[Author note: I have invented very little, if anything, new concerning space colonies. Most information about them in Robot Dawn comes from the studies of Gerard K. O’Neill at Stanford University in the 1970s, although I have deviated from his concepts in significant ways. I attended Stanford University in 1968 and received my master’s degree in astronautical engineering from there in 1969, several years before O’Neill’s space colony study.]
In the year 2070, several space colonies populate the Solar System. First of all, and although it isn’t actually a “space” colony, the lunar colony at the south pole of the Moon was the first constructed. It was designed and initial construction accomplished starting in the 2020s but wasn’t completed until the early -30s. Tourism to the south pole in 2070 was still heavy but constitutes only twenty-five percent of industry there. Morale is poor and worker turnover high. Population at any one time is estimated at two-hundred, with another three-hundred robots working the mines for precious materials. Several other lunar colonies followed, most around the lunar equator and in lunar lava tubes, one located at the volcanic domes in Marius Hills and another at Mons Hadley, a massif in the Moon’s northern hemisphere.
On Mars, private corporations built the initial stages of the Percival Lowell colony in 2025, but five years later sold it to the American government when the presence of poisonous perchlorate, which had been know to exist there from the beginning but was thought to be a minor problem, proved to be an overriding issue, leading to the death of five astronauts. Since then, the colony has grown substantially to house upwards of five-hundred people. Lowell functions as the hub of a complex network of buildings for both scientific research and tourism, plus of course mining and manufacturing. The manufacturing operations were mostly for use at Lowell and other smaller facilities scattered about on Mars.
The largest space station is at Lagrange point SE-L4, where the two interconnected O’Neil colony cylinders, each 5 miles (8 kilometers) in diameter and 20 miles (32 kilometers) long, reside. Since the cylinders have to spin about their longitudinal axis to provide one-g at the internal edge, they have to occur in pairs to counteract gyroscopic precession. O’Neil was built primarily from materials mined on the Moon at a collection of temporary sites all over the surface. More recently, materials have been obtained by mining capture astroids brought close to SE-L4 by spacetugs.
The second largest is the military complex at EM-L5, where all configuration information is top secret.
The above figure shows the relationship between the diameter of a space colony cylinder and its required rotation rate to produce one-g on the interior. Note that as the diameter of the cylinder gets larger, the required rotation rate for one-g goes down. For the DSO Torus it is one revolution per minute. For the O’Neil cylinder, it is almost one-half revolution per minute. The governing equation is:
Gs = r x ω^2
Research has shown that one rpm is comfortable for humans, but some can withstand four rpm without a great deal of disorientation. Coriolis forces are the primary concern.