Category Apollo Saturn V News Reference

Saturn V vehicles are assembled, checked out, and launched at Launch Complex 39 at Kennedy Space Center. Complex 39 embodies a new mobile concept of launch operations which includes superior re­liability and time savings offered by assembly and checkout in a protected environment and reduc­tion of actual pad time as much as 80 per cent with

a consequent increase in launch rate capability. The ability to adapt economically to future program requirements is another advantage. For example, the service platforms used in the Saturn/Apollo program could be used for other vehicles of similar configuration, and the area can accommodate space boosters with thrusts up to 40 million pounds.

Facilities

The major components of Launch Complex 39 in­clude: (1) the Vehicle Assembly Building, where the space vehicle is assembled and prepared; (2) the mobile launcher, upon which the vehicle is erected for checkout, and from which, later, it is launched; (3) the crawlerway, upon which the fully assembled vehicle is carried by transporter to the launch site; (4) the mobile service structure, which provides external access to the vehicle at the launch site; (5) the transporter which carries the launch vehicle, mobile launcher, and mobile service struc­ture to various positions at the launch complex; and (6) the launch area from which the space vehicle is launched.

THE VEHICLE ASSEMBLY BUILDING

The Vehicle Assembly Building (VAB) consists of a high bay area 525 feet tall, a low bay area 210 feet tall, and a four-story launch control center iLCC) connected to the high bay by an enclosed bridge. The VAB, with 130 million cubic feet, is the world’s largest building in volume. It covers eight acres of land. There are four assembly and checkout bays in the high bay area. The low bay area contains eight stage preparation and checkout cells equipped with systems to simulate stage inter­face. The launch control center houses display, monitoring, and control equipment for checkout and launch operations. There are four firing rooms in the LCC, one for each high bay and checkout area. Work platforms, mounted on opposite walls in the high bay area, are designed to enclose various work areas around the launch vehicle. Platforms extend or retract in less than 10 minutes. Twenty – ton hydraulic jacks are used to align platforms.

The Saturn V, after prelaunch checkout on its mo­bile launcher, is carried by the transporter from the VAB through a door shaped like an inverted “T”. The door is 456 feet high. The base of the door is 149 feet wide and 113 feet high; the remainder is 76 feet wide. There are four such doors in the VAB, one for each of its four high bays. In keeping with the protective environment of the building, doors were designed to withstand winds of 125 miles per hour.

There are 141 lifting devices in the VAB, ranging from one-ton mechanical hoists to two 250-ton high-

Checkout Vehicle—The Saturn V facilities vehicle begins its journey from the Vehicle Assembly Building to the launch pad. Its purpose was to check out facilities, train launch crews, and verify procedures at KSC.

INTRODUCTION

When the United States made the decision in 1961 to undertake a manned lunar landing effort as the focal point of a broad new space exploration pro­gram, there was no rocket in the country even approaching the needed capability. There was a sort of “test bed” in the making, a multi-engine vehicle now known as Saturn I. It had never flown. And it was much too small to offer any real hope of sending a trio to the moon, except possibly through as many as a half dozen separate launchings from earth and the perfection of rendezvous and docking techniques, which had never been tried.

That was the situation that brought about the an­nouncement on Jan. 10, 1962, that the National Aeronautics and Space Administration would de­velop a new rocket, much larger than any previously attempted. It would be based on the F-l rocket en­gine, the development of which had been underway since 1958, and the hydrogen-fueled J-2 engine, upon which work had begun in 1960.

The Saturn V, then, is the first large vehicle in the U. S. space program to be conceived and de­veloped for a specific purpose. The lunar landing task dictated the make-up of the vehicle, but it was not developed solely for that mission. As President Kennedy pointed out when he issued his space chal­lenge to the Congress on May 25, 1961, the overall objective is for “this Nation to take a clearly lead­ing role in space achievement which in many ways may hold the key to our future on earth.” He said of the lunar landing project: “No single space pro­ject in this period will be more exciting, or more impressive to mankind, or more important for the long-range exploration of space: and none will be so difficult or expensive to accomplish…”

The Saturn V program is the biggest rocket effort undertaken in this country. Its total cost, including the production of 15 vehicles between now and early 1970, will be above $7 billion.

