Question regarding the Thermoelectric Generator and the Ion engines

[Hacktech]

I've been thinking about building a big ass ship, probably with ion engines. But I also thought about filling it up with those Thermoelectric generators instead of those solar panels.

How many generators does it take to run a Ion engine?

[Loocas]

I never tried that but if your ship is really big and you are going to use only ion engines then... a LOT. And it may barely move.

[Aeshi]

I think it'd take about 10 reactors to run 1 Ion engine non-stop. You'd be far better off using Gigantor XXL Solar Panels instead.

[Eric S]

I think all out an ion engine takes 15 electricity a second, and a thermoelectric generator provides 0.75, so it would take 20 generators per ion engine.

[capi3101]

Count I've heard is 15 PB-NUKs to power 1 Ion Engine. Problem with ion propulsion is the lousy thrust. Just as an academic exercise, add up all the mass of everything you'd need to keep an ion engine running. Take the thrust you'd get and divide it by that mass; what results is your acceleration in m/s^2. You'll find it sucks. Badly. Like leave your computer on overnight to perform a transfer burn kind of suck.

You'd probably be better off with LV-Ns unless you're planning to have a very small probe for your payload.

[Hacktech]

Thanks for all your answers. I'll probably skip the Ion Engines and go with the LV-Ns instead.

[architeuthis]

Thanks for all your answers. I'll probably skip the Ion Engines and go with the LV-Ns instead.

Good idea:)

RTG unfortunately don't make much sense for powering ion engines, the PB-IONs are just too power hungry. The best thing you can do from both a TWR and delta-v standpoint is to use OX-4 solar arrays (they have by far the best power to weight ratio 12X better than the RTG at Kerbin's orbit). To run the PB-ION engine at close to full power you would need 8 arrays at Kerbin's orbit or 16 at Jool's. For comparison if you wanted to use RTGs you would need 22 of them for full power, but such a craft would have horrid acceleration and a somewhat limp noodle delta-v budget for an ion craft. Gigantors are not as good as OX-4; their power to weight ratio is half that of the OX-4. Also if you wanted your center of mass to be along the line of thrust (generally a good thing unless you really like spinning uncontrollably) you would need at least two of them, but this much power is massive over kill for one ion engine. To use that much power you would want 2 PB-IONs, but all of this extra mass will ding your delta-v. The bottom line is don't ever use RTGs to power ion engines, (at least until the devs fix the inverse-square law for solar insolation, at which point they will make sense for outer-planets missions). Also if you can make it work use OX-4 instead of Gigantors, they always will give you more delta-v and you actually will get better thrust with them too (54% more at Kerbin's orbit, 13% more at Jool's orbit). More thrust means shorter burns:)

Edited May 10, 2013 by architeuthis

[numerobis]

Pod torque is generally plenty enough to overwhelm the torque from the ion engine, actually. You'd have to place it way off center to have trouble.

The fixed solar panels are even more power-dense than the rotating panel (unsurprisingly) -- if your spacecraft is pointing the right way.

[CalculusWarrior]

1 ion requires 12 units of electricity per second.

RTG's used to provide 1 per second, but were nerfed and now only provide 0.75/s.

12 units * 1 RTG / 0.75 units = 15 RTG's required to power a single ion engine.

15*0.08t = 1.2t : the mass of all these RTG's. Not large in comparison to some of the engines/fuel tanks, but when factoring the ion engine (0.25t), xenon tank (0.12t), and lightest probe core (0.04t), we get a total mass of 1.61t.

One ion engine produces 0.5 kN of thrust, so this gives us a Kerbin TWR of 0.031--which would take an eternity to change orbits!

I guess you could just put it on 4x time warp, then go watch TV or something...

[Eric S]

Count I've heard is 15 PB-NUKs to power 1 Ion Engine.

Correct, my numbers got inflated because I was counting the electricity drain of the probe pod as well.

EDIT: I just retested with a manned pod so that it wouldn't cause any drain, and I'm still seeing a 14.55 unit/sec drain from the engine.

