A Survey of Space Settlement Designs

The paper “A Survey of Space Settlement Designs” by Thomas Marotta has been just been published in the NSS Space Settlement Journal.


The author compiled every known orbital space settlement design into a database. Grouped into chronological ‘eras,’ the database describes basic information for each design: population capacity, dimensions, gravity level, energy source, etc. Using this information one can conclude that interest in space settlement is increasing, 1g is the preferred gravity level, solar power is the preferred energy source, and a torus is the preferred geometry. As for location, Earth-Moon Lagrange points dominate but there is a budding movement to place settlements in low Earth orbits. The database is accessible at www.nss.org/settlement/journal/Space-Settlement-Designs-Database-12.19.16.pdf.

A Radically Easier Path to Space Settlement

By Al Globus

Copyright © 2016 Al Globus
Published in the French language magazine Diplomatie
PDF version of this article

Very smart and capable people have been dreaming about space settlement for decades, but these dreams have not come to fruition. Why? Because building space settlements is extraordinarily difficult. There are two ways to overcome this: a lot of money or an easier way. An enormous pile of government money doesn’t seem to be headed our way, but it turns out there is a much easier way.

The location of the usual space settlement suspects includes the Moon, Mars, asteroids, and the Earth-Moon L5 point (or other high Earth orbit). They all suffer from one very serious problem: they are very far away, anywhere from 363,000 to 400,000,000 km from Earth. This makes everything we want to do extremely difficult.

All space settlements need pressurized habitat, power systems, thermal control, communications, life support, materials recycling, and radiation shielding. As radiation levels in space are high compared with Earth, the mass of the radiation shielding completely dominates the mass of most space settlement designs because inadequate shielding can lead to cancer, cataracts, and sterility. In orbits beyond Earth’s magnetic field, radiation protection requires about seven tons of water, or eleven tons of lunar regolith, per square meter of hull and a little bit less on the surface of Mars or the Moon. This amounts to millions of tons of material for a settlement big enough that people might actually enjoy living in it once the excitement of moving to space wears off, perhaps 100 m across at least. If the radiation shielding was not needed space settlement would be vastly easier. [See “Orbital Space Settlement Radiation Shielding,” Al Globus and Joe Strout, preprint, June 2016, which contains data and references for radiation related claims in this article.]

Figure 1. Radiation measurements taken on the ISS (International Space Station). Note the very low levels (blue) near the equator, which is on the horizontal line starting at 0 on Latitude scale. Image credit NASA.
Figure 1. Radiation measurements taken on the ISS (International Space Station). Note the very low levels (blue) near the equator, which is on the horizontal line starting at 0 on Latitude scale. Image credit NASA.

It is our incredibly good luck that there is a region of space, very close to Earth, where radiation levels are much, much lower than at the usual suspects. This is Low Earth Orbit (LEO) directly over the equator (or ELEO)—see figure 1. The Earth’s magnetic field protects this region from all but a small fraction of space radiation, albeit the most energetic part. Radiation levels are so low that below about 500 km it is possible, even likely, that no dedicated radiation shielding will be necessary. This means that a 100 m diameter cylindrical settlement in ELEO might have a mass of around 8.5 kTons, hundreds of times less than above the Earth’s magnetic field. [See “Space Settlement: an Easier Way,” by Al Globus, Stephen Covey, and Daniel Faber, June 2016, which contains data and references for settlement related claims in this article.] This entire mass could be launch by about 160 Falcon Heavy launches. This is not for a few capsules connected by tunnels, but an open living area comparable in size to a large cruise ship with zero-g recreation at the axis of rotation, full 1-g pseudogravity just inside the hull, and recreational space walks.

Figure 2. Artist concept of a small early space settlement. Note the curvature necessary to generate pseudogravity by rotation. Image credit Bryan Versteeg.
Figure 2. Artist concept of a small early space settlement. Note the curvature necessary to generate pseudogravity by rotation. Image credit © Bryan Versteeg.

If you are familiar with free space settlement issues you might object that to get Earth-normal pseudogravity with a 100 m diameter you need to rotate a settlement at about four rpm (revolutions per minute), which will make many people sick. That is true, but it is also true that people adapt to rotation at four rpm within a few hours or days and are subsequently just fine. If you were to move to Nepal you would be altitude sick for a few days, but Nepal is still a beautiful place to live. [See “Space Settlement Population Rotation Tolerance,” Al Globus and Theodore Hall, preprint, June 2015, which contains data and references for human response to rotation claims in this article.]

