In another question I've been corrected that batteries don't weigh that much in ion drive powered probes. Well, I thought a can of xenon would have a chance to be lighter than a solid block of plutonium, but truth of the matter, I have no clue.

Could someone clue me on what are the proportions of mass between fuel(plus container), power source and the engine itself in ion engines used nowadays to propel probes into regions so distant from the Sun that solar panels are not practical to use there?

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    $\begingroup$ Ion drives aren't frequently used for outer Solar System missions. Please be more specific on the mission you have in mind, since the mass of fuel would depend on the mission plan (how many gravity assists, for instance). The proportion would be changing also depending on the mass of science payload. $\endgroup$ Jul 29 '13 at 8:56
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    $\begingroup$ @DeerHunter: I don't have any specific mission in mind. I wanted to learn the orders of magnitude used in practice, so an answer citing any random mission will be quite satisfactory. $\endgroup$
    – SF.
    Jul 29 '13 at 11:09
  • $\begingroup$ @DeerHunter I thought that deep space and ion drives went hand-in-hand because of the long duration and large impulse needed. $\endgroup$
    – AlanSE
    Jul 29 '13 at 12:13
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    $\begingroup$ @SF. - Oberth effect $\endgroup$ Jul 29 '13 at 13:08
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    $\begingroup$ Rule of thumb: burn at highest velocity and tangentially to the local gravity vector. $\endgroup$
    – Erik
    Aug 20 '13 at 20:31

Well, I can give you a couple data points. First, we can look at NASA's Dawn mission, which uses an ion propulsion system (IPS) based on the system demonstrated on Deep Space 1 (which we'll look at next).

This paper gives details of Dawn's IPS. It notes that this system should give the spacecraft a total of about 11 km/s. Here's the break down:

The paper notes that Dawn will carry 450 kg of xenon.

Here's a graphical representation:

Now, this report gives the breakdown for DS1. The total amount of xenon propellant on DS1 was 81.5 kg. Keep in mind, this would be a significantly less mature system:

To answer the title question more directly: the propellant contributes the most total mass by far. Of the hardware, it's typically the PPUs.

Acronyms list:

  • PPU: Power processor unit
  • DCIU: Digital Control and Interface Unit
  • XCA: Xenon Control Assembly
  • TGA: Thruster Gimbal Assembly
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    $\begingroup$ What does the power processing unit do? And why is it the heaviest piece of hardware? $\endgroup$
    – user11377
    Dec 2 '15 at 2:39

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