Edited May 10, 2013 by Eric S

[architeuthis]

According to the wiki the actual unpublished power consumption of the PB-ION is 14.442e/s add this to 1.7e/s for a probe core and decide by .75e/s produced by the RTGs and you get 22 RTGs, rounding up:)

[Hacktech]

Nerds seriously, are you all math professors or something like that?

[SunJumper]

Good idea:)

RTG unfortunately don't make much sense for powering ion engines, the PB-IONs are just too power hungry. The best thing you can do from both a TWR and delta-v standpoint is to use OX-4 solar arrays (they have by far the best power to weight ratio 12X better than the RTG at Kerbin's orbit). To run the PB-ION engine at close to full power you would need 8 arrays at Kerbin's orbit or 16 at Jool's. For comparison if you wanted to use RTGs you would need 22 of them for full power, but such a craft would have horrid acceleration and a somewhat limp noodle delta-v budget for an ion craft. Gigantors are not as good as OX-4; their power to weight ratio is half that of the OX-4. Also if you wanted your center of mass to be along the line of thrust (generally a good thing unless you really like spinning uncontrollably) you would need at least two of them, but this much power is massive over kill for one ion engine. To use that much power you would want 2 PB-IONs, but all of this extra mass will ding your delta-v. The bottom line is don't ever use RTGs to power ion engines, (at least until the devs fix the inverse-square law for solar insolation, at which point they will make sense for outer-planets missions). Also if you can make it work use OX-4 instead of Gigantors, they always will give you more delta-v and you actually will get better thrust with them too (54% more at Kerbin's orbit, 13% more at Jool's orbit). More thrust means shorter burns

Don't you mean better acceleration? Thrust is identical for all ion engines, unless you're powering one with a potato battery.

[ThePsuedoMonkey]

Since we're nitpicking, the Ox-Stat panels give the best power-to-mass ratio. You just need a whole lot more of them and have to keep them oriented toward Kerbol and stuff.

[nyrath]

1 ion requires 12 units of electricity per second.

RTG's used to provide 1 per second, but were nerfed and now only provide 0.75/s.

12 units * 1 RTG / 0.75 units = 15 RTG's required to power a single ion engine.

15*0.08t = 1.2t : the mass of all these RTG's. Not large in comparison to some of the engines/fuel tanks, but when factoring the ion engine (0.25t), xenon tank (0.12t), and lightest probe core (0.04t), we get a total mass of 1.61t.

One ion engine produces 0.5 kN of thrust, so this gives us a Kerbin TWR of 0.031--which would take an eternity to change orbits!

I guess you could just put it on 4x time warp, then go watch TV or something...

Great analysis!

Things will be much worse if the game implemented the VASIMR. Compared to the ion drive it is a power hog. Solar cell arrays and RTGs are too weak, you'll need something like a small nuclear reactor. Since reactors components are all constructed of fantastically dense elements, this makes for truly pathetic thrust-to-weight ratios.

[nyrath]

Nerds seriously, are you all math professors or something like that?

Well, it does help when one is playing a game that is literally rocket-science.

[architeuthis]

Don't you mean better acceleration? Thrust is identical for all ion engines, unless you're powering one with a potato battery.

Thanks, I was being lazy. Acceleration is what I mean. Lower mass for the same thrust gives more acceleration as per Newton's second law.

[Spartwo]

I've been thinking about building a big ass ship, probably with ion engines. But I also thought about filling it up with those Thermoelectric generators instead of those solar panels.

How many generators does it take to run a Ion engine?

8 (look at it sideways)

[Crush]

This is my Solar-Sailor. 24 OX-STAT solar panels on a 2x2 Structural Panel. No batteries, but it has a PB-NUK on the other side of the panel for emergencies.

The solar cells are easily able to keep the ion engine at full thrust, as long as they are kept oriented towards the sun. But that's not as hard as it sounds, because they have about 45° of tolerance. Just hope that this is the general direction where you want to go

Total mass: 920 kg

Edited May 10, 2013 by Crush

[Noticeably FAT]

It wouldn't be a stock solution, but I've been wondering if the Damned Robotics parts are too heavy to make it worth the time to create a rotating OX-STAT array. Keeping it on target would a a manual process, but as Crush said you do have a pretty wide tolerance.