Best Engine for Long Distance?

[Andrew Ridgely]

Hi everyone!  I just was wondering what engine would be best for long distance interplanetary missions.  Which engine is the most efficient (in a vacuum) Fuel wise and dV wise?  Imagine a trip from Kerbin to Jool, or even farther.

 

Thanks everyone!

[Waseemq1235]

Short answer:

The nuclear engine

Well, it has a problem of overheating and is veryyyyyyyyy slow.

But it's one of the most efficient ones.

[foamyesque]

By Isp, it's ions, then nuclear engines. A lot of the ion engine Isp advantage is clawed back by the powerplant and dry mass of the tanks eating into your mass ratio, though. The nuclear engine, on the other hand, is really heavy and only really worth it if you're pushing something that is both heavy and doesn't much care about TWR.
 

Almost all of my interplanetary missions are done on Terriers, Poodles, Rhinos, or Vectors, all of which give you good vacuum Isp and good TWR. Some superlight stuff I will use Ants on

[DD_bwest]

i generally use nuclear for the outter system,  and ions for arriving and leaving Moho(you can slap on extra ion engines since your solar panels will cranking out the juice).

nuclear ships tend to get rather large, and the lack of 2.5m liquid fuel only tanks on stock can get frustrating.  the high ISP tho makes it worth it.  

engine isp is your measure of efficiency. but you also have to pay attention to engine weight.  a larger high isp engine might seem good, but depending on the weight it might be better to use a smaller engine, even if it has a lower isp.

[Jaeleth]

Ion engines have the best ISP, but since the drills and converters have been implemented and xenon is the only fuel you can't drill, they're dead. Use them for one way small probes for extreme dV requirements only.

nuclear all the way, is the best. Unless you wish to move a VERY large ship with an acceptable burn time, in which case you will opt for Rhinos.  Still, if you are patient, you can always make multiple burns at Pe.

For smaller shuttles to non atmosphere worls you could consider the poodles, terriers, etc, (see foamyesque post) but if gravity is not that much, the nuclear is still the best, even for a shuttle, I use them in packs of 4 to haul large tanks of fuel from low grav worlds mining stations to orbit.