The Titan 4B rocket launches Tuesday with Milstar 6. Photo: Russ Underwood, Lockheed Martin Space Systems

The Air Force Titan 4B launch vehicle is the nation's largest, most powerful expendable space launch vehicle and provides access to space for the United States government's largest payloads. In 1989, a follow-on procurement to the existing Titan 4 space lift vehicle resulted in the Titan 4B model. The upgraded rocket incorporates significant technology advancements to decrease operational processing time and increase overall reliability. The Titan 4 is capable of placing 47,800 pounds into low-Earth orbit or more than 12,700 pounds into geosynchronous orbit - 22,300 miles above the Earth's equator.

The Titan 4B consists of two solid-propellant stage "0" motors, a liquid propellant two-stage core and a 16.7-foot-diameter payload fairing. Upgraded three-segment solid rocket motors increase the vehicle's payload capability by approximately 25 percent over the Titan 4A.

During a Titan 4 launch the strap-on solid rocket motors are fired first. When the solid propellant is almost depleted (approximately 130 seconds into flight), the first stage is fired and the solid motors are separated from the vehicle. The second stage and upper stage are fired as the previous stage is depleted of fuel and separated.

Heritage
The Titan family of launch vehicles was established in December 1955 when the Air Force awarded the Martin Company (today Lockheed Martin Astronautics) a contract to build an Inter-Continental Ballistic Missile that would be more advanced than the Atlas. It became known as the Titan 1, the nation's first two-stage ICBM. The Titan 1 rocket provided many structural and propulsion techniques that were later incorporated into the Titan 2 which became the first underground silo-based ICBM in 1964.

Martin Company and the Martin Marietta Corporation built more than 140 Titan ICBMs - the vanguard of America's nuclear deterrent force for 23 years. NASA selected the Titan 2 as a space launch vehicle for the Gemini manned space program in 1961. Deactivation of the Titan 2 ICBM system began in July 1982, and the last missile was taken from its silo at Little Rock Air Force Base, Arkansas, on June 23, 1987. The Titan 2 space launch vehicle that flew 12 Project Gemini missions evolved into the Titan 3 and Titan 3C in the mid 1960s. Titan 3s sent 82 military and civilian satellites into orbit between 1965 and 1982. Titan 3E rockets with Centaur upper stages carried Viking and Voyager missions into space. The larger Titan expendable space launch vehicle was originally developed as a backup for the space shuttle in the 1980s, but has become a mainstay for heavy payloads. The Titan 4B represents significant improvements from the Titan 34D and Titan 4A from which it evolved. The first Titan 4B flew February 23, 1997.

The Vehicle
The Titan 4B's launch vehicle core consists of an LR87-AJ-11 Stage 1 liquid-propellant rocket that features structurally independent tanks for its hypergolic fuel of Aerozine 50 (hydrazine and unsymmetrical dimethyl-hydrazine) and oxidizer (Nitrogen Tetroxide). This minimizes the hazard of the two mixing if a leak should develop in either tank. Additionally the engines' propellant can be stored in a launch-ready state for extended periods. The use of propellants stored at normal temperature and pressure eliminates delays and gives the Titan 4B the capability to meet critical launch windows. The second stage consists of an LR91-AJ-11 Stage 2 liquid propellant rocket engine attached to an airframe, like stage 1.

Operational Improvements
The Titan 4B uses a "clean vehicle" approach for delivering hardware to the launch sites. This method shifts production-oriented tasks, such as liquid rocket engine installation and electronic system installation, to the factory. When the rocket is shipped to the launch site it requires only check-out testing and a minimum of final processing.

Assembly and integration of the Solid Rocket Motor Upgrade occurs in the new Solid Motor Assembly and Readiness Facility at Cape Canaveral Air Station and the Solid Motor Processing Facility at Vandenberg Air Force Base, California. These facilities reduce workload from two shifts per day to a single shift and decrease Titan 4B booster overall processing time by 43 days at Cape Canaveral AS and 134 days at Vandenberg AFB.

Standard Vehicle Configuration
The Titan 4B common core design provides a standard mechanical and electrical configuration to the various upper stages and payloads. With this feature, all Titan 4B vehicles are identical up to the interface just below the payload fairing. The Titan 4B standard vehicle design allows hardware to be quickly reallocated to different missions as launch dates or national priorities are changed. It also eliminates the need for unique engineering and specialized processes for each individual core vehicle.

Solid Rocket Motor Upgrade (SRMU)
The new SRMU provides increased payload capacity and improved safety, reliability, and launch site operability, while reducing cost per pound of payload. The SRMU features a three-segment design. Light-weight graphite composite cases coupled with the use of high performance propellant results in a 25 percent increase in lift capability. The number of critical field joints has been reduced from eight on a Titan 4A to two on the Titan 4B, with each field joint having redundant seals. Five full-scale static test firings qualified the motor design in 1993.

Advanced Avionics
Obsolete technology and unprocurable hardware necessitated upgrades to the Titan 4's electrical systems. The new systems on the Titan 4B were designed to improve overall reliability and maintainability. Guidance system technology advancements include ring laser gyros and a new computer that doubles data processing capability. The system is packaged in a single guidance control unit which weighs 40 pounds less than its Titan 4A equivalent. By using modern parts and manufacturing techniques, the recurring cost of the guidance system has been decreased by more than 50 percent. A new data distribution and acquisition system provides higher data rates and more accurate telemetry for systems evaluation. The upgraded wide-band telemetry system has improved capability for additional launch vehicle and payload environment data.

Range Safety Improvements
The Titan 4B procurement also provided an opportunity to bring the Flight Termination System (FTS) into a configuration that meets the latest range safety requirements. The Titan 4B automatic and command destruct systems are completely redundant. The system was streamlined by combining multiple functions in a new flight termination controller.

Programmable Aerospace Ground Equipment (PAGE)
Titan 4B pre-launch vehicle check-out and launch countdown are controlled by a new automated ground processing system, called Programmable Aerospace Ground Equipment (PAGE). During the countdown, PAGE controls vehicle processing, continuously monitoring vehicle systems status and trends. In the event of a vehicle or ground system malfunction, PAGE can hold or abort the launch process up to ignition of the solid rocket motors. The new PAGE system will eliminate obsolete hardware and resolve maintenance problems with the existing system.