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The latest NASA New Frontiers selection did not select any finalist proposals to Enceladus, which is one of the most promising targets for life in the solar system. It did however select Dragonfly, the Titan quadcopter.

What if a nano-probe were attached to Dragonfly, and deployed while entering Saturn orbit, flying by Titan but not touching it. Just as Cassini flew by Titan while Huygens landed, this nano-probe would continue onwards, with its ultimate target being Enceladus.

Would it be possible to get it to Enceladus from there? Given gravity assists and all, how much delta-v would you need to get to Enceladus post-deployment?

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The key to navigation when in Saturn's moon system is Titan.

Cassini flew by a vast numbers of targets while barely spending any fuel. This was accomplished by a gravity assist scheme where the key component is successive flybys of Titan for every orbit.

Titan is relatively massive, so it can alter your probe's trajectory dramatically. Exactly how it's affected is determined by what altitude the flyby happens at, which can be arbitrarily chosen by very small navigation burns some time before the flyby. This way it's possible to "pick" new orbits, at barely any cost. The only thing to be careful about is to pick an orbit with the same orbital period of Titan (or 2x or 3x), so you get a new flyby and new choice in two weeks.

(They coined the name The Ball or Yarn for Cassini's trajectory over the years)

Enceladus is easy to reach in this way.

Flyby cost: ~ $0m/s\Delta v$ + some small navigation costs.

Getting into orbit is an entirely different beast. Enceladus is small, so it doesn't provide much help in capturing. A perfect Hohmann transfer from Titan would still mean a $3.5 km/s \Delta v$ burn at Enceladus in order to get captured (equivalent to landing on the Moon and taking off again). A perfect Hohmann transfer from Titan is achievable from an initial "Ball or Yarn" trajectory by bleeding off some excess velocity by passing through the upper parts of Titan's atmosphere. Less perfect transfers, Enceladus directs, Saturn aerocapture, etc. all end up in the $4.0 - 4.5 km/s \Delta v$ range.

The extra $\Delta v$ needed to get into a circular low orbit is a lot smaller, just a mere $70 m/s \Delta v$. Landing is just another $160 m/s \Delta v$. There's little reason to not go all the way if one decides to pay the huge cost of getting captured into a n orbit.

In summary:

  • A flyby is low cost,
  • A capture is very expensive because of Enceladus low mass and high orbital velocity
  • Proceeding further with a circularisation or landing is relatively cheap after the initial capture cost is paid.
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