(U.S. Air Force)

Epic Proportions: The Titan Launch Vehicle

Art Falconer

For decades, Titan boosters have provided unflagging medium and heavy launch capacity for critical military payloads.

The history of the Titan space launch vehicle covers more than 40 years and has its roots in the early age of space rocketry. From its earliest role as an ICBM, the Titan has evolved through dozens of configurations to serve diverse military and scientific missions. With more than 360 launches to its name, the Titan has deservedly earned a reputation as the workhorse of the U.S. fleet of expendable launch vehicles. Aerospace personnel count among the thousands of dedicated individuals who share credit for the Titan's remarkable long-term success.

The Early Impetus

The Titan II ICBM was first converted into a space launch vehicle to support the Gemini program (see "A Stellar Rendezvous"). At about the same time, the Air Force asked the newly formed Aerospace Corporation to evaluate two proposals for launching a piloted orbital glider. The first involved a new vehicle using a solid-motor first stage with a liquid-powered second stage; the second was the liquid-powered two-stage Titan II, modified by adding strap-on solid motors for the initial stage. The Titan II approach won out, and the booster was renamed Titan III. The Air Force established a system program office in November 1961.

Although the Air Force had not identified any payloads for the Titan III other than the orbital glider (which was canceled before final testing), it became clear that future payloads would cover a spectrum of space needs: reconnaissance, communications, military orbital development systems, satellite inspection and interception, surveillance and early warning, and nuclear test detection. A modular approach to the Titan III would accommodate this variety quite well. Indeed, the early Titan III concept would permit at least four configurations: the two-stage core vehicle, the core vehicle with a final upper stage, the core with solid-rocket boosters for an initial stage, and the core with solid boosters and an upper stage.

The first Titan IIIC was launched on June 18, 1965. This was the first Air Force vehicle specifically designed and developed as a military space booster. Using two strap-on, five-segment solid-rocket motors, this vehicle was capable of placing a 1450-kilogram payload into a geosynchronous equatorial orbit. Several of the Titan IIIC flights involved multiple-payload missions with four to eight spacecraft. (U.S. Air Force)

The Air Force hoped to achieve first flight of the standard two-stage core vehicle by mid-1963 and a flight of the core with solid-rocket motors by mid-1964. Ultimately, these goals proved unreasonable, but they served to expedite the project startup. Five major "associate contractors" were selected, including Aerospace, which was responsible for general systems engineering and technical direction. The "associate" concept was a departure from the usual "prime contractor" concept and placed considerably more burden on the Air Force. Aerospace was centrally involved in the development of the Titan III vehicle and a new launch-site processing concept called "Integrate, Transfer, and Launch." This revolutionary concept was driven by the configuration variability of the vehicle and the predicted launch rates as high as 60 per year (see "A Complete Range of Launch Activities").

The ABCs of Titan III

The first of the Titan III variants—Titan IIIA—consisted of the Titan II core vehicle strengthened to incorporate a third stage (known as the Transtage). The maiden flight in September 1964 failed when the Transtage pressurization system malfunctioned and the engine shut down prematurely. Three subsequent test flights were successful, the last in May 1965.

The next Titan III to reach orbit—Titan IIIC—was the first version to use solid-rocket motors to boost the performance of the liquid-fueled core vehicle. The solid-rocket motors were the first to use the stacked-segments concept. Aerospace assisted their development and qualification. The five-segment solid motors were ignited for liftoff and propelled the vehicle through "stage zero" of the flight before the stage-one liquid-fueled engines kicked in, at which point the solids were cast off. This configuration could deliver a payload to a geostationary orbit. Ultimately, 36 Titan IIICs were launched from Cape Canaveral, the first in June 1965 and the last in March 1982. The payloads were almost exclusively military. Five of these missions failed, but three of those failures occurred during the initial eight-vehicle development phase of Titan IIIC.

