darkness. Alternate energy solutions will likely be needed for for these times and during dust storms. Options include reducing operations temporarily, batteries, chemical energy storage of methane and oxygen made from local CO2 and water, thermal storage in local bulk rock, nuclear power, long distance transmission lines, and beamed power from orbit. Wind and geothermal are not likely to be useful, but will not be ruled out categorically until more analysis is done. Martian basalts may contain on the order of 5 ppm of Uranium and Thorium. If geologic processes have created concentrated deposits, they may be useful for local energy supply.

Material Resources


Planetary Surface - Our detailed understanding of Mars is the result of a large number of orbital and surface instruments sent there since the mid-20th century, and over 100 Martian Meteorites delivered to Earth by natural processes. It is a differentiated terrestrial planet, with an iron-nickel-sulfur core, a less dense silicate mantle, and a relatively light crust. The surface has a Varied Geology as a result of internal melting, Volcanism, and other active processes earlier in the planet's history (Figure 4.14-3 and see USGS Map 3292 (2014) for a more detailed version). The surface composition, as measured by rover instruments, consists mainly of a variety of metal oxide minerals, with smaller amounts of volatile compounds like water and bromine (Figure 4.14-4). In terms of rock types, the original surface was primarily Basalt. This is made of different mineral crystals which form in a sequence as lava cools. Asteroids added their own components and mixed the crust by forming craters. Higher early levels of water and atmosphere caused oxidation, erosion, and chemical modification of the original materials. There is some evidence of Tectonic Activity, but much less than for Earth. These processes slowed after the first billion years as the planet cooled, the asteroid population was depleted, and water and atmosphere were lost to space.

&emsp;The surface has large amounts of sand, dust, and smaller rocks making up the native soil layer (regolith). Early mining and excavation of the soil should be relatively easy. Hard rock mining and tunneling of outcrops and bedrock should be of comparable difficulty to Earth. Due to lesser gravity and thermal gradients, mining and drilling to depths of 30 km should be feasible with current technology, making over 4 billion km3 of total material accessible. This is hundreds of millions times Earth's current annual mining needs.

Orbital Region - This is mostly empty aside from the two natural moons. Depending what materials are needed, they may have to be imported from the surface or other regions. Small amounts of solar wind particles and interplanetary dust pass through the region, along with occasional larger asteroids. Phobos and Deimos average 22.2 and 12.6 km in diameter, but are irregular in shape. Their escape velocities average only 11.4 and 5.5 m/s respectively, so modified mining techniques will be needed to prevent loss of surface material and creating an orbital debris hazard. They have a combined mass of 12.8 trillion tons, or two centuries of Earth's total mining output, so represent a significant material resource in convenient orbits. Central pressure on Phobos, the larger moon, is only 120 kPa, or 1.2 times Earth atmospheric pressure. This presents no difficulty in tunneling or excavating to the center of the moon, so the entire volume of both moons are accessible.

&emsp;The composition of the moons 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 formed from orbital debris after a large asteroid impact. The many large craters on Mars support this idea. The moons could later have directly accumulated asteroid material by impact, as their own collection of craters indicates. Resolving this question and determining their detailed composition requires closer observation.

&emsp;The Mars Trojans, who share Mars' orbit, and tens of thousands of other Inner Interplanetary Asteroids, 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 mine and return materials from. These asteroids can provide more varied source materials than the two moons alone. The planet can serve as an additional source of materials, but chemical rockets using a methane/oxygen mix would need several times the payload mass to reach orbit, which is not efficient. Alternate approaches for large-scale delivery from the surface include electromagnetic and centrifugal ground accelerators, and space elevators.

Industry Survey
Our next step is to identify possible economic activities which would justify development of the Mars region. Our approach is look at all existing Earth industry categories, and identifying ones that can potentially operate in the region at some point in time. To these we add any unique activities that only apply to Mars. The activities include those needed internally in the region, and products and services supplied to Earth or other space regions. We will use the latest version of the North American Industry Classification System (NAICS) for the list of categories, and apply their numbering system and sequence for our survey. Unique Mars activities are inserted as they are identified, under the most relevant heading.

11 - Agriculture: Wherever people live they need food, and closed ecologies can help recycle human wastes. Importing food from distant regions is likely to take more energy than cyclic agriculture, once it is set up. Biological growth can also supply other useful products besides food. So we consider agriculture a likely activity after the earliest stages of development. Sufficient sunlight is widely available in the orbital region, and a natural day-night cycle occurs on the surface. In orbit it requires filtering of harmful wavelengths, and in both orbit and on the surface, natural sunlight needs moderate concentration due to greater distance from the Sun. It is not obvious if artificial grow lights, such as Light-Emitting Diodes, can increase overall growth efficiency over natural light, but is worth investigating. Dust storms can block nearly all light at the surface, but food storage is well understood, and the natural temperatures on Mars are cold enough for refrigeration.

&emsp;The major elements in typical plant tissue are oxygen (45%), carbon (44%), hydrogen (6.3%), nitrogen (1.3%), silicon (1.2%), and potassium (0.9%). The atmosphere, water, and soils on the surface can supply all of these. Of the remaining ~1% in needed trace elements, some are also available in the soil. All of the elements may need processing into forms that plants can use. Asteroids, and probably the Martian moons, have a wide variety of elements and compounds, so they can serve as source materials in orbit. Once efficient transport is developed from the surface, it can also be used as a supply. These materials will also likely need processing to usable form. Any remaining missing ingredients can be supplied from previous regions or Earth, but should be a small percentage.

