Ion Engines: When and Why?

[hawkwing]

I've never really liked ion engines. They take up very large amounts of resources, produce very little thrust, and after accounting for the additional needed parts to support the power requirements, I can't seem to create an ion powered craft that wouldn't be better implemented with a nuclear engine and a T400/T800 fuel tank. In all cases I've tried, nukes end up providing far better thrust, nearly the same Delta V, much lower part count and don't force you to worry about your craft being on the right side of a planet.

So: When do you use Ion engines, and why?

Edited September 7, 2013 by hawkwing

[Temstar]

There are some specialised purposes that Ion engines are uniquely suitable for. For example:

This low Kerbolar orbit observatory has 8000m/s of delta-V in its final ion stage. At this distance from Kerbol the two solar panels generate phenomenal amount of power that could easily drive three ion engines (and then some) continuously. So for this use the ion engines give 8000m/s of the total 18,000m/s at launch for very little payload mass.

[UmbralRaptor]

Low mass, high ÃŽâ€V, TWR insensitive missions. Say, sending a <5 tonne probe to Jool, or low Kerbol orbit. Or interstellar probe shenanigans.

nearly the same ISP

The PB-ION has 5.25x the Isp of the LV-N. That's a... rather substantial difference. Also, see my above comments. An LV-N + FL-T400/800 might well increase the probe mass by >5x.

much lower part count and don't force you to worry about your craft being on the right side of a planet.

Good points, but mind the extra launcher part count. (And mass if you care about that sort of thing)

[Skorpychan]

Light weight. I can slap four ion probes onto a standard transfer stage and get it somewhere, and have room for four tiny little landers as well.

[Dispatcher]

An experimental ion driven rover. It masses at just over 3 tons and is compact. Its only intended for image (F1) or video capture. Its max speed on a level surface is about 3.8 m/s and its max range is about 16 km; on Kerbal. A better design would incorporate an appropriate battery set up.

The large arrays broke off after hitting the ground due to the angle at the bottom of the dip just past the end of the runway. It wasn't strutted. Without enough electricity, its not very good for going up hill.

Edited September 7, 2013 by Dispatcher
More detail.

[Actzoltan]

You could use ion engines as an close rendezvous cargo transfer space tug and as linear RCS system.

Edited September 7, 2013 by Actzoltan

[Tank Buddy]

In my opinion, they are useless for practical purposes. I simply don't have the time or span of interest to sit and make excruciatingly long burns multiple times.

[sgt_flyer]

Several people use the ion engine as a spoiler for their rovers on low gravity moons or planets, giving the rover's wheels a better grip

[xub313]

Ion engines are great for Interplanetary probes. They are especialy useful for visiting many planetary bodies in one launch without a large rocket.

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The whole thing weighs less than 4 tons and was able to visit five celestial bodies, and the longest burn was only 10 minutes long.

Ions are pretty mutch useless for manned missions but they have plenty of uses.

[hawkwing]

Haha, derp. Meant to say nearly the same dV, not ISP. Edited my post. =P

Still not sold on ion engines, but those are a number of interesting examples.

[Captain Sierra]

Ions are great for going interplanetary. The one thing I have found with them is avoid attempting to circularize low. At low altitudes, you get substantially less change of apoapsis/periapsis per dV. So long as you don't go for low orbits, a couple of xenon tanks could give you a grand tour probe with ions. The one shown above has way more power than necessary at most locations. It would be quite capable of going out to Eeloo, where solar panels are less effective. As a rule of thumb, a single ion engine consumes ~14.5 power and a single gigantor produces 18 at kerbin. It only takes one gigantor per engine as far out as Duna. Past that, you'll want a gigantor and another panel and maybe as many as 2 gigantors per engine if you feel like going out to Eeloo.

EDIT: something I have taken to doing is placing my ion probes in really high orbits. It gives you higher time warp and it significantly lessens the time required for the ejection burn. It increases the dV required but in the end, I find it a better option than my old method of making the ejection burn from LKO with an LV-T45 engine like I used to.

Edited September 7, 2013 by Captain Sierra

[xub313]

Ions are great for going interplanetary. The one thing I have found with them is avoid attempting to circularize low. At low altitudes, you get substantially less change of apoapsis/periapsis per dV. So long as you don't go for low orbits, a couple of xenon tanks could give you a grand tour probe with ions.

I usually use a LV-909 or a 45-7s to boost my probe into a munar slingshot trajectory and then use the PB-ION. Low altitudes also block sunlight for the solar panels most of the time.

The one shown above has way more power than necessary at most locations. It would be quite capable of going out to Eeloo, where solar panels are less effective.

Yeah, those solar panels are overkill. That probe was meant to go too Jool and Eeloo but I didn't feel like waiting for a the launch window.

[Captain Sierra]

My latest mission to Eeloo:

Eeloo probe lander, Eeloo long range com sat (not remotetech) asparagus IP drive with somethin like 14000 dV.

*ahem*

back on ion engines now.

Since ion is the topic of the day, I have a challenge going on for a minmus (and now some other moons) ion lander. Yall should go check it out.

[Blue]

If you're particularly clever, you can use ion probes as low-gravity world landers, such as on Pol, Gilly and Minmus.

[magnemoe]

One world: Moho.

Going to Moho and back usually cost you 8-10km/s unless you wait forever for the perfect transfer windows where Moho is both far from sun and the orbital planes are close

No problem for the Moho rider

It has far more than 11 km/s dV as you can disconnect the side tanks and engines and continue with the center part.

Acceleration is not so bad for something with 11 km/s dV.

Lander in front. no seat as they are heavy. In short, if you use ion engines you want to cut weight everywhere.

Do not use the large solar panels use packs of small as they give more power / kg.

Another use is an probe grand tour, replace seat with kethane scanner and the ladder with an xenon drop tank and you should get far.