What are the design principles of Nuclear Rockets?

[Red Iron Crown]

Again, it must be emphasized that nuke engines are utter ....e in atmosphere. They are far and away the worst engines in all categories when not used in a vaccum. This is the most likely problem I can see.

Depends on the atmosphere. In Duna's thin atmosphere the LV-N's efficiency is higher than any chemical rocket's, same with Kerbin once above 1500m or so in altitude. Eve, though, is not a place for nukes.

[EtherDragon]

Hi TigerClaw,

So the general advice on Nuclear Engines:

1: Go Big Fuel or Go Home.

This is often the case for many kinds of rockets actually. It simply boils down to this: The total Delta-V available to any rocket has to do with what percentage that rocket is made up of fuel (higher percentages mean more Delta-V) and how efficient the rocket motor is at using the fuel to change momentum.

There is a strait forward crossover point at lower percentages of fuel where the LV-N is less efficient than a simple rocket motor because it's so heavy by itself.

2: Low ATM Pressure or Bust.

Yep, definitely hit the nail on the head. Take a look at the LV-N's stats in the VAB. You'll notice the ISP in atmosphere is dismal - it might even be the worst in the game. Simply put, don't bother lighting it up in anything but the thinnest of atmospheres, like Duna.

3: Best for Transfer Stages.

Correct again. The reason for this is because it's a much lower powered engine than anything else of similar mass. But transfer burns usually give you plenty of time to execute them so the lower thrust of the LVN is perfect for this task.

Here is an example of a rocket built for heading to Duna, and landing a manned mission on Ike.