You might also note that most Mars/Lunar settlement schemes involve putting a module on the Martian/Lunar surface with far less than 160 launches. But that’s for a module a few meters across, similar to vehicles that have been in LEO off and on since the 1960s and much smaller than the ISS which has been continuously inhabited since 2000. For a given size, the total mass of the material needed from Earth for early ELEO vs Mars/Lunar settlements is about the same. Low radiation levels in ELEO mean settlements there require little or no radiation shielding. Although radiation levels on the Martian/Lunar surface are high, about half that in free-space, local materials can be used for radiation shielding. However, Mars/Lunar residents will rarely leave their habitat due to the radiation and LEO development will continue to be far ahead because LEO is at least 100,000 times closer than Mars and 720 times closer than the Moon giving ELEO a massive logistical advantage.

While space settlement may be vastly easier to get started in ELEO than anywhere else, it is still a massive task. Launch vehicle prices need to come down by a factor of perhaps 50, reliable nearly-closed large-scale life support must be developed, and a million engineering problems must be solved so that people can live comfortably, safely, and enjoyably in space. Absent a gigantic pile of government money, how can this been done? One word: tourism.

Tourism can supply the two things essential to market-driven equatorial LEO settlement development:

  1. A very high flight rate to make fully reusable launchers economically viable. We estimate at least > 10,000 flights per year is needed, compared to < 100 today.
  2. A market for ever larger and more sophisticated space hotels starting with the ISS.

Seven paying tourists have flown to the ISS (one twice) on a 7-10 day trip, but right now no seats are for sale. Rumor has it that the first few space tourists paid about $20 million and the most recent flight was on the market for $50 million. While this is discouraging (the price is absurdly high and headed in the wrong direction) surveys suggest that if someone could drop the price a bit, much larger numbers of people would want to go.

The good news is that the best advertised price to fly to LEO so far is $26.25 million, although the vehicle is still in development. If this is successful and makes a profit, as more flights are booked economies of scale can reduce the price, which in turn increases the size of the market, which enables a reduction in price, which increases the size of the market … and so on. We need to get on this virtuous spiral of dropping costs leading to bigger markets leading to lower cost. If the cost is low enough the market is measured in millions of customers per year, which is the sort of market needed for the kind of low-cost high-flight-rate transportation system necessary to settle space regardless of destination.

All those tourists need somewhere to go, meaning we will need space hotels. The first ones may be small to keep up-front costs down but if space tourism is successful the desire for bigger, more sophisticated, and more comfortable hotels could drive constant improvement.

As luck would have it, most of what is needed for ELEO settlements is also important for hotels: recycled air, water, and food, power systems, communications with Earth, etc. Hotels may even want artificial gravity, achieved by rotation, so that guests need not learn how to use a 0-g toilet—which is difficult and, when you screw up, disgusting as everything floats around and gets into places you would rather it not. Also, staff can have longer tours of duty, reducing transportation costs, as their bodies will not be continuously subject to weightlessness, which can cause a number of problems. Once hotels have developed most of the necessary technology and supporting infrastructure, building the first space settlement should be not much more difficult than building another hotel.

The first settlement in ELEO might look something like Kalpana Two:

Image credit: Bryan Versteeg.
Image credit © Bryan Versteeg.

In an internet survey of space enthusiasts, 30% of respondents said they would very much like to live in Kalpana Two in ELEO, including raising their children, and are willing to spend 75% of their wealth and lifetime income to do so. That’s enough to get space settlement started.

Although building Kalpana Two after a few decades of space tourism development may be much easier than starting from scratch, it is still a monumental effort requiring a great deal of money and those funds will be easier to raise if Kaplana Two and later settlements have a mass-market product to sell to Earth.

Kalpana Two residents could assemble and test extremely large communication satellites, much larger than those launched today. Large comsats are attractive because the larger the spacecraft antenna and the larger the power-producing solar arrays the smaller the antenna on the ground must be and the less battery power is needed, two things for which there is a large and growing market. ELEO is also a good place to manufacture ultra-light solar sails, as the sails need not be folded into a fairing, launched and unfolded. While the market for solar sails is small, if you cover one side of the sail with power-producing electronics you have extremely light power arrays which can be used for large comsats. Put fiber lasers on the other side of the sail and you can beam power, first for in-space applications, such as power for Kalpana Two, and later to deliver power to Earth—a gigantic market. [See “Towards an Early Profitable PowerSat,” Al Globus, Space Manufacturing 14: Critical Technologies for Space Settlement, NASA Ames Research Center, Mountain View, CA, October 29-31, 2010, and “Towards an Early Profitable PowerSat, Part II,” Al Globus, Ion Bararu, and Mihai Radu Popescu, International Space Development Conference 2011, National Space Society, Huntsville, Alabama, 1822 May, 2011.]

