Extreme Punchout: The Ejection Seat of the X-15

The hypersonic speed and extreme altitude performance of the North American X-15 demanded one of the most complex ejection seats ever put into service. Earlier NASA research rocket aircraft like the Douglas D-558-2 Skyrocket and the Bell X-2 featured ejectable nose sections that the pilot would then bail out of conventionally once it had separated from the aircraft and stabilized. However, the weight and volume restrictions on the X-15 made such a system impractical and North American in conjunction with engineer/test pilot A. Scott Crossfield, North American Aviation designer Jerry Madden and the David Clark Co. (who had long made pressure suits for the military and NASA) designed an integrated system that combined the pressure suit design along with an advanced ejection seat.

The X-15 ejection seat in the aircraft
(USAF Museum)

David Clark's MC-2 pressure suit was the key to making an open-faced ejection at high Mach and high altitudes possible. It not only protected the pilot from the extreme windblast of hitting the airstream at Mach 3+, it also functioned as a pressure suit to protect the X-15 pilot at altitudes in excess of 250,000 feet. Despite the advanced nature of the pressure suit, it was understood that kinetic heating during a high-Mach ejection would probably result in mild burns to the head, knees, and toes which in effect projected into the airstream.

Because the rocket motor of the X-15 ejection seat had to be powerful to propel the pilot clear of the X-15's hypersonic shockwave, a novel means was used to transfer loads from the pilot's rear end to the seat pan. Each X-15 program pilot sat on a weather balloon filled with plastic beads and wiggled into it like a bean bag. A vacuum was applied which held the shape of the balloon. Once the pilot stood up, plaster of Paris was poured into the depression, creating an exact copy of the pilot's rear end. A block of Balsa wood was then carved to precisely fit the mould and this became the seat cushion of the X-15's ejection seat- not only was it custom fit which allowed the optimum transfer of shock loads from the pilot's body to the seat pan, it also made for a very comfortable seat!

Scott Crossfield in the MC-2 pressure suit
(NASA/Dryden Flight Research Center)

To prevent the flailing of the arms and legs during a high-Mach ejection, special articulated restraints would protect the pilot's legs and feet (also acting as a windblast deflector to minimize heat burns on the feet) as well as to the arms and hands. The articulated arms deployed gauntlets to protect the pilot's hands from aerodynamic heating as well.

Once the articulated arms deployed into place, the emergency oxygen supply took over pressurization of the suit and a heating unit activated to keep the pilot's helmet visor clear of ice. Once the canopy was blown off and the seat traveled up the rails, special wings on the sides of the seat deployed to stabilize the seat in the high-Mach airstream. In a conventional ejection seat, a drogue chute would be deployed to slow the seat down but at the X-15's speeds, such a chute would have melted instantly, so the X-15's seat deployed a pair of telescopic booms that projected aft and outward from the bottom of the seat to provide aerodynamic braking and helped the wings stabilize the seat.

Rocket sled test of the X-15 seat- note the deployed booms
(Boeing)

If ejection took place over 15,000 feet, a built-in barostat kept the pilot attached to the seat which allowed use of the seat's emergency oxygen supply. Once 15,000 feet was reached, the seat automatically released the pilot and activated his parachute. If ejection took place below 15,000 feet, a three second timer allowed the wings and drogue booms to deploy and stabilized the seat before separating from the pilot.

One little-known fact was that the X-15 cockpit was pressurized with nitrogen instead of oxygen as was used in the Mercury and Gemini spacecraft. The pilot breathed oxygen from the his suit which was only pressurized upon ejection. This meant the cockpit was fireproof, something that NASA tragically learned with the launch pad fire on Apollo 1.

The X-15s set an absolute speed record of Mach 6.7 and an absolute altitude record of 354,000 feet which qualified several of its program pilots for astronaut wings. Fortunately the ejection system was never needed and the one fatality, Michael Adams, occurred when his X-15 lost control and broke up on re-entry into the thicker levels of the atmosphere and the X-15's complex ejection system might not have saved him.

Interestingly, the David Clark MC-2 pressure suit served as the basis for the space suits for the Mercury and Gemini programs. The aluminized fabric exterior of the MC-2 suit carried over to the space programs and heavily influenced Hollywood cinematic depictions of space suits well into the 1970s.

Related reading: 

Lockheed's Contribution to the Space Shuttle Program
The Boeing 747 SCA Shuttle Carrier Aircraft
Flight Testing on the Cheap: The Groundbreaking M2F1 Lifting Body
How the Shuttle Orbiter Lost Its Jet Engines

Source: Eject!: The Complete History of U.S. Aircraft Escape Systems by Jim Tuttle. MBI Publishing, 2002, p136-143.

