To Mars and Beyond: on Becoming an Interplanetary Civilization
The Seed Factory Project,
6485 Rivertown Rd, Fairburn, GA, 30213
- Abstract - Current national space programs are based on a limited vision. They involve missions to a given destination only for science and national prestige. Missions have finite goals and end when they are reached, so they don't include full development of the destinations. Instead, equipment and supplies come from Earth, which keeps costs high. The finite accomplishments and high costs result in a poor benefit/cost ratio. We propose a broader goal of upgrading and extending civilization on Earth first, and full development of the entire Solar System, and eventually beyond it. Accessing unbounded physical space, materials, and energy resources provide much larger benefits. Our approach is a modern way to organize production. It makes more of itself first, using local energy and materials and a core starter set of machines (a "seed factory). It then expands to the full range of production, habitation, transport, and service industries. Each new location repeats the growth process, produces products for local residents and the rest of society, and becomes economically self-supporting. Existing locations then send new starter sets to the next locations. Locations are developed in logical progression from easier to harder and more distant. Since locations grow to support themselves, the net cost of such a program is just the initial start-up, and the benefit/cost ratio is high.
1.0 - Introduction
Sending humans to Mars is a current stated goal of the U.S. national space program, and considerable budget is being expended on that goal, primarily on the Space Launch System and Orion capsule. The program concept to reach this goal is directly descended from plans first made in the mid-20th Century such as Von Braun's in 1954. In the decades since, the technologies to be used in the program have advanced, but the overall concept has not, for example in this recent NASA Mars Mission Concepts The "mission to Mars" approach includes a number of assumptions:
- It is a round trip made non-stop from Earth to Mars, with limited duration on the Martian surface.
- Because the number of missions is small and they are short, it is not economic to develop local resources.
- Most or all equipment and supplies are launched from Earth.
- High risk is accepted from radiation exposure, equipment failure, and lack of fallback positions, because dedicated astronaut crew are willing to take these risks.
These assumptions drive high mission costs and low returns, so actual attempts to reach Mars have stalled for decades, and gone very slowly more recently. In terms of just exploration and science, a trip going to only one place for a short time, and bringing back perhaps a few hundred kg of samples, is not much return for the effort expended. In Von Braun's time there were only 50-60 near-Earth objects (NEOs) known. They were ignored because they were not in very useful orbits, and ways to exploit them were unknown. As of 21 November 2015 there are 13,419 discovered, and about 1500 more per year. The much greater number means more of them are in useful orbits, such as easy to reach from Earth or on the way to Mars. NEOs are defined as those which come closer than 1.3 AU, where 1 AU is the Earth's average solar distance. Since Mars ranges from 1.38 to 1.67 AU, then NEO's are "on the way" there. We now have very efficient electric thrusters, computers, robotics, and high speed communications unknown in Von Braun's time. We have also done early research in how to mine these objects and produce useful products from them. Using them as stepping stones to refuel and restock supplies greatly reduces what you need to bring from Earth.
The total number of known objects in the Solar System has increased by a factor of 100 in the same time period, from about 7,000 to 700,000. Although the majority are still in the Main Asteroid Belt between Mars and Jupiter, many others are in other orbits throughout the Solar System. An even larger number are waiting for better telescopes to be found. The total size of the Solar System has increased by 54 times, from 49.3 AU for Pluto to 2656 AU for the maximum distance of scattered object 2012 DR30. We think all these places should be explored and used, not just Mars.
Even for Mars, relatively short round trips do not allow for full exploration of the planet. The lack of infrastructure limits the exploration radius around a given landing site. Lack of refueling stations and reusable landers limits sample mass that can be returned to Earth, where the vast bulk of researchers and equipment can analyze them. If most items have to be launched from the deep gravity well of Earth, then delivery costs will be high, and proportional to the number of missions, their mass, and destination distance. Finally, the high cost and difficulty means you cannot afford the mass of adequate radiation shielding, backup vehicles, and spare parts and supplies. As a consequence, what you do build must be lightweight and near-perfect, and thus expensive. Despite that, crew safety is compromised. We think a new approach based on 21st Century ideas and technology is needed.
2.0 - Program Concept
When a nation or group of nations pursues government-funded space research and exploration, we traditionally call it a space program. The concept we propose is broader than that, encompassing the full range of civilized activities. For convenience we will still refer to it as a program, with component phases and projects. Our approach incorporates knowledge and technologies developed in the last half century, and some new technology which is within reasonable reach in the short term. It includes advanced computers, networks, automation, and robotics. These enable production that grows from a starter set by self-expansion and upgrade. The production uses an increasing percentage of local energy and materials to grow. Some outside supplies of parts and materials will still be needed, and some human labor when tasks are too hard to automate. Existing locations eventually build new starter sets and transport them to new locations, repeating the growth process.