NASA formally assigned the task of developing the Saturn V to the Marshall Space Flight Center on Jan. 25, 1962. Launch responsibility was committed to the Kennedy Space Center. (The Manned Space­craft Center, the third center in manned space flight, is responsible for spacecraft development, crew training, and inflight control.)

DESCRIPTION

Marshall Center rocket designers conceived the Saturn V in 1961 and early 1962. They decided that
a three-stage vehicle would best serve the immedi­ate needs for a lunar landing mission and would serve well as a general purpose space exploration vehicle.

One of the more important decisions made early in the program called for the fullest possible use of components and techniques proven in the Saturn I program. As a result, the Saturn V third stage (S-IVB) was patterned after the Saturn I second stage (S-IV). And the Saturn V instrument unit is an outgrowth of the one used on Saturn I. In these areas, maximum use of designs and facilities already avail­able was incorporated to save time and costs.

Many other components were necessary, including altogether new first and second stages (S-IC and S-II). The F-l and J-2 engines were already under development, although much work remained to be done. The guidance system was to be an improve­ment on that of the Saturn I.

Saturn V, including the Apollo spacecraft, is 364 feet tall. Fully loaded, the vehicle will weigh some

6.1 million pounds.

The 300,000-pound first stage is 33 feet in diameter and 138 feet long. It is powered by five F-l engines generating 7.5 million pounds thrust. The booster will burn 203,000 gallons of RP-1 (refined kerosene) and 331,000 gallons of liquid oxygen (LOX) in 2.5 minutes.

Saturn V’s second stage is powered by five J-2 engines that generate a total thrust of a million pounds. The 33-foot diameter stage weighs 95,000 pounds empty and more than a million pounds loaded. It burns some 260,000 gallons of liquid hydrogen and

83.0 gallons of liquid oxygen during a typical 6- minute flight.

Third stage of the vehicle is 21 feet and 8 inches in diameter and 58 feet and 7 inches long. An inter­stage adapter connects the larger diameter second stage to the smaller upper stage. Empty weight of the stage is 34,000 pounds and the fueled weight is

262.0 pounds. A single J-2 engine developing up to 225,000 pounds of thrust powers the stage. Typi­cal burn time is 2.75 minutes for the first burn and

5.2 minutes to a translunar injection.

The vehicle instrument unit sits atop the third stage. The unit, which weighs some 4,500 pounds, contains the electronic gear that controls engine ig­nition and cutoff, steering, and all other commands necessary for the Saturn V mission. Diameter of the instrument unit is 21 feet and 8 inches, and height is 3 feet.

Directly above the instrument unit in the Apollo

configuration is the Apollo spacecraft. It consists of the lunar module, the service module, the com­mand module, and the launch escape system. Total height of the package is about 80 feet.

The electrical power and distribution system of the

first stage provides power for controlling and mea­suring functions of the vehicle. The system operates during static firing, launch preparation and check­out. launch, and flight.

The electrical system consists of two batteries, a main power distributor, a sequence and control distributor, propulsion distributor, timer distrib­utor. measuring distributors, thrust OK distributor, and measuring power distributor.

Two independent 28-volt DC power systems are installed on the stage. System No. 1, the main power battery, energizes the stage controls. The battery has a 640-ampere-minute rating, weighs about 22 pounds, and is used to control various solenoids. Battery No. 2, the instrumentation battery, ener­gizes the flight measurement system and gives power to redundant systems for greater mission reliability. It has a 1,250-ampere-minute rating and weighs approximately 55 pounds. The range safety system can be operated by either battery.

Preflight power is supplied from ground equipment through umbilical connections. The supply for each system is 28 volts. Ground sources supply power for heaters, ignitors, and valve operators that are not operated during flight.

The distributors subdivide the electrical circuits and serve as junction boxes. Both electrical sys­tems share the same distributors. The main power distributor houses relays, the power transfer switch, and electrical distribution buses. The relays con­trol circuits that must be time-programmed. The motor-operated, multi-contact, power transfer switch transfers the stage load from the ground supply to the stage batteries. The transfer is tried several times during countdown to verify opera­tion. Power is distributed by the main buses.

