Launch Vehicles Then and Now: 50 Years of Evolution
Launch Vehicles Then and Now: 50 Years of Evolution
The launch industry has come a long way from the risk-filled early forays into space to the well-orchestrated launches of today—and Aerospace has been there, every step of the way.
Randy Kendall and Pete Portanova
Early launch systems were far from reliable, but by 1960, the nation was hurriedly working to send an astronaut into space—along with a host of national security payloads—to overcome the Soviet Union’s early lead in space technology. In such an environment, The Aerospace Corporation was founded. Among its core responsibilities was the conversion of ballistic missiles into space launch vehicles. Since that time, the corporation has fulfilled a vital role in supporting Department of Defense (DOD) launches and has also played a significant role in numerous NASA launches. Today, Aerospace is widely recognized for its expertise in launch systems, not to mention its comprehensive archive of historical launch data going back to the earliest launch vehicles.
Atlas, Delta, Titan—The Early Years
The Atlas Intercontinental Ballistic Missile (ICBM), a system with roots in the World War II German V-2 rocket, developed rapidly during the early years of the Cold War. Having a quick response with about 30 minutes to target, the Atlas ICBM stood ready to defend the United States against a Soviet nuclear attack until April 1966, when the last missile was retired. Some were destroyed, while others were refurbished for future space missions. The Atlas D launch vehicle, derived from the Atlas ICBM, became operational in mid-1959. It carried John Glenn on his first orbital flight in 1962 as part of the Mercury-Atlas Program. The Atlas E launch vehicle remained operational through 1995. Subsequently, the Atlas evolved into the Atlas II/III, and in the late 1990s became part of the Atlas V family of evolved expendable launch vehicles (EELVs).
The Thor Intermediate-Range Ballistic Missile (IRBM), another early ballistic weapon system, used the Navaho booster engine for the Thor main engine, also adapted from the V-2 rocket. At the same time that the first Atlas ICBM became operational in mid-1959, the first squadron of Thor IRBMs became operational and were deployed to the Royal Air Force at Feltwell in eastern England. By 1963, the Thor IRBM became obsolete. By then, Thor was already being modified and converted to a space launch vehicle. During the 1960s, the modified Thor had a variety of upper stages: Thor/Able, Thor/Able Star, and Thor/Agena, which launched Corona satellites from Vandenberg Air Force Base, California, from 1959 through 1963. Thor/Delta became the Delta II series. This evolution culminated in the late 1990s as the Delta II evolved into the Delta III and then into the Delta IV family of EELVs.
When Aerospace was formed, the first Titan series of missiles were also being developed, using an airframe design completely different from that of Atlas. The thin-skinned Atlas design could support only a limited weight, severely restricting the second-stage performance. Studies performed by various contractors concluded that a two-stage ICBM was feasible, and the Titan I ICBM was deployed in 1962. Titan II development began at the same time. It was a second-generation liquid-propellant ICBM, and it used a different propellant combination than the Thor, Atlas, and Titan I, which used a combination of liquid oxygen and high-purity rocket propellant (RP)-1 kerosene. The Titan II ICBM used storable propellants (nitrogen tetroxide and aerozine-50), yielding a large increase in payload capacity compared with Thor, Atlas, and Titan I. The Titan II ICBM was operational from 1963 to 1987.
Launch Vehicle Technologies
While the liquid-propellant Atlas, Titan, and Delta boosters were flying, solid fuel technology was progressing as well, starting with the Scout, America’s first solid-propellant launch vehicle (first launched in 1961), Polaris, and the Minuteman ICBM. This solid-propellant technology was used in conjunction with the liquid rockets for the Delta series, the Titan III/IV strap-on solids, and many other small launch vehicles and now provides increased performance to the Delta IV and Atlas V EELVs.
The Centaur was the first American high-energy, liquid-hydrogen/liquid-oxygen upper stage. Initially, Centaur was assigned only to the Atlas, but after 1974, it was also assigned to Titan IIIE and Titan IV missions. Propulsion system concepts and technologies from these vehicles contributed to the development of space shuttle main engines, which in turn eventually contributed to the development of the Delta IV rocket system (RS)-68 and upgraded RS-68A main engines.
|Early Launch Vehicles||Current Launch Vehicles|
|Comparison charts describing early and current launch vehicles including their performance, years flown, length, width, and weight.|
Titan III/IV Program
The family of Titan III space launch vehicles included a program spanning 49 years. Its conceptual phase began shortly after Aerospace was founded and attained operational status later in the 1960s. Titan III was a redesign of the Titan II core, with two solid rocket motors of five segments each, and a new Transtage upper stage, which used hypergolic propellants (which spontaneously ignite when they come in contact). This configuration had significantly greater payload capability than the Atlas, Thor, and Titan II.