The laws of nature are the same everywhere, so the same general growth pattern can be applied on Earth too, starting with the easiest ones. It can first supplement or replace conventional jobs in developed regions. These are always at risk from layoffs, and may be permanently displaced by the same automation technologies we intend to use. Self-built and self-owned production can more securely supply people's basic needs. It can then be extended to less-developed regions, and allow them to skip the fossil fuel stage of development and the problems it creates, while gaining the comforts, health, and safety of modern civilization. Instead, the self-expanding production is based on renewable sources such as solar and wind. Thirdly, self-expanding systems can be extended to difficult and extreme locations on Earth that are currently unused or barely used. The expansion would be done with care to prevent environmental side-effects. We do not have to wait until a given type of location is completely developed before moving to the next category. Rather, the starting points are staggered in order of difficulty. Once sufficient progress and experience is gained on Earth, we can then move to a sequence of locations in space.
Unlike traditional space programs, our approach is not expected to be under centralized government direction. It can include independent businesses operated for profit, public/private partnerships, incentive prizes, and other alternatives to the conventional government funded/contractor-built methods. These older methods have little incentive for either side to finish promptly or keep costs under control. Government agencies want to continue their existence, but getting approval for new projects is hard. Contractors want to earn as much as possible, and winning new contracts is uncertain. The incentives on both sides have led to numerous examples of tacit underestimation of costs to get initial funding approval. This is followed by cost growth as the real work progresses, but avoids getting approval for a new project or competing for new work.
2.1 - Upgrading Earth
Our program changes the goal from a mission to Mars to upgrading and extending civilization. We do this on our own planet first, then the rest of the Solar System, and in the long run, beyond. We begin with Earth because we have large and immediate needs here. Much of our civilization is underdeveloped and unsustainable, and the vast majority of people will live here for many decades. Starting on Earth allows us to gain experience with the technologies we will later use in space. It is also easier and less expensive to apply them here first, and they can produce economic benefits to sustain themselves. Our program widens participation from the U.S. national space program, or a joint effort of several national programs, to all of civilization. The NASA budget is about 0.025% of gross world product, and only part of that is devoted to exploration and science beyond Earth. By being more inclusive, we hope to increase the available effort to apply to the tasks.
Our current civilization is actually quite limited, even on Earth. The urban, forest, and farm land we use in any significant way amounts to only 13.5% of the planet's surface. The remainder are oceans and lakes, deserts, and ice caps that are only traveled through or barely used. Of the areas we use, most of it is a thin surface veneer. The world's biosphere plus the human built environment averages about 25 kg/m^2, versus the Earth's total mass to area of 11.71 billion kg/m^2. At the density of water, our civilization amounts to a 2.5 cm (1 inch) thick layer across the surface. This is increased by 7.4 times if we consider only the 13.5% of the planet we use. The perceived scarcity of resources is thus an illusion, because we are restricted to using 2 billionths of the planet's mass and one ten-thousandth of the available energy flow. In a literal sense we are only scratching the surface of our own planet. When we consider the whole of the Solar System, the available resources increase by hundreds of times in mass, and two billion times in energy. This gives a resource/current use ratios of 250 billion in mass and 20 trillion in energy. Scarcity is not a problem if we can only figure out how to use what's there.
We currently depend on fossil fuels for 86% of civilization's energy sources. While they have powered growth from pre-industrial levels to our current state, they have the side effect of adding greenhouse gases, mainly CO2, to the atmosphere. These gases reduce infrared radiation to space, and thus alter the balance between incoming sunlight and outgoing heat. Venus' surface temperature of 462C is an example of why this is a bad idea. Only 50C of Venus' higher temperature is due to being closer to the Sun. The rest is primarily heat trapped by a thick, mostly CO2 atmosphere. Ironically, a lack of sufficient energy means we cannot afford, as a civilization, to capture and reprocess all waste materials, nor extract new materials from abundant low-grade sources. Rather, we get new materials from natural concentrations, called "ores", which take less energy to process. However, high-grade ores are in finite supply, and if we do not reprocess used materials, those ores will eventually run out. Thus the current course of civilization is unsustainable. We will either cause severe problems by increasing temperature, run out of necessary materials, or both. At the same time, the world's population is growing, and not everyone has obtained the benefits of full development. Such development demands even more energy and materials, and it isn't fair to deny these benefits just because some people were not the first to get them.