The Titan II still provides medium launch capability for military payloads. Shown here, a Titan II lifts off from Vandenberg with a Defense Meteorological Satellite Program payload. (U.S. Air Force)

In 1965, the Air Force directed its space efforts toward the Manned Orbiting Laboratory (MOL), a massive structure that would require something larger than a Titan IIIC to reach orbit. The resulting design—Titan IIIM—represented a substantial change from the Titan IIIC. Almost every system was modified or redesigned to meet the increased performance and safety requirements. This included lengthening the first stage, upgrading the liquid-rocket engines and their propellant-feed systems, developing a seven-segment solid-rocket motor, upgrading the avionics, and installing a new ground checkout system. Titan IIIM development continued for several years, successfully getting through ground tests of the new engines and seven-segment solid-rocket motors; however, MOL was cancelled in 1969 before any Titan IIIMs were produced. Nonetheless, even though Titan IIIM never got to the launchpad, its development became the foundation for many improvements phased into future Titan configurations.

Following Titan IIIC into space was Titan IIIB, which looked very similar to Titan IIIA but used an Agena instead of a Transtage upper stage. Of the 57 Titan IIIBs launched from Vandenberg between 1966 and 1983, 56 were successful. Yet another variation—Titan 34B—used an elongated first stage and Agena upper stage in a 3-meter fairing. The 34B achieved 11 of 11 successful launches from Vandenberg between 1975 and 1987. Typically, the Titan IIIB and 34B carried satellites into polar near-Earth orbits.

The Titan IIID—created to deliver even heavier reconnaissance satellites—had the Titan IIIC core and five-segment solid-rocket motors, but without the Transtage. Of the 22 Titan IIIDs launched between 1971 and the early 1980s, all were successful.

In a departure from the usual Air Force operations, NASA had system responsibility for the Titan IIIE. By adding a Centaur upper stage to the Titan IIID and developing a larger, 4.3-meter-diameter payload fairing, NASA was able to use the rocket for planetary exploration. The first launch took place in 1974. Although it flew only seven times, the Titan IIIE made a significant contribution to planetary science, sending the Viking probes to Mars and the Voyager space vessels to the far reaches of the solar system.

The first Titan IIID prior to its launch on June 15, 1971, from Vandenberg Air Force Base in California. All 22 Titan IIIDs launched between 1971 and the early 1980s were successful. (U.S. Air Force)

In the late 1970s, the Air Force ordered yet another class of Titan III vehicles. This version, called Titan 34D, was to provide launch services for military payloads until the space shuttle became fully operational. The initial order was for seven, but as shuttle schedules slipped, eight more had to be built for payloads that couldn't wait. Titan 34D employed the high-performance 34B core but with new five-and-one-half- segment solid-rocket motors strapped to each side. Extremely versatile, the Titan 34D could accommodate three different upper stages—the Transtage, the Agena (although the Agena never flew on a Titan 34D), and the Inertial Upper Stage (IUS). Although Titan 34D provided a bridge to the shuttle era as intended, it had its share of setbacks. Three of the 15 missions ended in failure. Nevertheless, Titan 34D was considered the military powerhouse of the 1980s.

Critical Responsibility

Aerospace's role as associate contractor during the early years of the Titan III program was quite different from its role today. In addition to general systems engineering responsibility, Aerospace had technical direction authority—meaning it could issue directives, approved by the Air Force, to the other associate contractors regarding design, construction, testing, and launch. This authority was generally not exercised because a collaborative team approach became the mode of operation.

In addition to contractor oversight, Aerospace had several inline functions, including independent verification and validation of guidance software and vehicle loads, writing the guidance steering equations, developing mission specifications, and "pedigree review" of all critical flight hardware. Aerospace also had technical responsibility for all government-furnished equipment—such as the command-control receivers required by range safety.

The Aerospace contribution to postflight reconstruction of flight data was particularly noteworthy. The contractor's initial analytical approach was very simple and risked missing potentially important indicators of performance. Aerospace devised a much more sophisticated model using all significant flight parameters. This model identified several critical performance deficiencies, such as reduced specific impulse of the propulsion systems, incorrect payload weight, and a bias in the solid-rocket motors.

