Don't know why I'm bothering, as asking for stuff on DA has had a litterally 0% success rate for me in the past, but what the hell.

I'm doing some calculations for a sci-fi story and came to the conclusion that I'm going to need to accellerate 23,000 tonnes of payload to roughly 520 kilometers per second. I have tenatively decided to go with a nuclear salt water rocket in spite of the controversy in the scientific community surrounding it (I want the story to be fairly hard, hence why that's a concern) because my rough estimations indicate that getting this beast up to speed in anything like a reasonable amount of time takes roughly all the newtons.

Anyway, if anyone can find an internet calculator that will tell me the amount of fuel it will take to get this up to speed and then back down again, or do it themselves, that would be real helpful.