The switch selector, actuated by the instrument unit (IU), commands the sequence and control dis­tributor, which in turn amplifies the signals re­ceived. The sequence and control distributor then energizes the various circuit relays required to implement the flight program. The switch selector is an assembly of redundant low power relays and transistor switches, which control the sequence and control distributor. It is activated by a coded signal from the instrument unit computer.

The propulsion distributor contains the monitor and control circuits for the propulsion system.

The thrust OK distributor contains the circuits that shut down the engines when developed thrust is inadequate. Two of the three thrust OK switches must operate or the engine will be shut down.

The timer distributor houses the circuits to delay the operation of relay valves and other electro­mechanical devices. The programmed delays are essential for optimum performance and safety.

The measuring power distributor contains electrical buses, and the measuring distributors route data from measuring racks, serve as measurement sig­nal junction boxes, and switch data between the hardwire and telemetry.

The engine interface panel, mounted above the turbopump LOX and fuel inlets, provides the ve­hicle connect location for electrical connectors be­tween the engine and the vehicle. It also provides the attachment point for the vehicle flexible heat – resistant curtain. The panel is fabricated from heat – resistant stainless-steel casting made in three sec­tions and assembled by rivets and bolts.

ELECTRICAL SYSTEM

The electrical system consists of flexible armored wiring harnesses for actuation of engine controls and the flight instrumentation harnesses.

HYDRAULIC CONTROL SYSTEM

The hydraulic control system operates the engine propellant valves during the start and cutoff se­quences. It consists of a hypergol manifold, a check­out valve, an engine control valve, and the related tubing and fittings.

Hypergol Manifold

The hypergol manifold directs hypergolic fluid to the separate igniter fuel system in the thrust cham­ber injector. It consists of a hypergol container, an ignition monitor valve, a position switch, and an igniter fuel valve. The hypergol container, position switch, and igniter fuel valve are internal parts of the hypergol manifold.

A spring-loaded, cam-lock mechanism incorporated in the hypergol manifold prevents actuation of the
ignition monitor valve until after the upstream hypergol cartridge diaphragm bursts. The same mechanism actuates a position switch that indicates when the hypergol cartridge is installed. The igniter fuel valve is a spring-loaded, cracking check valve that opens and allows fuel to flow into the hypergol container. The hypergol cartridge diaphragms are ruptured by the resultant pressure surge when the igniter fuel valve opens.

Ignition Monitor Valve

The ignition monitor valve is a pressure-actuated, three-way valve mounted on the hypergol mani­fold. It controls the opening of the fuel valves and permits them to open only after satisfactory com­bustion has been achieved in the thrust chamber.

When the hypergol cartridge is installed in the hypergol manifold, a cam-lock mechanism prevents the ignition monitor valve poppet from moving from the closed position. The ignition monitor valve has six ports: a control port, an inlet port, two outlet ports, a return port, and an atmospheric reference port. The control port receives pressure from the thrust chamber fuel manifold. The inlet port re­ceives hydraulic fuel pressure for opening the fuel valves. When the ignition monitor valve poppet is in the deactuated position, hydraulic fuel from the inlet port is stopped at the poppet seat. When the hypergol cartridge diaphragm bursts, the spring- loaded cam-lock retracts to permit the ignition moni­tor valve poppet unrestricted motion. When thrust chamber pressure (directed to the control port from the thrust chamber fuel manifold I increases, the ignition monitor valve poppet moves to the open (actuated) position and hydraulic fuel is directed through the outlet ports to the fuel valves.

STAGE DESCRIPTION

Basically, the Saturn V third stage, the S-IVB, is an aluminum air-frame structure powered by a single, J-2 engine, which burns liquid oxygen and liquid hydrogen. The engine has a maximum thrust of 225.000 pounds. The structure has a bipropellant capacity of 228,000 pounds of fuel and oxidizer.

STAGE FABRICATION AND ASSEMBLY

The third stage structure consists of a forward skirt assembly, propellant tank assembly, thrust structure assembly, aft skirt assembly, and aft in­terstage assembly. The propellant tank assembly consists of a single tank separated by a common bulkhead into a fuel compartment and an oxidizer compartment.