21 - Mining: Extraction of local materials is a basic assumption of our program, because it takes less energy than importing everything from Earth. The Mars surface has large areas of broken rock (regolith), sand, and dust on the order of meters in thickness, which amounts to millions of tons/km2. This is more than enough for early mining, although concentrations of specific useful ores is yet to be determined. The moons and nearby asteroids can supply enough materials for early use in orbit, and efficient transport from the surface can supply more materials later. We don't expect large-scale delivery of mined products to Earth, but there may be moderate amounts exported from Mars to nearby regions.

22 - Utilities: Nearly all activities in the region will need local power in some form. At first this can be supplied by imported solar panels and batteries, possibly supplemented by small fission reactors or thermal storage. Concentrating reflectors can supply direct heat and drive thermal cycle electrical generator. These can be built locally once manufacturing is developed. Solar energy is more available and more constant in orbit, so that may be the preferred location for energy-intensive activities. Beamed power from orbit to the surface may be useful as a supplement, especially at higher latitudes where sunlight is weaker and seasonally intermittent. Beam attenuation during dust storms is expected to be on the order of 50% at 32 GHz, and less at lower frequencies. So this may be a solution for lack of surface solar energy at these times.

23 - Construction: Relative to the Earth's land area, Mars' surface is nearly the same size, and the orbital region has 2,400 times the cross section. We use cross section rather than volume for orbit, because sunlight can only be intercepted once for power and natural lighting. Although the Earth will not be overcrowded from a purely physical space standpoint, environmental pressures and a desire for more personal room, flexibility in design, and novelty may drive local residential construction. Any non-residential operations involving people and other living things will also require suitable habitats, and some industrial activities will need protection from the local environment. All of these will in turn require some level of construction activity.

31-33 - Manufacturing: Local manufacturing is also a basic assumption of our program. Any product which is easier to make in the Mars region than imported from elsewhere is a candidate, along with export products which are easier to supply from Mars than at their destination. At first only the most necessary, easy to produce, and high-leverage products would be made. These include items like radiation shielding, propellants, life support supplies, and basic construction and fabrication materials. Manufacturing would evolve over time, using bootstrapping, smart tools, and import of key items. Eventually all the local products which make economic sense will be made. Mars has significant amounts of Iron, Aluminum, Magnesium, Titanium, Chromium, Manganese, and Nickel for structural and machine alloys, Silicon for solar energy and electronics, and Sodium, Phosphorus, Sulfur, Chlorine, Potassium, and Calcium for chemicals. So it has a reasonable variety of material inputs for manufacturing.

42 - Wholesale Trade: We expect activities in the region will trade with each other and with other regions according to the principle of comparative advantage. We cannot predict at this time which specific activities in the region will have such advantages, but we can identify likely contributors. Transport from Earth or distant parts of other regions involves a lot of energy. Where local material supply and production can be performed for less energy, it would have an advantage. Surprisingly, it takes less energy to reach high Earth orbits from the Martian surface than from Earth. However, from a cost standpoint the break-even point is likely to be closer to Mars. More energy is available in orbit than on the surface, so operations that need high energy would prefer being there. Mining on land on Earth is relatively easier than in the oceans. The equivalent land area, and lower gravity and thermal gradient, makes several times the total volume of crust available to be mined on Mars. However we have little information about high grade ores as yet. Total available material is also about 4 times the mass of the Asteroid Belt, but compositions are different. So it is likely inter-regional trade will evolve based on relative scarcity.

44-45 - Retail Trade: We expect retail trade to take time to evolve on Mars. Early populations will be there for scientific and industrial reasons, and their personal needs for habitation space and life support will be supplied for them. As communities evolve past this early stage, more time and resources can be devoted to personal choice and non-essential items, and therefore suppliers at the retail level can evolve. It is hard to predict the form this will take, given the development of online marketplaces and automated delivery on Earth. It may be central warehouses rather than retail shop fronts. On the other hand, people may still want to select items in person, with the assistance of human staff.

48-49 - Transportation and Warehousing: Transport is necessary from other regions to start any activity on or around Mars, and is accounted for in previous phases from where such transport originates. Internal transport within the Mars region, and departing the region for other destinations belongs to this phase. Operation of transport fleets and infrastructure is covered under this activity, while their manufacturing and construction are covered under their respective headings. Storage and warehousing of all kinds is also included here. We expect all of these to continue in the region, so long as any kind of activity is present.

51 - Information: Delivering information through open space needs no mass, and little energy, so is relatively easy to do. Communications to and from Mars already exists through deep space networks to the spacecraft operating there. As remote control of equipment and human occupancy increase, local networks will likely be built. This can start with relay satellites in orbit to connect points on the surface, in the orbital region, and with other regions. Local networks will also be provided as various locations grow. Local storage and processing will be needed for most modern activities. Equipment for these activities is complex and low mass, so at first will mostly come from Earth and older regions, with local production growing over time.

52 - Finance and Insurance: At first, most finance and insurance for the region would be handled from Earth. They involve non-material relationships between rights, contracts, and money which can be transacted remotely. Local offices and agencies may be needed for things like damage claim inspection. They would also make setting up new accounts and agreements easier due to the time delay communicating with distant regions.

53 - Real Estate, Rental, and Leasing: The Outer Space Treaty of 1967 prohibits national claims to celestial bodies, but ownership and use of private equipment, such as satellites, is already well developed. We expect the legal gray area about land, orbits, and mining rights in space to be settled in previous regions first. By the time significant development in the Mars region starts, the legal procedures needed should be available, but we cannot say at this time what they will be. Derived activities, like sale and leasing of satellites and their use, is already an active market around Earth, and such activities would likely be extended to Mars.

54 - Professional, Scientific, and Technical: Some activity in this category can only be carried out locally in the Mars region, and has already begun with scientific and technical research. We expect this to increase over time, and represent a large part of early Mars activity. To date, most of the people involved in these activities have been on Earth - astronauts in space are the rare exceptions. We expect this situation to continue in the near term, with gradually increasing numbers of people local to the Mars region over time.

