NASA X-15 PROGRAM

NASA HIGH RANGE -- AREA 51 - BATTLEFIELDS OF THE COLD WAR

NEVADA - THE BATTLE BORN STATE

NASA X-15 PROGRAM
By: T.D. Barnes - NASA Contractor - 1960s

NASA contractors for the X-15 program were Bendix Field Engineering followed by Unitec, Inc. The NASA High Range Tracking stations were located at Ely and Beatty Nevada with main control being at Dryden/Edwards AFB in California.

Personnel at the tracking stations consisted of a Station Manager, a Technical Advisor, and field engineers for the Mod-2 Radar, Data Transmission System, Communications, Telemetry, and Plant Maintenance/Generators. NASA had a site monitor at each tracking station to monitor our contractor operations.

Though supporting flights of the X-15 was their main objective, they also participated in flights of the XB-70, the three Lifting Bodies, experimental Lunar Landing vehicles, and an occasional A-12/SR-71 Blackbird flight.

On mission days a NASA van picked up each member of the crew at their residence for the 4:20 a.m. trip to the tracking station 18 miles North of Beatty on the Tonopah Highway. Upon arrival each performed performed preflight calibrations and setup of their various systems. The liftoff of the B-52, with the X-15 tucked beneath its wing, seldom occurred after 9:00 a.m. due to the heat effect of the Mojave Desert making it difficult for the planes to acquire altitude.

At approximately 0800 hours two pilots from Dryden would proceed uprange to evaluate the condition of the dry lake beds in the event of an emergency landing of the X-15 (always buzzing our station on the way up and back). The most popular of these launch lakes were Mud, Delamar, Hidden Hills, Smith Ranch, Silver, Railroad Valley, Rosamond, and Cuddeback. EMERGENCY LANDING SITES
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Each mission commenced with B-52 Zero-Zero-Eight and the chase planes (F-104s and an occasionally NASA'S T-33) lifting off at Rogers Lake and circling Edwards AFB as they ascended to the 45,000 feet altitude required for the launch. The B-52 usually reached altitude as it flew over Baker, California, during which time the X-15 pilot was performing preflight checks of the X-15, testing various communications channels, etc. The airways were quite busy.

As the aerial entourage proceeded up range, Beatty radar and telemetry would acquire track along with its counterparts at Dryden, giving NASA the option of using the track of whichever radar it desired. When the planes proceeded beyond the range of NASA/Dryden radar, Beatty radar would provide the tracking functions. Meanwhile, Ely radar and telemetry would be trying to acquire tracking for when the flight tracking passed from Beatty to Ely tracking station. (All three tracking stations kept their radar and telemetry system slaved to the one with the most solid track until they acquired their own tracking capabilities) If everything was go for the mission, the X-15 would launch and 7 minutes later be landing at Dryden, an hour or more ahead of the mothership
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X-15 Movie Clip

THE PLANES
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Mod II radar system used by the U.S. Air Force at Cape Canaveral prior their modification and use on the NASA High Range
Mod II 584 Radar used by Air Force at Cape Canaveral prior to installation as primary radar on the NASA High Range

Mod II 584 Radar used by Air Force at Cape Canaveral prior to installation as primary radar on the NASA High Range

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Mod II radar used at Cape Canaveral prior to use on X-15 program