The first equatorial LEO settlement is the hardest to build. The second and subsequent ones will be easier because lessons will be learned and infrastructure developed. We estimate there is room for at least a few million people spread out in a few hundred settlements in equatorial LEO. This can provide the key requirement for commercially viable lunar and asteroid mining: a decent sized market in space. It is hard for extraterrestrial materials to compete on Earth due to transportation costs. However, in space lunar and asteroidal materials have the edge due to high launch costs from Earth. The problem today is that the in-space market is a single satellite designed for in-space refurbishment (the Hubble Space Telescope) and six people on the ISS, which is tiny. Equatorial LEO settlement is a game changer for lunar and asteroidal mining.

Once the mining infrastructure to deliver substantial materials to equatorial LEO is in operation and ELEO fills up with settlements, it will be time for the next step: settlements in orbit beyond the Earth’s protective magnetic field. These settlements will require millions of tons of radiation shielding, which can provide a market for a huge expansion of lunar and asteroidal mining. This, in turn, can provide economic support for mining settlements on the Moon and co-orbiting with asteroids. This network of settlements can then expand to Mars and the asteroid belt. Of course, for Mars and the Moon the problems associated with raising children in partial-g including but not limited to growing up with weak muscles and bones will have to be addressed.

At this point we will be well on our way to turning the resources of this solar system into living, breathing settlements in huge numbers. The next step, of course, is to send groups of settlements to Alpha Proxima and start the billion-year project of greening our galaxy. After all, if you have lived for 50 generations in orbital space settlements does it matter much if you are close to Sol or on the way to the nearest star? Probably not, at least for some, but that is a task for future generations. Our mission, should we decide to accept it, is to get space tourism on track to develop the technology and infrastructure necessary to build Kalpana Two in equatorial LEO. This tape will not self-destruct.

Al Globus is a member of the National Space Society Board of Directors.

National Space Society Space Settlement Campaign Supports Elon Musk’s Mars Settlement Plans

At today’s meeting of the International Astronautical Congress (IAC) in Guadalajara, Mexico, Elon Musk, CEO of Space X, announced his bold plan to build a city on Mars. For over 40 years the National Space Society has led advocacy for space settlement. According to Mark Hopkins, economist and Chair of the Executive Committee of the National Space Society, “The vast majority of the resources of our solar system lie in space rather than on the Earth. By settling Mars and other locations in space we can overcome the resource limits of Earth leading to a hopeful, prosperous future for all of humanity.”

During the talk Musk detailed the Interplanetary Transport System (ITS) for the first time. The first stage of the ITS towers 77.5 meters with a diameter of 12 meters and uses 42 Raptor engines to provide a total of 28 million lbs of thrust. The second stage is 49.5 meters long, 17 m in diameter, uses 9 Raptor engines, and comes in both a crew/cargo model and a tanker model. Musk’s plans are based on four key approaches: full reusability of all components, refueling in orbit around Earth, refueling on Mars with locally produced propellant, and using a rocket fuel (methane/oxygen) that can be easily manufactured on Mars. Musk envisions that the eventual cost of a ticket to Mars will be in the $100K-$200K U.S. dollars range, allowing ordinary people to eventually travel to Mars.

SpacX ITS launch
SpacX ITS launch
SpaceX ITS reusable first stage return
SpaceX ITS reusable first stage return
SpaceX ITS refueling in orbit (image: SpaceX)
SpaceX ITS refueling in orbit
SpaceX ITS approaching Mars
SpaceX ITS approaching Mars
SpaceX ITS nearing Mars
SpaceX ITS final approach to Mars
SpaceX ITS Mars entry
SpaceX ITS Mars entry
SpaceX Raptor engine test
SpaceX Raptor engine test
SpaceX has already built an ITS prototype composite fuel tank
SpaceX has already built a prototype ITS composite fuel tank

What has been a bold vision of the future for humanity is now becoming reality. Humanity has begun the first concrete steps towards space settlement. The next decade will be one of the most pivotal in human history. Today we are beginning the journey to becoming a multiplanetary species.