A way out of this dilemma is to provide abundant renewable energy by using highly automated self-upgrading and self-expanding production. Such production makes more of itself exponentially, including the power sources it needs to run. Renewable energy will have much less impact on the planet's heat balance, and large amounts would allow increased reprocessing and extraction from lower grade ores or even common rock and ocean water. Rapid expansion enables bringing the rest of the world up to developed levels faster, and automation lowers the relative costs of energy and materials. Automation is already a well-developed field of engineering. What is needed is purposeful design for self-growth. Once that technique is mastered, it can later be applied to space.
2.2 - Developing Space
Our first steps into space are to support existing space industry, such as communications satellites. That provides a ready market to justify the first investments. But in the longer term we want to serve larger needs. Renewable energy and reprocessing of wastes has less impact on Earth than current methods, but it does not have zero impact. A growing population with a high standard of living will put stress on the remaining natural world, and deplete the finite accessible resources on Earth. Eventually it becomes easier to access the abundant resources of space than, for example, digging ever deeper to find quality ores. There is seven times as much solar energy in nearby space as the average location on Earth. Atmospheric absorption, night, and weather account for the difference. There are also a wide variety of material resources in space, some of which are quite scarce on the Earth's surface. The combination of energy, raw materials, and automation would allow rapid growth of space industry, and relieve the limits imposed by a finite Earth. It is currently very expensive to do anything in space, but that is an engineering problem, not a fundamental limit due to nature's laws. For example, potatoes at retail cost about USD $1000/ton, and the wholesale electric energy to put those potatoes in Earth orbit (8.7 MWh) costs $450, less than the potatoes do. Sending even cheap bulk commodities to space would be affordable if we could do it efficiently. Current launch costs are quoted at a minimum of $1.7 million/ton, or 3750 times base energy cost. This represents how much room there is for improved efficiency and economics.
Reaching space requires equipment on Earth, historically rocket factories, rocket hardware, and launch sites. Automated production that makes more of itself can lower the cost of this equipment. You would begin with a core starter set (a Seed Factory), and grow it until you have mature factories that produce the hardware you need. Currently, rocket hardware is mostly used once and thrown away. That is a major contributor to the high cost. Improved technology can allow using the vehicle hardware multiple times, lowering transport cost further. Automated production in space, using materials and energy already there, would reduce how much has to be launched from Earth. More efficient technologies, like electric propulsion, reduce the mass further. The closer we can source items to the desired destination, the less effort is required to move them there. So a Lunar or Mars base would ideally get most of what it needs locally, or from not too far away, and only get from Earth what can't be found otherwise. The combination of all these methods would bring us much closer to "potato cost".
The self-expanding Seed Factory approach also applies to building factories in space. The starter factories extract and process metals and other basic materials. These are used to build parts for more equipment and habitats. Other materials are then extracted with the additional equipment to produce additional products. Once a given factory has matured enough, it can build a new Seed Factory and send it off to the next location. This creates an expanding wave of development as far as people wish to carry it. The first equipment at a new location arrives pre-built, and does simple extraction and processing. This is followed by starter set machines to bootstrap expansion and produce more complex products. In the early stages there are fewer machines available, so a larger percentage of parts and materials must be delivered from previous locations. As more equipment accumulates, a higher percentage can be produced locally. The developing location can start exporting a surplus of items it can make to trade for those it can't, or that require materials that are locally rare. By export and trade it becomes economically self-supporting, and therefore no longer a cost burden, like a base supported from Earth would be. It becomes part of an expanding civilization growing throughout the Solar System, and in the long term, beyond it.
2.3 - Program Phases
We divide the program into a number of phases and projects for several reasons. First, it is a long term and complex, and therefore easier to explain than an undifferentiated whole. Next, we intend each phase to provide revenue and benefits to support later phases. Trying to do it all at once would require too much funding. Third, new technologies will be needed, such as Seed Factories and improved space transport. These take time to develop, and in some cases terrestrial versions can be developed first to gain experience. Lastly, while we can lay out a long terms program, we don't know what new technologies will be invented or when. So it makes sense to concentrate on the early phases, and leave details of the later ones flexible until their time approaches.
In general, phases don't end, but rather operate in parallel once started (see Figure 1). For example, industrial factories grown from a starter set will continue to operate once new locations are set up. The phases do have a logical sequence, where later steps generally depend on earlier ones.
