By Steve Bartlett
Location, location, location. That’s what real estate agents will tell you is all-important when buying a home. By the same token, location is the critical factor when it comes to resources in space: Where are they and can you get to them? Space researcher and former OASIS president Dr. Seth Potter discussed these issues in his talk “Where’s the Stuff” on October 12 at the Long Beach Public Library.
Space exploration and settlement require a wide range of things that might be considered resources: structural materials, propellants, water, organic materials, and other materials that can be used to build and sustain a colony; real estate on which to put it; and the energy available to get there and run it. Dr. Potter showed how each of these is distributed throughout the Solar System among the myriad bodies there.
He started his briefing with an overview of the Solar System – how mass is spread out between the Sun, planets, minor planets, asteroids, and comets. Someone once described the Solar System as consisting of the Sun, Jupiter, and various debris. Potter reinforced this view when he showed that nearly all of the mass of our planetary system is tied up in these two bodies. In fact, the combined masses of all of the other bodies smaller than Jupiter are substantially less than that of Jupiter alone. Similarly, the sum of the masses of all the bodies smaller than Saturn are less than that of Saturn alone, and so on for smaller and smaller bodies until the 15th smallest body is reached.
But while the masses of the Solar System may primarily involve the Sun and the gas giant worlds, the places where humans might want to settle are elsewhere. Earth is the largest body that we know of that has a solid surface. But three-fourths of the Earth’s surface is covered by water, significantly reducing the amount of surface available for human habitation.
Potter pointed out that Venus has the largest clear surface. Unfortunately, that surface is at a temperature of almost 900 degrees Fahrenheit, far higher than any human could tolerate. The available surface area of Mars is nearly as large as that of the Earth and its temperature can be accommodated with present technology, making it a very inviting place to explore and settle.
Looking at other bodies, Potter said that there are an estimated 1.2 million asteroids, and their combined surface area is about that of Venus. The fact that these worldlets are small and relatively close to the Earth, cosmically speaking, makes them an excellent place to go to mine structural materials, organics, and a variety of fluids necessary to build and sustain a space colony.
But before a colony can be established, future settlers would first have to get there. There are a few different ways of getting around the Solar System, but the most popular involve rocket propulsion, ion propulsion, and using a gravity-assist to slingshot a spacecraft from one place to the next.
Rocket propulsion for ships carrying people requires large amounts of propellant and large rocket engines to get out of Earth orbit and to the intended target. The craft usually has a near-empty propellant tank when it gets where it’s going.
Ion drive engines are very efficient, but they have low thrust and so take a long time to get where they’re going unless a large nuclear power supply is available. So they’re currently impractical for moving humans around the Solar System.
The gravitational slingshot approach is simple and elegant – borrowing some of a planet’s orbital energy to speed up or slow down a spacecraft to move it about the Solar System. But using this technique depends on finding a favorable alignment of bodies, like some cosmic game of billiards to bounce from one planetary body to the next. Different bodies can be used to sling a spacecraft around, depending on where you want to go. Most (60%) of the orbital kinetic energy, known as angular momentum, that’s available lies in the planet Jupiter. So it has been used extensively to send unmanned spacecraft to different places. Probe that have made use of the Jupiter gravity-assist include Pioneer 10 and 11, Voyager 1 and 2, the Cassini mission to Saturn, the New Horizons mission to Pluto, and the Ulysses craft to explore the Sun’s polar regions, among others.
But Jupiter isn’t the only planet that can be used this way. “Sometimes it’s better to go down when you want to go out,” said Potter, in referring to flying a spacecraft into an orbit that brings it near a planet that’s closer to the Sun in order to use some of its angular momentum to take the craft even further out. He showed how the planets Mercury, Venus, and Earth could be used to help get a craft to the outer Solar System. In fact, the Galileo mission to Jupiter relied on one fly-by of Venus and two fly-by’s of Earth in order to pick up enough speed to send it on its way to Jupiter.
Potter, who has worked extensively on solar power satellites over the past several years, also examined how solar energy is available at a number of places in the Solar System for providing electrical power for space colonies, as well as for cargo spacecraft that use solar electric ion propulsion.