And it became my possession for $2. And now yours, via SoundCloud, for nothing.

The X-15 was built by a company called North American Aviation, which is now a part of Boeing via a sale to Rockwell International. The recordings saw the light of day because one of the company's employees, Martin Halperin, "who recorded, supervised, or revivified the sounds from their original sources." According to the album cover, "The sound department of North American Aviation, Incorporated (Los Angeles Division) has one of the largest libraries of documented aerial sounds on earth."

Before you listen to the title track, let me tell you a couple more things about the X-15. The rocket-powered plane was carried into the sky by a B-52 bomber. Once untethered and under its own power, it could reach speeds of 4,500 miles per hour and altitudes over 100,000 feet before gliding back to Earth. "The X-15 paved the way for America's piloted space program, setting unofficial world records for flight speed and altitude along the way," NASA says. Also, Neil Armstrong flew one. Here's one being dropped from a B-52.

And here's the test flight audio from the X-15, introduced with a wonderful guarantee: "The voices are actual. All things are as they occurred."

Another truly fascinating track was recorded in the nosecone of an Atlas intercontinental ballistic missile! "As a passenger in the nosecone of Atlas intercontinental missile, you will be on top of the result of more than a million man-hours of work," Magnus narrates. "In the uninterrupted sequence which follows, actually recorded in the nosecone, you will hear the following: the countdown and launch, the separation of the first stage at burnout, the intermittent sounds of the guidance rockets, the separation of the second stage, the separation of the nose cone, and the sound of the guidance rockets as they guide you to your final destination. Now get ready for countdown and launch!"

Why the nose cone? One, that's where a warhead would have been placed. Two, the initial test of the Atlas missile had problems with the nosecone, leading one military officer to ask, "What's the value of shooting a missile 9,000 miles if the warhead is worthless when it gets there?" So they might have wanted as much data from that part of the missile as possible.

Still, I have no idea how they made this recording -- or rather, I can imagine how they made the recording, but not how they recovered it.

Though the Atlas eventually got converted to civilian duty, lofting astronauts into orbit not bombs across the ocean, it's worth reflecting on what "your final destination" would have been at the time this recording was made: some Soviet city.

Another fascinating section of the record runs through the American defense capabilities. We get to hear missiles like the Nike, Minuteman, and Titan ("which fills the land and sky with thunder").