55-56 - Management and Organizational Support: Business management and administration will likely be handled from Earth at first, for cost reasons. As the size and complexity of operations grow in the Mars region, time savings will start to favor local management. With increasing development of smart tools and networks, traditional organization trees may no longer be needed. Management and organizational support may be distributed and automated instead. So it is hard to predict the form this activity will take in the longer run.

61 - Education: The first people in the region will be educated elsewhere, and information systems are becoming advanced enough to support local training as-needed. Local education of young people would be deferred until permanent habitation exists with children being born and raised locally. The form it will take is unknown. By then it may be mostly via augmented reality devices rather than classrooms with human teachers.

62 - Health and Social Services: Due to the unusual conditions and hazards in the region, health monitoring and first aid capacity would be needed as soon as people are in the region. At first it would be by training the crews themselves, with remote monitoring and advice. As the local population grows, additional specialized equipment and staff would increase the level of care. Telepresence, artificial reality and intelligence, and haptic robots my be good enough by this time to provide health care remotely within the region, but signal delays are too large from other regions. Nursing and residential care would be provided on Earth at first, requiring return of people needing it. Once sufficient population is in the region, local facilities may be established. Social assistance would likely be handled remotely if needed. The basics like habitation and food need to be provided for everyone in the region by design, because the natural environment cannot support them.

71 - Arts, Entertainment, and Recreation: Entertainment can start with remote delivery and stored media for people in the region, because their mass and energy requirements are low. Activities like creative and dramatic arts would likely be deferred until surplus time and resources are available. Active recreation would begin with exercise for health maintenance, and may develop towards sports later. Early exploration and geographically unique locations may be preserved for future generations.

72 - Accommodations and Food: As noted under Health, basic living space, food, and drink are required for people in the region. Sponsoring organizations would provide them at first for crews, who would self-operate them. As local capacity grows and people establish long-term residences, there will be opportunity for rentals, temporary travel accommodations, tourism, and specialty food and drink. Tourism is a large industry on Earth, and the Mars region is unique enough to be attractive, but time and cost will limit voluntary travel at first.

81 - Other Services: This includes miscellaneous activities not covered elsewhere. Repair and maintenance will be highly desired for imported items. They are either expensive or slow to replace, and may be critical equipment. Once local production is established, surplus items can be stockpiled for replacement and repair needs. Personal services will start out self-provided. Private and civic organizations are likely not needed at first. Later they can be extensions of existing organizations, or self-organized locally.

92 - Public Administration: Support for this category will start from Earth or previous regions. Local fire and public safety would start out self-provided, and develop as specialties with larger populations. Environmental quality and monitoring are necessary functions and would be included by design. Publicly funded civil space activities are the only ones carried out in the region so far, and will likely continue to be important. National security activity has not been needed in the Mars region so far, and may stay minimal through agreements and collaboration. Private activity has not yet begun in the region, but once it does, public supervision will likely be necessary. For time and distance reasons, some of the supervision will be local. Public-private partnerships are quite possible.

Project Drivers
Many of the activities noted in the above survey will not begin until the middle or distant future, and technical and organizational changes are likely by then. So it is hard to predict which of them will make sense, and when. However, we can start to identify important factors which will drive projects in the region when their time comes. These include human motivations, economics, available technology, and the place of a project among prior, parallel, and later ones. We expect the importance and status of these factors to change over time, affecting which projects get started, and when.

Motivations
Motivations to develop the Mars region can be personal, organizational, or social. Human curiosity about the world around us drives current scientific exploration of Mars, and is likely to continue. Mars can eventually support other scientific work in other regions. The desire for safety from natural and artificial hazards is another major motivation for people. In this context Mars has been proposed as a backup location for civilization, in case something happens to Earth. Our program assumes much wider development of the Solar System, partly for this reason. Most of space is devoid of life and already full of radiation. So moving hazardous activities off our original planet to other regions would increase safety there.

&emsp;In the economic realm, the desire for profits if ever-present. If they can be gained in the Mars region, that would be a strong motivation to develop it. Since the material and energy resources of the region are currently unclaimed, they would not need to be bought, merely exploited. [Additional motivations to be supplied].

Economics
Economics is a key driver for what projects will be started, their scope, and their timing. Currently, most activity around Mars is publicly funded. Governments and public institutions are limited by their available budgets, which pace what projects get initiated. Future activity at Mars is likely to have a large private component, which implies customers, markets, and the usual business considerations for what gets done and why. These include principles like comparative advantage and returns on investment. Private activities at Mars are more likely to happen if they are easier to do there than elsewhere, and can generate better returns on capital.

&emsp;The natural advantages of Mars include a large and diverse source of materials, and the most Earthlike environment beyond the Earth's surface. Escape energy is 20% that from Earth, so efficient transportation is easier to build. By exploiting gravity assists and aerobraking, even transport to Earth orbit could take less energy than launch from the Earth's surface. Mars is distant compared to the earlier Earth orbit regions and the closest parts of the interplanetary region to us. However, it is close to the outer portion of the Inner Interplanetary region, from 1.25 to 1.8 AU, and would be a preferred source for that region. Since Earth already has a complete civilization, we don't expect Mars to supply large mounts of physical products. Trade would therefore depend on other types of value, or supplying nearby regions. An example would be using the Martian moons as a starting point for large-scale construction using low gravity and materials from both the surface and local asteroids.

Development Projects
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 longer 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 include full optimization and integration of the projects to each other and to projects in other phases of the program. After describing our general approach, we list summaries of the projects by time, function, and location.. This is followed by a start at program integration. Where more concept details have been developed, they are provided as the last major portion of this section.

