I recently saw an Elon Musk talk on YouTube where he commented on how if Earth's gravity were just a little stronger, then it would have been impossible to generate enough thrust to get into space. He cited that as the reason why only a handful of national governments have successfully reached space. However, I know of a few independent projects involving sending satellites to space via balloons. Peter Forsythe, a British 13-year-old, managed to do it. There's a handful of Kickstarter projects trying to get funding to do the same thing, SkyCube is one example. It seems like something isn't adding up. If thrust is a fundamental requirement for reaching space, then how exactly are these balloon-based satellites pulling it off? They surely don't have enough thrust. If anyone could clear this up for me it'd be really helpful. Thanks!