The initial test flight of Titan IIIA took place from Cape Canaveral Air Force Station on September 1, 1964, with only the core and Transtage. The Titan III family had additional configurations such as IIIB, IIIC, IIID, IIIE, 34D. All but the Titan IIIB used solid motors from Minuteman technology. Titan IIIM, intended to launch the Manned Orbiting Laboratory (MOL), featured seven-segment solid motors. The MOL program was canceled in June 1969, so the Titan IIIM was never built; however, its seven-segment solids would later appear on the Titan IVA, significantly increasing its performance. In the 1970s, the Titan family increased with the Titan IIID launched from Space Launch Complex (SLC)-4E at Vandenberg and the Titan IIIE, which had two strap-on solid rocket motors but with a Centaur upper stage for NASA missions, launched from SLC-41 at the Cape. The Titan 34D was a common core booster that incorporated stretched stage-1 tanks of Titan 34B for increased performance. The solid rocket motor stage 0 (booster rockets used to assist in liftoff) increased to five-and-one-half segments to provide greater thrust.
Titan IV, the last member of the Titan family, consisted of three propulsion subsystems: two solid propellant strap-on boosters, a two-stage liquid core, and when applicable, an upper stage (Centaur or Inertial Upper Stage). By increasing stage-1 and stage-2 propellant tank length and upgrading the solid rocket motor, payload capability was again significantly increased.
The integrate-transfer-launch (ITL) complex, which includes SLC-40 and SLC-41, was built and activated at the Cape in the early 1960s for the Titan III and was a major advancement in launch processing efficiency. The major facilities were the vertical-integration building, which provided for assembly of the first- and second-stage core and systems checkout; the solid-motor-assembly building, where the two solid rocket motors were attached to the core and checked; and the railway system that connected the major buildings and allowed transfer of the core launch vehicle to the launchpads at SLC-40 and SLC-41. The two launchpads each had a fixed and mobile service tower for upper stage/payload mating, final checkout, propellant loading, countdown, and launch. The ITL concept allowed for more efficient use of facilities and greatly increased potential launch rates.
ITL and SLC-41 were later reconfigured for the Atlas V. During the design of EELV launch-processing facilities and ground systems, Aerospace was able to assist the contractors in avoiding many of the major design problems inherent in the heritage systems, improving the operating efficiency and affordability of both new systems. For example, the Atlas V launch vehicle is fully integrated and mated to the payload on a mobile launch platform in a vertical integration facility and ready for transport to the new SLC-41 “clean pad” via a railway system. It then may be launched within one day.
The clean pad has no fixed or mobile tower and is a significant improvement compared with the many weeks or months needed to prepare heritage launch vehicles on the pad. Basically, assembly of the launch vehicle can take place entirely at the vertical integration facility and then it can be moved, fully assembled, to the launchpad. The concept derives from preliminary studies conducted by Aerospace and contractors in the mid-1980s and early 1990s and is similar to systems used by both the Russian Zenit and the Ariane V launch systems. The benefits include the capability to launch multiple vehicle configurations (medium and heavy launch vehicles) from the same pad, reduce operation and maintenance costs, streamline launch operations, and ensure access to space.
EELV—The Culmination of 50 Years of Evolution
Genesis of EELV
EELV was the first family of launch vehicles initiated by the DOD for the primary mission of space launch. Prior to that, existing ballistic missile systems were adapted into space launch vehicles. However, the specific concept for this new space launch system took some time to define. During the 1980s and early 1990s, there was no consensus among the space community on a direction for the future of U.S. space launch capability. While U.S. space launch was struggling because of high launch costs and limited demand, the international community was developing its own launch capabilities that eventually would be significantly more price competitive than Titan and Delta systems (see sidebar, Market Forces).
The U.S. attempt to build consensus on the future of space launch led to a number of studies in the early 1990s, culminating in the 1994 Space Launch Modernization Plan, also known as the Moorman Study, led by then Lt. Gen. Thomas S. Moorman Jr., vice commander of Air Force Space Command (and later an Aerospace trustee). The study team recognized that the aging infrastructure and inefficiencies associated with the ICBM-derived launch vehicles were making the heritage Titan, Atlas, and Delta systems too expensive. The plan provided a range of options to reduce recurring costs while improving operational effectiveness. This study led to the National Space Transportation Policy, which directed DOD to evolve current expendable systems (and directed NASA to develop a new reusable system). The DOD response was the EELV program in 1995.