General Approach
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. Like the Lunar region, the Mars region is therefore 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. They also interact with other program phases which are operating in parallel, and with the rest of civilization.

&emsp;The various activities can be generally 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 list these early activities after this general approach. Longer term projects follow them. Since they are not yet combined into an integrated sequence, 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 features of the region in general, and of specific operating sites. Preparation for Mars development therefore involves tasks like exploration, surveys, prospecting, and site investigation. Scientific investigation of Mars, beyond merely determining its orbit, began as soon as large telescopes allowed seeing more than a point of light in the sky. It accelerated starting in 1964, when rocketry enabled sending instruments much closer to and landing on the planet, and communicating the data they collected back to Earth. We have not yet brought back pristine samples from the planet, but starting in 1983 over 100 Martian meteorites have been identified that came to Earth by natural means. These have been exposed to space and Earth environments, so are somewhat modified from their original condition. A number of spacecraft have orbited Mars, so the orbital region is now understood well enough to start development. Phobos and Deimos have not been orbited or landed on yet, and need closer inspection. A smaller number of landers and rovers have operated on the surface. Much more work is needed on the surface, since it is more diverse and variable than the orbital region. Exploring the whole planet will take a long time, so detailed investigation can at first start with proposed early landing sites.

Orbital Development - Orbital development is expected to lead work on the surface. This is because it is easier to reach from previous regions, and because of the existing material resources at Phobos and Deimos and nearby asteroids. Sites on the moons may need physical preparation, such as providing anchorage due to the low gravity or by gathering surface material to provide radiation shielding. Covers may need to be installed over active work areas to prevent loss of loose material. Open orbits elsewhere in the region don't need preparation, but also lack raw materials, so they must be imported. Due to long time delays from Earth, remote controlled operation would be difficult and slow. So we expect significant operations will require either advanced automation, or delivery of human crew to the region. These operations would begin with the delivery of starter equipment from previously developed regions, by means of electric tugs. An initial stock of supplies and propellants would also be delivered, but local production would be a priority in order to sustain operations. Phobos is likely to be used as a base of operations because of the large amount of materials available and convenient orbit to later reach the surface.

Surface Development - Once an orbital base of operations is built up, and a network of relay satellites are in place, site preparation on the surface can begin. At first this can use remote control of equipment from orbit. The time delays are short enough for near real-time control, and at first there will not be enough equipment on the ground to sustain people. A priority would be setting up a landing field and surface propellant production. Landers can then start shuttling from orbit carrying more equipment. When sufficient equipment is in place, crew visits can start, extending to full time occupancy. As in other locations, starter sets of production equipment are used to bootstrap larger scale production, then end-use products. Chemical rockets are inefficient, so in the longer term better transport infrastructure would be built up. Both orbital and surface operations would continue to get deliveries from previous regions, and start to export products once they have the capacity.

Current and Near-Term Projects
Research and Development -

Transport from Earth -

Transport from Low Orbit -

Missions to the Mars Region -

Long-Term Projects
As of 2017, a lot of R&D is needed before making definite plans for long-term development of Mars. Development of earlier regions will also significantly affect Mars projects because people, equipment, and supplies have to come from those regions. So the following list is only a summary of candidate projects, and, where known, what work is needed to prepare for them. As more work is done on Mars development, the list is very likely to change in terms of what projects are included, and their details. Linking these projects to each other and other parts of the program to form an overall plan is even more preliminary.

Mars Orbit Production
The Mars Orbit region is easier to reach than the surface, and requires low energy to reach from the Inner Interplanetary region which it is embedded in. We expect early production at Mars to start here, with basic products like radiation shielding, propellants, and crew consumables. Production build up would be an outgrowth of preparation stage tasks, such as remote control of exploration vehicles from orbit. Preparatory work would have delivered people, pre-made equipment, and supplies from prior regions to Mars orbit. Local extraction will reduce supply needs, and local production of equipment will further reduce external needs. Therefore it is highly desirable. The growth path would follow the standard bootstrap and self-expansion approach, using smart tools and local energy and material resources. As production expands, the orbital region can start to export to the surface and neighboring regions, both to support further development and generate economic returns.

Supply Sources - Large amounts of solar energy is available throughout the region, and is a logical way to power production. Availability is quite high except in lower orbits around the planet. The orbital region has two natural moons with a combined mass of 12.8 trillion tons. Using a combination of gravity assists, electric propulsion, and solar sailing, much of the Asteroid Belt and Inner Interplanetary region, with their thousands of asteroids, are accessible with low propellant use. Since the Earth Orbit and Lunar regions are previously developed, equipment and supplies can be imported from them. Eventually efficient transport from Mars would allow import of materials and equipment from the surface.

Processing - Aside from bulk radiation shielding, most products require conversion of raw materials by any of a vast selection of mechanical, thermal, chemical, electrical, or other methods. Equipment is needed to do these tasks and supply the energy to perform them. The growth path would then begin with processes that supply the most useful products relative to the amount and complexity of equipment needed. Equipment can either be imported or made locally. So the relative costs and difficulty of each source is a factor. Further growth pursues lower leverage processing, until it is no longer a benefit relative to product import, reaching an equilibrium with other regions.

Fabrication - Products like propellants and fluids don't require further fabrication after processing, just storage until used. However solid stock materials usually need additional work to make finished parts. There are a huge number of possible fabrication methods. Like the processing steps, they would be first be selected for highest output and simplicity relative to equipment and energy needs. Later expansion pursues lower leverage methods, until they are no longer an advantage relative to import.

