[sjducb]

Yea. Some kind of nuclear scramjet would be the way to get off a big planet with a dense atmosphere.

To explain for all of the non engineers:

On earth scramjets work because airflow enters the front of the engine and the shape of the inlet compresses the gas, fuel is added and burnt, then the exhaust gasses go out the back really fast.

With a nuclear scramjet the fission reaction heats up the middle of the scramjet so air comes in, is compressed then heated so it expands and goes out the back really fast.

That would move you very quickly and efficiently through the dense atmosphere, using almost no fuel, and you do not have to carry much reaction mass.

Then once in space you feed compressed hydrogen into the front of the engine heat it up and send it out the back really fast, just like the nuclear rocket motors that nasa is developing right now.