Forward Skirt Assembly

The forward skirt is a cylindrical aluminum skin and stringer structure that provides a hard attach point for the instrument unit. In addition, the for­
ward skirt provides an interior mounting structure for electrical and electronic equipment that requires environmental conditioning, as well as range safety and telemetry antennas mounted around the ex­terior periphery. Environmental conditioning for electronic equipment is provided by cold plates which utilize a coolant supplied from the IU thermo­conditioning system.

Propellant Tank Assembly

Structural elements of the propellant tank assembly are a cylindrical tank section, common bulkhead, aft dome, and forward dome. Seven segments are machined from aluminum alloy plate to form the tank section. A waffle pattern is then machine – milled into each segment to reduce weight and pro­vide shell stiffness. The formed segments are joined into a complete cylinder by single-pass internal weld on a Pandjiris welding machine.

Aft and forward domes are made by forming "orange peel” segments on a stretch press. Orange peel segments are then joined in a dome welder. Each

Third Stage Production Sequence

6-і

Slosh Baffle…. Horizontal rings are installed inside LH2 tank for

propellant stabilization during flight.

Third stage vehicles reach end of assembly sequence with final assembly and checkout in 115-foot vertical towers.

Engine I nstalled—J-2 engine is attached to stage in final assembly tower at Huntington Beach.

Final installation of various subsystem components is performed in a checkout tower, along with the installation and alignment of the,1-2 engine. The stage is in a vertical position in the tower where a complete stage checkout of subsystems and systems is conducted except for actual ignition of engine. After satisfactory checkout, the stage is removed from the tower, placed on a dolly, and ground sup­port rings are installed at each end of the stage. It is then painted, weighed, and prepared for ship­ment to the Douglas Sacramento Test Center for simulated and static firing of APS engines and J-2 engine.

This system consists of the gas generator, gas gen­erator control valve, turbine exhaust system and exhaust manifold, heat exchanger, and oxidizer turbine bypass valve.

GAS GENERATOR

The gas generator is welded to the fuel pump tur­bine manifold, making it an integral part of the fuel turbopump assembly. It produces hot gases to drive the fuel and oxidizer turbines and consists of a combustor containing two spark plugs, a control valve containing fuel and oxidizer ports, and an in­jector assembly.

When engine start is initiated, the spark exciters in the electrical control package are energized, pro­viding energy to the spark plugs in the gas genera­tor combustor. Propellants flow’ through the con­trol valve to the injector assembly and into the com­bustor outlet and are directed to the fuel turbine and then to the oxidizer turbine.

GAS GENERATOR CONTROL VALVE

The gas generator control valve is a pneumatically operated poppet-type that is spring-loaded to the closed position. The fuel and oxidizer poppets are mechanically linked by an actuator. The gas genera­tor control valve controls the flow of propellants through the gas generator injector.

When the mainstage signal is received, pneumatic pressure is applied against the gas generator con­trol valve actuator assembly which moves the piston and opens the fuel poppet. During the fuel poppet opening, an actuator contacts the piston that opens the oxidizer poppet. As the opening pneumatic pres­sure decays, spring loads close the poppets.

TURBINE EXHAUST SYSTEM

The turbine exhaust ducting and turbine exhaust
hoods are of welded sheet metal construction. Flanges utilizing dual (Naflex) seals are used at component connections. The exhaust ducting con­ducts turbine exhaust gases to the thrust chamber exhaust manifold which encircles the thrust cham­ber approximately halfway between the throat and the nozzle exit. Exhaust gases pass through the heat exchanger and exhaust into the main thrust chamber through 180 triangular openings between the tubes of the thrust chamber.

HEAT EXCHANGER

The heat exchanger is a shell assembly, consisting of a duct, bellows, flanges, and coils. It is mounted in the turbine exhaust duct between the oxidizer turbine discharge manifold and the thrust chamber. It heats and expands helium gas for use in the third stage or converts liquid oxygen to gaseous oxygen for the second stage for maintaining vehicle oxi­dizer tank pressurization. During. engine operation, either liquid oxygen is tapped off the oxidizer high – pressure duct or helium is provided from the ve­hicle stage and routed to the heat exchanger coils.

OXIDIZER TURBINE BYPASS VALVE

The oxidizer turbine bypass valve is a normally open, spring-loaded, gate type. It is mounted in the oxidizer turbine bypass duct. The valve gate is equipped w’ith a nozzle, the size of which is deter­mined during engine calibration. The valve in its open position depresses the speed of the oxygen pump during start, and in its closed position acts as a calibration device for the turbopump perform­ance balance.

