This is an amusing background that resulted from me combining a couple of existing ideas. It was intended as a background for some kind of science fictional wargame, but it would work well for a novel. In any event, it will provide a nice playground for toying with the equations from this website.
(The page name "Ring Raiders" is a homage to the classic juvenile SF novel "Raiders from the Rings" by Alan E. Nourse. Though in that novel the "rings" were the asteroid belt.)
Here is an Excel spreadsheet with Hohmann orbit information for the Saturn system of moons.
Somebody on one of the usenet newsgroups asked if combat in the asteroid belt would look like Han Solo and the TIE fighters from THE EMPIRE STRIKES BACK. I answered No, since the average separation between asteroids is approximately 16 times the distance between the Terra and Luna, ships in the asteroid belt might never even see an asteroid.
Then I remembered the article by Jerry Pournelle in A STEP FARTHER OUT entitled "Those Pesky Belters and their Torchships".
A lightbulb went on above my head.
The real reason to use Saturn as the background for a game or novel is because combat in a dense asteroid field is really cool. But we can make additional justifications.
According to Pournelle  in a gas giant's system of moons, Hohmann delta V requirements are quite reasonable. This contrasts with the excessive Hohmann requirements for, say, travel among the asteroids. Crude NERVAs using various ices as reaction mass work just fine. Indeed, in the outer moons, a backyard kerosene rocket will do. Most of the Saturnian moons are almost entirely composed of ices so there is plenty of reaction mass for a fleet of ships.
A backyard kersosene rocket (exhaust velocity 3,330 m/s) with a mass ratio of 2 will have about 2,300 m/s of deltaV, mass ratio of 3 will have 3,660 m/s, and a mass ratio of 4 will have 4,620 m/s. As you can see this could easily do almost half of the possible trips.
A NERVA rocket using water as reaction mass (exhaust velocity 4,042 m/s) with a mass ratio of 2 will have about 2,800 m/s of deltaV, mass ratio of 3 will have 4,440 m/s, and a mass ratio of 4 will have 5,600 m/s.
A NERVA rocket using hydrogen as reaction mass (exhaust velocity 8,093 m/s) with a mass ratio of 2 will have about 5,600 m/s of deltaV, mass ratio of 3 will have 8,890 m/s, and a mass ratio of 4 will have 11,200 m/s.
Hohmann transit times are relatively short, as are synodic periods of launch windows.
Gas giants are also pretty far away from Terra, to encourage wars of liberation and local autonomy. While Jupiter is closer, it also has a nasty radiation belt. Saturn doesn't. Saturn's radiation belt is far weaker than Jupiter's blue glowing field of radioactive death, being more on par with Terra's Van Allen belt. This would mean that the various moons of Saturn could be independent nations, fighting each other over "whatever" without having to worry about interference from Terra.
The table below was generated by Erik Max Francis' Hohmann orbit calculator. They are for one-way trips to various moons in the Saturn system.
- Start and destination moons are labeled along axes, it does not matter which axis you use for start or destination.
- In both sections, "y" means "years", "m" means "months", "d" means "days", and "h" means "hours"
- Values below the diagonal in blue: First value is delta V (meters per second) needed for a Hohmann transfer from orbit around one world to orbit around the other, landing on neither. Second value is the transit time for the transfer.
- Values above the diagonal in red: First value is delta V (m/s) needed for a Hohmann transfer between the worlds, including take-off and landing (If either is a gas giant, a 100 kilometer orbit is used instead of the planet's surface). Second value is the Synodic period (i.e., frequency of Hohmann launch windows).
- Diagonal values in gold are delta V (m/s) needed to take off from the surface of a world and go into circular orbit around it, or to land from a circular orbit.
According to Zubrin  fusion power reactors work splendidly with He3 as fuel. The teeming billions of Terra will be screaming for He3. Alas, He3 is almost non-existent on Terra, and rare in Lunar regolith. It is, however, available in enormous amounts in the atmospheres of Gas giants. Hybrid air/space craft could harvest this from the atmosphere.
However, using NERVA propulsion, escaping from Jupiter would require an impossible mass ratio of 20. It isn't clear if it is even possible to build a NERVA with a mass ratio higher than 7. Even if it was, a mass ratio of 20 will make harvesting Jovian He3 uneconomical.
But wait! A NERVA powered harvester in Saturn would only need a modest mass ratio of 4. This means that Saturn could become the "Persian Gulf" of the solar system. In other words, we've discovered a plausible reason to colonize the Saturn system in the first place, and the basis for an economy (we will ignore that annoying little man in the front row who just pointed out that Uranus has more He3 than Saturn, and has even less gravity.).
( We will also ignore the fact that nobody has yet manage to make a usable He3 fusion reactor as a mere engineering detail. )
According to Zubrin , terraforming Mars could require large crashing ice asteroids onto its surface. The farther out the asteroid's orbit is from the Sun, the less delta V is required to re-direct it to Mars impact. Saturn would do nicely. Most of the ring fragments are solid ice, and Saturn is quite far from the Sun.
There will be military bases of all space faring nations, to keep an eye on each other and to prevent unauthorized asteroid re-direction. Of course there will be such bases in the vicinity of Saturn. They will probably be indifferent to the political situation among the various moon of Saturn, so long as nobody tries to alter an asteroid orbit. These bases will make the situation more interesting.
Boomtowns and settlements would spring up around any large industrial operation and around military bases. Gambling, whiskey, and prostitutes. This will also make the situation more interesting.
There might be life on Titan. There will certainly be a scientific base or two full of exobiologists. If the Titanian life is intelligent, there will be a couple of hundred bases.
How thick are the rings? There is some controversy about that, but a good ballpark estimate is from 10 meters to 1 kilometer depending upon location (well, originally the estimate was one to five kilometers, but since that was written the Cassini spacecraft has discovered it is closer to 10 meters thick in spot. Yet again a romantic planetary setting has been shot down by cold science).
Isaac Kuo throws a monkey wrench into the works by making a case for Jupiter. Alas Jupiter has no extensive ring system, which was the point behind this exercise. But the attractive delta V and synodic periods do apply to Jupiter. Here Isaac is responding to prior comments by Ken Burnside.
- What causes the "spokes" in the rings?
- Why does Saturn's south pole have a giant hexagon?
- Why does Titan have a dense atmosphere while the other large moons do not?
- Why is Hyperion so weird?
- Why does Iapetus have a huge wall along its equator? (see below)
- Why are the two hemispheres of Iapetus so different?
- Why is Iapetus' orbit not in the plane of the other moons?
- Is Phoebe really the source of the dark material on Hyperion and the leading hemisphere of Iapetus?
- Epimetheus is co-orbital with Janus. Suspicious.
- Mimas's "Death Star" crater is suspicious.
- Telesto is in Tethys' leading Lagrange point.
- Calypso is in Tethys' trailing Lagrange point.
- Helene orbits in Dione's leading Lagrange point.
Interesting novels featuring Saturn:
- Pournelle, Jerry. "Those Pesky Belters and Their Torchships." A Step Farther Out. Pournelle, Jerry. New York NY: Ace Books, 1979.
- Zubrin, Robert. "Colonizing the Outer Solar System." Islands in the Sky. Ed. Schmidt, Stanley & Zubrin, Robert. New York NY: John Wiley & Sons, Inc., 1996.