The first Titan 34D launching two DSCS II satellites from Cape Canaveral on October 30, 1982. The 34D was a "stretched" version of the 34B core vehicle and incorporated two five-and-one-half-segment solid-rocket motors. This vehicle was used with several upper stages, payload fairings, and guidance configurations.(U.S. Air Force)

Similarly, Aerospace was intimately involved in all phases of testing, from development through qualification, hardware acceptance, and systems checkout. In addition to developing test requirements, Aerospace witnessed and supported much of the development and qualification testing. All test failures were assessed by Aerospace engineers, who would typically work concurrently with the contractors to analyze failures and formulate corrective actions and recovery plans.

During these years, Aerospace was developing the analytical methodologies, tools, models, and databases it would need to provide totally independent assessments of every technical aspect of Titan capabilities and performance. This foundation grew and improved as new technologies and requirements were introduced.

Rebirth of a Titan

By the mid-1980s, the Titan program seemed to be reaching the end of its useful service life. DOD was moving its payloads to the space shuttle manifest, and only about a dozen Titan missions remained. Still, some DOD decision makers questioned the wisdom of putting all their eggs in one basket, and sought some means to complement the space shuttle capability, at least in the short term. Thus, in 1985, the Air Force placed an order for 10 so-called complementary expendable launch vehicles, or CELVs. The name reflected their status as a supplement or backup to the space shuttle. Ten rockets represented a rather modest expansion by Titan standards, and so a "going out of business" mentality persisted among program managers. This was especially true in terms of Aerospace's involvement. Although Aerospace launch verification was to continue through the last Titan mission, Aerospace support for CELV was limited to source selection. After contract award, there were very limited plans to engage Aerospace further.

The Titan 34D provided the starting point for the CELV. The 3-meter-diameter propellant tanks were lengthened to hold more fuel, and this enhancement in turn drove more upgrades to the liquid engines to increase thrust and burn time. The 34D five-and-one-half-segment solid-rocket motors were replaced with seven-segment stacks, first proposed for the Titan IIIM years before. To be compatible with shuttle payload capacity, the Titan payload fairing was increased to 5.1 meters in diameter. The CELV would include a Centaur upper stage and launch exclusively from Cape Canaveral.

A Titan IVB blasts off with a Milstar communication satellite. The Titan IVB can boost payloads weighing 17,600 kilograms into a low Earth polar orbit, 21,680 kilograms into a low Earth equatorial orbit, or more than 5760 kilograms into a geosynchronous orbit. (U.S. Air Force)

With the loss of the Challenger in 1986, DOD payloads were taken off the space shuttle manifest. CELV was renamed Titan IV, and the 10-vehicle contract was expanded to 23. For a while, Titan IV became the sole heavy-lift launch vehicle for the military. With this expanded role came the need for increased versatility to meet a spectrum of different payload and mission-specific requirements.

Seemingly overnight, the Titan program shed its "going out of business" mentality and began expanding once again. The resurgence, coupled with concerns over two Titan 34D failures in 1985 and 1986, made it clear to the Air Force that Aerospace's expertise would be needed to recover from the failures and embark on development, acquisition, and operation of the new fleet. Accordingly, the Air Force contracted Aerospace for general systems engineering and integration support. Aerospace would provide fully independent launch verification for each Titan mission.

The basic configuration of the Titan IV comprised a common-core vehicle and solid-rocket motors; however, thanks to a modular approach, the basic model could be configured to accept either the IUS or Centaur upper stage for missions requiring delivery beyond low Earth orbit. The payload fairing would also be modular, and could be provided in lengths from roughly 17 to 26 meters. Launches could take place from Vandenberg as well as Cape Canaveral. Five basic Titan IV configurations were created: two with no upper stages for launching satellites into low Earth orbits from Vandenberg, and one with the Centaur, one with the IUS, and one with no upper stage for launches from Cape Canaveral. Lift capability grew to nearly 18,000 kilograms for a low-Earth orbit.

