Ion Engines, Good or Bad?

[Archgeek]

Quote

Another relevant con (if you're playing career) is cost. That is, unless you have several trillion funds. Otherwise, Ion engines are amazing for anything less than 5 tons and good for anything less than 10.

You don't need trillions.  I'm looking at a screenshot of a bit of a monster that runs .06-.1 TWR at something over 20km/s (KER bug means the number I'm seeing is low) that I can't upload from here that's under 800k, and patently re-usable.

Edited April 28, 2016 by Archgeek
'Ran me off the page, so it needs a quote now.

[Xannari Ferrows]

It's a good little engine. You will however sometimes find yourself building a bit of a bigger probe than you would otherwise prefer because you have to pack on all that power generation. If you're using it simply for orbital transfers, the thrust limiter helps. I remember the first Gilly "lander" I built used one, and it worked quite well getting to the surface and all the way back to Kerbin.

[panzer1b]

I have nothing against the current ion, but it just has no place in my space program (err warzone) because 90% of the ships/fighters/whatnot i make is over 20t, with the only things that ion is even viable on being micro-fighters that are carrier based, and thats a very small niche and imo not worth bothering with since said fighters are almost exclusively short range (i rarely use more then 200dV per mission on them, and actually RCS ports are enough to accomplish this). 

The second a 1.5m ion engine is released that has 10-20 times the thrust of the current one (higher electric use, and also perhaps a hair lower ISP like 3800 to make the small one matter) im not touching anything but the new ion.  I really like the idea, super power hungry (you need to make a decent power unit, or failing that spam batteries to no end), hard to work with, and also very low TWR, but comes with very good efficiency unbeated by anything else in game.  The small one is just so small that id need at a bare minimum 100 of them to push a 50-60t warship at a TWR that i can stand (we have no way to burn while timewarping at higher then 4x stock and the mods are buggy not to mention laggy).  Only major use i have for ion arrays would be my interplanetary SSTO starfighters, where ion has become the only practical propulsion system since it allows you to actually get into LKO after the rapier dies (40+ ions pushing a 30t ship isnt half bad TWR wise).  The best part is that said fighter has more part count then most 60-80t warship hulls and the rather extensive weapons arrays.

All in all, please consider adding a larger ion for those of us that arent a fan of super tiny ships, but still want to be able to use said engines.

[Cresseliator]

Ion engines are great if you use them correctly. Otherwise, just don't use them.

They have a TWR of 0.2, need lots and lots of electricity, and their fuel is very hard to get more of.

But, they have lots of Delta-V and I_sp and aren't that heavy (1/12^th the weight of the NERV).

Of course, the electricity is very hard to get after Dres, meaning they are better suited for the inner planets.

[Hypercosmic]

Why are you reviving old topics?

 

Anyways, speaking about ion engines, I proudly presents the magnetoplasmadynamic thrusters. Hogging some neon and a few gigawatts, and the kt-size craft with milli-g level of acceleration is ready!

[Razorforce7]

EDIT: Old topic is old so is my grandfather

Ion engines aren't really Ion engines.
They're some new age electric plasma engine.
Drop the near future propulsion mod, because the dawn ion engine is nothing but futuristic.

I made interplanetary vessel for a crew of 3.
It allows me to send Kerbals to places far outside launch windows while maintaining a single stage.

10480: ∆v
Twr: 0.11 (which is actually good for Ions)
Only 120 parts or somewhere within that vicinity.
You can make all your craft Ion vessels as long as your willing to scale up your design and tolerate excessively high part counts.

 

 

Edited April 5, 2017 by Razorforce7

[Aegolius13]

I would say they have a very narrow range of effectiveness, but within that range, they're very good.  

The pros (ridiculously ISP) and cons (terrible TWR, bad mass ratios on the xenon tanks, high cost, electrical usage) have been pretty much covered.  Given those I find Ions are useful when:

• Generally, you need a high delta-v mission. Not really worth it when you just need to go to the Mun or something - an Ant and an Oscar-B can take care of that.  And even if your mission is bigger than that, keep in mind that if you have a really small payload (which is often the case with ion-friendly missions), you can get huge delta-v with regular engines just by starting small and working up.  
• Your payload is light enough, and/or TWR needs are low enough, that the low thrust will not kill you (or drive you mad from boredom).  
• The electricity requirement is not going to be debilitating.  Three main sub-cases here:
  • You're operating close enough to the sun that you can maintain charge without a lot of weight devoted to solar panels.  Eve is good, Moho or closer is great.  OR:
  • Your individual maneuvers are low enough in delta-v that you can afford to do your burns on battery, and let the batteries trickle charge in between.  An example would be the scooting around Pol or Bop.  On my Jool 5 I had a little ion lander that could make every necessary maneuver with 2k batteries, and slowly recharge in between with an RTG.  Worked great.  OR:
  • Your TWR needs are so ridiculously low that you can continuously operate the engine on a trickle charge, even if that means you're getting even less than the advertised 2kN of thrust.  Maneuvers around the sun's orbit might fit the bill.  But the limiting factor here may be your patience.  