Assembly and Construction - Finished parts, whether imported or made locally, are then usually assembled into finished equipment and facilities. Unless imported as complete units, the assembly and construction would be a local operation. Free fall in the orbital region, and very low gravity on the moons, allows large scale assembly with low effort. Some tasks may be easier to do under artificial gravity, so assembly and construction areas can provide it by rotation if needed. Due to relative ease of transport, large items may be built at dedicated factories, then towed to final operating locations.

Mars Surface Production
The Martian surface has a varied topography, climate, and geology. Therefore some places will be more suited to particular production activities than others. Early operations will not have the benefit of transport infrastructure, and will therefore have limited travel distances. Equatorial sites generally get more sunlight, and are easier to reach from the moons. These factors plus the choice of early production operations will guide site selection. Candidate sites would have been explored remotely with robotic equipment during the preparation stage. The first mining and construction equipment can then be delivered from orbit, and continuing remote operation until enough capacity to support people is in place. Early electrical power for production operations may be most easily done with stationary solar arrays, cables for stationary equipment, and charging points for mobile ones. Solar thermal energy can be used for operations that require heat. Additional energy sources can be added over time. Potential products include:

Minimally Processed Materials - This includes clearing and leveling for building sites and access roads by moving surface soils. Equipment which needs radiation, thermal, or debris protection would need excavation, placement, then covering with local materials. Unprocessed rocks can be used for slope retention and berms, and prefabricated arches can support soil coverage. Materials like metallic meteorites and useful ores may be gathered from the local area and stockpiled near a production site for later use. Bulk rock may also be used for thermal energy storage.

Water and Fluids - Water has numerous uses, including propellant production, life support, chemical processing, and in heat engines. Equatorial regions appear to have less water than the polar ones, but hydrated minerals may contain enough to be useful. It can be extracted by moderate heating and condensation. Permafrost ice can be extracted by heating soil above the triple point (0 C and 611 Pa), which is only slightly above ambient Mars daytime conditions. Electrolysis of water produces oxygen and hydrogen. The latter can be combined with carbon from the atmosphere to produce methane. This can be a propellant, fuel cell energy source, or feedstock for organic chemicals. Nitrogen can be extracted from the atmosphere and added to oxygen to provide a normal breathing mix.

Metals - Steel and Cast Iron are the most commonly used metals on Earth. They are primarily iron with 0-4% carbon, and other elements to produce Alloy Steel with different properties. The soil contains about 20% iron oxides, and the atmosphere is mainly carbon dioxide, which can supply the carbon. Manganese, chromium, nickel, and silicon are common alloying elements, and are present in Martian soils in significant percentages. Metallic meteorites are found on the surface and contain an iron-nickel-cobalt alloy which may be suitable as-is for early uses, but their quantity is limited. Large-scale production and more specialized alloys will need bulk reduction of mineral ores to provide the main elements. Magnesium, Aluminum, and Titanium are useful structural metals which are also present in reasonable percentages. Particular alloying elements for all the structural metals may need to be imported if they are not present locally in enough concentration.

Glass and Plastics - Common glass is made up of silicon, sodium and calcium oxides, and sodium carbonate. The first three are common components of native rock. Sodium is available, but mineral deposits of the carbonate form may be scarce, and need to be produced chemically. Pure silicon dioxide is used for quartz glass, which is useful for industrial processes. Native carbon compounds from which to make plastics are scarce on Mars, although carbon dioxide is abundant. Therefore chemical or biological processes would be used to make complex carbon compounds, or they would be imported from asteroid sources and the moons. Natural textiles would require large amounts of growing area, so are likely to be imported. Synthetic textiles are feasible with organic compounds.

Building Materials - Wood is unavailable on Mars unless it is imported, or the effort made to grow trees. Native materials may be used for clay-sand or sulfur-soil bricks and blocks. Concrete requires significant amounts of water and carbonates to form the cement binder. It is not clear if this will be a preferred process. Steel and basalt fiber can serve as reinforcement, although the latter needs an epoxy resin as a binder. For pure tension uses, bare fiber can be used, and it can also be used for fiber-reinforced metals. Mineral wool and vacuum-powder insulation can be produced locally.

Other Products - Electronics are low mass and high value, and are likely to be imported. Electrical goods like wires and motors need suitable metals, but are needed in enough quantity to make locally. It is not clear if coatings such as paints can be made from local materials.

Mars Orbit Habitation
Orbital habitats around Mars will share many similarities with those from previous regions, because the functions they perform and the operating environment are similar. Detail differences will result from things like lower solar flux and average temperatures, and a different mix of supply sources versus distance and difficulty. There would be a general trend from prefabricated to locally built and from small to large.

Prefabricated Habitats - We expect the first habitats will be delivered as completed elements from previous regions, along with an initial stock of supplies. They would either be delivered unoccupied by electric tugs, or carried along with a crew. Our general program approach is to use local materials and energy when possible. So we prefer an approach where the elements are delivered by the same kind of tugs used for asteroid mining, which is also the source for propellants and other supplies for the trip. We want the people to travel safely and efficiently, so we prefer a cycling transfer station approach. They get dropped off near Mars, then use high thrust propulsion for orbit capture. The habitat elements are already in position there, and are occupied in transit to a resource site, likely Phobos. An alternate approach is for the transfer station to grow by accretion of prefabricated and locally made elements. When it has grown sufficiently, part of the station separates, with enough crew and equipment to operate on its own. It then gradually adjusts its orbit to rendezvous with Mars. While it does so, it continues to mine local asteroids and get necessary supplies and equipment, which are delivered by separate tugs from Earth orbit.