The first launch of Titan IV, later named Titan IVA, took place in June of 1989 from Cape Canaveral. Eventually, 22 Titan IVAs were launched, the last in August 1998. Only two of these missions failed.

At about the same time that Titan IV was initiated, the Air Force decided to convert a number of deactivated Titan II ICBMs for use as medium-lift space launch vehicles. From the fleet of 54 deactivated Titan IIs, 14 were modified to provide launch capability from Vandenberg into the polar orbit plane. Modification entailed removing the core vehicle's warhead interface and replacing it with a space payload interface and a 3-meter payload fairing. The electronics, avionics, and guidance systems were also upgraded using Titan III technology. An attitude-control system was added for stabilization during the coast phase after second-stage shutdown and before payload separation.

In April 1999, this Titan IVB launched a Defense Support Program missile-warning satellite from Cape Canaveral, Florida. Although the Titan performed successfully, the Inertial Upper Stage suffered an anomaly and failed to deliver the satellite correctly into orbit. (U.S. Air Force)

To date, 12 of 13 planned missions have been successfully completed. Payloads have included military reconnaissance and weather satellites as well as civil meteorological and imaging satellites. The success of the modified Titan II is especially remarkable considering its use of nearly 40-year-old hardware, designed to 1960s technology but still meeting modern needs for access to space.

The Final IV

Even before the first Titan IVA was launched, the Air Force wanted to upgrade its performance and reliability. Thus was born the final member of the Titan family, Titan IVB. Procurement began in 1989 with a contract for 28 vehicles (though only 17 were ever built). A new three-segment solid-rocket motor upgrade replaced the seven-segment units. This upgrade not only provided a 25-percent increase in payload capability, but yielded a more reliable stage-zero booster, thanks to the reduction in number of components and improvements in manufacturing and inspection techniques (see Composite Solid-Rocket Motor Cases). Extensive upgrades of Titan's electrical and guidance systems were implemented to replace obsolete technology and vintage parts that were growing increasingly difficult to procure. Production processes were redeveloped to employ a "factory-to-launch" approach. The goal was to deliver problem-free hardware requiring a minimal amount of assembly at the launch site. The manufacturing would be kept at the factory, and the launch site would only be used for the final stacking, checkout, countdown, and launch. Accordingly, the checkout equipment was modernized and automated to improve vehicle health checks during the final assembly and countdown.

The end result was the Titan IVB standing 61 meters tall, with a lift capability of 21,680 kilograms to low Earth orbit and 5760 kilograms to geosynchronous orbit. Its maiden launch in February 1997 used an IUS to deliver a payload for the Defense Support Program. Of the 12 Titan IVB launches so far, all but one (the 1997 Cassini mission to Saturn) carried critical military satellites. Of these 12 launches, 11 were successful. The sole failure, in April 1999, was followed by seven successes in a row. (Another anomalous mission in April 1999 was attributed to the IUS and is not counted as a Titan IVB failure.) Five Titan IVB missions remain, four from Cape Canaveral and one from Vandenberg, all with DOD or NRO payloads.

Aerospace functioned as a full partner with the Air Force and contractors in verifying that each Titan IV and modified Titan II was ready to launch with acceptable risk. Independent analyses and evaluations performed by Aerospace contributed to improved risk assessment and sometimes even failure avoidance. A good example was the evaluation of a proposed change to the Titan IV stage-two engine-nozzle skirt. The nozzle's ablative liner was made of asbestos phenolic impregnated with resin, and an alternate resin was being proposed. Aerospace became concerned about the thermostructural capability of the new skirt because of uncertainty regarding resin properties at high temperatures. These concerns were key in driving the need to demonstrate that the skirt was structurally sound under engine hot-fire conditions. The skirt failed the test and was declared unsuitable for flight. A new skirt using quartz phenolic in place of asbestos phenolic was next proposed. Aerospace was instrumental in developing the testing requirements to qualify the new design. Subsequent hot-fire tests proved its suitability.