The main objective of the EELV program was to reduce the costs of space launch systems while maintaining comparable or better levels of performance and reliability. The idea was to eliminate the wide variety of specific expendable launch vehicles that had been developed over many years for various requirements (Titan II/IV, Atlas II/III, and Delta II). Instead, a single family of launch vehicles would be developed, based on a common core that would meet Air Force, National Reconnaissance Office, NASA, and commercial mission requirements. The resulting common systems and higher flight rates would facilitate reliability and make the EELV systems competitive in the commercial international space launch market. Unfortunately, the launch demand anticipated in the late 1990s never materialized, and while the program has been successful at meeting its performance and reliability goals, some of the operability goals have been cut to contain costs.
Launches in 1960
Launches in 2009
Aerospace and EELV
Although EELV started as an “acquisition reform” program, in which the government and Aerospace had only a limited role in the design and qualification processes, Aerospace was nonetheless a key partner helping the Air Force manage the program under this paradigm. Aerospace applied its resources to key roles in the early development, especially in systems requirements and standardization. Although evolution from heritage hardware was the focus, hardware commonality and standardization across the family of vehicles and missions was of paramount importance.
Aerospace played a large role in defining key performance parameters, which included standard payload interfaces, standardization of launchpads, mass-to-orbit performance, and vehicle design reliability. This Aerospace effort continued from conceptual and preliminary design through the critical design reviews of EELV families—Atlas V and Delta IV. In addition, Aerospace provided the key technical assessment to the Air Force in all source selections.
Following a string of three DOD and three commercial launch failures in 1998 and 1999, the Air Force called for a comprehensive review of the launch failures and their causes. This Broad Area Review recommended a series of changes to both heritage and EELV programs to reinstate more traditional, rigorous government oversight and mission assurance processes. Accordingly, Aerospace’s role in the EELV program has grown steadily over the last decade, to the point where it is similar today to what it was on the heritage Titan, Atlas, and Delta programs.
EELV—Two Families of Launch Vehicles
The Delta IV and Atlas V represent significant steps forward in simplicity of design, development, testing, and streamlined manufacturing and launch operations (see sidebar, The Clean Pad). Each family is based on a two-stage medium vehicle that can be augmented by solid rockets to increase payload capability. The Atlas V and Delta IV can support military, intelligence, civil, and commercial mission requirements. Both contractors have achieved significant reductions in personnel, facilities, and processing time
The Atlas V family of vehicles is built around a structurally stable common core booster, using the Russian-built RD-180 (liquid oxygen and kerosene) main engine with 860,000 pound-force sea level thrust—the only high-thrust staged combustion main engine currently in use in the United States—and the heritage Centaur upper stage/RL10A-4-2 engine. The Atlas V family consists of medium, intermediate, and heavy (designed but not built) vehicle configurations, and each includes a standard payload interface. As a family, they offer the flexibility to meet mass-to-orbit requirements for missions from low Earth orbit to geosynchronous transfer orbit. Furthermore, by adding up to five solid rocket motors, the Atlas V capability can be significantly increased in incremental steps.
The launch processing facilities have been reduced from 36 for Atlas II and Titan IV to three. The major difference is that the Cape’s SLC-41 is now a clean pad; Atlas V uses an integrate-transfer-launch concept for launch vehicle processing. A newly modified SLC-3E at Vandenberg uses more conventional integrate-on-pad procedures for Atlas V processing because of its lower launch rate. Between these two facilities, the Atlas V has been successful in launching its first 20 vehicles.
The Delta IV family of vehicles is built around a 5-meter-diameter common core booster, using the newly developed Rocketdyne RS-68 main engine and a modified Delta III upper stage powered by the cryogenic RL10B-2 engine. The RS-68 is a 663,000 pound-force, sea level thrust engine using cryogenic liquid-oxygen/liquid-hydrogen propellants in a gas generator cycle. Since 2005, an upgraded version has been in development to increase performance and will be designated RS-68A. The RS-68A is more than twice as powerful as the space shuttle main engine, with 705,250 pound-force sea level thrust.
The Delta IV core and upper stage are processed in a horizontal integration facility and then transported and erected at a pad with a conventional mobile service tower, at which point the payload is hoisted and mated and final launch preparations completed. The Delta IV launches from SLC-37B at the Cape and SLC-6 at Vandenberg. It, too, has a perfect string of 10 operational launches, although it should be noted that a major anomaly on the EELV heavy lift test vehicle demonstration launch could have caused a costly operational failure.
Throughout its 50-year history, Aerospace has played a key role in serving the Air Force and the nation in developing and operating numerous launch systems. Launch in 2010 is similar in many ways to launch in 1960—vertical liftoff, expendable systems, and relatively low flight rates; however, the SLC-41 clean pad concept revolutionizes the ability to launch satellites, and capability and reliability have improved dramatically. The future will most likely bring more changes to launch systems, but what will remain is Aerospace’s unwavering focus on mission success, helping to ensure access to space for national security.
The authors would like to thank Joe Tomei and Art Joslin for their contributions to this article.
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