 

So again, the situations where all of these criteria are going to be met are fairly limited, but they certainly exist.  My most ion-friendly projects thus far:

• The aforementioned Pol/Bop lander on my Jool 5.  Mass was super-important here because I needed to cart this lander and its fuel supply all over creation before it was even deployed.  Thanks to the rocket equation, a small mass savings at the end of my itinerary made a big difference in initial cost and mass.
• Contracts to send a ship to a whole bunch of SOIs ("Ultimate ______ voyage").  The delta-v budgets for these can be huge, especially if Moho is involved, but you don't need anything in the way of a payload.  It works great to start by visiting the outer planets with your chemical rockets, and then finish on inner planets with ions to make use of the ample solar energy.  
• Low sun orbit (i.e., inside Moho orbit) rescue contracts.  These are absolutely perfect for ions. Delta-v demands are immense, solar energy is plentiful, TWR is nearly irrelevant, and you don't need much more than a capsule.  Just get ready for hour-plus, 6000 m/s burns on your little 2kN engine.

[Raptor9]

I've only used them on reusable craft due to their high cost, however those craft were well over 60 tons.  I just had a lot of them to maintain a decent TWR.  But I will admit, even refueling them to take advantage of reusability isn't cheap either.  Xenon is quite expensive too.

The cost and limiting them to the inner planets are the biggest disadvantages in my opinion.

EDIT: Wow, this topic really was necro-ed, lol.  Whoops.

Edited April 6, 2017 by Raptor9

[Foxster]

1 hour ago, Raptor9 said:

The cost and limiting them to the inner planets are the biggest disadvantages in my opinion.

They aren't limited to the inner planets if you use them with fuel cells. 

[Whisky Tango Foxtrot]

I once tried to send a small satellite to Moho using an ion engine, which quite frankly is the only practical use I can think of for the things. The trip required burns of upwards of half an hour and in the end didn't have enough dV for orbital capture (granted I was using a pretty inefficient flight plan as I hadn't discovered transfer windows yet, but still.)

Even if you can get past their extremely low power and high electricity use (my probe was constantly running out of power for its transfer burn on two 1x6 arrays, although things worked better once I got to Moho) the fact that their fuel can't be generated by ISRU converters makes them all but useless for anything other than a single-use probe, and although I haven't done the calculations I wouldn't be surprised if you could get the same dV cheaper with disposable chemical rockets in that case.

[blakemw]

In career Ion Drives, their power system and Xenon (especially) tend to be so expensive that it works out cheaper to use 1 LV-N rather than 1 Dawn, even for a 10kg payload (this is partly because both engines are relatively heavy and can easily dominate the weight of the payload). The ion drive will be A LOT lighter than the LV-N which does equate to a smaller launch vessel, but launchers of the scale required to launch a single LV-N are very cheap, but that lightness becomes a bigger benefit the deeper the staging goes.

Where the ion drive shines, is when you can't get enough dV out of a single LV-N, what you then do is put an Ion Drive stage on top of the LV-N stage, this results in my standard low cost high ejection thrust high-deltaV stack for small (<1t) payloads which I only really use for Kerbol rescue contracts:

1. 3000m/s chemical (Twin-Boar first stage)
2. 3000m/s chemical (Skipper second stage)
3. 8000m/s nuclear (LV-N third stage)
4. 10000m/s ion (Dawn forth stage - can easily be raised to as high as 20000m/s)

It's hardly ever economical to skip the LV-N and go directly to the Dawn, but using a Dawn on top of an LV-N is a lot better than using an LV-N on top of 5 LV-Ns which are on top of a Triple Mammoth...