Local Construction - Since some asteroids contain native iron alloy, an easy approach to local construction would be to heat that alloy in a solar furnace, then cast and machine structural shapes from them. Later construction can use more advanced materials and construction methods. Solar flux is about the same across the orbital region, so where to place the habitats would depend on the balance between access to asteroid, Martian moon, and surface materials. The surface requires a lot more energy to deliver from by chemical rocket, and has less energy supply than orbit, so at first the favored locations would be higher orbits. As orbital infrastructure is built up, closer locations using surface resources become more feasible. No single location will be best for all purposes, so we expect a number of habitats to be built. Larger habitats can be built by an incremental layering approach. The initial version would use several smaller prefabricated or locally made elements. A larger pressure shell is built attached to them. Once sufficient systems are installed, the larger shell is occupied. Later expansion adds additional larger shells around this core, which are occupied in succession as they reach completion. Later on, older shells can be dismantled and recycled to open up interior space.

Mars Surface Habitation
We expect surface operations on Mars to go through several stages. The one we are currently in is remote operation of equipment from Earth. Round-trip communications from Earth is 6 - 45 minutes, so this type of operation is necessarily slow. Once habitats occupied by people are in the orbital region, this will be reduced to less than 2 seconds, and from Phobos is 100 ms or less using a relay satellite to the far side. So near-real-time or real-time remote control will be possible. This will allow extensive preparation of surface sites, including preparation for people to be on the surface. Some activities will need people on the surface in person, and some people will want to be there for their own reasons. Once surface refueling capacity is available for landers, crews can visit the surface for short times, then return to orbit where more habitat capacity is available. After enough habitat elements are delivered and assembled on the surface, they can stay for extended times. Further construction will allow for larger resident populations. Various activities on the surface, like resource extraction, will likely need multiple operation sites. Therefore multiple habitats and surface transport between them will evolve.

&emsp;The natural Mars environment is hostile to human life, so all living accommodations, from space suits to entire cities, must protect from the environment and one way or another provide for people's basic needs. These include air, water, food, temperature control, sleep, sanitation, and for longer stays radiation protection and artificial gravity. Small artificial environments, such as space suits and rover cabins, will have limited power and supplies. Therefore they will have time limits on occupancy, after which they will need to transfer occupants to a larger and more capable habitat, recharge, and restock.

Site Preparation - Habitation sites on the Mars surface are unlikely to be usable in their original state without some preparation. We expect that mining and construction robots will have been delivered for surface production, and remote-controlled from orbit. They can also be used to prepare the first habitat areas. Vehicle landings and launches, and propellant production and storage represent hazards. So the habitat sites should be located some distance away, and protected by local terrain, such as crater walls or hills, if available. Access roads will be needed between parts of the site. They would need clearing and leveling, and possibly gravel fill for load-bearing and traction.

Early Habitats - Landers carrying people will need at least a minimal crew cabin, but to save transport mass they would not be larger than needed. Crew can work out a lander cabin for very short surface stays, on the order of a few days. This is similar to how the Apollo Lunar Module functioned. Longer stays need additional supplies and equipment, which can be delivered ahead of time by uncrewed landers and unloaded by remote control. If needed, the habitat can go through a "construction shack" stage, where a minimal number of modules on a temporary site provide living quarters, while a larger and more permanent site is prepared.

&emsp;A permanent habitat would likely be partly buried to provide radiation, thermal, and blast protection from transport or production accidents. It could take advantage of natural landforms such as craters, which are additionally cleared and leveled as needed. Both prefabricated pressurized modules and unpressurized vehicle and storage areas would be covered by arched supports, which are then covered by local soil and rock. For thermal and maintenance reasons, the modules would not rest directly on the ground, but on raised frames. The frames may rest on the ground if it is stable enough, or on foundation piles drilled and set deeper. At least one set of lifts and carriers will be needed to move and place the larger elements, and the final support frames should be adjustable to account for ground irregularities and settling. In order to provide pressure-tight living space, the various modules will need accurate alignment or flexible docking ports, but flexible sections are a weak point. It would be preferable to rigidly attach pressure shells. The habitat will need a variety of utility services, like power and fluid storage. These may be supplied from a production area if it is near enough.

Long Term Habitats - Zero gravity is a known health risk to people, but at present we don't have any data on partial gravity effects. We especially don't have any data on pregnancy and child development in low gravity, because no such astronauts have been to space. The 3/8ths of Earth natural Mars gravity may not be sufficient, even with added measures like exercise and body weights. In that case artificial gravity using rotating habitats on the surface would be needed. For ethical and child safety reasons, we should assume such facilities will be needed once Mars habitats reach the permanent colonist stage, until it is proven they are not required. For long-term stays, on the order of years, for adults who can make informed decisions, artificial gravity may not be needed. Artificial gravity is somewhat simpler in orbit, because it doesn't require mechanical moving parts, or dealing with friction and gyroscopic forces. So one possibility is restricting pregnant women and children from the surface, to avoid building rotating structures. But that imposes added transportation needs, and at present we don't have enough information to decide the best approach.

Mars Orbit Transport
Reusable Landers -

Orbital Tugs -

Mars Skyhooks -

Program Integration
&emsp; -

Phobos Base
Phobos has an orbit altitude of 5980 km (1.76 Mars radii) above the surface, and a mass of 10.66 trillion tons. This makes it a convenient starting point for orbital development, and an eventual base of operations for surface development. A Phobos base would eventually grow to include the full range of production, habitation, transport, and service functions. But it would start with the minimum viable scale and activities, and bootstrap up from these. Prior to starting, dedicated orbiter and lander missions should thoroughly survey the moon. Due to the low gravity, a lander may hop between multiple sites and get increased coverage. Problems with the Philae lander on a similar-sized comet may require a different approach, such as a "spiked ball", which can land in any orientation, then pivot to observe and use propulsion to hop to the next. Once the moon has been surveyed, we would know what set of starting equipment and supplies need to be brought from other regions. We expect that development of Lunar orbit and mining of the Earth's Moon and Near Earth Asteroids would have already begun. So initial deliveries would be via electric tugs from these regions. Additional raw materials may be imported from near-Mars asteroids if needed. Since Mars skims the inner edge of the Asteroid Belt, there are many nearby candidates.