Control System

The control system includes a pneumatic system and a solid-state electrical sequence controller pack­aged with spark exciters for the gas generator and the thrust chamber spark plugs, plus interconnect­ing electrical cabling and pneumatic lines.

PNEUMATIC SYSTEM

The pneumatic system consists of a high-pressure helium gas storage tank, a regulator to reduce the pressure to a usable level, and electrical solenoid control valves to direct the central gas to the vari­ous pneumatically controlled valves.

Located Southeast of the VAB is the launch control center (LCC). This four-story building is the elec-

SATURN V NEWS REFERENCE

tronic brain of Launch Complex 39. Here final count­down and launch of Saturn V’s will be conducted. The LCC is also the facility from which a multitude of checkout and test operations will be conducted while space vehicle assembly is taking place inside the VAB.

Two separate, automated computer systems are used to check out and conduct the countdown for the Saturn V. The acceptance checkout equipment, or ACE, is used for the Apollo spacecraft. The Saturn ground computer system is used for the various stages of the vehicle.

Located in the launch control center is the heart of the Saturn ground computer system. Here check­out and preflight countdown are conducted.

This system has as its “brain" two RCA 110A com­puters. One is located in the launch control center and the other is in the mobile launcher upon which the Saturn V is erected.

Moving Tower-Personnel watch a mobile launch tower moving along the crawlerway at Kennedy Space Center.

Through the process control system, all stages are checked, and data from the engines and from the guidance, flight control, propellants, measurement, and telemetry systems is provided.

The Saturn ground computer system also includes a DDP 224 display computer located in the LCC. It can drive up to 20 visual cathode ray display tubes.

possible for the computer in the mobile launcher to return 1,512 discrete signals.

A digital data acceptance system collects and makes available onboard analog data to the computers.

A triply redundant system for discrete output in­formation allows more reliability. There are 1,512 signals going to the mobile launcher showing "on” and “off” commands. If one signal fails or reports a wrong command and the other two signals trans­mit another command, the majority command is indicated in the display and transmitted to the vehicle.

There are 15 display systems in each LCC firing room, with each system capable of giving digital information instantaneously.

Sixty television cameras are positioned around the Saturn V transmitting pictures on 10 channels.

Additionally, the LCC contains several hundred operational intercommunication channels which en­able the launch team and the launch director to be in voice contact with the astronauts aboard the spacecraft.

Automatic checkout of the Apollo spacecraft is ac­complished through acceptance checkout equipment (ACE). Through the use of computers, display con­soles, and recording equipment, ACE provides an instantaneous, accurate method of spacecraft pre­flight testing. ACE also is used at the spacecraft contractor plants and in testing at the Manned Spacecraft Center in Houston.

SATURN V NEWS

REFERENCE

Computerized checkout of the Saturn stages at the launch pad and the Apollo ACE system at the Man­ned Spacecraft Operations Building at the Kennedy Space Center are tied together by instrumentation.

The Saturn V employs completely automated com­puter controlled checkout systems for each of its stages. The system uses a carefully detailed com­puter program and associated electronic equipment to perform a complete countdown checkout of each stage and all its various systems, subsystems, and components.

With electronic speed, it moves through a thorough and reliable countdown, yet permits test engineers to monitor every step of the operation and to over­ride the computer functions, if necessary.

To monitor fuel and oxidizer mass for the three stages of the Saturn V vehicle, a propellant tanking computer system (PTCS) is used. This system con­trols propellant tank fill and replenishment. Liquid oxygen and liquid hydrogen must be replenished constantly to compensate for boil-off.

The jumping-off place for a trip to the moon is NASA’s Launch Complex 39 at the Kennedy Space Center. After the propellants are loaded, the three astronauts will enter the spacecraft and check out their equipment.

While the astronauts tick off the last minutes of the countdown in the command module, a large crew in the launch control center handles the complicated launch operations. For the last two minutes, the countdown is fully automatic.

At the end of countdown, the five F-l engines in the first stage ignite, producing 7.3 million pounds of thrust. The holddown arms release the vehicle, and three astronauts begin their ride to the moon.