So in career my opinion is the Dawn is mainly only useful as an upper stage on top of an LV-N when the LV-N alone can't provide enough dV. In non-career the Dawn is useful for ultra lightweight challenges. Also if you have a superior power system (i.e. small fission reactor) it can be more attractive to skip the LV-N - half the niceness of the LV-N is that it doesn't require a power system which for Dawn is either heavy (solar panels), extra heavy (fuel cells), heavy and expensive (RTGs) or tedious & limiting (batteries + many small burns with long breaks to recharge), a micro fission reactor can make those problems go away - though the other half the niceness of the LV-N is it provides 4-10x the TWR with an appropriate fuel load, making burns quicker and taking more advantage of oberth effect.

Edited April 7, 2017 by blakemw

[wumpus]

While ion engines have the ability to break the tyranny of the rocket equation (by delivering fuel for human use at 4 figure Isp).  If the humans are using chemical stages delivered by ions, suddenly the rocket equation becomes irrelevant, the inefficient chemicals no longer have to push heavy chemicals).

The  Achilles' heel in all this are the solar panels.  Not only that, they aren't exactly compatible with the Van Allan belts: so getting them from 500km up to ~GTO (i.e. most of the trip to Mars by delta-v) is a problem.  To be honest, I think this same issue will doom VASIMR as well (or be enough to put the nuclear reactor on board it really needs).

[MiffedStarfish]

Ion engines are incredible, solely for the blue thrust trail. And maybe the efficiency. But mostly the thrust trail.

I mean look at this, I'm playing an semi realistic game about orbital mechanics and I can feel like I'm in Star Wars! Thank you ion engines. (Also, I realised a few days ago you can run 2 ion engines on one large fuel cell for practically no fuel, so no more hideous function before form solar panels!)

[Temeter]

On 6.4.2017 at 9:44 AM, Foxster said:

They aren't limited to the inner planets if you use them with fuel cells. 

Do those actually work for ions? I remember experimenting with purely fuel cell driven Ion's, and it didn't work out that well.

These days I'm mostly using Near Future Propulsion combines with electrics for nuclear reactors.

[Foxster]

3 hours ago, Temeter said:

Do those actually work for ions? I remember experimenting with purely fuel cell driven Ion's, and it didn't work out that well.

These days I'm mostly using Near Future Propulsion combines with electrics for nuclear reactors.

They work well. 

Obviously your dV is reduced a bit because you have to carry some LF+O for the fuel cell. You need Xenon*0.2 of LF+O. 

[Temeter]

1 hour ago, Foxster said:

They work well. 

Obviously your dV is reduced a bit because you have to carry some LF+O for the fuel cell. You need Xenon*0.2 of LF+O. 

Thanks, I was about to do the math myself

[Foxster]

1 hour ago, Temeter said:

Thanks, I was about to do the math myself

Sorry - should have been Xenon*0.02.

[EpicSpaceTroll139]

I find ion engines to be great in sandbox and science saves at least. I've sent probes to Moho and Kerbals to Eeloo using them. I'm not sure whether I'll use them in my career, considering how expensive they are. They also seem to be just barely usable for aircraft on Duna, although again, they're expensive. My latest design gets about 20 meters to the 

[Piper]

In my earlier saves, I didn't use ion engines much at all, however now in my third career save, I've begun using them more and more, especially with contract satellites where I'm not looking at satellites with tons of instruments and payload, but instead can keep the weight down and can load it up with dV.  Doing it that way, I can use a single craft to fulfill multiple satellite contracts.  I also find they work really well with relay sats where again, I don't need a huge spacecraft, but may need a lot of dV.  Cost isn't a huge issue for me, as my career mode is set up that I don't need to do nearly as many contract missions for the same amount of cash (however the flip side is I don't get nearly as much science points, meaning missions are cheap, but I need to do more of them).

With manned missions however, I don't use them all too often.  I find it much better to simply go nuclear.  However, I will likely try and use it for smaller moons like Gilly, as it seems like an easy way to science-mine those places.

[suicidejunkie]

17 hours ago, EpicSpaceTroll139 said:

I find ion engines to be great in sandbox and science saves at least. I've sent probes to Moho and Kerbals to Eeloo using them. I'm not sure whether I'll use them in my career, considering how expensive they are. They also seem to be just barely usable for aircraft on Duna, although again, they're expensive. My latest design gets about 20 meters to the 

I like those units.

For comparison, my car gets about 15000 m/$

[Temeter]

Is it just me that I see the last two posts 4 times in a row? Oo

edit: Yup, just a bug with the thread updating I guess.

Edited April 11, 2017 by Temeter

[Firemetal]

Great for small spacecraft, not great for much else. The Xenon which they run on is very light and their thrust is tiny. Not my engine of choice but I have used them on occasion like for instance when I did JacobJHC's low mass Moho challenge.

Fire