The Starship and the Canoe. Kenneth Brower
innermost moon, is only 115,000 miles from the planet’s surface. Seen from Mimas, Saturn would fill much of the sky. Orion’s crew could watch Saturn’s atmospheric bands rotate at their different speeds. They could study the thin tropic of shadow cast by Saturn’s rings. From one of Jupiter’s inner moons, they could watch that planet’s rapid spin, the centrifugal force bulging the equator and flattening the poles. They could watch the Jovian Red Spot change color from its salmon red to its pale green.
Freeman figured the velocity increments necessary for trips to various moons and he set down the results in tables. “The inner satellites,” he summarized, “which are much the most interesting for observing the planets, were substantially harder to reach than the outer satellites. Fortunately, the help available from refueling is most certain where it is most needed, namely at the inner satellites.”
Happy coincidence. If Orion could refuel, everything became easier. For propellant, Orion could use ice, ammonia, or hydrocarbons, and “these substances are certainly to be found on Mimas, which has density 0.52 and is probably composed mainly of ice or snow.” (The density of water is 1.) “The mass of Jupiter 5 is unknown, but it is likely to have a density and composition similar to those of Mimas. The big intermediate satellites, Callisto and Titan, have densities 1.7 and 2.1. For comparison, the earth’s moon, which is of comparable size and is made of rock, has density 3.3. It is, therefore, almost certain that Callisto and Titan have thick outer layers of ice which would be available as propellant. In addition, we could, if necessary, convert the methane in Titan’s atmosphere into propellant.”
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