Figure 2 shows the main sequence of phases. It does not show all their relationships, since that would make the diagram to complicated to read. Their general order is from easier to harder, and from local to more distant. Each phase typically involves multiple projects and locations. In many cases a given location will evolve from one phase to the next through expansion and upgrade. We have identified six main phases, shown in different colors, with a number of sub-phases indicated by letter. These are described in more detail in the following sections. This article is by no means a complete description or a final design. It is intended to propose new goals and methods, but much more work is needed.
[Insert examples of seed and growth industries per phase]
3.0 - Research and Development (R&D)
Our program must starts with R&D because we are developing a new way to organize production, and will need new hardware for particular environments. We number this as Phase 0 because it supplies technology and designs, but is not intended to develop new locations as such. We need places to do the R&D, and thus construction and incidental production will happen as part of testing, but that is not the main purpose. The main purpose of the R&D phase is to output final designs for later phases to use. A goal of the program is the most benefit to the most people. Therefore we plan to open-source the designs, while individual machines and factories, and the products they produce, can be privately owned. Since R&D is the first program phase, it can't evolve from previous ones. Instead it must start with conventional buildings, tools, machines, design methods, and skills.
The R&D Phase can develop new methods and technologies to use for itself in the course of working towards later phase designs. It may produce some products for sale, to help fund more R&D, as a consequence of testing prototype equipment, and use production outputs internally to help expand and upgrade the R&D equipment. Final designs should have a long operating life. Prototypes built and tested before making the designs final will then last longer than needed to test. Therefore prototypes can also be sold, or delivered to other locations or later phases to use. Lastly, the R&D phase may produce final versions of elements for starter sets (seeds). These starter sets are then used to establish new locations.
The R&D Phase is functionally divided according to the later phases the designs are needed for. Items needed for multiple phases are assigned to the first phase they are needed. Since new designs are likely needed even for the last phase, R&D will continue for the whole life of the program. In addition to new designs, technology progress elsewhere, the growth of locations, and unique conditions of a given location will require design updates, new hardware models, and customization.
The R&D work is grouped into projects according to the technologies being developed or type of end use. So far we have initiated the Seed Factory Project to develop designs for self-expanding factories. Future projects may involve items like interplanetary tugs or orbital construction equipment. Those would be for later phases, so we have not identified a specific project for them yet. There is lots of science and technology work happening elsewhere in civilization. We do not expect to duplicate that work, but use their results where it makes sense, and contribute back our own results to the general fund of knowledge.
4.0 - Temperate Locations
Our definition of temperate is not identical to the climatic one. It includes the types of climates where most people currently live, and are actually inhabited and developed to some degree. These are the easiest conditions to build the first factories and locations.
4.1 - Phase 1: Starter Locations and Network
The goals of this phase are (1) to develop experience building and expanding locations, and (2) develop networking between locations. Networks of nodes and locations will be used in all later phases. The reasons include (1) not all locations have the same raw materials and energy sources available, (2) individuals and groups who own and operate a node have variable skills and interests, and may not want to travel far to work on items, (3) physical space, utilities, safety, and legal limits may divide the work done at given nodes. We can call such networks "Makernets", because they make things. Makernets can trade physical items as needed, and coordinate their work electronically to complete larger or more complicated projects.
New locations may first use conventional tools and equipment, but would gradually upgrade as designs for self-production and expansion become available from the R&D Phase. Later locations have the benefit of more designs being available, and can therefore build or acquire more complete starter sets right away. The trade network would grow as more nodes and locations are built. Equipment for starter locations is designed for personal scale hobby and home use. This puts it in reach of ordinary people or small groups. Their duty cycle (percentage of time in operation) is less than full time, and the equipment is smaller and less expensive. People can afford a number of these smaller items, and house them in space they already have or can build or rent without too much difficulty. Like other parts of the program, people's skills and the equipment they work with are not intended to reach a static end point, but grow and develop over time.
A location is an area that can easily be crossed in reasonable travel time, such as a metropolitan area around a city. That is close enough for people to work together and easily trade physical items. A given location may have multiple network nodes under different ownership. They may be physically distributed, or grouped into clusters on one property (i.e. a factory). Individual nodes may not grow once built, but the network as a whole is intended to gradually add more prototypes and new final designs, copy existing items, and scale them to larger (and sometimes smaller) sizes. As the network expands and upgrades itself, it can produce more items internally for further upgrades, and more end products for members to use. Production items can be grouped into (1) tools and machines intended to make more tools and machines, (2) items intended for production but not for making more equipment, such as a greenhouse, and (3) end products to be used, like furniture or food.