In recognition of these momentous developments taking place the National Space Society is convening the first “Space Settlement Summit” in January to bring together leading people, companies and organizations that are making space settlement a reality. Participation in this event will be by invitation only and limited to entrepreneurs, scientists, engineers, venture capitalists, and thought leaders deeply involved in making space settlement a reality. The objective of the event will be to show the synergistic in-space ecosystem that is emerging; to facilitate a convergence of interests and opportunities among the key players; and to identify critical issues along the path to space settlement. We are at the dawn of a new era for humanity and the National Space Society is continuing its role as the leading voice for space settlement.

Musk’s reveal of his Mars colonization plan follows the announcement September 12th of the Blue Origin “New Glenn” heavy-lift vehicle by Jeff Bezos. The New Glenn is 7 meters in diameter and comes in both a two stage and a three stage version. The reusable first stage is powered by seven BE-4 engines fueled by liquid natural gas and liquid oxygen, providing 3.85 million pounds of thrust. The second stage uses a single BE-4 engine, and the optional third stage a single liquid hydrogen-oxygen BE-3 engine, the same engine used in the flight proven reusable New Shepard sub-orbital vehicle.

“The New Glenn is a major step forward for commercial space,” said Dale Skran, NSS Executive Vice President. “With the SpaceX ITS and Falcon Heavy, the United Launch Alliance Vulcan, and the Blue Origin New Glenn operational, the U.S. will have four domestic options for commercial medium to heavy lift. This will allow NASA to make use of commercial heavy lift services with greater confidence than if only a single operator existed.”

The U.S National Space Policy of 2010 states “To promote a robust domestic commercial space industry, departments and agencies shall: Purchase and use commercial space capabilities and services to the maximum practical extent when such capabilities and services are available in the marketplace and meet United States Government requirements.”

“NASA ought to welcome the usage of the ITS, Vulcan, the New Glenn and the Falcon Heavy in future NASA planning,” said Skran. “NASA can only benefit from the existence of multiple commercial medium to heavy lift providers with re-usable first stages that offer the possibility of significant cost reductions.”

Milestone 2 on the NSS Space Settlement Roadmap is titled “Higher Commercial Launch Rates and Lower Cost to Orbit” (http://www.nss.org/settlement/roadmap/RoadmapPart2.html). Future NASA usage of commercially available partially or fully re-usable medium to heavy lift vehicles will be critical to achieving this milestone.

“Competition like that seen between Blue Origin and SpaceX is key to rapid progress in space,” said Bruce Pittman, NSS Senior Vice President. “Elon just presented a plan for settling the solar system in this century that is realistic and affordable. In my paper, ‘A Pathway to a Thriving Commercial Space Economy’ at IAC, I also laid out a path forward to a thriving new economy in space that produces new opportunities for all.”

Musk’s plan’s address MILESTONES 15 (“Logistics System”), 16 (“Base”), and 17 (“A True Martian Settlement”) in the evolving NSS Space Settlement Roadmap (see http://www.nss.org/settlement/roadmap). NSS supports the exploration, development, and settlement of space, including free space, the Moon, asteroids, and other locations in addition to Mars.

NSS has been pushing hard via legislative outreach in cooperation with the Alliance for Space Development to make space development and settlement part of the objectives that guide NASA. In March 2016 Rep. Dana Rohrabacher introduced H.R.4752 the “Space Exploration, Development, and Settlement Act (see https://www.congress.gov/bill/114th-congress/house-bill/4752/text) to make development and settlement of space part of the fundamental law governing NASA.

More recently, on September 21, 2016, the Senate Commerce, Science, and Transportation Committee marked up S.3346, the NASA Transition Act of 2016. This bi-partisan Bill, co-sponsored by Senators Cruz, Nelson, Rubio, Peters, Wicker, and Udall, contains the following ground-breaking statement:

Section 202(a) of the National Aeronautics and Space Administration Authorization Act of 2010 (42 U.S.C. 18312(a)) is amended to read as follows:
“(a) LONG-TERM GOALS—The long-term goals of the human space flight and exploration efforts of NASA shall be—
“(1) to expand permanent human presence beyond low-Earth orbit and to do so, where practical, in a manner involving international, academic, and industry partners; and
“(2) the peaceful settlement of a location in space or on another celestial body and a thriving space economy in the 21st century.”

