Hint: if altitude were such a problem, why don't rockets go straight up to 80km or so, and only then thrust sideways? Rockets clear the most dense portion of t

Hint: if altitude were such a problem, why don't rockets go straight up to 80km or so, and only then thrust sideways? Rockets clear the most dense portion of the atmosphere very quickly. Building up speed is what takes time (and fuel). Of course, the exponential nature of the rocket equation means that you'd get to save a lot of fuel. You'd still have to lift a lot of rocket though. With a balloon so big that would put the ships from the original Independence Day movie to shame. Maybe it would be worth it on Venus.