H-1 engines for the S-IB booster stage
The eight H-1 engines at the base of the S-IB stage. These pictures were taken in the in the final assembly area of Michoud Assembly Facility (MAF) near New Orleans. credit to NASA Scanning credit to Kipp Teague

H-1 engine

Technical drawings of the H-1 engine. The highlighted components are mentioned in the explanation of the H-1 ignition sequence below. A part of the heat exchanger and two small parts of the turbo pump have been cut away for illustration purposes. The H-1 produced about 91 metric Tons of thrust. Eight of these engines were used to lift the 590 metric Tons heavy Saturn IB from the launch pad. credit to NASA

The H-1 rocket engine is a complex machine with a network of valves, lines, and pipes around a thrust chamber and turbopumps to feed the thrust chamber with liquid oxygen and RP-1. In order to ignite the H-1 engine, an elaborate ignition sequence had to be devised to bring every component of the engine online in a proper sequence at just the right moment. Two main steps in the ignition sequence can be distinguished: The start of propellant pump The ignition inside the combustion chamber of the engine. The first stage (S-IB stage) has eight H-1 engines which are ignited by an ignition sequencer. The purpose of this sequencer is to ignite the H-1 engines in pairs in a particular sequence in time intervals of 100 milliseconds to increase the load on the S-IB thrust structure gradually. The four inner H-1 engines were ignited first and then the four outer engines.

START OF IGNITION SEQUENCE The main purpose of the turbopump is to pump propellants under high pressure into the H-1 engine combustion chamber. The gas of the first generator is created with solid propellant and was used in the first second after the ignition was initiated. The purpose of this Solid Propellant Gas Generator (SPGG) is to accelerate the turbopumpto generate sufficient propellant pressure. Since the RP-1 fuel is also used as the hydraulic fluid to operate valves, the required hydraulic pressure has to be obtained first to put a cascade of events in motion of opening valves in a particular sequence. The second gas generator is the main gas generator and runs on the available liquid propellants and drives the turbo pump during the main stage of operation of the H-1 engine. The ignition sequence is started by the initiators igniting the SPGG. Start of 6-second burn of 4 engine igniters. 2 Igniters are located inside the combustion chamber of the gas generator. The SPGG produces a high-pressure gas to accelerate the turbopump. Combustion gas, produced by the SPGG, passes through turbopump, heat exchanger, exhaust manifold and nozzle extension. Hydraulic pressure is provided to the control port of the Main LOX Valve (MLV) and the input port of the Igniter Fuel Valve (IFV).

START OF PROPELLANT TURBO PUMP BUILD-UP OF PROPELLANT DISCHARGE PRESSURE The turbo pump is still accelerating, and propellant pressure is still increasing. When the fuel pressure has increased to 20 times atmospheric pressure, the Main LOX Valve (MLV) is opened. LOX starts to flow via the turbopump into the H-1 engine thrust chamber. LOX is also fed to the control valve of the Liquid Propellant Gas Generator (LPGG) Combustion has not started yet, so LOX exits the H-1 engine as a dense white cloud. The MLV mechanically opens the Igniter Fuel Valve (IFV)

PRIMARY IGNITION The turbo pump is still accelerating, and propellant pressure is still increasing. When the Igniter Fuel Valve (IFV) has been opened, fuel is fed to the hypergolic cartridge and the inlet of the Ignition Monitor Valve (IMV). When the fuel pressure applied on the burst diaphragms increases to approximately 20 times atmospheric pressure, it ruptures the hypergolic cartridge. The hypergolic fluid and the fuel are forced through the cartridge holder into the thrust chamber, where they mix with the LOX to cause ignition. The Ignition Monitor Valve (IMV) is a so-called shuttle valve. The Outlet port, through which hydraulic control pressure is fed to the control port of the Main Fuel Valve (MFV), is connected to the Drain port and disconnected from the Inlet . This remains the case as long as the control port of the IMV senses a thrust chamber pressure below 2 atm. Above 2 atm., the Outlet port is connected to the Inlet port and disconnected from the Drain port.

MAIN PROPELLANT IGNITION Ignition causes the combustion zone pressure to increase. The engine thrust chamber pressure is sensed by the Ignition Monitor Valve (IMV) through its control port. As the pressure inside the thrust chamber has increased to 2 atm., the IMV is opened and hydraulic pressure is applied to the control port of the Main Fuel Valve (MFV). When the fuel pressure has increased to about 7.5 atm., the Main Fuel Valve is opened. Fuel enters thrust chamber Fuel is fed to the control valve of the LPGG (Liquid Propellant Gas Generator). Pressure inside the thrust chamber increases; transition to main propellant ignition is accomplished.

TRANSITION TO STEADY-STATE Now that the propellants have been ignited in the thrust chamber, the Liquid Propellant Gas Generator (LPGG), which is the main gas generator, has to be ignited to take over from the SPGG to bring the turbopump up to operational speed and to sustain that speed as long as the LPGG is fed with propellants. A steady state is attained in which the H-1 engine provides full thrust as designed. Ignition causes the combustion zone pressure to increase. The engine thrust chamber pressure is sensed by the LPGG Dual Control Valve through its control port. The LPGG Dual Control Valve is opened in stages. As the pressure inside the thrust chamber is 7 atm., the fuel valve is opened. The LOX valve is opened at 13 atm. pressure. This procedure ensures a fuel-rich ignition of the LPGG. The propellants are ignited in the LPGG by two igniters. The gas produced by the LPGG accelerates the turbopump to operational speed. If the triple redundant "Thrust OK" pressure switches sense a fuel injection pressure of 54 atm., a THRUST OK signal is sent to the IU (the Instrument Unit, the electronic heart of the launch vehicle). (The steady-state thrust chamber pressure is 48 atm.)

Acronyms
GSE Ground Source Equipment IMV Ignition Monitor Valve LPGG Liquid Propellant Gas Generator LOX Liquid Oxygen MFV Main Fuel Valve RP Rocket Propellant SPGG Solid Propellant Gas Generator

References
Skylab Saturn IB Flight Manual Section IV George C. Marshall Space Flight Center MSFC-MAN-206, September 1972

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Copyright 2021 by   Sander Panhuyzen All pictures and drawings contained on and through these pages are the author's, unless otherwise noted. No unauthorized reproduction without permission.