The entire S.3346 “NASA Transition Act of 2016” can be found at: https://www.congress.gov/bill/114th-congress/senate-bill/3346/text. NSS applauds the Senate for taking this forward-looking position in favor of space development and settlement, but much remains to be done to make space development and settlement a reality. Join us in the fight for a better future at www.nss.org.

Elon Musk talk “Making Humans a Multiplanetary Species” to be webcast September 27

On Tuesday September 27, on the second day of the International Astronautical Congress (IAC) in Guadalajara, Mexico, Elon Musk will deliver a special keynote presentation on “Making Humans a Multiplanetary Species.”

Musk will discuss the long-term technical challenges that need to be solved to support the creation of a permanent, self-sustaining human presence on Mars. The technical presentation will focus on potential architectures for colonizing the Red Planet that industry, government and the scientific community can collaborate on in the years ahead.

The presentation is scheduled for one hour beginning at 2:30 PM Eastern Daylight Time, 1:30 PM Central Daylight Time (Guadalajara), 12:30 PM Mountain Daylight Time, and 11:30 AM Pacific Daylight Time.

This and other IAC plenary sessions will be webcast on this direct link to IAC webcasts on livestream.com. For a schedule of other sessions see the IAC website plenaries and highlight lectures page.

Olympus Mons

Image courtesy SpaceX

Dropping the Ball in a Rotating Space Settlement

Here’s a virtual space settlement “ball drop” experiment courtesy of Joe Strout. The ball starts out six meters above the deck, initially stationary with respect to the rotating settlement. Then it is dropped, much like Galileo dropping stones from the Leaning Tower of Pisa, but it results in a behavior that Galileo never saw:


The viewpoint is lined up for optimally seeing the slight pull to the left. In reality, of course, there is no pull to the left… the ball is traveling in a straight line, at a constant velocity from the moment it was released, and the settlement is rotating around it. Note that the appearance of moving toward the viewer is an illusion: the ball is not being dropped from the vertical dark pillar but from an invisible platform the same distance toward the viewer as where the ball lands.

Details for the curious: The deck here has a 224-m radius and spins at 2 RPM, simulating 1G. The white ceiling at the top of the view is about 130 m up. Those deck plates are 2 m squares, though unfortunately they don’t line up perfectly with the ball’s starting position — but if you can detect a slight bend in the plating, that does align with where the ball starts.  So the ball’s apparent sideways motion is about a meter or so, over a 6 meter drop.

Note that this simulation assumes there is no air here; the ball is falling as in a vacuum. In a real settlement, of course, air would apply a force in the direction of the settlement’s spin, reducing this Coriolis effect by some amount that depends on the aerodynamics of the object.

Courtesy of Joe Strout of High Frontier Forums.

New in the NSS Space Settlement Journal: Bootstrapping Lunar Industry

Making It on the Moon: Bootstrapping Lunar Industry
, a paper by Dave Dietzler, has just been published in the NSS Space Settlement Journal.

Abstract: The cost of rocketing cargo into space is very high. Great savings can result if local resources like oxygen and materials from lunar regolith are used to build and expand Moon bases and create industrial settlements to supply materials for solar power satellites and space settlements, tourism, planetary defense, asteroid mining and research stations. This paper attempts to illustrate the components of a lunar “industrial seed” consisting of equipment needed to produce materials on the Moon and establish a growing industrial presence there that leads to space settlement. The first section discusses some of the issues surrounding transportation to the Moon and the second section quickly examines materials production, manufacturing and construction. Space settlers and industrialists must get an idea of how much propellant and cargo must be launched from Earth and plan out the actual cargoes to determine the size of capital outlay for a Moon mining project.

Read full paper.

Space Colonization and the Space Movement

By Mark Hopkins
Chair of the Executive Committee, National Space Society

The National Space Society (NSS) and its precursor organization, the L-5 Society, have been promoting Space Settlement since 1975. Our ultimate goal is nothing less than the settlement of space and the use of the vast resources of space for the dramatic betterment of humanity. This goal has been moving toward the mainstream at an accelerating pace.

A discussion of recent progress (up until May 2015) can be found in “We Are Winning” (Ad Astra, Fall 2015). Since then the pace has continued to accelerate. Both SpaceX and Blue Origin, using only non-government funds, have returned launch vehicles to Earth for reuse, signaling an imminent reduction in space transportation costs. Space Settlement is the goal of both of these companies. The Space Exploration Development and Settlement Act was introduced in Congress on March 16, 2016. If passed, the SEDS Act would make Space Settlement an official goal of NASA (see “Victory: The Vision of NSS May Soon Become an Official Objective of NASA”). Most recently, Elon Musk, head of SpaceX, announced his company’s plans to send the first human mission to Mars as early as 2024. Musk also announced that he will detail SpaceX’s plans to settle Mars during the International Astronautical Congress in late September 2016. This announcement is likely to cause the goal of Space Settlement to make a major jump toward the mainstream.

