Reddit mentions of Rocket Boys (The Coalwood Series #1)

What everyone said is correct: math, math, math, and enjoy your last summer ;) You may also want to learn how to code in C++ or Fortran (yes, yes, it's ancient, but pretty much all NASA codes are written in C++ or Fortran) or even Matlab, if you have access to it.

Also, if you want to read some inspirational type books: Kelly Johnson's Memoir, the man basically invented Skunk Works. I also loved Flying the SR71, which is all about the Blackbird. It may sound corny, but Rocket Boys is my go-to book and/or movie when I feel discouraged and like I can't hack it as an engineer. And Bill Bryson's "A Short History of Nearly Everything" was really interesting to me.

What I found pushed me through the grueling classes, assignments, 50% on a test... was my passion for space exploration and propulsion methods. So I suggest in addition to the math and enjoying the free time you have left that you find what makes you passionate to be an engineer :). Because sometimes, at 2 am in a computer lab, after staring at the same chunk of code for 3 hours and not understanding why it doesn't seem to friggin work out... passion is all you have!

Best of luck to ya!

Late to the game, but people always need more books...

The World Without Us was great, really interesting read about humanity's effects on the planet, with lots of references to expand on if you wanted to do that.

A Year of Living Biblically was interesting, even if you aren't a Christian or a Jew, if you find religion interesting.

And last but not least, Rocket Boys by Homer H. Hickam. This was made into the movie 'October Sky', and it's a memoir, one of the best I've ever read. But all the science of the rockets is in there too, I learned a lot about propellants and DeLavalle nozzles lol.

I heard the book is even better; so I ordered a copy.

read his book!