The Orbital Ring

Chapter 1

What's Out There

The solar system is not empty. It is full of water, metals, energy, and destinations that could sustain a civilization far larger than the one we have now. The Moon has billions of tons of water ice sitting in permanently shadowed craters at its poles. Mars has a surface area roughly equal to all the dry land on Earth, with enough water ice to fill lakes. Asteroids contain metals and volatiles in quantities that dwarf anything we have mined in all of human history. The moons of Jupiter and Saturn harbor subsurface oceans that may be the most promising places to look for life beyond Earth, and several of these oceans are estimated to contain more water than all of Earth's oceans combined.

None of this is speculative. Every claim in the previous paragraph is backed by direct observation, sample return missions, or radar measurements. The data are in hand.

What we lack is the infrastructure to do anything about it. Getting to these places, and getting back, with the kind of regularity and volume that would make a real difference, requires a transportation system that does not yet exist. Rockets alone cannot do it. They are too expensive per kilogram, too limited in payload, and too dependent on propellant that must be carried from Earth. What is needed is a mass transit system to space, something that can move millions of people and thousands of tons of cargo per day, at velocities high enough to reach Mars in weeks rather than months, and that can sustain this pace indefinitely.

That system is an orbital ring, and this book will make the case for building it.

However, before examining the mechanics of how we leave Earth, we must understand why the destination justifies the immense effort. This chapter surveys the solar system as a destination and as a resource, starting close to home and working outward.

The Moon is 384,400 km away, which is close enough that a radio signal makes the round trip in about 2.5 seconds. Apollo astronauts reached it in about three days using 1960s technology. It is, by far, the most accessible destination beyond Earth, and it turns out to be far more interesting than the lifeless rock people assumed it was after the Apollo program ended.

The Moon's axis of rotation is tilted only 1.5 degrees relative to the ecliptic plane. This means that deep craters near the poles contain regions that have not seen sunlight in billions of years. These permanently shadowed regions, or PSRs, act as cold traps where temperatures can drop below 40 K (about −233°C). At these temperatures, water molecules that wander in from comet impacts, solar wind interactions, or micrometeorite deliveries get stuck. They accumulate over geological time.

NASA's LCROSS mission confirmed this in 2009 when it deliberately crashed a spent rocket stage into Cabeus crater near the south pole and measured the resulting debris plume. The impact revealed a water concentration of 5.6 percent by mass in the regolith. India's Chandrayaan-1 mission, using the Moon Mineralogy Mapper, detected surface ice concentrations ranging from 2 to 30 percent by weight at latitudes above 70 degrees.

Combined estimates for both poles suggest the Moon may hold up to 6 billion metric tons of water ice, split roughly evenly between north and south. That is about 6 cubic kilometers of ice. Modest compared to Earth's ice sheets. Enormous for the purpose of supporting a lunar base or manufacturing rocket propellant. Water can be split into hydrogen and oxygen by electrolysis, giving you both breathing air and the two components of a high-performance rocket propellant.

[Chapter 1 continues in the book, covering Mars, the asteroid belt, and the outer moons]