Interplanetary travel? No one ever thought it would be this hard, especially the folks that are not literally 'rocket scientists' Why is it that 50 years after the official start of the Space Age we do not have colonies on the moon and Mars already? Why are we still plodding along in Earth orbit? There are a million of these kinds of questions you can ask, but when you dig into their answers you uncover something very odd indeed. In my previous book 'Interstellar Travel: An Astronomer's Guide' I laid out all of the astronomical challenges to interstellar travel and colonization. The bottom line was that this was an adventure filled with dreams but no technology to get us there. In this companion book, 'Interplanetary Travel: An Astronomer's Guide', we discover that in fact we have all the technology we need to make it happen, but our current problem is we lack dreams. Think about it. Most of the science fiction you read is all about interstellar travel. Our little neighborhood in the universe is almost always given short shrift. We have no dreams about our own solar system that can stand toe-to-toe with the technological fantasy of interstellar empires and exploration. We have no dreams about planetary colonization, or stories to entice us to invest in this effort. There are no great expectations about what we will find that is worth going after. So as an astronomer, I look at interplanetary travel as very much the odd duck. It's not that we don't have the technology. The problem is Congress can't see the point in the investment and rushed timetable. Yet engineers keep plugging ahead, literally on their lunch-hours and coffee breaks, and developing what is needed on their benches and in their laboratories. Funded by their own dreams, and small pots of money cobbled together from government and private grants, they steadily advance the limits of what we can do. In this book, I want to show you some of the best ideas we have about interplanetary travel. Does it really make sense to travel outside the asteroid belt, when all you will find there are moons made of ice? There is an entire mythology that has grown up in science fiction that has human miners spread across the solar system, but the astronomical reality is that beyond Mars, all you will find is ice. Mining the ice on the moons of Saturn is far more expensive than on the moons of Jupiter, so astronomy limits our economic activities to basically the inner solar system This book is not just a about limits, but about what kinds of considerations go into making interplanetary travel an economic reality. In the end, you will discover that our future in space will depend on some very hard thinking about how we see ourselves interacting with the universe in the near future.