Final Flight of the X-15 Left a Legacy of Success


X-15 in flight.
X-15 just after launch.

If residents of Western Nevada had looked high up in the sky on the morning of Oct. 24, 1968, they might have seen the sun glinting off the fuselage of a silver, eight-engine NB-52A Stratofortress as it made a graceful turn over Smith Ranch Dry Lake. Within a black, stiletto-shaped vehicle slung beneath its right wing, research pilot William H. “Bill” Dana completed his cockpit checklist in preparation for a flight in the rocket-powered X-15. The vehicle was essentially a propellant tank with stubby wings, tail fins and a cockpit attached to a 57,000 lb.-thrust rocket engine.

Dana wore a pressure suit that enabled him to survive the hostile environment at the edge of space. Donning it was an ordeal akin to a medieval knight putting on a suit of armor. First, technicians attached a host of biomedical sensors to the pilot’s body to measure vital signs. Next, the pilot squeezed himself into a rubbery, tight-fitting garment bearing numerous hoses, fittings and a metal neck ring. After zipping the inner garment shut, technicians helped the pilot into a baggy, silver outer suit, boots, gloves and, finally, a helmet. A lengthy checkout procedure verified that all suit components were functioning and that there were no leaks.

Dana was familiar with the suit-up procedure. He had made 15 previous flights in the X-15, attaining a maximum speed of Mach 5.53 and a maximum altitude of 306, 900 feet. The latter had earned him his astronaut qualification, and was the last X-15 flight to exceed 300,000 feet. His 16th flight (the 199th of the X-15 program) was to be his last, and was scheduled as the second-to-last mission for the aircraft.

X-15 pilots
Left-Right: X-15 pilots Joe Engle, Bob Rushworth, Jack McKay, Pete Knight, Milt Thompson and Bill Dana.

Four minutes before launch, the NB-52A pilot leveled the wings of the mothership at an altitude of about 45,000 feet. Dana completed his pre-launch checklist.

“Looks good here, Pete,” he told Maj. William J. “Pete” Knight, another X-15 pilot and launch controller for this mission.

Knight responded from the control room, “Looks good here, Bill.”

Five seconds later, Dana flipped the final switch to “Launch.” The X-15 dropped away from the NB-52A and Dana ignited the engine. Trailing a white exhaust plume, the X-15 was soon passing through 80,000 feet.

The engine’s mighty thrust pushed Dana back in his seat. His workload increased as he struggled to maintain his desired heading and prepared to activate various experiments. Nearly 84 seconds after launch, the X-15 attained a maximum velocity of Mach 5.38 at 148,000 feet altitude, and continued to climb after engine shutdown.

The X-15 launch had been coordinated to coincide with a missile launch from Vandenberg Air Force Base on the California coast. At 235,000 feet, Dana extended the Launch Monitor Experiment and called out, “It’s up, Pete, and I saw the missile.” Less than three seconds later, however, the experiment package unexpectedly lost power and retracted.

As the X-15 reached 255,000 feet, it followed a ballistic arc and began the downhill slide toward Edwards Air Force Base in California. Several other onboard experiments functioned automatically, collecting valuable data on aerodynamics and hypersonic airflow. Unfortunately, a high-altitude sky-brightness experiment failed due to a blown fuse. The vehicle crossed over Death Valley and, as the pilot’s workload decreased, Dana had time for a little sightseeing.

X-15 in flight.
X-15 in flight

He then began preparations for entering the traffic pattern at Edwards. Descending through 75,000 feet, the X-15 slowed to Mach 3.2 and Dana finally caught a glimpse of his landing site on Rogers Dry Lake.

The rocket plane made a steep approach as chase planes raced to join it for the landing sequence. As Dana entered the pattern, he had time to banter with Knight.

“We got you coming downwind. Looks real good, Bill,” Knight commented.

“Looks real good to me,” Dana replied.

“That’s the one I was worried about,” said Knight, wryly.

“The downwind?” asked Dana.

Knight shot back, “No. Looking good to you.”

The black plane, now just a stub-winged glider, touched down on the hard-packed clay surface of the lakebed, raising a plume of dust. Two silver F-104 chase planes followed it to the ground then climbed away as the X-15 continued its long slide across the dry lake.

Former X-15 pilotsRobert White, Bill Dana, Neil Armstrong and Joe Engle were on hand when astronaut wings were presented to the three NASA pilots who flew the X-15 into space.

Dana celebrated his final X-15 flight, but for program engineers it was business as usual. Data from Flight 199 were collected and reduced as plans were completed for the final flight of the program. Unfortunately, due to a series of technical problems and weather issues, the 200th flight never took place and the program was soon terminated.

The X-15, however, did not fade into obscurity. Perhaps the most successful research aircraft program in U.S. history, the X-15 program left a legacy of scientific data and aeronautical firsts that remains unparalleled. The program generated more than 760 technical reports, earned awards and honors for the X-15 team, and contributed to numerous advances in aerospace technology in the areas of materials, hypersonic aerodynamics, astronomy, and spaceflight.

The airplane that made the first and last flights of the program now resides in the Smithsonian Institution’s National Air and Space Museum in Washington D.C.

For more information on the X-15, see the NASA Dryden X-15 Hypersonic Research Program fact sheet at:

By Peter W. Merlin Historian, NASA Dryden Flight Research Center

Related article: Joe Henry Engle (Colonel, USAF, Ret.) Biography