Mod II, SRC 584 S-Band radar used by the Air Force at Cape Canaveral

THE HIGH RANGE The Mod II radar we used on the NASA High Range for the X-15, XB-70, Blackbird, and Lifting Body tests in the 1950s and 60s was a World War II vintage S-band radar system used previously by the U.S. Air Force at Cape Canaveral for missile and rocket launches. Originally, this S-band radar had a range of only 60 miles. Modified for use on the High Range, the range of the radar was basically limited by the strength of the transponder on the target aircraft and the curvature of the earth. During a tracking mission, the target cursor on the radar scope would travel to the end of the base line of the scope every 60-miles at which time it would disappear for a moment and then reappear at the beginning of the base line. The wiring was so old that the insulation would crumble off the wiring at the least disturbance. Often the scope would black out completely because of an intermittent wiring problem. Illumination could usually be regained by the operator banging on the chassis with the palm of his hand. During an overhead track, the Mod II elevated until it hit a stop, at which time the radar had to slew 160 degrees and then resume track. This was a particularly stressful moment at the Beatty site as the X-15 would be passing almost directly overhead at a Mach-6 speed. The range and elevation indicator dials would be spinning too fast to read. If for some reason the radar failed to regain auto track, the X-15 would be in its landing maneuver at Edwards AFB before the Beatty radar operator could physically align the radar on the plane to resume track. It is a credit to North American for its production of a superb aircraft, and to NASA, its High Range personnel and contractor support personnel that the X-15 program paved the way for space exploration and in the process produced several of the first United States astronauts as the X-15 surpassed 50 miles altitude during a mission. The X-15 was flown over a period of nearly 10 years -- June 1959 to Oct. 1968 -- and set the world's unofficial speed and altitude records of 4,520 mph (Mach 6.7) and 354,200 ft. DRYDEN/EDWARDS Click photos to enlarge. Place mouse over photo to see its caption.

BEATTY, NEVADA

ELY, NEVADA

Ely High Range Tracking during winter - 12/30/61, NASA DFRC

The X-15 flew to an altitude of 354,000 feet and reached a Mach number of 6.70. It flew its last flight over thirty years ago, but to this day, except for the Space Shuttle no aircraft has flown half as high nor half as fast. The late Dr. Hugh L. Dryden termed it "the most successful research airplane in history."

The X-15's beginnings were in 1952. It was the year of the first flight of the YB-52, and the aeronautical community was struggling to advance aircraft speeds from Mach 1.5 to Mach 2. Men of vision, however, already were looking to the higher speeds and altitudes that would eventually take us to orbital flight. For it was that year that the NACA Committee on Aeronautics recommended an increase in research dealing with flight to speeds of Mach 10 or 12 and to altitudes from 12 to 50 miles.

In 1954, NACA submitted to the Air Force-Navy-NACA research airplane program a technical proposal for a hypersonic research airplane. The plan was accepted and in December 1954, the Air Force issued invitations to industry for the design and manufacture of a hypersonic research airplane. Several contractors submitted proposals with maximum speeds in the Mach 6 to Mach 7 range.

The ultimate winner of the contract was North American Aviation, and the result was the X-15. The X-15 program called for the production of three aircraft designed for a speed of Mach 6.6 and an altitude of 250,000 feet. The Mach 6.6 represented the maximum speed that state of the art structures could support; the 250,000 foot altitude was an arbitrary design point which would force adequate attention to exo-atmospheric control and to reentry techniques.

The X-15 was 50 feet long and had a wingspan of 22 feet. It (SLIDE 3) weighed 33,000 pounds at launch and 15,000 pounds empty. Its flight control surfaces were hydraulically actuated and included all-moveable elevators, all-moveable upper and lower rudders (the lower rudder extended below the landing gear; it had to be jettisoned before landing), speed brakes on the aft end of the fixed portion of the vertical fins, and landing flaps on the trailing edge of the wing. There were no ailerons; roll control was achieved by differential deflection of the horizontal tail.

All three X-15's were delivered with simple rate-feedback damping in all axes. The number three X-15, however, was extensively damaged during a ground engine run before it ever flew; when it was rebuilt it was fitted with a self-adaptive flight control system which included command augmentation, self-adaptive damper gains, several autopilot modes, and blended aerodynamic and ballistic controls.

Two other steam turbines, called auxiliary power units, each furnished hydraulic pressure and the electrical power for the X-15. Their propellant also was decomposed hydrogen peroxide. Liquid nitrogen was used for cooling the payload bay, cockpit, windshields, and nose. Steam rockets in the nose and wings provided altitude control when out of the atmosphere.