&emsp;Solar energy is available for at least 88% of the 7h 39m orbital period, with a 53 minute maximum eclipse. The moon is near-equatorial to to Mars, while the planet is tilted 25 degrees to its orbit. Therefore Phobos misses Mars' shadow entirely near the solstices, and has reduced eclipse times away from the equinox dates. The moon rotates once per orbit (i.e. keeps one face towards Mars), so surface locations have a day-night cycle. Energy-intensive operations may want to locate near, but not on the moon. This is to avoid loss of solar power from Phobos' shadow. Since the composition of this moon is not yet known we cannot plan out mining and processing in detail. At the least, bulk rock can be extracted for radiation shielding. Whatever the composition turns out to be, certain elements and minerals will be available, and we can find uses for whatever they are. Crater density and structure indicates a deep regolith, with a 1 meter layer of dust and small rocks, so excavation of this material should be fairly easy. If carbon or water are available in sufficient quantity, they can directly be used for propellants and life support. Otherwise, such materials would need to be imported.

&emsp;A Phobos base would serve development of the orbital region and the surface in several ways. First, as a supply of bulk materials for shielding and counterweights for artificial gravity. These uses don't require processing. Next, whatever minerals and elements turn out to be there can be used in expanding local production and for end products. Some amount of materials would be imported from Earth and previous space regions, and later on from Mars, to make up whatever Phobos lacks. Over time, orbital infrastructure would be built up to enable larger scale and more efficient transport to and from the surface. The orbital vantage point allows for real-time control of ground equipment over the entire planet, with the assistance of several relay satellites. This is helpful before surface facilities can support human occupation, and later on as a relay network for dispersed ground locations. The resources of the Mars region can later support development in the Asteroid Belt and beyond.

Mars Skyhooks
Skyhooks are more efficient than chemical rockets for transport around large bodies. This is because they can use electric propulsion for orbit adjustment, which is about ten times more efficient, and store orbital energy for traffic going the other direction. In the limit of balanced traffic rates, they require no net energy or propellants to operate. They are easier to build than space elevators because they are physically smaller and lower stress, and therefore lower mass for any given task. However, they are still large-scale transportation infrastructure. Infrastructure is relatively expensive to build, but low cost to use each time. So they are not the first thing you build at Mars. Rather they are built when there is enough traffic to justify their construction.

&emsp;We will look at three concepts for skyhooks as part of a Mars transport system. The first is is a pair of smaller skyhooks capable of reaching from low Mars orbit (LMO) to Phobos orbit, and provides whatever suborbital velocity to the Mars surface and velocity above Phobos that results. The second is a single larger skyhook capable of doing a full velocity transfer to the Martian surface. Third is an orbital skyhook combined with a ground accelerator. In reality, such systems can grow and evolve over time, and some other size or version may turn out to be optimal. It will take more detailed analysis and understanding what the traffic needs are before choosing an approach. For now, we just present these three as starting concepts.

LMO to Phobos Skyhooks
&emsp;Orbit Mechanics - The product of a planet's mass M and the universal gravitational constant G is called the Standard Gravitational Parameter or $$\mu$$. For Mars the value is $$\mu$$ = GM = 42.828 x 10^12 m3/s-2. This value is useful for calculating circular orbit velocities by the formula


 * $$v_o \approx \sqrt{\frac{GM}{r}}$$

&emsp;The average radius of Phobos from the center of Mars is 9,377,000 meters (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 at any point can be found from


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

&emsp;We want our lower skyhook to avoid atmospheric drag, which starts to become significant at 160 km altitude. We then tentatively set our arrival at 240 km above the surface to account for the length of the lower skyhook. If we want to transfer from Phobos to 240 km above the Mars surface ( r = 3636 km ), then the velocities at the high and low points of the transfer orbit, and of the center of the lower skyhook can be calculate as follows:


 * Transfer High point: r = 9,377,000 m ; a = half of high + low altitudes = 6,506,000 m ; from formula $$ v^2 = $$ 2,551,844 m^2/s^2, and so v = 1597 m/s.
 * Transfer Low point: r = 3,636,000 m ; a is the same as previous = 6,506,000 m ; therefore $$ v^2 = $$ = 16,974,909 m^2/s^2 and v = 4120 m/s.
 * 200 km skyhook center velocity: r = a = 3,636,000 m ; v = 3,451 m/s.

&emsp;The velocity difference from Phobos to the transfer orbit is 540 m/s, and from the transfer orbit to the lower skyhook center is 669 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 29.75 km, and the LMO one would be 45.6 km. Our initial assumption about an 80 km total length is then fairly close, and the structure only reaches below 160 km when vertical, so for now we ignore the difference. 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.

&emsp;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 it's own orbit velocity minus rotation velocity, or 3,451 - 669 = 2,782 m/s. Mars' equatorial rotation is 241 m/s, so the relative velocity to the surface will be 2,541 m/s. This is 73.6% of orbit velocity and 54% of orbit kinetic energy, which can be dissipated by drag. To reach Mars escape from Phobos requires adding 884 m/s. Since our Phobos Skyhook can add 540 m/s, that leaves 344 m/s to be done by other means. In total our two skyhooks can provide of the 2,418 of the 5,027 m/s from the Mars surface to escape, or 48%. This is a significant propulsive savings for such a small system, and mass ratios and payload fractions for the rocket portion of transport to and from Mars would be much improved.

