Astronomy on Titan: Visiting the Solar System

After getting into orbit around Titan, let us what we need to do to visit the rest of the Saturn system, and also the rest of the Solar System.

Where we left off, we were in an orbit with an altitude of about 1000 km, not much less than Titan’s radius. We travel at 1.4 km/s relative to Titan with a period of 4 hours. To escape from that orbit, we need about 2.0 km/s or only 0.7 km/s more. So we won’t need much rocket fuel for that.

Let’s now consider going to Iapetus. That moon is 2.9 times as far as Titan from Saturn, and while Titan orbits at 5.56 km/s, Iapetus orbits at 3.26 km/s. So if one slowly spirals outward over several orbits, one will need a delta-V of 2.3 km/s. If one uses a fast “Hohmann transfer orbit”, one will need only 2.15 km/s and take about 22 (Earth) days to get there. Once one gets there, it will be easy to land, since its escape velocity is about 0.6 km/s.

Hyperion should be even easier, but the inner moons, Saturn’s rings, and Saturn itself will present some big challenges.

First, let us consider going to the farthest of the inner moons, Rhea. One will need a delta-V of 3.0 km/s if slowly and 2.86 km/s if quickly (Hohmann orbit), though the latter takes only 5 days of travel time. Despite the greater difficulty of getting there, Rhea is easy to land on, however, with an escape velocity of about 0.6 km/s.

Going inward to Mimas, the numbers are 8.7 km/s (slow) and 7.2 km/s (fast), with a 4-day travel time for the latter. This paradoxical result is because one has to slow down at Titan by a sizable fraction to drop toward Mimas’s distance, and when one reaches that distance, to slow down by another sizable fraction to avoid returning to Titan’s distance. Mimas orbits Saturn at 2 1/2 times Titan’s speed, pushing the numbers up further.

However, Mimas’s escape velocity is 0.16 km/s, making it very easy to land on.

Saturn’s rings are more difficult to get to, and Saturn’s surface the most difficult of all. Or more properly its cloud tops. One needs 20 km/s (slow) or 13 km/s (fast) to get to an orbit just above Saturn’s atmosphere. If one decides that one wants to drop into Saturn without slowing down, one needs much less delta-V: 4 km/s. If one wants to go to Saturn and then return, one will need a delta-V of at least 25 km/s to get into a low Saturn orbit, and one will need a huge rocket for that.

Now for the rest of the Solar System.

To escape from Titan’s orbit in one’s orbit direction, one needs 2.3 km/s of delta-V.

To go to Jupiter, one will need 3.3 km/s, but Jupiter will be in a good position for a Hohmann transfer orbit only every 20 years, and the trip will take 10 years.

At first sight, one will need 6.3 km/s to go to Jupiter, but according to the “Oberth effect” for escaping a celestial body or an orbit, if one combines one’s delta-V’s into a big burst, it becomes much easier. One needs to find the square root of the sum of squares of the velocities, and one thus needs only 2.8 km/s to escape from Titan, and only 1.8 km/s to arrive at Jupiter, with a total of 4.6 km/s.

The inner Solar System is more difficult. One needs 16 km/s (fast) or 20 km/s (slow) to arrive at the Earth, though if one only wants to do a flyby, one only needs 5.4 km/s. All referred to long distances from Saturn. The trip time will only be about 6 years, however.

So space exploration from Titan will be easier than from the Earth.


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