The X-15 had three flight controllers. The center stick provided conventional pitch and roll control, and was intended for use after engine burnout. Mechanically linked to the center stick was a right hand controller used during the boost. When the pilot was using the side controller, the back of his right elbow was braced to not allow aft movement; this prevented the mass of the pilot's forearm and hand from causing spurious pitch inputs in the acceleration field existing during boost. On the left side of the cockpit was a three-axis ballistic controller, which was mechanically linked to steam rockets in the nose and wings.

On the instrument panel was an attitude indicator whose source was inertially derived. Also provided were inertial velocity, altitude, and rate-of-climb. Barometric instruments included an altimeter and a combined Mach-airspeed indicator; these instruments were usable only below about 75,000 feet and were used mainly in the traffic pattern. An angle of attack and a sideslip indicator were provided; the source of these two instruments was selectable, inertial for high altitude flight and barometric for the end of the mission.

The X-15 was actually the second stage of a two-stage system. The first stage was a B-52 bomber, specially modified for the program, which carried the X-15 uprange into Nevada, pointed it towards Edwards, and launched it at 45,000 feet and 0.8 Mach number.

The X-15 was usually launched about 200 miles from Edwards. The engine was lit immediately after launch and burned for about 85 seconds. During that period, it would boost the X-15 to an altitude of 160,000 feel and a Mach Number of 5.4. The X-15 would then coast to 250,000 feet, reenter, and glide to a landing on the dry lake at Edwards. A typical X-15 flight lasted eleven minutes, including about four minutes in the traffic pattern.

The X-15 first flew on June 8, 1959, and within four years had completed all the objectives of the original research program. It reached a Mach number of 6.06, which due to weight growth was less than the Mach 6.6 design speed, but it also reached an altitude of 354,000 feet, some 40 percent higher than the program goal of 250,000 feet. The altitude capability was made possible by the blended aerodynamic and reaction controls of the self-adaptive flight control system in the X-15 No. 3. (Only X-15 No. 3 flew significantly above 250,000 feet.)

Problems anticipated for the X-15 prior to the first flight.

The mechanics of atmospheric exit and entry were quite straightforward. The pilot flew a constant pitch altitude to engine burnout, then an angle of attack schedule---a low angle of attack to peak altitude, and a high angle of attack for reentry. Reentry angle of attack varied from 15 to 26 degrees, depending on peak altitude.

There were some aeromedical effects of interest during boost. One was the ability of the pilots to function in the acceleration during boost. After engine light, the pilot was under 2g chest-to-back acceleration which increased to about 4g at burnout. The pilots felt that four gs was about enough. Milt Thompson once stated that "the X-15 was the only aircraft I ever flew where I was glad when the engine quit. "

The fact that the X-15 pilots were willing to call 4gs of axial acceleration a limit when current-day fighter pilots fly and fight in much higher normal acceleration environments may have been due to another phenomenon concerning X-15 power-on flight----the phantom pitch rate perceived during the boost. In the absence of a horizon reference, the pilot tends to define "down" as the way acceleration is forcing him. When the X-15 pilot lost sight of the horizon during pullup, the acceleration along the flight path gave the pilot the sensation of pitching steeply up. As the acceleration increased during fuel burn, the pilot had the sensation that the X-15 was rotating even more steeply up. This was a fundamental sensory illusion; there was no cure for it. Strict reference to the flight instruments was required until engine shutdown to prevent the pitch rate illusion from ruining the flight profile.

Entry was a less-demanding pilot task. There was no acceleration due to thrust, and the horizon was in view throughout. At constant angle of attack, the normal acceleration gradually built up to 5gs and then was maintained there (usually for a period of about 15 seconds) until the X-15 had broken its fall. It might be noted that the X-15 pressure suit was equipped with an integral g suit.

