Jet engine with an Ion toggle

[Gameslinx]

For small SSTO probes or larger, long term long distance SSTO travel, I feel like our 0.625m Dawn ion engine needs a bit of love.

Well. Not the Dawn engine itself, but the Ion engine mechanic.

We have a huge whopping/gaping hole in Ion engines or Ion fuel tanks which desperately needs filling. Sure, we have nuclear engines... I guess? But they are also somewhat limited to LFO, and man - that stuff's heavy!

Xenon gas and electric power is as light as air!... Hence... "Gas". Bad pun, huh.

As more ION engines are needed/wanted, this is an idea for an SSTO based Ion drive:

An inline Ion engine which doubles up as a jet engine. 

Mode 1: Liquid Fuel, wet mode. It should be moderately inefficient with this mode due to its upper stage efficiency. 

Mode 2: Ion Xenon/Electricity mode. Slightly less efficient than the Dawn drive, but has 1.7KN extra thrust. This is because the engine is a 1.25m/MK1 drive. Like really, who builds a 0.625m SSTO? Just put it in a bay! But when efficiency Is needed, it would be awesome to have a 1.25m/MK1 Ion engine. And with that? 1.25m xenon tanks. In use with the Gigantor solar array, I think this could work rather well.

[TwinKerbal]

IDK I feel like a bigger Ion engine should have more thrust but less efficiency.

Bigger is less efficient but more powerful.

[Gameslinx]

35 minutes ago, TwinKerbal said:

IDK I feel like a bigger Ion engine should have more thrust but less efficiency.

Bigger is less efficient but more powerful.

Yeah that's what I (poorly) tried to convey in my post. It gets you there faster, but uses a bit more fuel and sacrifices efficiency because of its weight in doing so. But still, would make for great planes without having to add a payload bay and deploy a probe that way.

[tater]

The two technologies would never be combined.

[passinglurker]

Bit of a problem. real ions and jets have no where near the thrust of ksp ions and jets (its a matter of game play everyone wants ssto's and no one wants to play the months long spiral out of real ions) if you want to "engineer" this by assembling it together in game or making a mod based on this idea then more power to you, but ksp's ion and jet antics is not a fact we want to draw attention too by combining them into one overpowered official part.

[TheKosanianMethod]

One could clip a Juno with a Dawn, might look cool. Or any jet, really.

[magnemoe]

14 hours ago, tater said:

The two technologies would never be combined.

Agree here, first they have nothing in common, second you want to save weight then using an ion engine so you ditch the jet then out of atmosphere. 
The only plausible use is an Laythe mission but here solar panels is pretty pointless so you could not use the ion to reach orbit. 

Edited October 13, 2016 by magnemoe

[Technical Ben]

Calculate the amount of gas you would need and the electric charge required.

KSP interstellar has nuclear jets and some electric propulsion options. Often the generators and cooling systems for these are very large and make building such a SSTO entirely electric based hard (but doable in the mod IIRC).

[Streetwind]

15 hours ago, TwinKerbal said:

IDK I feel like a bigger Ion engine should have more thrust but less efficiency.

Bigger is less efficient but more powerful.

Counterintuitively, in real-life, plasma thrusters (which gridded ion drives like the Dawn belong to) actually scale the other way around. As you keep dumping more and more electric power into it, Isp scales up more and more, but you struggle to increase thrust as much. Additionally, there comes a point somewhere (depending on which engine technology we're talking about) where you just can't add any more power without destroying your engine, and those points are way lower than engineers would like them to be. In order to use more power and/or get more thrust at the same Isp, you must cluster smaller engines, or find completely novel approaches (see: the X3 nested hall thruster, the helicon radiowave based VASIMR, or ESA's dual-stage 4-grid ion concept).

This has little to do with the suggestion, and just serves to educate

[Kertech]

Errr aren't these literally two completely different technologies!! With two drastically different methods of function. I'm not saying you couldn't put an ion engine in the middle of a jet engine, but you'd lose efficiency of the jet engine that way, or put it round the outside, but either way you have two engines not one combined!

[Red Iron Crown]

Just stick an ion on the back of a Rapier and disable the Rapier's gimbal. Example (check out the dV in orbit, though the TWR is painfully low):
 

Spoiler

 

 

[Stoney3K]

Would that make it a Dawnpier? Or a Rapion? I really can't tell.

I doubt this would be any use in stock. It may have some limited uses in stock, but in that case I would guess it becomes more along the lines of a mixed mode airbreather and arcjet with some VASIMR-like properties. Great for near future Firefly-esque roleplaying, but not much good for other things.

[Wjolcz]

This kind of engine is kinda pointless tbh. I don't think Dawn has enough TWR to be of any use for SSTOs. I feel like it would be better to have a smaller NERVA engine than this hybrid ion-jet... thing.

Even the flying stove pipe (was it Project Pluto?) would be more sensible and useful than this.

[Jonfliesgoats]

I think the OP's goals may be met by other technologies that were under consideration in the fifties and sixties and subsequently abandoned.  In those cases we would still be talking about different motors sharing a power source rather than a single motor.

History Trivia:

US and Soviets both worked on different types of nuclear jet engines when they envisioned B-36s and the like flying for months on continuous patrol.  Both designs used nuclear fission to provide the heat which is usually provided by jet fuel.  

One design, which was simple and reliable, actually ran air through or past fissile material.  Extraction turbines drove compressors just like other jet engines.  Unfortunately, the downside to this design was radioactive exhaust.  This was considered irresponsible even by 1950s standards.  Also, having air run past or through fissile material makes one wonder how the engine's reactor was controlled.  Were air channels supposed to be installed in the fuel control rods of the reactor?  I presume this was addressed in the design.

Another design used a liquid metal or liquid salt to transfer heat from a central reactor to the hot parts of these jet engines, much like a Soviet nuclear submarine gets heat from its reactor to its steam plant.  This was awfully complex and came with its own, new sets of hazards.  Hot air in an airplane's bleed system is capable of starting fires and melting components.  Imagine a broken joint in a liquid salt heat transfer system in an airplane!

The most promising nuclear airplane was not a jet.  Americans built a B-36 that was supposed to have its propellers driven by electric motors supported by an onboard nuclear reactor.  This actually flew.  Other problems made this project a bad idea.  We didn't get the whole parasite fighter issue worked out, so this craft would be a giant nuclear disaster waiting for any hostile MIG 15 to take it down.  Also, just like parasite fighter docking and deployment was a risky move, crew changes in flight were impractical.

 

In relation  to the OP:

In KSP these technologies could provide nuclear jet engines that use no fuel (since there is no mechanic for consumption of fissile material, I'd suggest they use high quantities of electricity to simulate the heat from fission in these proposed motors).  The player could switch to a NERV engine at altitude.

Electric propellers could get the OP's craft to altitude, but it would be very slow for any sort of NERV or LFO rocket use.

Anyway, it's tempting to be derisive of odd ideas.  Real aerospace programs invested in radioactive, nuclear jets, so it's hard for any of us to really exceed the limits of impracticality set IRL.