Ion drives?

[Scottiths]

I don't understand the point... I thought they were for small probes. However I sent one to Moho and it had just barely enough dV to circularize, but it didn't have the TWR to actually do so before Moho escape.

Why would you use an ion drive? For anything interplanetary the burns are in excess of 30 minutes or more (which even at 4x physical time warp is a full 7 minutes of burn) and they are almost impossible to actually execute capture burns because by the time you enter the SOI you don't have enough time to slow down before exiting again (at least for small planets).

So what are ion drives actually good for?

[leopardenthusiast]

Ion engines are a complete joke. Sure, they have insane ISP, but it takes an absurdly long time to actually use it, even with the smallest possible ion probe.

[RoboRay]

You don't have to wait until you're in the SOI before starting your capture attempt. My Moho mapper started the capture burn an hour before entering the SOI.

The reason to use them is to have a small, lightweight, efficient vehicle.

If you don't have much patience, don't use them.

[3_bit]

If they didn't have such long burn times they'd be overpowered. Besides, they make great landing engines for anything heading towards Gilly.

[Scottiths]

I tried to start my capture burn before entering the SOI. The map didn't update as I was updating my maneuver node. Might be a bug I guess. It showed my solar orbit changing, but it didn't show any effect on the Moho side of things.

The burns are not bad if you have a craft small enough to handle the 4x physical time warp. Its just difficult to get a planet capture.

[RoboRay]

Oh, I wasn't using a maneuver node for my long capture. I expected to be in Moho's SOI for a little over an hour at my arrival speed and calculated it would take right about two hours to match velocities. With that long a burn, I knew the exact start point wasn't critical. So, with Pe set at 40km, I oriented the craft with the nozzle right on Moho's limb and started firing about an hour before the SOI transition.

Even with 4x timewarp, it was tedious. I doubt I'll do it again, but I'm glad I did it once.

Edited April 25, 2013 by RoboRay

[Scottiths]

At least for any Ion powerd device 4x physical warp won't break it (since it is necessarily quite small). Still, would be nice if we could do a higher physical warp with them.

[M5000]

If they didn't have such long burn times they'd be overpowered. Besides, they make great landing engines for anything heading towards Gilly.

This. Also, OP I don't know what kind of fiddlefarting you're doing, but I've gotten a probe to Gilly and slowed down enough on ion engines alone... Also, you probably didn't have enough Delta-V because you didn't put many Xenon containers on there. My Jool system mapping probe had something like 8000m/s of delta-V...

[Scottiths]

I did have enough delta-v. I just didn't have the time (it was a 1.5 hour burn and I was only in SOI for 1 hour). The biggest annoyance is the huge times involved. If I could time warp past 4x it would be nice.

[K^2]

There are two things you should be using Ion Drives for.

1) Corrections on long inter-planetary voyages.

2) Changes of orbit for various probes.

Former tends not to require much dV, so it's not that important. Later is not relevant now, because you can just chose a good orbit from the start. But once we have mining, and you need to re-position survey satellites over some remote object, I imagine that's where ion drives will shine.

You can, in principle, use ion drives for ejection/insertion burns. However, you should not be using them the way you do with chemical/nuclear rockets. You cannot wait until you are in SOI to start the burn, because TWR is too low. What you need to do is start matching speed of the body whose system you are going to enter in advance. That way, once in SOI, you are basically just starting a free fall from the edge. Then you need just a small amount of velocity to circularize and then spiral down to a low orbit. All of this can be done with ion given sufficient advance thought.

[Noticeably FAT]

You cannot wait until you are in SOI to start the burn, because TWR is too low.

Sure you can, you just have to really want it. And carry a couple extra ion drives. And lots of solar panels. And plenty of zenon. I did a Jool braking burn inside the Jool SOI on four ion drives (had a wee miscalculation on the fuel supply). Sure, I burned (ionized?) through about six tanks of zenon, but I did it.

[K^2]

Never say never, right? Yes, you can achieve sufficient TWR if that's really your goal. Ion drive by itself is 0.2, which isn't all together horrible. It's just that you need quite a few of these on a moderately large craft for the overall TWR to be sufficient.

[RoboRay]

If you're carrying multiple ion drives and lots of xenon tanks and all the power generation equipment they need and all the supporting structure for them, maximum efficiency isn't your goal and you'd probably be better off with a single LV-N.

[Psycho0124]

Yeah, I've been trying like crazy to build a workable spacecraft with these Ion engines ever since they were released. My latest has 100 ion engines and many hours of fuel:

~70 Gigantor panel arrays:

A detachable lander to refuel the xenon tanks (kethane mining and processing equipment, xenon tanks with a NERVA for low-grav landing):

After a little testing, I scrapped the first model and added a few extra panels to bring the maximum throttle to 100% in good sunlight:

The 100 ion engines produce 50 thrust; less than the NERVA on the lander (which can't be fired while the Command module is docked as it would cook the docking port behind it). I've got an i7 3770k processor with an Nvidia 660 Ti in this rig but I still get a little framey with this beast. Burn times are crazy long because of all the mass but the fuel gauge doesn't move much. Maybe when/if they add another star in later versions, this thing might become useful. I'm just leaving it parked in high Kerbin orbit for now though.