Control Outside the Atmosphere There were no serious problems controlling the X-15 using the ballistic control rockets. Care had to be exercised to keep angular rates small, because the task could get confusing while attempting to control all three axes simultaneously. The main problem with ballistic flight was that the airplane was neutrally stable; the pilot was the only thing keeping the X-15 pointing down the flight path. X-15 No. 3 had aerodynamic and ballistic controls blended automatically through the autopilot, one of whose features was heading-hold mode; so that as far as the pilot was concerned, X-15 No. 3 was directionally stable while ballistic.

Control at Zero Gravity It turned out there were no control problems at zero gravity, nor were there any other problems related to weightlessness. There was no pilot nausea, as later occurred in the Apollo program. There was one humorous incident where the pilot hit the latch on his checklist binder while shutting down the engine; he thereby released 27 pages of checklist that floated around the cockpit for the two minutes before the weightlessness ended.

Aerodynamic and Structural Heating During the entire program, the X-15s were exposed to surface temperatures as high as 1350 degrees F and all the airplanes exhibited minor buckling of the exterior skin. During the rocket boost phase of the flight, when the aircraft was accelerating and heating rapidly, the pilot could hear this skin buckling. As Joe Walker observed, "The airplane crackled like a hot stove."

The leading edges of the wing were formed in several pieces and had small slots between segments to allow thermal growth. These slots tripped the boundary layer and caused high temperature and skin buckling downstream of the slots. The slots were eventually capped and an additional rivet was added behind the slot, curing the problem.

On two occasions the right outside windowpane crazed forcing the pilot to fly and land with only left-hand vision. Buckling of the window frame caused this crazing. The Inconel frame was replaced by one of titanium, which has a lesser thermal expansion and which prevented further recurrences of window crazing

Simulation: For planning X-15 flights and for pilot practice, extensive use was made of a fixed base analog simulator. Every flight was preceded by ten or twenty hours of simulation of normal and emergency procedures.

The simulator had to be continually updated with data gathered in flight. For example, early simulation based on wind tunnel data indicated that the X-15 would be flyable with the lower rudder turned on and the roll damper turned off. Flight test proved this not to be the case. When the roll damper was turned off, a test also revealed that the lower rudder was not required for directional stability. The lower rudder was discarded, the X-15 then became stable even with a roll damper failure, and the simulator was updated to reflect the actual aircraft characteristics.