Martin, the Titan I, and the Titan II Ballistic Missiles

Titan I ICBM elevated out of its silo for laugh
(USAF Museum)

When George M. Bunker took over the reins of Martin Aircraft from Glenn Martin in 1952, Bunker wanted to diversify Martin which up to that point had produced only aircraft. With an able group of lead engineers that Glenn Martin had literally hand picked in the years prior to his retirement from his company, Bunker moved some of Martin's engineering and research efforts into the rocket and missile arena that bore first fruit with the Viking research rocket and the Vanguard light satellite launcher built for the Navy. While many in the growing rocket and missile division were focusing their efforts on the Vanguard program, it was Jess Sweetser, Martin's VP for Sales and Requirements, who pushed the company to bid for the second USAF ICBM contract. At the time, General Bernard Schriever was heading the Western Development Division (WDD) in Los Angeles which directed the ICBM effort that started off with the Atlas ICBM built by Convair. Schriever wanted a second ICBM system fielded as a backup to the Atlas and the WDD issued a requirement that spelled out the range, guidance and throw weight (the payload of the missile, which was the nuclear warhead). Left up to the contractors would be the missile configuration, liquid vs. solid propellants, staging and number of engines.

Sweetser got to know General Schriever so well they became golfing buddies* in their free time and as a result, he was able to anticipate the need for a second ICBM program from his conversations with the general. As a result, when the WDD issued the requirement, Martin's team of engineers was already doing preliminary work in addition to their work on the Vanguard launcher for the Navy. It became clear from further directions from the Western Development Division as well as the operator of the ICBMs, the Strategic Air Command, that not just a backup ICBM was wanted, but one that was a true alternative to the Atlas ICBM and if possible, more advanced. With both Boeing and Lockheed in the competition for the alternative ICBM contract, George Bunker split the rocket and missiles team into two parts- one group stayed on the East Coast and worked on the Vanguard launcher, the other group set up shop in Los Angeles next to the WDD to work on their ICBM design. Martin's design was based on work that had been already done for the Vanguard launcher- instead of the thin, pressurized balloon skin arrangement used on the Atlas, the Martin proposal used two liquid propellant stages made of a rigid framework of copper-aluminum alloy with the tank wall integral to the rocket walls for weight savings as had been done on the Vanguard. The first stage would use two powerful 150,000 lb thrust engines and the second stage used a single 80,000 lb thrust engine that would be ignited in zero-gravity in near-space, a first for such a large engine. The Vanguard had proved that near-space ignition of the second stage was possible, but this would be the first large-scale application. 

In addition, Martin's ICBM design would be modular, allowing the design to be enlarged over time for heavier payloads. The sweetener of the proposal that would win the USAF contract for Martin in December 1955 was the creation of an all-new development, testing, and production facility in one location at the base of the Rocky Mountains in Littleton, Colorado. This was chosen for two reasons- first, the valleys in some of the mountains could house engine test stands with the mountains acting as natural sound insulators for the surrounding area, and secondly, Martin pointed out that a mid-continent facility was furthest away from the coasts which could be vulnerable to Soviet submarine missile launches and bomber attacks. Ground was broken on the Littleton facility outside of Denver in February 1956 for the missile that the USAF christened the Titan. As a result of the USAF's requirement that everything that went into the Titan missile be thoroughly tested, the first facilities built were the test stands, some of which replicated full size launch pads were complete Titan missiles could be tested. 

Just three years after the start of construction on the facility itself, the first Titan I missile was flight tested from Cape Canaveral on 6 February 1959. The second, third, and fourth test flight were a success, unprecedented in a new rocket or missile program. The fifth and sixth flights were failures with explosions on the launch pad, but the seventh flight was a success and by 1960 Martin had 11 more successful Titan I test flights. Out of 18 test flights, only two Titan I test flights failed, a success rate that was stunning and groundbreaking given the technology of the time. 

Titan I 3x3 ICBM base layout
(USAF Museum)

The first Titan I silos were built in 1959 in the Lowry AFB gunnery range just east of Denver. The first Titan I ICBMs went on nuclear alert on schedule in August 1962 at Lowry AFB. As the Titan I used liquid oxygen as an oxidizer, the missiles were kept the silos until the launch order was given. At this point a massive elevator lifted the Titan I out its silo to an above ground position where it was fueled for launch. All of the necessary facilities were deep underground, even the propellant storage tanks. Each ICBM squadron had nine Titan Is in groups of three. Each group of three missiles were part of a single launch complex. Once the missiles were fueled, the radio guidance domes also were elevated from their own silos. The radio guidance system tracked the missiles after launch and fed the necessary course corrections, much like the guidance system used on the Atlas ICBMs. 