In spite of the dedicated efforts by the contractors, Air Force, and Aerospace to verify that each launch vehicle was flight-worthy, Titan missions sometimes ended in failure. In these instances, Aerospace was always part of the return-to-flight process. For example, the first failure of a Titan IVA occurred in August 1993: About 100 seconds into flight, the casing of one of the solid-rocket motors burned through, and the vehicle was destroyed. Through extensive image analysis, graphical modeling, and analytical work, Aerospace identified a suspect segment of the solid-rocket motor. A subsequent search of build records showed that a defect may have been introduced by a procedural change many years earlier. A void in the restrictor bond required repair, which involved a knife cut from bore to case. Testing showed that undercutting into the propellant could result in flame propagation at motor ignition and burning at the wall until the thin insulation was reached. Aerospace performed grain analysis and assisted in testing that supported the theory. Segments with restrictor repairs were removed from the fleet, and all subsequent solid-rocket motors have been successful.

Aerospace was also involved in the analyses that followed two other Titan launch failures. In August 1998, a Titan IVA was destroyed when a radical steering maneuver forced the vehicle into an ascent position beyond its capabilities, leading to structural breakup. Months of investigation were required to determine the cause (most likely an electrical short in a wire harness in the second stage) and formulate a recovery plan. Aerospace handled many portions of the investigation solely and separately. Aerospace experts also assumed roles ranging from cochair of investigation panels to specific analysis or test tasking. The efficiency of this arrangement enabled a return to flight within eight months.

The second of these Titan IV failures, the Titan IVB in April 1999, was separated from the first by just one successful Titan IV flight. In this instance, the cause of the failure was actually known within minutes: An incorrect constant in the control-system software caused radical roll errors, eventually resulting in a loss of control during the Centaur upper-stage flight. The erroneous constant resulted from simple human error (a misplaced decimal point). There were indications of this error before flight, but initial concerns were not adequately pursued; Aerospace's traditional validation and verification role had been assigned to a subcontractor under the dictates of acquisition reform, so Aerospace was not required to check for such a transcription error. After the failure, the contractor, with Aerospace assistance, developed a process-proofing improvement plan that started with software but was ultimately applied to every critical analytical and test process employed on the Titan program. Aerospace also revisited its own software-validation process and developed improved processes to check mission software more rigorously. Thanks, in part, to these efforts, the basic Titans were returned to flight within a few weeks and the Centaur upper stage within a few months.

Assembly of the Titan IV core boosters. The manufacturing facility was built from scratch in 1956 and delivered the first Titan ICBM three years later. The last Titan core vehicle produced at this facility, a Titan IVB, was delivered in 2002. In total, 526 Titans were built—305 ICBMs and 221 space launch vehicles. Of these, 148 ICBMs were test-launched, and 214 space launch vehicles have been launched to date. (U.S. Air Force)

Titan in Reflection

By any standard, the Titan program has compiled a formidable track record, delivering into orbit hundreds of satellites that were ultimately able to perform their tasks as required. More than 360 Titans have been launched, with a total success rate of 86 percent. This figure is especially impressive because it includes the Titan ICBM (which did not need pinpoint accuracy to achieve effective deterrence). Without the ICBMs, the historical success rate jumps to 93 percent (see Titan Launch History Summary).

During every phase of the Titan's evolution, Aerospace was there to provide invaluable technical support. By virtue of its objectivity and independence, Aerospace could apply its unique strengths and technical competence in all areas of space systems engineering, design, computational modeling, and simulation to establish high confidence of mission success. The Titan's final launch in a few years will mark the close of a remarkable chapter in the history of rocketry and of Aerospace support for the nation's most venerable launch system.

Acknowledgement

The author would like to thank Aerospace retirees Don Moses and John Bauer for their assistance and guidance during the research and preparation of this article.

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