Landing Prior to the X-15 flight program there was considerable reservation about the pilots' ability to consistently land a power-off, low lift-drag ratio airplane. The X-15, however, had good handling qualities and large variable deflection speed brakes and it proved easy to land. All the pilots used a circling approach that was commenced at 30,000 to 50,000 feet above the runway and they stayed high on profile until it was assured that they would reach the runway, at which time speed brakes were used to descend onto a nominal glideslope. The landing gear was left retracted, for drag reduction, until the landing flare was complete and the aircraft was in level flight.   Three X-15s made 199 flights during a research program which lasted from 1960 through 1968. It was a daring, yet highly successful program that resulted in hundreds of technical reports. It made contributions to the NASA space program of the 1960s and also on the design and flight of the Space Shuttle many years later.   An unofficial motto of flight research in the 1940s and 1950s was "higher and faster." By the late 1950s the last frontier of that goal was hypersonic flight (Mach 5+) to the edge of space. It would require a huge leap in aeronautical technology, life support systems and flight planning. The North American X-15 rocket plane was built to meet that challenge. It was designed to fly at speeds up to Mach 6, and altitudes up to 250,000 ft. The aircraft went on to reach a maximum speed of Mach 6.7 and a maximum altitude of 354,200 ft. Looking at it another way, Mach 6 is about one mile per second, and flight above 265,000 ft. qualifies an Air Force pilot for astronaut wings.   The X-15 was a rocket-powered aircraft 50 ft long with a wingspan of 22 ft. It was a missile-shaped vehicle with an unusual wedge-shaped vertical tail, thin stubby wings, and unique side fairings that extended along the side of the fuselage. The X-15 weighed about 14,000 lb empty and approximately 34,000 lb at launch. The XLR-99 rocket engine, manufactured by Thiokol Chemical Corp., was pilot controlled and was capable of developing 57,000 lb of thrust. North American Aviation built three X-15 aircraft for the program.   The X-15 research aircraft was developed to provide in-flight information and data on aerodynamics, structures, flight controls, and the physiological aspects of high-speed, high-altitude flight. A follow-on program used the aircraft as a testbed to carry various scientific experiments beyond the Earth's atmosphere on a repeated basis.   For flight in the dense air of the usable atmosphere, the X-15 used conventional aerodynamic controls such as rudders on the vertical stabilizers to control yaw and movable horizontal stabilizers to control pitch when moving in synchronization or roll when moved differentially.   For flight in the thin air outside of the appreciable Earth's atmosphere, the X-15 used a reaction control system. Hydrogen peroxide thrust rockets located on the nose of the aircraft provided pitch and yaw control. Those on the wings controlled roll.   Because of the large fuel consumption, the X-15 was air launched from a B-52 aircraft at 45,000 ft and a speed of about 500 mph. Depending on the mission, the rocket engine provided thrust for the first 80 to 120 sec of flight. The remainder of the normal 10 to 11 min. flight was powerless and ended with a 200-mph glide landing.   Generally, one of two types of X-15 flight profiles was used; a high-altitude flight plan that called for the pilot to maintain a steep rate of climb, or a speed profile that called for the pilot to push over and maintain a level altitude.   The plane was air launched by NASA's converted B-52 at 45,000 feet and a speed of 500 mph. Generally there were two types of flight profiles: high-speed, or high-altitude. High-speed flights were usually done below an altitude of 100,000 feet and flown as a conventional airplane using aerodynamic controls. High-altitude flights began with a steep, full-power climb to leave the atmosphere, followed by up to two minutes of "coasting up" to the peak altitude after the engine was shut down. "Weightless" flight would last for 2 - 5 minutes as it made a ballistic arc before reentering the atmosphere. A reaction control system was used to maintain attitude above the atmosphere. The reaction controls employed hydrogen peroxide thrusters located on the nose and wings.   Depending on the mission, the rocket engine provided thrust for the first 80 to 120 seconds of flight. The remainder of the normal 8- to 12-minute flight was without power and ended in a 200-mph glide landing. Because the nose landing wheel lacked steering and the main landing gear employed skids, the X-15 had to land on a dry lakebed. The Rogers Dry Lake adjacent to Edwards and Dryden was the intended landing location for all flights, but there were numerous emergency lakebeds selected in advance for emergency landings.   The X-15 program made many accomplishments, here is list of some of its contributions to space flight:   First application of hypersonic theory and wind tunnel work to an actual flight vehicle.  First use of reaction controls for attitude control in space.  First reusable super alloy structure capable of withstanding the temperatures and thermal gradients of hypersonic reentry.  