The Saturn V S-IC stage had five F-1 engines, hydraulically controlled, each with a thrust of 1.5 million lb., generating a total thrust of 7.5 million pounds. The central engine was fixed, and it used hydraulic controls for gimbaling four of its five engines.
Thrust Vector Control (TVC) actuators were used to “steer” the rocket by changing the angle of the engine relative to the rocket body. The Saturn V was able to carry up to 260,000 lbm to Low Earth Orbit, making it the most powerful rocket at the time.
How does Saturn V Hydraulic Servoactuator work?
A hydraulic servoactuator is a device that uses the pressure of fluid to produce linear motion. In the case of the Saturn V rocket, the hydraulic servoactuators were used to control the movement of the rocket’s engines and other systems during flight. The actuators were controlled by electrical signals from the rocket’s onboard computer, which would adjust the pressure of the fluid in the actuator to move the engine or other system to the desired position. The fluid used in the Saturn V’s hydraulic servoactuators was a high-pressure mixture of fuel and an oxidizer, which was used to power the rocket’s engines as well as its hydraulic systems.
Thrust Vector Control, or TVC, is critical to control the rocket’s flight path. Thrust Vector Control actuators vary in size and capability, including the actuator’s extended distance or stroke and the force needed to move the rocket engine, and the speed of the actuator.
The S-IC had the task of getting the massive Saturn V rocket off the ground, taking it to an altitude of about 40 miles, and accelerating the rocket to a velocity of about 6,000 mph.
When the Saturn V left the ground, it weighed about 6.5M lbs and generated about 7.5 million lbs of thrust. After just 150 seconds, when the S-IC completed its launch role and was jettisoned, what remained of the rocket weighed only 1.32M lb.
The S-1C, which weighed 303,000 lb empty, had depleted 4,578,000 lb of propellant in just 150 seconds; over half of the weight of the rocket was in its first stage.
Another key portion of the Saturn V was the control of the liquid propellants to the F-1 engines. These valves need to be able to control often very high flow rates.
The first stage (S-1C) carried five F-1 engines that used Liquid Oxygen (LOx) and RP-1 (refined Kerosene) as propellants.
The S-IC stage used a smart fluid power arrangement valve actuation and thrust vector control. High-pressure RP-1 tapped off the fuel pump outlet and replaced rotary pumps and traditional hydraulic fluid for this application.
During checkout and before engine start, GSE had to deliver hydraulic pressure, and RP-1 was dangerous due to its flammability.
Instead of RP-1, GSE fluid power used RJ-1, a ramjet fuel whose physical properties were similar to RP-1 but whose flash point was high enough to avoid it being classified as flammable.
Once the engines were running, GSE-supplied hydraulic pressure was replaced by engine fuel pressure. The rocket had five fluid power systems, one for each engine.
The fixed center engine directs its fluid pressure to close the main fuel valves, gas generator valves, and main LOX valves; outboard fluid pressure serves the thrust vectoring servoactuators.
The Saturn V’s servoactuators were things of beauty. Weighing 300 lb and 5 ft long, they had a stroke of 11″ and could articulate the running F-1 engine through its full 5.25° of travel in just 1 second.
MSFC engineers knew that quality servoactuators would be necessary for mission success and released a very strict request for proposals.
Two companies, Hydraulic Research and Manufacturing Co., of Burbank, California, and Moog, Inc. of East Aurora, New York, both offered proposals that met the requirements equally.
NASA decided to select both vendors, and as a result, some S-IC stages flew with Hydraulic Research servoactuators while others flew with ones from Moog. Moreover, Moog produced over 1,500 TVC actuators to support the Saturn program.
The gimbal system for Saturn V needed to be beefed up due to the greatly increased requirements of the S-IC compared to previous rockets like the type used for the Jupiter and Saturn I vehicles. They needed a new concept/design based on the latest concepts in hydraulic actuation.
The design stood between a high-pressure, closed-loop, conventional hydraulic system utilizing MIL-H-5606 or a fueldraulic system in which RP-1 (kerosene) fuel, taken from the high-pressure side of the turbopump, should be used as the fluid medium in a single-pass system. And the flow from the actuator returns to the fuel system, rather than to a hydraulic reservoir.
The requirements would necessitate redesign and qualification of most major components. Cost and delivery schedules appeared to favor the fueldraulic system instead of a conventional system.
Principally because of the smaller number of components. And also, it has fewer potential leak points and would constitute a less complex and, therefore, more reliable system.