Turhopumps, working together with the strength of 31) diesel locomotives, force 15 tons of fuel per second into the engines. Steadily increasing accel­
eration pushes the astronauts back into their couch­es as the rocket generates 1-1, If times the force of earth gravity.

After 2,5 minutes, the first stage has burned its

4,192,0 pounds of propellants and is discarded at about 38 miles altitude. The second stage’s five,1-2 engines are ignited. Speed at this moment is 5,330 miles per hour.

The second stage’s five 4-2 engines burn for about (5 minutes, pushing the Apollo spacecraft to an altitude of nearly 115 miles and near orbital velocity of 15,300 miles per hour. After burnout the second stage drops away and retrorockets slow it for its fall into the Atlantic Ocean west of Africa.

The single 4-2 engine in the third stage now ignites and burns for 2.75 minutes. This brief burn boosts the spacecraft to orbital velocity, about 17,500 miles an hour. The spacecraft, with the third stage still attached, goes into orbit about 12 minutes after liftoff. Propellants in the third stage are not depleted when the engine is shut down. This stage stays with the spacecraft in earth orbit, for its en­gine will be needed again.

Throughout the launch phase of the mission, telem­etry systems are transmitting continously, track­ing systems are locked on, and voice communica­tions are used to keep in touch with the astronauts. All stage separations and engine thrust terminations are reported to the Mission Control Center at Houston.

The astronauts are now in a weightless condition as they circle the earth in a “parking orbit” until the timing is right for the next step to the moon.

The first attempt at a lunar landing is planned as an “open-ended” mission with detailed plans at every stage for mission termination if necessary. A comprehensive set of alternate flight plans will be laid out and fully rehearsed for use if such a de­cision should prove necessary. For example, a de­cision might be made in the earth parking ortm not to continue with the mission. At every stage of the mission, right up to touchdown on the moon, this termination decision can be made and an earth flight plan initiated.

During the one to three times the spacecraft circles the earth, the astronauts make a complete check of the third stage and the spacecraft. When the precise moment comes for injection into a trans­lunar trajectory, the third stage J-2 engine is re­ignited. Burning slightly over 5 minutes, it acceler­ates the spacecraft from its earth orbital speed of 17,500 miles an hour to about 24,500 miles an hour in a trajectory which would carry the astronauts around the moon. Without further thrust, the space­craft would return to earth for re-entry.

If everything is operating on schedule, the astro­nauts will turn their spacecraft around and dock with the lunar landing module. After the docking maneuver has been completed, the lunar module will be pulled out of the forward end of the third stage, which will be abandoned. Abandonment com­pletes the Saturn V’s work on the lunar mission.

The first stage instrumentation system measures and reports information on stage systems and com­ponents and provides data on internal and external environments. It keeps abreast of approximately 900 measurements on the stage, such as measure­ments of valve positions, propellant levels, tem­peratures, voltages, and pressures. The measure­ments are telemetered by coaxial cable to ground support equipment and by radio frequency trans­mission to ground stations.

The instrumentation system consists of a measure­ment system, a telemetry system, and the Offset Doppler tracking system. A remote automatic cali­bration system provides remote rapid checkout of the measurements and telemetry systems.

MEASUREMENT

The measurement system reports environmental situations and how the first stage reacts to them. Making use of transducers, signal conditioners, measuring rack assemblies, measuring distributors, and the onboard portion of the remote automatic calibration system, this system involves many phases of stage operation. Included are measure­ments of acceleration, acoustics, current, flow, flight

TELEMETRY

Telemetry is a method of remote monitoring of flight information accomplished by means of a radio link. The first stage telemetry system is composed of six radio frequency links.

Most of the components of the telemetry systems are located in the thrust structure; RF assemblies and a tape recorder are located in the forward skirt. The telemeter transmits data through two common antenna systems.

Links FI, F2, and F3 are identical systems which transmit narrow-band, frequency-type data such as that generated by strain gages, temperature gages, and pressure gages. The system can handle 234 measurements on a time-sharing basis and 14 mea­surements transmitted continously. Data may be sampled either 120 times per second or 12 times per second.