Development of [a servo-actuated ball] nose flow direction sensor for operation over an extreme range of dynamic pressure and a stagnation air temperature of 1,900 degrees Fahrenheit [for accurate measurement of air speed and flow angle at supersonic and hypersonic speeds].  Development of the first practical full pressure suit for pilot protection in space.  Development of inertial flight data systems capable of functioning in a high dynamic pressure and space environment.  Discovery that hypersonic boundary layer flow is turbulent and not laminar. Discovery that turbulent heating rates are significantly lower than had been predicted by theory.  First direct measurement of hypersonic skin friction and discovery that skin friction is lower than had been predicted.  Discovery of hot spots generated by surface irregularities. [These last 4 discoveries led to improved design tools for future hypersonic vehicles, including the Space Shuttle.]  Discovery of methods to correlate base drag measurements with tunnel test results so as to correct wind tunnel data [and thereby improve design criteria for future air- and spacecraft].
First application of energy-management techniques [for the positioning of the vehicle for landing; these were essential for the landing of the Space Shuttle and all future reusable launch vehicles following their reentry from space.] Use of the three X-15 aircraft as testbeds carrying a wide variety of experimental packages.
More intangibly but no less importantly, in the words of the distinguished Langley aeronautical researcher John Becker, who had been an early advocate of the X-15 program, the X-15 project led to "the acquisition of new manned [today, we would say piloted] aerospace flight 'know how' by many teams in government and industry. They had to learn to work together, face up to unprecedented problems, develop solutions, and make this first manned aerospace project work. These teams were an important national asset in the ensuing space programs."   The X-15 was flown over a period of nearly 10 years -- June 1959 to Oct. 1968 -- and set the world's unofficial speed and altitude records of 4,520 mph (Mach 6.7) and 354,200 ft in a program to investigate all aspects of piloted hypersonic flight. Information gained from the highly successful X-15 program contributed to the development of the Mercury, Gemini, and Apollo piloted spaceflight programs, and also the Space Shuttle program.   The North American Aviation X-15s made a total of 199 flights. There were 196 successful landings in the program, and the two landing accidents that occurred were related to system or structural failures and not to pilot error.   X-15-1, serial number 56-6670, is now located at the National Air and Space Museum, Washington DC.   North American X-15A-2, serial number 56-6671, is at the United States Air Force Museum, Wright-Patterson AFB, Ohio. X-15-3, serial number 56-6672, crashed on 15 November 1967, resulting in the death of Maj. Michael J. Adams. Parts of the X-15-3 are on display at the Air Force Flight Test Center Museum at Edwards AFB, and the San Diego Aerospace Museum, San Diego, California.   --------------------------------------------------------------------------------
The X-15 program made many accomplishments, some of which include: First use of a full-pressure suit for spaceflight. First use of reaction controls for maneuvering in space. First use of a flight control system that automatically blended aerodynamic and reaction controls. Development of thermal protection for hypersonic reentry. Development of the first large, restartable, and throttleable rocket engine.Development of inertial flight data systems capable of functioning in a high-dynamic-pressure and space environment. Demonstration of a pilot's ability to operate in "micro-gravity". Demonstration of the first piloted reentry-to-landing from space. Acquisition of hypersonic acoustic measurements, which influenced structural design criteria for Mercury capsule. Verification of the validity of hypersonic wind tunnel data, which were later used in the design of the Space Shuttle.
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X-15 Flight Summary X-15 Pilots in chronological order with total flights: A. Scott Crossfield, NAA, 14 Joseph A. Walker, NASA, 25 Robert M. White, USAF, 16 Forrest S. Petersen, USN, 5 John B. "Jack" McKay, NASA, 29 Robert A. Rushworth, USAF, 34 Neil A. Armstrong, NASA, 7 Joe H. Engle, USAF, 16 Milton O. Thompson, NASA, 14 William J. "Pete" Knight, USAF, 16 William H. Dana, NASA, 16 Michael J. Adams, USAF, 7
Fastest speed (basic aircraft) was 4,104 mph (Mach 6.06) on flight 1-30-51 with pilot Joe Walker.
Fastest speed with tanks was 4,520 mph (Mach 6.70) on flight 2-53-97 with pilot William Knight.Highest altitude was 354,200 ft (67 miles) on flight 3-22-36 with Joseph Walker.Total flight time was 30 hr, 13 min. and 49.2 sec.Total distance flown was 41,763.8 miles (statute).Total flights of the X-15 was 199 between 1959 and 1968. Hours above Mach (Cumulative): Mach 1 - 18 hr, 23 min. and 11.6 sec Mach 2 - 12 hr, 13 min., and 50 sec Mach 3 - 8 hr, 51 min., and 12.8 sec Mach 4 - 5 hr, 57 min., and 23.8 sec Mach 5 - 1 hr, 27 min., and 15.8 sec Mach 6 - 1 min. and 16.8 sec

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