Dawn engine

[Cannon]

i don't see people using these engines very often, even though they seem so efficient (lsp in vacuum 4200).

what's wrong with them?

[Randazzo]

i don't see people using these engines very often, even though they seem so efficient (lsp in vacuum 4200).

what's wrong with them?

Nothing is necessarily wrong with them. They just have extremely low thrust which makes for long burns (though it's apparently higher than IRL), and they consume an enormous amount of electricity.

[Cannon]

so in which cases is it best to use them?

[Randazzo]

so in which cases is it best to use them?

I've never actually bothered to use one, but I imagine the best case scenario would be a low-mass probe below Kerbin orbit.

I find the challenges of the engine too costly to overcome, mostly in time expenditure required.

Edited August 11, 2015 by Randazzo

[-ctn-]

The ion engine in the game produces about 9 times more thrust than the NEXT ion engine at NASA, and about 22 times more thrust than the NSTAR engines currently on the Dawn spacecraft.

People don't like to use it because it requires a lot of electricity and a 15 second burn with a typical engine can easily be a 20 minute burn with an ion engine.

EDIT: I use them quite frequently, because I'm a big fan of ion engines.

I use them mostly on probes for the inner solar system, but recently I used one on a probe that orbited the outermost planets in the Outer Planets Mod. They were powered by three RTGs and even then could only operate at around 15% throttle, otherwise they would drain the electricity too fast.

They are nice because you can be very, very precise with them, you can keep the mass of the spacecraft down, increase your delta-V to tens of thousands of meters per second, and (eventually) get anywhere you want to go - just like in real life. But it takes a heck of a lot of time and even more electricity to get there.

"Zero to sixty in four days."

Edited August 11, 2015 by -ctn-

[Coga19000]

Mostly because the burn times are immensely long, generally too long to bother. Even though they are overpowered compared to real -life engines, 2knewtons are pitiful for KSP.

Now, you can always use Orbit Manipulator (if it still works) to time warp while burning your ions, which can let you reliably use them for a variety of purposes. Without it, you can still use them- but it may test your patience. My favorite use is to get probes at Interstellar space. An unusual way to exploit their efficiency is to make a hopper for Gilly, the only body you can reliably get a TWR of more than 1 with them. In that case, a single hopper could possibly make hundreds of jumps without refueling. Finally, you can use it for rovers and ion powered planes for unbreathable atmospheres.

Oh, and there is also the problem of the intense energy consumption. This is generally easily countered, though.

[Hagen von Tronje]

I find that stock ion engines are best served on extremely lightweight probes that merely want to get into a particular, likely distant, orbit. For example, putting survey satellites around other planets and their moons. You could also utilize their very low mass by, say, pushing four such probes out to Jool with the same interplanetary transfer tug, then detaching them to enter their own orbits around each moon. Without breaking out pencil and paper, I think common sense would suggest that even in career that's cheaper than sending four lifters and four interplanetary mids to carry four satellites.

Note that even for tiny probes they're all but worthless in atmosphere. If you want a probe to land and return consider other options, at least for that stage.

[Geschosskopf]

so in which cases is it best to use them?

Because of their low thrust, ion engines can't push much of a payload without the burn time being unbearably long (it's already bad enough even with very light payloads). So they're used almost exclusively for small probes that need lots of dV, such as the real Dawn mission which has gone all the way out to the asteroids and captured into orbit around 2 different bodies.

HOWEVER, ion engines need a lot of electric charge, such as from Gigantor solar panels. This is just to run at full power. You can run at less power but that means lower thrust which means even longer burn times, so most folks try to run at full power. From Duna inwards, this is no problem with solar panels. But from there (or from Dres at most) outwards, solar panels are pathetic. So out there, your only option with stock is to use fuel cells, which means carrying LF/O for the fuel cell to run on. IIRC, a 6-pack fuel cell running 2 ion engines has an ISP of about 1900, not nearly as good as the ion alone but considerably better than even nuke engines. But the fuel cell and its fuel are heavy so TWR suffers even at full power.

Another use for ion engines, however, is flying on Duna. If you build a light plane with a lot of wing, and give it some other means of thrust to take off with, you can use ions to keep it flying at cruising speed.

[DancesWithSquirrels]

Take a look at BetterTimeWarp for faster physics warping - the thread header says 1.0.2 compatibility, but the more detailed ChangeLog and the last author comment (8/5/15) state that 1.0.4 is supported as well.

The author says that a 1 hour ion engine burn was completed in only 3 minutes with 20x physics warp. I'm going to be installing this one...

[Sharpy]

Extremely high delta-V crafts.

Currently I finished building a fuel station to prepare launch of the rescue craft for a kerbal in retrograde orbit somewhere between Jool and Eloo. About 10,000m/s there, with nukes, three stages involving multiple large MK3 tanks, and then another 10,000m/s back using asparagus staged ion craft utilizing fuel cells. (that's not counting getting to the orbit from Kerbin, and landing - the rescuee will be picked from Kerbin orbit by a separate craft fit for reentry).

Edited August 11, 2015 by Sharpy

[ajburges]

Actually, I had a fun little Minmus biome hopper in .90 that ran off a single Dawn for surveys.

