My aliens want to build the heaviest chemical rocket possible: They never were much into space travel, since their planets' gravity is about 1.5 of ours. They made lots of bad experiences fighting against gravity and 'decided' to keep their technology on the ground. Suddenly the world's biggest corporation decides that it's absolutely necessary and very urgent to send a few drives, a breeding station, and some robots into space. They don't care about everything they've built up or the rest of the world. They go with chemical engines because they don't have any experience with stronger ones. That would be about 100 tons of rocket for 1 gram of payload? Can we also use nanotubes and diamonds to make it hold together? Nice.
The best place for launch is the planets largest mountain, letting you skip a part of the atmosphere and also letting you abuse some of the planets rotation. Still, there's a good amount of distance to cover, because the atmosphere goes about 2 times further than earths. (50% hydrogen, 40% nitrogen and some heavy stuff that doesn't matter) If the air was warmer, it would be easier to pierce through, right? What could be better suited to warm up the atmosphere than a bunch of bombs? They'd shoot up a few rings of nuclear warheads that detonate at various heights, wait until pressure and wind are ok, uncover the rocket and launch it.
Of course air density is one of the less important factors when thinking about launching a rocket. I want it to be important, because I want to nuke the sky. I also know that there are better ways to escape a planets gravity than chemical engines, but that's what we're working with here. Try to work with a lunatic, please.
Is this way of heating up the atmosphere realistic?
If not, what would be the best way?
I'd also be thankful for comments that mention more variables to think about. What else would the aliens have to do to launch their monster of a rocket? It's not about solving a problem, but about creating new ones which the aliens can barely solve.