The final attempt to get an X-15 off the ground for the 200th flight: 20 Dec. 1968.

courtesy Jack Kolf collection

The X-15 team huddles against the snow: 20 Dec. 1968.

courtesy Armstrong Flight Research Center

The X-15 and Space Shuttle side-by-side. Detail of mural by Mike Machat at Edwards.

photo by author

An X-15 delta wing concept model.

courtesy Armstrong Flight Research Center

The next step in the evolution of the X-15: Hypersonic delta wings. The loss of X-15 No. 3, which was to have been modified with the new wings, brought the program to a halt.

computer art courtesy Thommy Eriksson

One idea had the delta-wing X-15 being launched from the back of an XB-70.

courtesy Edwards History Office

A computer-generated image of the XB-70 carrying the X-15 to launch altitude.

courtesy author's collection

An advanced conformal ramjet configuration with lineage directly to the X-15.

courtesy North American Aviation

North American Aviation personnel gather to celebrate the end of the X-15 program.

courtesy North American Aviation

Six X-15 pilots give their version of The End.

courtesy Armstrong Flight Research Center

Two surviving X-15s in storage at the Flight Research Center prior to leaving for permanent display. X-15 No. 1 in foreground and rebuilt X-15A-2 with no markings is behind.

courtesy Armstrong Flight Research Center

X-15 No. 1 arrives at the Smithsonian Institute and rolls beneath the Wright Flyer.

courtesy Armstrong Flight Research Center

Crossfield, Engle, Knight, Thompson, Rushworth, McKay, and Dana: Jun. 1969

courtesy Armstrong Flight Research Center

X-15 No. 1 is prepared for display at the new National Air & Space Museum: 1975.

courtesy NASA Headquarters

X-15 No. 1 as it hangs in the Milestones of Flight Gallery at the Smithsonian.

photo by author

X-15A-2 on display with an LR-99 engine at the National Museum of the US Air Force.

photo by author

Extreme close-up of the skin of the X-15A-2 showing an original part number stamp.

photo by author

One of the more outlandish proposals for getting the X-15 into orbit involved mounting it on the nose of a modified Titan rocket.

computer art courtesy Thommy Eriksson

The X-15 rides into orbit on top of an early Saturn 1 rocket.

courtesy author's collection

Concept art of an X-15 attached to the SM-64 Navaho booster for launch into orbit.

courtesy author's collection

Space Shuttle Discovery launches on mission STS-121: 4 July 2006.

courtesy NASA Kennedy Space Center