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Getting around the Saturn system
Every leg of the Saturn network is flown by the engine whose exhaust speed matches the speed change the leg needs.
See it in the tour: chapter ringed world, shot 1.1.
The chain
Goods and people move through five legs fiction.
- Inner system to the Gateway: the Long Passage, fusion, about a year over 8.5 AU, with a 100 km/s speed budget.
- Gateway to Titan orbit: the nuclear-thermal shuttle, on Titan methane, in days.
- Titan orbit to Kraken Shore: an entry capsule down and a methalox ascent vehicle up.
- Around Kraken Mare: a rotorcraft in hours, and a 500 t barge on the sea.
- Titan or the Gateway to Enceladus: the nuclear-electric tug in months, then a lander and a sampling drone.
Propellant flows outward from Titan: methane and oxygen for the shuttles and ascent vehicles, and hydrogen for the fusion transports design. Imports flow inward through the Gateway. Saturn exports no water to Earth.
Why the Gateway sits at 750,000 km
The Gateway orbits Saturn at 750,000 km, 12.4 Saturn radii, inclined 15° to the equator. One orbit takes 7.7 days at 7.11 km/s design.
Three reasons set the radius design. It is 613,000 km outside the A ring, so no part of the orbit can cross the main rings. It lies 270,000 km beyond the dense E ring and beyond the strongest trapped radiation. And it sits between Enceladus at 239,000 km and Titan at 1.22 million km, so both destinations are in reach.
The 15° tilt splits a plane change. Ships from the inner system arrive near Saturn's orbital plane, tilted 26.7° to the moons' plane. A tilted hub costs incoming ships about 1.45 km/s and departures to the moons about 1.86 km/s physics. Real transfers fold both into other burns, often far out where they are cheaper.
One engine per leg
The rocket equation punishes a leg whose speed change is large next to the exhaust speed.
- The Long Passage needs 100 km/s and exhausts at 200 km/s: a mass ratio of 1.649 challenge.
- The shuttle needs 1.92 km/s one way. On methane at 600 s it carries a 4.5 km/s budget with a mass ratio of 2.149 design.
- The ascent vehicle needs 3 km/s at 345 s: a mass ratio of 2.427. Titan's escape speed is low and the methane and oxygen are local design.
- The tug needs 7.05 km/s at 2,500 s. Its mass ratio of 1.358 covers 7.5 km/s, a margin over the spiral, and the trip takes 120 days design.
- The drone needs 500 m/s at 250 s: a mass ratio of 1.226 design.
Where a vehicle meets Titan's air, it uses it: the capsule brakes on a parachute and the rotorcraft flies on rotors. The tug and the shuttle never touch a surface.
Key numbers
| Quantity | Value | Basis |
|---|---|---|
| Gateway orbit | 750,000 km, 15°, 7.7 days | design |
| Gateway speed | 7.11 km/s | physics |
| Plane change, arrivals / departures | 1.45 / 1.86 km/s | physics |
| Gateway to Titan orbit, one way | 1.92 km/s | physics |
| Kraken Shore to orbit | 3 km/s | design |
| Titan to Enceladus spiral | 7.05 km/s | physics |
| Long Passage crossing | about one year | challenge |
| Enceladus / Titan orbit radius | 239,000 / 1.22 million km | physics |