I took the opportunity to read it (which I hadn't done since I was in elementary school). It's exactly what it tries to be -- a boy's-own adventure (written in 1959) in which a teenager tours the solar system. Invent the minimum possible plot which could require this; you've probably replicated this book's gimmick.
The author is optimistic about the invention of antigravity, which he admits in the foreword is probably necessary for manned travel to other planets. Sadly, still waiting.