6. The Launch Vehicle

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1 6. The Launch Vehicle With the retirement of the Saturn launch vehicle system following the Apollo-Soyuz mission in summer 1975, the Titan III E Centaur is the United State s most powerful launch vehicle (Figure 6-1). It is launched from the U.S. Air Force Eastern Test Range at Cape Kennedy Air Force Station, Complex 41. It became operational in February, FUNCTION The function of the Titan III E Centaur launch vehicle is to lift the total Viking spacecraft into Earth orbit, then boost it into a trajectory that will take it to Mars. The three Titan stages and an initial burn of the Centaur upper stage place the spacecraft in a 90 nautical mile high parking orbit around Earth. Then, at the proper moment between six and 30 minutes later, the Centaur fires again to push the spacecraft on the proper course to Mars. VEHICLE The two Titan III E Centaur vehicles (Figure 6-2) that launch the Vikings on their trip to Mars, are a combination of the Titan III E booster and the Centaur D-1T upper stage. This is a new combination of two systems that have been used extensively in other combinations. This vehicle is well suited for high performance deep space missions, and for placing large spacecraft in synchronous orbit. The most visible change to the standard Titan III appearance is the enlarged payload shroud necessary because the diameter of the Centaur with its shroud is greater than the diameter of the Titan main core. The Titan III E consists of the O-stage, which is two solid rocket motors strapped to the center core, and liquid propelled stages one and two which make up the center core. The Centaur is the fourth stage. The Titan family of launch vehicles began with the Titan I, Air Force and includes the Titan II, the Titan Gemini launch vehicle, Titan IIIB, IIIC, IIID and now the IIIE. Figure 6-1 Titan Centaur Launch Vehicle The Titan III E Centaur is 159 feet tall. Ill-73

2 Stage 0 Contractor: United Technologies Corporation Chemicals Systems Division Sunnyvale, California Initial thrust for the Titan IIIE at liftoff is provided by two identical, segmented solid propellant rocket motors. These 10 foot diameter motors are mounted 180 degrees apart on the liquid propellant core vehicle. They are 85 feet tall with the nose fairing, and each weighs more than 500,000 pounds. Together they produce 2.4 million pounds of thrust and burn for 122 seconds. The solid rocket motor propellant case is constructed of heat-treated steel with a strength of 195,000 pounds per square inch. The motors burn solid propellant which contains powdered aluminum as fuel and ammonium chlorate as the oxidizer. The propellant also contains polybutadiene acrylic acid acrylonitrile as a binding agent. The solid rocket motors are steered by a liquid injection thrust vector control system mounted vertically alongside each engine. This system is capable of changing the vector angle of the thrust by 5 degrees using a maximum side force of 110,000 pounds on each motor. The system injects nitrogen tetroxide pressure fed into the engine nozzle by nitrogen gas. The thrust vector control system tanks are 22 feet long, 3.5 feet in diameter and carry 8424 pounds of nitrous oxide and 636 pounds of nitrogen each. Stage 1 t or: Martin Marietta Aerospace Denver, Colorado The firs stage of the liquid propellant core vehicle ignites about 112 seconds after liftoff. About 12 seconds later, the solid rocket motors are jettisoned over the Atlantic Ocean. Figure 6-2 Titan IllE Centaur Cutaway View Thrust for this stage is provided by a single Aerojet General liquid rocket engine. The single engine is technically two engines attached to a single frame and operates simultaneously from a single control system. III-74