Links SI and S2 transmit wide-band, frequency – type data generated by vibration sensors. Each link provides 15 continuous channels or a maximum of 75 multiplexed channels depending on the specific measuring program.

Telemeter PI transmits cither pulse code modu­lated or digital type data. Five multiplexers, four analogs, and one digital supply data to the PCM assembly. This provides the most accurate data and is used for ground checkout as well.

A telemetering calibrator is used to improve the accuracy of the telemetry systems. The calibrator supplies known voltages to the telemeters periodi­
cally during the stage operation. Their reception at tracking stations provides a valid reference for data reduction.

The effects of ullage and retrorocket firing attenu­ation can seriously degrade the telemetry trans­mission during stage separation; therefore, a tape recorder installed in the forward skirt records data for delayed transmission. The commands for tape recorder operation originate in the digital computer located in the instrument unit.

ODOP SYSTEM (Offset Doppler Tracking System)

The ODOP system is an elliptical tracking system that measures the rate of motion at which the ve­hicle is moving away from or toward a tracking station. The total Doppler shift in the frequency of a continuous wave, ultra-high frequency signal transmitted from the ground to the first stage is measured. The signal is received by the transponder at the stage, modified, and then retransmitted back to the ground. Retransmitted signals are received simultaneously by three tracking stations. Separate antennas on the stage are used for receiving and retransmitting the signals.

The checkout valve consists of a ball, a poppet, and an actuator. The checkout valve provides for ground checkout of the ignition monitor valve and fuel valves and prevents the ground hydraulic return fuel, used during checkout, from entering the en­gine system and consequently the vehicle fuel tank.

When performing the engine checkout or servicing, the checkout valve ball is positioned so fuel enter­ing the engine hydraulic return inlet port will be directed through the ball and out the GSL return port. For engine static firing or flight, the ball is positioned so fuel entering the engine hydraulic re­turn inlet port will be directed through the ball and out the engine return outlet port.

Engine Control Valve

(Hydraulic Filter and Four-Way Solenoid Valve Manifold)

The engine control valve incorporates a filter mani­fold, a four-way solenoid valve, and two swing check valves.

The filter manifold contains three filters. One filter is in the supply system and one each in the opening and closing pressure systems. The filters prevent entry of foreign matter into the four-way solenoid valve or the engine. Two swing check valves are "teed” into the supply system filter. The check valves permit hydraulic system operation from the ground supplied hydraulic fluid for checkout and servicing procedures or engine supplied hydraulic fluid for normal engine operation.

The four-way solenoid valve is comprised of a main spool and sleeves to achieve two-directional control of the fluid flow to the main fuel, main oxidizer, and gas generator valve actuators. The spool is pressure-positioned by two three-way slave pilots. Each slave pilot has a solenoid-controlled, normally open, three-way primary pilot.

The de-energized position of the engine control valve provides hydraulic closing pressure to all engine propellant valves. Momentary application of 28 VDC to the start solenoid will initiate control valve actuations that culminate in the positioning of the main spool so that hydraulic pressure is applied to the opening port, and the pressure previously applied to the closing port is vented to the return port.

An internal passage in the housing maintains com­mon pressure applied between the opening port and start solenoid poppet. This pressure, after start solenoid de-energization, holds the main spool in its actuated position thereby maintaining the pres­sure directed to the opening port without further application of the start solenoid electrical signal. Momentary application of 28 VDC to the stop so­lenoid will initiate control valve actuations that culminate in positioning the main spool so that pres­sure is vented from the opening port and applied to the closing port. The override piston may be actuated at any time by a remote pressure supply, which, in the event of an electrical power loss, would re­position the main spool and apply hydraulic pres­sure to the closing port. If electrical power and hydraulic pow-er are both removed, the valve will return to the de-energized position by spring force. If hydraulic pressure is then reapplied, pressure will be applied to the closing port. If an electrical signal is simultaneously sent to the start and stop solenoids, the stop solenoid will override the start and return the valve to a deactuated position.

Swing Check Valve

There are two identical swing check valves installed on the engine control valve. They allow – the use of ground hydraulic fuel pressure during engine start­ing transient and engine hydraulic fuel pressure during engine mainstage and shutdown. One check valve is installed in the engine hydraulic fuel supply inlet port, the other in the ground hydraulic fuel supply inlet port.