Robert A. Heinlein
Only a year or so ago that I read this before (and, of course years ago). Just a great "family story" that holds up, despite the things that seem quaint and dated. (hundreds of years from now and still using slide rules! Difficulty communicating back to Earth when traveling in space.) You don't have to look to hard to find Heinlein's gentle libetarianism beneath the surface. Amusing how little orbital traffic he thought there'd be around earth.
I wish I could fill the gap - someone needs to raise the banner of this kind of good-hearted story that stirs the interest in space travel!