In the 1970s, Princeton physicist Gerard O’Neill led two Stanford/NASA Ames Research Center summer studies that supported the feasibility of kilometer-scale orbital cities. These studies assumed that the NASA space shuttle would operate as expected, a flight every week or two, $500/lb. to orbit, and one failure per 100,000 flights. The studies also assumed that a more efficient follow-on heavy-lift launcher would be developed.
Now the SpaceX BFR being developed over the next 5 years or so could deliver low-cost launch that did not happen with the Space Shuttle. The SpaceX Falcon Heavy with reusable first stages could achieve the $500 per pound to orbit target. A fully reusable SpaceX BFR should be able to get well below $500 per pound. SpaceX BFR has a target of $5 to 10 million per launch of 150 tons. A cost of $30 million per launch would enable $100 per pound. SpaceX BFR plans more redundant engines to improve the safety and reliabilty.
* 10,000 launches at $10 million a piece is $100 billion which is half the cost of the 135 Space Shuttle launches and program
* Over $200 billion was spent on the International Space Station which only has from about 3-8 people
* Once SpaceX BFR is proven safe and reliable it could transport 200-400 people at $25K to $50K per ticket
* A $20 billion per dedicated space colonization, industrialization budget could afford this build out by 2040. The US has been spending $62 billion in space for NASA, spy satellites and defense.
* 50-80% of the space stations could be sold to foreign markets and customers
Using the latest space designs and analysis from the National Space Society
Al Globus at the National Space Society has proposed putting space stations in Equatorial Low Earth Orbit would eliminate the need for radiation shielding. Radiation shielding is 95% of the weight of many space station designs.
1. space radiation computations suggest that orbits below about 500 km and close to the equator have radiation levels so low that little or no radiation shielding is required [Globus 2016].
A computational data for a 500 km circular ELEO using polyethylene shielding. Even at 10 kg/m2 shielding, the equivalent of which is very likely to be provided by any reasonable hull, the 20 mSv/yr and 6.6 mGy/yr are met. Indeed, with no shielding at all the general population limit is met and the pregnancy limit is very nearly met. This has an interesting consequence: spacewalks in ELEO may be safe enough from a radiation point of view to be a significant recreational activity.
2. a careful examination of the literature suggests that permanent settlers can tolerate much higher rotation rates (4 to 6 rotations per minute are tolerated to get 1g) than was commonly thought, allowing much smaller settlements to provide 1g artificial gravity
135 Falcon Heavy launches could place a 490 person Kalpana style space station into equatorial orbit with 4 rotations per minute and a diameter of 56 meters. The Falcon Heavy without reusability could launch 63 tons into low earth orbit.
57 launches of a fully reusable Falcon BFR (150 tons per launch) could place the space station into orbit.
A 4 rotation per minute unshielded Stanford Torus would need 4 times fewer launches and one-quarter of the Kalpana population.
14 or 15 launches of a Falcon BFR could place a space station without gravity and radiation issues.
Using lunar mining or near earth asteroids could lower the cost for orbital fuel and other materials by 2 to ten times.
Once a few ELEO settlements have been built and successfully operated we will be able to fill ELEO with an industrial civilization. A 500 km altitude circular orbit at the equator is about 43,000 km long. Assuming a spacing of 1,000 km, that means there is room for 43 settlements. If we assume we can populate orbits every 50 km in altitude from 400 to 600 km we get about 200 settlements. While the first settlements should be as small as possible to take advantage of space hotel development experience, most people, particularly technical people, are accustomed to living in cities with large populations. Thus, it is probably desirable to build larger settlements as quickly as possible and decommission the early small ones once the slots fill up. If each settlement has at least a population of 10,000 that makes for a total ELEO population of over two million.
About 500 Falcon BFR launches to build a 10,000 person space station in ELEO with no gravity or radiation issues. There would also need to be regular flights to provide supplies.
200 settlements would need 10,000 Falcon BFR flights. If each BFR flew four times per week then 50 Falcon BFR could transport the materials to build those settlements.
Starting in 2023 with the first BFR and building about 10 Falcon BFR per year then full orbital production rate could be achieved by 2028. Around 2040, all the settlements in ELEO could be completed.