With advances in Soviet ICBMs, though, while the Titan I flight test program was taking place, Martin's engineers were already working on a successor, Titan II. Titan II had an even bigger warhead and the modularity of the Titan design paid off as the engineers merely had to fatten the second stage to the same diameter as the first stage and then lengthened both stages for a bigger missile. To replace the radio guidance system on the Titan I, AC Delco and MIT created a new inertial guidance system that set the standard for ICBMs. No longer would radio signals from the launch site be necessary, minimizing the Titan II's vulnerability to a counterstrike. The liquid oxygen was also replaced as the oxidizer and Titan II now had non-cryogenic storable liquid propellants- Aerozine-50, which was a mix of hydrazine and unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide as the oxidizer. As a result, no fueling process was needed. 

Titan II silo "hot launch"
(USAF Museum)

The simplification of the Titan II launch complexes compared to the Titan I was dramatic. Major underground structures dropped from 42 to just 18 structures, 6,000 feet of service tunnels were reduced to just 945 feet, the power requirements dropped from 12,000 kilowatts per squadron to just 2,700 kilowatts. Only half the wiring connections were needed and the need for periodic checkout of missile systems dropped by an astounding 90%.  As a result, the silos could be more widely dispersed. With a formal contract awarded in 1960, the Titan II flight test program went smoothly- of 33 test launches, 25 were successful- in fact, the last 13 test launches were so successful and reliable, the Titan II was selected by NASA to be the launcher for Project Gemini. 

With this reliability came the need to solve the basing issue. The Titan I was housed in silos, but it was lifted out of the silo for launch. Martin's engineers argued that it was possible to launch the Titan II right out of its silo, dramatically reducing its response time. Significant debate ensued about the feasibility let alone the safety of launching the 110-foot Titan II with its 430,000 lbs of first stage thrust right out of a silo. On 19 February 1963, a test Titan I was successfully launched from a Titan II test silo at Vandenberg AFB in California, validating the concept so clearly that the USAF had Boeing incorporate silo-launch on its Minuteman ICBM. The first Titan II missiles went on nuclear alert in 1963 just one year after the first Titan I missiles went on alert! 

The Titan I missile squadrons were operational from 1962 to 1965 at Lowry AFB in Colorado, Ellsworth AFB in South Dakota, Beale AFB in California, Larson AFB in Washington, and Mountain Home AFB in Idaho. Only Lowry AFB was home to two Titan I missile squadrons while the other bases only hosted a single squadrons. The Titan II missile squadrons were grouped three squadrons to a missile wing and were operational from 1963 to 1987 at McConnell AFB in Kansas, Little Rock AFB in Arkansas, and Davis-Monthan AFB in Arizona. The modularity of the Titan design, though, made it a versatile heavy-lift space launcher. Not only did the Titan II launch the manned Gemini missions, but it was also used as a satellite launcher until 2003. Titan III and Titan IV were exclusively space launchers, with the last Titan IV launch in 2005. In 1995, when Lockheed merged with Martin Marietta, the Colorado facility became part of the Lockheed Space and Missiles Division. Since the retirement of the Titan IV launcher, the Littleton facility is now the headquarters of United Launch Alliance, the joint venture of Lockheed Martin and Boeing for the Delta and Atlas launch vehicles. Although no production takes place there any longer, ULA still has its mission control, testing and engineering facilities at the same location that was the birthplace of the Titan missile when ground was broken over fifty years ago.

Historical tangent: 

I had mentioned above how Martin Aircraft's VP for Sales and Requirements Jess Sweetser, had become a golfing buddy of USAF General Bernard Schriever. Before he came to work for Martin Aircraft, Jess Sweetser was a championship golfer in the 1920s. While a student at Yale, Sweetser had won the National Intercollegiate Championship in 1920, placed 11th at the US Open the following year despite his youth, and won the Metropolitan Championship  in 1922 in his junior year at Yale. He then won the US Amateur Championship that same year and then became the first American to win the British Amateur Championship in 1926 despite having the flu. He played on the first Walker Cup team (a trophy for amateur golfers in the United States, Great Britain and Ireland) in 1922 and five more teams in years following. After graduation from Yale, he worked as a stockbroker and played golf on weekends. His first job in aviation was with Curtiss-Wright before he came to Martin Aircraft. 

Source: Raise Heaven and Earth: The Story of Martin Marietta People and Their Pioneering Achievements by William B. Harwood. Simon and Schuster, 1993, p299-325