I have to design a space mission to Saturn as part of a course on spacecraft and system engineering. I found a suitable trajectory but, as the Δv is quite high, I would like to adapt it to Ion propulsion.

What are the proper assumptions I have to do to make it "realistic" for low thrust propulsion? How can impulse thrust trajectory be adapted to a low thrust system?

The simplest would probably be to find a trajectory with multiple gravity assists, like Cassini did (EVVEJS), but since this is just an assignment project, I haven't the tools nor the time to compute such a trajectory.

  Example trajectory to Saturn employing DSM and Earth flyby

 Example trajectory to Saturn employing Deep Space Maneuver and Earth flyby. Made using NASA's Trajectory Browser

  • $\begingroup$ Do you have any specifics about the spacecraft, such as wet mass, thrust and specific impulse? $\endgroup$
    – TildalWave
    Commented Oct 25, 2015 at 22:16
  • $\begingroup$ @TildalWave: I was planning to use a NEXT thruster. It has an ISP of 4190s. My wet mass will be around 5'500 kg. $\endgroup$
    – Tonio
    Commented Oct 25, 2015 at 22:26
  • 1
    $\begingroup$ You won't be able to use patch conics to do this, you'll have to simulate the equations of motion with the thrust force applied -- which isn't actually too difficult, especially if you simplify your problem in 2D. $\endgroup$ Commented Oct 25, 2015 at 23:24
  • $\begingroup$ If you're using low thrust propulsion you're unlikely to have a simular trajectory to a single impulse burn. Have a look into gaussian variational equations of orbit. $\endgroup$
    – ThePlanMan
    Commented Oct 27, 2015 at 2:21

1 Answer 1


To make this happen, you have to write a simulation. There are a couple of ways you could approximate this, but to give the best example, I would have 3 gravity point sources, one for each Saturn, Earth, and the Sun. You could add objects if desired for higher accuracy, or remove them if you get to be a sufficiently far distance from them. Then calculate at some appropriate interval (Smaller for near Earth/ Saturn, larger if further away from them would work), increasing the delta v in that direction.

I suggest you first find the path that will take you to Saturn's orbit, then find the Earth/ Saturn angle that will get you there. Then find a point in the orbit where the Earth/ Saturn angle is that angle, and you should be fine.


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