4.2 - Phase 2A: Distributed Locations
The goals of this phase are (1) increased scale of nodes and locations, and (2) relief of job insecurity and displacement by automation. As Phase 1 locations build more and larger equipment, some of them will move beyond hobby and home use, towards small business and commercial operation. This is characterized by part or full time operation, and selling products outside the network. The larger scale and higher duty cycle will require new designs optimized for those purposes. Phase 1 equipment was optimized more for flexibility than speed. That way a smaller number of machines could do more tasks, and thus lower startup costs. When running a business, speed and efficiency become more important, so the designs are optimized to do particular tasks well. This results in a larger collection of more specialized items. Skills and training also become more specialized and take longer to learn. Particular nodes will tend to become more specialized and trade for other things they need, although a comprehensive large location that does most things is still possible.
Separation of ownership and labor results in the problem of job insecurity. The owners of a for-profit business have the incentive to remove workers as soon as possible, to save on labor costs. The removal may be from lower production and sales, or changes in business methods and technology that require less labor or different skills. Where a person or group has built and expanded their own equipment and business, the owners and workers are the same people. They don't have the same incentive to remove themselves. If production decreases, they can work less on the original business, and build or buy into others to make up the difference. Automation is a threat to conventional jobs by requiring less labor. Owners who use the same automation for themselves are not threatened with unemployment. Rather they just work less time or more efficiently.
Business and commercial scale operation is not limited to production only, but can also serve the full range of habitation, transport, and service industries. For example, a restaurant is a service business, but the building, furniture, and equipment must first be manufactured. So the logical progression is from core machines that can make more machines for expansion, then producing end products like building materials and furniture, and finally industries that don't produce items, but use them to operate.
4.3 - Phase 2B: Industrial Locations
The goal of this phase is to reach the most efficient production capacity by additional growth in scale and specialization. Industrial locations are in the same kind of developed areas and temperate climate as Phase 2A Distributed Locations, so we group them together in Phase 2. Industrial nodes can evolve from distributed small business or commercial nodes by continuing self-expansion. They can also be built as new nodes of the final size, where the equipment is supplied by previous locations. In that case, supplying the larger equipment and space to house them will likely need outside capital, because individuals or a small group typically won't have enough funds. Gradual evolution from a smaller size by self-production would not require as much, or any, outside funding. Providing the larger work spaces with larger input and output flows will tend to limit industrial locations to fewer products. For example, if you are processing scrap metal on an industrial scale into new metal stock, it helps to be near a rail line to deliver the scrap and the finished products. The more products, factory space, and specialized needs you have, the less likely you will find one big location that can satisfy all of them.
The larger production scale means more customers for the products, or larger scale customers. The market area for a node will likely reach beyond a single location, to a region or even world-wide. Since outputs are sold to a wide range of customers at greater distances, transport capacity becomes more important. A narrow product range and large scale markets means demand can be more variable from general economic circumstances or competition. Distributed finance and ownership makes sense in this circumstance. Demand may be low for a particular product, but may be high for something else. In a distributed portfolio these tend to average out. Owners can then reassign their labor and equipment as needed to meet the higher demand products. Given a high capacity to recycle and self-produce, modifying equipment to meet changed needs is easier to do.
The combination of industrial, distributed, and starter scale industries can meet most needs that people have. If they own their own equipment, or shares in them, because they collectively built and grew them themselves, those needs are met securely, despite higher levels of automation.
5.0 - Other Earth Locations
The next major phase includes expansion from inhabited and developed areas on Earth to ones that are thinly or completely uninhabited and undeveloped, or that also have difficult or extreme local environments. These conditions are a matter of degree rather than absolutes with a clear dividing line. We have divided locations into difficult and extreme conditions according to how hard it is to support people in them. The extreme locations will involve more remote-control and automated operations, and fewer people actually living and working there directly.
We want to preserve the Earth's total environment, and the parts that are still in a natural state. So developing the difficult and extreme locations must be done with an eye to sustainability and renewable energy. An example would be building offshore fisheries to replace wild fish catches. The latter are putting a strain on the ocean food chain. But the offshore fisheries must consider all their inputs and outputs in a total system approach, so we don't get unintended side-effects.