It was fun to build! Not so fun to fly.

[K^2]

If you're carrying multiple ion drives and lots of xenon tanks and all the power generation equipment they need and all the supporting structure for them, maximum efficiency isn't your goal and you'd probably be better off with a single LV-N.

That depends on desired delta-V. Four ions + 3 solar arrays will be lighter than 1 LV-N. So that's always a win. But that will get you 1/30th of the thrust. As you add more ions, you are increasing your m_f, which eats into what you win from higher I_SP. If your delta-V is small, the later will be a deciding factor. But if your delta-V is high enough, eventually the exponential nature of fuel requirements will beat whatever losses you take from making your ship heavier with more ions.

[Merinsan]

Yeah, I've been trying like crazy to build a workable spacecraft with these Ion engines ever since they were released. My latest has 100 ion engines and many hours of fuel:

The 100 ion engines produce 50 thrust; less than the NERVA on the lander (which can't be fired while the Command module is docked as it would cook the docking port behind it). I've got an i7 3770k processor with an Nvidia 660 Ti in this rig but I still get a little framey with this beast. Burn times are crazy long because of all the mass but the fuel gauge doesn't move much. Maybe when/if they add another star in later versions, this thing might become useful. I'm just leaving it parked in high Kerbin orbit for now though.

It was fun to build! Not so fun to fly.

I did something like this too, though only had like 30 ion drives, along with an insane amount of solar panels. It was not too hard to launch, but it's so very slow to do anything. I named it the Inane Ion Array, and send it into a highly elliptical solar orbit (left it running for a number of hours). Once I get sick of it, I'll be deleting it. As far as I am concerned at the moment, ion drives are useless and I will not be touching them again unless they are changed somehow.

[RoboRay]

That depends on desired delta-V. Four ions + 3 solar arrays will be lighter than 1 LV-N. So that's always a win. But that will get you 1/30th of the thrust. As you add more ions, you are increasing your m_f, which eats into what you win from higher I_SP. If your delta-V is small, the later will be a deciding factor. But if your delta-V is high enough, eventually the exponential nature of fuel requirements will beat whatever losses you take from making your ship heavier with more ions.

Yeah, but the whole point is that you're adding more ion engines to increase thrust at the expense of delta-V. If TWR is more important than maximized delta-V... rather than the miniscule TWR improvement you get with more ion engines, going with the LV-N instead simply makes more sense.

[magnemoe]

I use an mod with a 5Kn ion drive, 10 times more powerful, heavier but not 10 times. I used two of them to put an probe in 18 km orbit around the sun.

9 tanks with 3000 units xenon, 6 can be dropped, the solar panes are larger than stock, now I would need three around Kerbin but close to the sun they are almost 10 times more effective so one would be enough.

Not sure how much you get with solar panels around Jool but it would be interesting for an mapping probe with lots of small jumps between the moons.

For probes to Eve and Moho they should be considered as you don't need much solar panels.

[Tw1]

You could go and download the more powerful ion engine pack from spaceport, but what would be the fun in that! That is an impressive craft, Psycho! What was the thrust/mass ratio on that?

The "best" craft I made with the stock ion engines:

I cut down on weight as much as possible, choosing the lightest components.

I lined the stayputnic with the smallest batteries, as they had the best charge to weight ratio.

I needed the OX-4B panels to get enough charge. Got it to the Mun by raising the orbit a couple of times.

Launching it with Jet engines was fun. I felt so efficient, and unconventional.

Edited April 26, 2013 by Tw1

[Monkeystador]

ION Engine are just for minor course correction then? I assume they are cheaper than nuclear engines in the game?

Whats the ISP of the ion engines in the game?

[Scottiths]

ION Engine are just for minor course correction then? I assume they are cheaper than nuclear engines in the game?

Whats the ISP of the ion engines in the game?

WoW... I hadn't thought of that. That is actually perfect. Why use 200 dv from your liquid fuel when you can use it from an ion drive for basically nothing! Great idea for practical use of Ion drives

Or you could even use it to do those last .1 m/s of your burns (since that actually makes a big difference in interplanetary travel)

Edited April 26, 2013 by Scottiths

[CalculusWarrior]

That's a great idea! Even if you have the ion drive system as a backup, you could still save yourself a bunch of delta-v by using it!

[Tw1]

ION Engine are just for minor course correction then? I assume they are cheaper than nuclear engines in the game?

Whats the ISP of the ion engines in the game?

No, a lot more expensive. And the isp is 4200.

[Aeshi]

I admit I haven't really gone any further than Minimus, but most of my satellites have an Ion engine for orbit adjustments (so I can lower my orbit to get a better surface view & then go back up when I'm done, etc.)

[Monkeystador]

Kinda silly that ion engines are more expensive than nuclear engines. The nuclear material needed for these engines is certainly not cheap. Neither are the safety consideration regarding these drives. A ion engine in mass production ist certainly much cheaper.