NASA is offering the book X-15: Extending the Frontiers of Flight by Dennis R. Jenkins as one of their small library of free e-books for most popular viewers. (Thanks to NASA Watch for pointing it out.) Personally, while e-books may indeed be the future (at least until civilization next stumbles, and they – trapped in their unusable viewers – all become inaccessible for a few centuries, if not outright lost), I still prefer real books, and couldn't care less about the e-book-ness of this text. It's just nice that it's available for free and in at least one semi-open format (PDF), and that it's about the X-15, which was a fascinating program. If you, too, find this sort of thing fascinating, have a look.
By the way, some related reading recommendations (in good, old-fashioned books) spring to mind:
- At the Edge of Space: The X-15 Flight Program by Milton O. Thompson
- Flying without Wings: NASA Lifting Bodies and the Birth of the Space Shuttle by Milton O. Thompson and Curtis Peebles. Personally, the reference to the Space Shuttle doesn't impress me (quite the opposite, actually), and therefore doesn't strike me as a reason to read the book. But the lifting bodies were fascinatingly novel technology, and should not be forgotten, and this is a good book on the subject.
- Wingless Flight: The Lifting Body Story by R. Dale Reed
- Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles by Roger E. Bilstein. What can I say? It's been about 50 years since development of the Saturn V started, and more than 50 since the Saturn I, and there's never been a rocket to match it, and, sadly, for the foreseeable future, its singular status seems to be assured. The story of how it came to be, and in some cases how it almost didn't (think F-1 combustion instability, for one thing), is a helluva story.
- The Soviet Space Race with Apollo by Asif A. Siddiqi – Nearly lost history extracted from behind the fallen iron curtain. While people who care about such things are now generally aware that the Soviets built and flew a massive rocket known as the N-1 (see this page, and this other page, for some details) as part of a program to land cosmonauts on the moon – a program that probably could have worked, but was cancelled after the first four test flights failed catastrophically (whereupon all of the N-1s built and waiting to fly were cut into scrap metal, and it became official Kremlin "truth" that they'd never, ever intended to land cosmonauts on the moon) – what most of even those people probably don't know is that even as America was preparing to launch Apollo 8 (the first human journey to the moon), the Soviets had a vehicle on the launch pad capable of the same task (albeit with a smaller crew and a spacecraft which could never have supported moon landings), and cosmonauts trained, ready and willing to fly it, waiting in frustration for the Kremlin to give a go-ahead that never came. Fascinating stuff.