The mechanics of developing these locations is the same as the earlier Temperate ones and the later ones in space. Appropriate starter sets are delivered from previous locations, and together with local materials and energy, they expand themselves to full production capacity. Then they produce whatever products are needed for local use, and to trade with the rest of civilization. Finally they participate in seeding new locations beyond Earth. This includes experience gained in working in harder conditions and remotely, and producing physical items and energy from places that start out completely undeveloped.
5.1 - Phase 3A: Difficult Earth Locations
We somewhat arbitrarily define "Temperate" as environment conditions where the middle 90% of the Earth's population lives, with 5% at the upper or lower ends of a given parameter. The "Difficult" environments are those that are at least 10% beyond the temperate range in at least one parameter. The temperate and difficult ranges for the various parameters are as follows:
- Temperature - This is measured by winter average daily lows and summer average daily highs. The temperate range is 260-310K (-13 to 37C). A given location is likely to exceed either the high or low limit, but not both. The difficult range is therefore below 234K (-39C) or above 341K (68C). These limits are breached at only a few locations on the Earth's surface. The high limit is more likely to be reached deep underground, because of the temperature gradient of ~25K/km.
- Water Supply - This is measured by fresh water in tons/m^2 per year from rain, rivers, snow, ice, and moisture condensation. Salt water or underground aquifers are not included. The former isn't fresh water (although it can be made so artificially), and aquifers are not a sustainable resource if they are drawn faster than they are replenished. The temperate range is 0.25 to 2.5 meters/year. Since this is a large range, we use a logarithmic scale, and define difficult as 26% below or above the temperate limits, or <0.185 and >3.15 meters/year.
- Atmosphere Pressure - This is measured by average local pressure in kPa. The temperate range is assumed to be from 80-100 kPa (near sea-level to 2000 meters altitude) Difficult pressures are below 70kPa (2750 meters altitude) or above 110 kPa (750 meters below sea-level).
- Ground Pressure - This is allowed ground design pressure at the surface, or ambient water or rock pressure below the surface, in MPa. The temperate range is 0.25 to 2.0 MPa. Difficult conditions are then below 0.19 MPa or above 2.5 MPa. The high limit is reached at ocean depths of 250 meters, and underground at depths of 100 meters in average rock. The low limit is reached by open waters (zero strength), fine sand or moist clay (low strengths).
- Gravity Level - This is one of the conditions for space environments. On and near the Earth's surface it does not vary by more than 10% unless you are in a centrifuge or an extremely high speed vehicle. We therefore skip it for this phase.
- Radiation Dose - This is measured by unprotected background radiation in milliSeivert/year. Industrial exposure, such as to medical imaging staff, or from mining, using, and disposing of radioactive materials, is not considered an environment condition. It would have its own designs for safety and shielding. Natural background radiation varies by location, according to altitude, magnetic field, and what materials are in the ground below. In most places it varies from 1 to 13 mSv/year. A few locations have high radiation levels from concentrations of radioactive elements and their decay products, up to 135 mSv/yr. People have lived in such locations for many generations, with no apparent ill effects. Since adaption may have occurred for long-term residents, we will be conservative and consider high radiation levels a hazard to the general population. Levels above 17 mSv/year would be considered difficult. Low radiation levels are no considered hazardous, so background levels below 1 mSv/year are not considered difficult.
- Ping Time - This is the round-trip communication delay to the next nearest 5% of population, in seconds or fractions of a second. Long delays create difficulty in voice communications or virtual-reality remote control, and slow down any computer network-based activity. There is no lower limit for this parameter, since short communications delays are a difficult condition. On or near the Earth's surface we consider ping times above 100 milliseconds to be difficult, as this much delay starts to be noticeable to people. There are few locations that have such high values to reach 5% of the remaining world. The 5% limit is because you can choose to do things like remote control from reasonably nearby, and not from the farthest place on Earth. This parameter becomes more important in space, since the speed of light limits operations to within 15,000 km to stay under 100 ms. That only reaches moderately high Earth orbit, and most of space is far beyond that distance.
- Travel Time - This is the maximum one-way normal travel time for people, to reach the nearest 5% of other people. Travel time for cargo is assumed to be proportional to that for people. High travel times makes it more difficult and expensive to bring in people with special skills, or necessary parts and materials. Very low travel times are not a difficulty, so we set no lower limit for this parameter. Most of the world's populated areas can be reached within 48 hours, so we set this as the upper limit for temperate (developed) travel. The upper limit is 10-20 days for parts of Tibet and ocean locations distant from any airports, requiring ship travel to reach. We will thus define difficult travel as needing more than 2.5 days to reach.