Ion utility is really hurt in 1.x because of lack of Xeon refining. All Xeon needs to come from Kerbin while a local refinery can provide the fuel for reusable Monoprop and LV-1 probes.

That means Ion engines are only optimal for one way and/or long range missions. Otherwise, they are too expensive and/or too low powered.

Another complication of Ion engines is power draw. Any solution that is not "burn with solar panels in the sun" requires extra weight and/or crazy Pe kicking. My probes often use a gravity turn around the Mun to avoid burning in Kerbin's shadow.

Tip: ox-sat panels have a better power to mass ratio than Gigantors.

[Kryxal]

To mangle a quote about the Dawn engine:

Phenomenal Delta-V! ... itty-bitty TWR

[-ctn-]

I'm quite fond of the ion engine, and if you're looking for more you may look into the Near Future Propulsion / Near Future Solar mods. They add a few different ion engines and a few more solar panels based on random things in real life. Although, I admit, I did edit the configuration heavily for the ion engines so that they don't suck so much energy. I left the stock one stock though.

Easily my favorite thing to incorporate into a design. Nothing beats having 13,000 meters per second of delta V.

[Alpha188]

Well, I use Ion engines a lot. I used them for the last time to make a Moho lander (9 Dawn engines ) powered by solar panels. I think the bigger problem is that, because of their low thrust, they can give big ∆V only to really small spacecrafts.

[Streetwind]

The ion engine in the game produces about 9,000 times more thrust than the NEXT ion engine at NASA, and about 22,000 times more thrust than the NSTAR engines currently on the Dawn spacecraft.

Fixed that for you

[-ctn-]

Haha, yes. I got really confused, then remembered real life ion engine thrust is measuring in millinewtons.

[MarvinKitFox]

i don't see people using these engines very often, even though they seem so efficient (lsp in vacuum 4200).

what's wrong with them?

The reason for people not using the ION engine is very long and complex.

Here it is...

Players

are

Impatient.

That's it. That engine is by far the best in the game, but it forces you to sit under acceleration for dozens of minutes at a time.

Also, of course, they are completely useless in any situation where a good TWR is needed. Such as takeoff, landing, etc.

[KerikBalm]

Well, its propellant is also really realy really expensive, so much so that its cheaper to use a LV-N to push things around... as long as the LV-N isn't too big for the job.

An ion powered tug for other stuff would have a really high part count, and a really high "fuel bill"

Also, you can't do ISRU to refuel ion craft.

Then... its a pain to use them much beyond Duna, due to solar power dropping, and RTGs being rather weak.

However, I do still use them for small probes.

I was using one as a minmus hopper, but its so cheesy...

Right now I've got two outbound ionprobes heading for the Jool system... it should have enough dV to get orbital science data for all the moons.

RTG powered, launched from a mk2 cargobay of an SSTO... still really really expensive....

Those RTGs are expensive... and 4 of them won't even fully power an ion engine (I think you need 12 for that).

A full 1.25m xenon tank is also really expensive...

I'm thinking they'll be good for a moho mission.... lots of cheap solar there.

FWIW, I modded a seperate part set to allow ISRU of Xenon gas from bodies with atmospheres... Duna is now my Xenon emporium.

[Tatonf]

The reason for people not using the ION engine is very long and complex.

Here it is...

Players

are

Impatient.

That's it. That engine is by far the best in the game, but it forces you to sit under acceleration for dozens of minutes at a time.

Also, of course, they are completely useless in any situation where a good TWR is needed. Such as takeoff, landing, etc.

Wow. I think that KSP players are among the most patients players. In which other game would you accept staring at your screen, doing nothing, except waiting that this 10 minutes burn ends ?

BTW I use Ion engine for landers. They are useful for Gilly, Bop, Minmus and Pol. Starting from Ike you'll probably need 2 Ion engine, meaning more electricity consumption, more mass, and ultimately something probably less efficient than something that use regular fuel.

There's no electricity problem with them. Just pack enough batterys for the time of the burn, and when landed, you deploy your solar panel and time warp. This work totally fine even on Bop/Pol (it takes less than a day if I remember correctly).

Here is my capsule lander, meant for landing and returning back to orbit :

And here is my Minmus lander, capable of gathering ALL the science of Minmus by itself.

Those are really simple craft, easy to reproduce and use !

[Foxster]

Incredibly useful engine.

As long as you keep your craft light then you can use them as lander/return craft like this...

And in in-game terms they do let you make the quickest journeys because they provide such high dV. This means you can burn them for a long time and so reduce trips to the outer planets from years to weeks.

I never bother with solar cells when using them. Fuel cells are much better. One fuel cell array and a small LF/O tank will power your craft for as long as the Xenon lasts.

[Tatonf]

How do you build this ? If you take the capsule as a root part, you can't attach something new with only struts.

[Foxster]

If you look closely you will see some extra ironwork at the bottom emerging from the round tank.

[Tatonf]

Cliping is bad for health !

[Foxster]

Cliping is bad for health !

There's actually little clipping. I tried to avoid that but this was designed to fit in a small cargo bay so some was unavoidable.

[Tatonf]

Ok. But isn't two ion engines a bit overkill for Minmus ?