SpaceX hopes to build rockets that can land and take off from almost anywhere. One interesting question, though it's not of much concern in our particular solar system, is how big can a terrestrial planet be before a modern rocket would no longer be able to launch off the surface? The bigger a planet gets, the more gravity it has, and if I'm not mistaken, at some size the gravity will exceed the capabilities of a modern rocket. You can use bigger rockets, but at some point the fuel can't even lift itself. I've heard or read something not too long ago that suggested if Earth was much bigger, we wouldn't be able to get into orbit. I know the margins is pretty slim for modern rockets on Earth. How much bigger could the planet be before we would be stuck down here? Anyway, I just though it was an interesting question to share that I have never seen any space shows answer.