3 The engine is hydraulically balanced and requires no thrust controls. Pitch and yaw control are provided by pivoting the thrust chambers independently on their gimbal mounts. A gas generator mounted near the engine provides roll control. The hydraulic cylinders that control the direction of the engine thrust receive their control signals from the launch vehicle flight controls system. The first stage propellant is a mixture of equal parts of hydrazine and unsymmetrical hydrazine as fuel, and nitrogen tetroxide as oxidizer. These propellants ignite spontaneously on contact, eliminating the need for an ignition system and related checkout and support equipment. Before launch, Stage I and II tank pressurization is provided by ground-supplied pressurized nitrogen. During flight, pressurization is supplied by gas generators in the rocket engine system. The first stage is 10 feet in diameter and 63 feet tall. Fueled, it weighs 273,000 pounds, it provides more than 520,000 pounds of thrust and burns for 146 seconds. The core vehicle structure (Stages I and I is a frame-stabilized, aluminum skin that provides structural strength by using stringers and frames attached to the inner surface. An ablative-coated heat shield assembly protects the Stage I engine from the high temperatures generated by the solid rocket motors. The heat shield encloses the engine from the thrust chamber upwards. Stage II Contractor: Martin Marietta Aerospace Denver, Colorado Stage II of the liquid propellant core ignites about 4.3 minutes after liftoff when the Stage I propellant is exhausted. About one second later Stage I separates from Stage II. Thrust for this stage is provided by an Aerojet General engine similar in construction and operation to a single engine in Stage I. Pitch and yaw steering control are provided by pivoting the engine on its gimbal mounting. Roll control is provided by turbine exhaust through a swiveled roll control nozzle adjacent to the engine. The hydraulic cylinders that control the direction of the engine thrust receive their control signals from the launch vehicle flight control system. The second stage propellant is a mixture of equal parts of hydrazine and unsymmetrical hydrazine as fuel, and nitrogen tetroxide as oxidizer, the same as Stage I. The second stage is 10 feet in diameter and 23 feet tall. Fueled, it weighs 73,000 pounds, provides 101,000 pounds of thrust and burns for 210 seconds. Centaur D-1T Contractor: General Dynamics, Convair Division San Diego, California The Centaur (Figure 6-3) begins its first burn about eight minutes after liftoff to provide the final thrust to put the Viking spacecraft into a parking orbit. This first burn occurs 10.5 seconds after Stage II separation. The Centaur D-1T is a high energy upper stage which includes major improvements in its guidance and payload systems over earlier versions. Earlier versions of the Centaur in various configurations have been launched with the Atlas launch vehicle. The Centaur is 31.5 feet tall and 10 feet in diameter, excluding the shroud which protects it atop the launch vehicle. The Centaur shroud (Figure 6-4) is 58 feet tall and 14 feet in diameter, 4 feet in diameter larger than the liquid propellant core of the Titan III on which it rests. Shortly after Stage II ignition, a signal from the guidance system severs and jettisons the shroud exposing the Centaur. The Centaur weighs 35,000 pounds including propellants. It burns cryogenic fuels, liquid oxygen and liquid hydrogen. The propellants are delivered to the two Pratt and Whitney engines by boost pumps that are driven by turbines fueled by hydrogen peroxide. Engine thrust is 30,000 pounds (in vacuum). III-75

4 Centaur Shroud Viking Lander Viking Orbiter Equipment Modu Tank Tank Boost Pump Helium Bottles Main Engines Figure 6-3 Cen taut- D- 7 T Upper Stage Figure 6-4 Centaur Shroud Cutaway with Viking Spacecraft Atop Centaur III-76

5 The Centaur has two identical and separate power systems that steer the two main engines. They receive their control signals from the guidance and control system. During coast, separation and retro-firing, the attitude of the Centaur is maintained by small engines, each with 6 pounds thrust, mounted on the bottom of the vehicle. They are hydrogen peroxide fueled. Guidance and Control-The purpose of the guidance and control system is to determine the vehicle s correct position and velocity, and send the appropriate signals to correct navigational errors. The entire system includes a Teledyne Ryan digital computer with a 16,384 word random access ory, a Honeywell inertial reference unit and electronics required to support the system. The system is mounted in an equipment area atop the Centaur, and provides navigation and control for the entire Titan IIIE Centaur launch vehicle. Computer-The digital computer plays a role in several functions: navigation, guidance, control, propellant control and pressurization, instrumentation and telemetry. The computer receives and processes data from the launch vehicle according to a prestored program, and sends the proper commands to control the vehicle. Inertial Reference Unit-The Centaur inertial reference unit contains a four gimbal, three axis stable platform that is stabilized by three gyros. If the platform rotates from the inertial reference, the gyros sense the error and send a signal which moves the platform back to its proper orientation. Rate data is provided to the flight computer by three accelerometers mounted on the platform. They continuously monitor velocity of the vehicle and send signals to the computer for its flight update information. Telemetry-The function of the instrumentation and telemetry system is to collect, digitize and send measurement signals to the ground from the launch vehicle during countdown and during flight. Capability is 1536 individually addressed measurements. The system transmits PCM digital information over the S band to the ground station network operated by the Eastern Test Range, that includes ground stations, ships and aircraft. In addition to the PCM system, an AM/FM system is installed on the Centaur stage to transmit analog data from the Viking spacecraft. Range Safety-Titan IIIE Centaur range safety is provided by two subsystems. One of those is a self-contained receiving system which can receive a command signal from the range safety officer to shut down the engines and destroy the vehicle. The second subsystem is independent of ground control. It is a wired circuit that senses any vehicle breakup that would prevent reception of a destruct signal from the ground, and sends the proper destruct signal to the vehicle. Ill-77