I am looking for a powerful propulsion system for deep space missions. I am between a powerful ionic motor or a VASIMIR (variable specific impulse magnetoplasm motor). What do you think? The idea would be to go from LEO to Titan (Saturn moon). The duration of the mission should not exceed 8 years.

It took the Cassini probe 8 years to land Huygens on Titan, but I need to land something much smaller, so I hope to have a faster mission with my less massive payload. I have to land a load of 15 to 35 kilograms. What do you recommend? Is there a more viable alternative?

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    $\begingroup$ Does your design breif allow use of nuclear reactors or RTGs? If politically you can only use solar power things collapse pretty quickly to conventional rockets and low power ion thrust. $\endgroup$ Commented Mar 1, 2020 at 3:03
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    $\begingroup$ no, i dont want nuclear debris $\endgroup$ Commented Mar 1, 2020 at 3:47
  • $\begingroup$ What does "The weight I save I hope to gain in duration" mean exactly? Gain over what? If Cassini was 8 years and yours is 8 years, what is the "gain" achieved by reduction in weight? $\endgroup$
    – uhoh
    Commented Mar 1, 2020 at 3:58
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    $\begingroup$ This question is generally pretty underconstrained, and what you would actually use is likely to be heavily affected by what is commercially available and well tested even more than what the performance of various options is. $\endgroup$
    – ikrase
    Commented Mar 1, 2020 at 4:09
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    $\begingroup$ I swapped out your ion tag for ion-thruster. Please take some time to review Should I create a new tag?. $\endgroup$
    – called2voyage
    Commented Mar 4, 2020 at 15:52

1 Answer 1


Ruling out nuclear propulsion in the comments pretty much rules out electric thrusters of all flavours as well since the Juno mission is notable for pushing the limits of solar power, and only needs enough to operate sensors and radio link and is still 1/5 solar panels by dry weight (340 kg making 486 W, where electric demands for thrusters are in kW).

For a simple landing of a short lifetime probe on Titan a low thrust continuous operation engine is probably not required. The mission would looks somewhat similar to Cassini. Launch from Earth, gravity assist from Jupiter and possibly some combination of Mars, Venus and Earth but the key thing would be careful selection of launch window rather than clever propulsion.

The majority of the delta V to reach Saturn would be happening at earth departure from a conventional rocket at high thrust to avoid lifting fuel out of Earths gravity as much as possible, and allow high performance propellants prone to evaporation or freezing on longer flights.

At Saturn the choices would be pure aim for Titan and aerobrake (heavy heat shield) or fuel for maneuver(s) to the establish Saturn and then Titan orbits. Decision would depend a bit on trying to have an orbiting relay station for the Titan probe or just communicating directly with earth.

Electric thrust is better suited to comet and asteroid missions where gravity assists and high thrust maneuvers are not useful, and the time to complete the maneuver much longer (not flying through the Saturn system with a couple of days to complete). It is notable that Dawn had Ion and Hydrazine engines since Ion engine thrust was not sufficient for some of the planned maneuvers, even though they provided a total Delta V of 11 km/s.

If design brief mandates electric propulsion the question is less about the exact thruster used and more about the power source since most of the craft mass will be power generation in some form so define the power generation and work back from that to available thrust per watt. The Dawn craft probably serves as a useful template for a deep space capable package to add lander and power systems to.


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