NSS has been using the term Space Settlement rather than Space Colonization since our beginning in 1975. All of the other organizations in today’s Space Movement were founded after us and almost all followed our lead, using the term Space Settlement. This was done because in 1975 the word colonization had negative connotations. Much of the world was made up of former colonies that resented their former status.

However, the rapid move of Space Settlement toward the mainstream in the last few years has shown that society outside of Space Movement circles, and particularly outside of space circles, prefers the term Space Colonization. The recent hit movie The Martian provides an example. NSS considers the two terms Space Settlement and Space Colonization to be synonymous. Despite the 40-plus years of the Space Movement using the term Space Settlement, society may well push us to using the term Space Colonization in the future.

The Space Movement began in 1975. Space Colonization is its goal. (For articles about the Movement, see “The Space Movement” at www.nss.org/spacemovement). The advancement of this goal toward the mainstream is energizing the Movement. The greatest obstacle for the Space Movement has been credibility. Time and time again we have convinced influential people of the importance of Space Colonization only to have them become disenchanted after talking to space “experts” who have questioned its credibility. The ongoing destruction of this obstacle is creating an environment favorable to the explosive growth of the Space Movement.

Rapid progress toward convincing society as a whole of the importance of Space Colonization to the human future is now possible. NSS can reenergize the belief in the American dream, an ever-improving dramatic betterment of humanity, and a hopeful future for all.

A potential space colony. Artwork: Richard Bizley

NSS Board Member Al Globus Provides Updates on Space Settlement Research

Al GlobusLast year National Space Society Board of Directors member Al Globus released three pre-prints that together suggested a radically easier path to space settlement. A major part of this is the discovery that space settlements in Low Earth Orbit very close to the equator (ELEO) will experience far less radiation than any other location—so little that dedicated shielding may be unnecessary. This massively reduces the mass of space settlement designs (roughly two orders of magnitude).

The paper focused on radiation has now been substantially revised incorporating information from a number of NCRP (National Council on Radiological Protection and Measurement) publications. The bottom line recommendations have not changed, however. This paper can be found at:

  • Orbital Space Settlement Radiation Shielding,” Al Globus and Joe Strout, preprint, June 2016. The major result of this paper is that settlements in low (~500 km) Earth equatorial orbits may not require any radiation shielding at all based on a careful analysis of requirements and extensive simulation of radiation effects. This radically reduces system mass and has profound implications for space settlement as extraterrestrial mining and manufacturing are no longer on the critical path to the first settlements, although they will be essential in later stages. It also means the first settlements can evolve from space stations, hotels, and retirement communities in relatively small steps.

These changes are also reflected in:

  • Space Settlement: An Easier Way,” by Al Globus, Stephen Covey, and Daniel Faber, June 2016 describes a relatively easy, incremental path to free space settlement by taking advantage of very low radiation levels in Equatorial Low Earth Orbit (ELEO) and higher rotation rates. Low levels of radiation in ELEO may permit settlements with little or no radiation shielding. Higher rotation rates permit much smaller settlements. Together this reduces settlement design mass by two to three orders of magnitude and places early settlements very close to Earth, radically reducing the difficulty of building the first space settlements and making launch from Earth practical. The mass model used in this paper is available here as an Excel spreadsheet.

For completeness, here is the third paper although there have been no revisions:

  • Space Settlement Population Rotation Tolerance,” Al Globus and Theodore Hall, preprint, June 2015. This paper reviews the literature to find that space settlement residents and visitors can tolerate at least four, and probably six, rotations per minute to achieve 1g of artificial gravity. This means settlements can be radically smaller, and thus easier to build, than previously believed.

The Billionaire’s Race to Colonize Space: Blue Origin and SpaceX

Elon Musk has made it clear that his mission with SpaceX is to colonize Mars and to help humanity become a multi-planet species.

Jeff Bezos states that Blue Origin is “working hard to bring closer the day when millions of people can live and work in space.”

See the interesting article on this subject by Trevor Nace on The Next Web Insider.