&emsp;Carbon fiber is an excellent material to build such structures. There are three possible sources for carbon to use in local production. The Martian moons, Phobos and Deimos may contain some carbon, but current observations indicate they are low in this element. No probe has yet visited these moons or observed them closely enough to be sure, so we cannot yet rule them out. Being in Mars orbit, they are a preferred source from a transport point of view. 75% of asteroids are the carbonaceous type, and there are many asteroids near Mars. The Martian atmosphere is 96% carbon dioxide. So those are alternate sources if the moons are not suitable. Basalt fiber is not as strong as carbon fiber, but the Martian surface is primarily basalt-covered. That is an alternate material to build with. Finally, for smaller skyhooks, transport from elsewhere with more developed industry is an option.

LMO to Surface Skyhook
&emsp;A full orbit to ground Skyhook is a much larger system. It probably will 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.

&emsp;Structural loads vary from zero at the center to 1 gravity at the tips, and therefore average 0.5 gravity. Total stress on the structure is then 423 g-km. The highest strength known carbon fiber is 7 GPa, with a density of 1790 kg/m3, and therefore a specific strength at 1 gravity of 399 g-km. Engineered systems are never designed at ultimate strength, because they fail at that point. Allowing a 2.4 design factor of safety, our design strength is then 166 g-km. Structural mass is exponential in the ratio of total stress to strength, so each arm of the skyhook is 11.78 times the payload mass, or 23.6 for the entire structure. This is a reasonable ratio for a system that will be used many times.

&emsp;Escape velocity from circular orbit is 41% higher, and this skyhook can supply 93% at the upper point of rotation. Therefore it can capture payloads from, and inject payloads to, higher than escape velocity by a significant margin. However the chance of a missed capture raises a safety issue, since the payload would then fly past Mars. If it were carrying people, an actual design would either only capture from below escape velocity, or carry a backup method of slowing down.

LMO Skyhook with Ground Accelerator
&emsp;Pavonis Mons is a 14 km tall shield volcano on the Martian equator. It has about 120 km of available slope in the direction Mars rotates. Assuming a limiting acceleration for people and cargo of 6 G's, a velocity of 3757 m/s is possible. This is higher than the 3313 m/s required for low Mars orbit, so either a shorter accelerator (93 km) or lower acceleration (4.5 G's) could be used. Atmospheric pressure at the top of the mountain is 140 Pa (0.14% of sea-level Earth), which is not an obstacle to acceleration, but will generate some drag, and a permanent orbit will need some propulsion to circularize. A ground accelerator this size would be a large construction project, so it makes sense to consider a combined system of smaller accelerator and a smaller skyhook instead of either providing the full velocity change to orbit.

&emsp;Let us take the case of a low orbit skyhook capable of reaching Mars escape. It can then reach Phobos, Deimos, or other intermediate orbits by choosing where on the skyhook to let go. We start by guessing the orbit height is 360 km, to avoid the atmosphere and allow for the skyhook radius. Orbit velocity is found from the above formula to be 3377 m/s. Escape from that point is 4775 m/s, which requires adding 1398 m/s. At 1 gravity, the radius is then 199 km, or less than a quarter of the full orbit-to-ground version in the previous section. Total stress is 99.65 g-km, giving an arm mass of 0.86 times the payload, and a total structure of 1.73 times the payload. This is 13.5 times less than the full orbit case. Like other small skyhooks, it requires significant ballast mass to avoid throwing itself out of orbit when it accelerates a payload. The 199 km radius results in a 161 km altitude at the low point, and confirms our guess to avoid drag.

&emsp;When we subtract the tip velocity from orbit velocity, which is what happens at the low point, we get a net velocity around Mars of 1979 m/s. Mars' rotation leaves 1738 m/s relative to the equator, or 49% of the 3554 m/s unassisted entry velocity. Therefore only 1/4 of the kinetic energy needs to be dissipated for re-entry, which should be easy. Going upwards, a ground accelerator at 6 G's has to be 25.2 km long, and longer at lower accelerations. This is 3.7 times shorter than the full speed accelerator, and requires the same amount less energy to operate. Thus both the skyhook and ground accelerator are significantly smaller in the combined case. The optimum division of work between the two, or whether to use only one or the other would depend on cost and design details, which it is too early to determine. We know enough at this point, however, to say a combined case should at least be considered for a future Mars transport system.

&emsp;Depending on the required velocity, acceleration time, and cargo, a ground accelerator can be linear or centrifugal, and in the linear case can be electromagnetic or gas pressure-driven. The centrifugal case would be driven by an electric motor. Gas pressure and centrifugal approaches are more suited to bulk cargo at high accelerations, which makes the accelerator compact. People and delicate equipment are limited to 6 G's or less, which requires longer acceleration paths. In all three major concepts, the advanced transport systems can be built incrementally over time. Whatever portion is not handled by the advanced system is supplied by conventional rocket propulsion. Whatever portion is supplied by the advanced system will lower propellant needs and increase payload fraction relative to the all-rocket case. Those savings are the justification for building an advanced system. Skyhooks don't eliminate the need for propulsion. If their traffic is unbalanced, they still need some to maintain a stable orbit. But electric propulsion is at least ten times as efficient, so propellant needs are greatly reduced. If more traffic is going down than up, the skyhook will increase in altitude. In that case, atmospheric drag can be used to intentionally slow it down. Ballast mass can come from the Martian moons or nearby asteroids, and slowed down with aerobraking. It should therefore not require a lot of energy to put in place.

Construction
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 Supply
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 Manufacture
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 Accelerator
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 Development
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".

Magnetosphere
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 its 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.

Greenhouses
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 Atmosphere
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).

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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.