F-1 engine ignition sequence

The row of engineers in front of the F-1 rocket engine illustrates the sheer size of the engine.
The F-1 produced about 680 metric Tons of thrust. Five of these engines were used to lift the 2800 metrics Tons heavy Saturn V from the launch pad.
credit to NASA / Marshall Space Flight Center

The five F-1 engines at the base of the first stage (S-IC stage).
credit to NASA
Scanning credit to Kipp Teague
The gigantic F-1 rocket engine is a very complex machine with a network of valves, lines, pipes around a thrust chamber and turbo pumps to feed the thrust chamber with liquid oxygen and RP-1. In order to ignite the gigantic F-1 engine, an elaborate ignition sequence had to be devised to bring every component of the engine on line in a proper sequence at just the right moment. Two main steps in the ignition sequence can be distinghuished:
  1. The start of propellant pump
  2. The ignition inside the combustion chamber of the engine.
The first stage (S-IC stage) has five F-1 engines which are ignited by a ignition sequencer. The purpose of this sequencer is to ignite the F-1 engines in a particular sequence in time intervals of 200 milliseconds to increase the load on the S-IC thrust gradually.


The check-out valve and the 4 pyrotechnic igniters are acvtivated by an ignition sequencer. The next sequence of events are interrelated. The control valve, for example, is activated when the igniters have burned through electrical links.

  • With the check-out valve, the hydraulic return is switched from Ground Source Equipment (GSE) to F-1 engine fuel inlet. At this moment, the hydraulic pressure is still supplied by the GSE
  • Start of 6 seconds burn of 4 engine igniters.
    2 Igniters are located inside the combustion chamber of the gas generator.
    The gas generator produces a high pressure gas to drive the turbopump. The purpose of the turbopump is to pump propellants under high pressure (129 bar, 129 times atmospheric pressure) into the F-1 engine combustion chamber.
    The other 2 Igniters are located in the turbine exhaust inside the F-1 engine nozzle and their purpose is to ignite the fuel rich turbine exhaust gases.


The control valve is activated and hydraulic pressure is applied to open the main LOX valves and the gas generator propellant supply valve.

  • Main LOX valves are opened.
  • LOX start to flow via the turbo pump into the F-1 engine thrust chamber. The flow of the LOX makes the turbo pump spin.
    Combustion has not started yet, so LOX exits F-1 engine as a dense white cloud.
  • Propellants (LOx and RP-1) start to flow into the combustion chamber of the gas generator.
  • Propellants are ignited in the gas generator combustion chamber by the 2 iginiters.
  • Combustion gas, produced by the gas generator, passes through turbopump, heat exchanger, exhaust manifold and nozzle extension.
  • The fuel rich combustion gas from the gas generator is ignited in the turbine exhaust manifold by the 2 igniters in the exhaust manifold.
  • Combustion gas accelerates the turbopump, causing the pump discharge pressure to increase.
  • Because of the increasing fuel discharge pressure, the igniter fuel valve opens, allowing fuel pressure to be applied on the burst diaphragm of the hypergol cartridge.
  • LOX is starting to flow under discharge pressure through the F-1 engine thrust chamber but the fuel valve is still closed.

  • The engine fuel pressure has increased above the ground supplied hydraulic pressure. The swing check valve switches the intake of hydraulic pressure from GSE to engine fuel high pressure duct.
  • As fuel pressure increases to approximately 26 times atmospheric pressure, it ruptures the hypergol 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.
  • When the hypergol cartridge is ruptured, hydraulic inlet pressure is made available for the Ignition Monitor Valve.

  • Ignition causes the combustion zone pressure to increase.
  • The engine thrust chamber pressure is sensed by the ignition monitor valve through its control port. As the pressure inside the thrust chamber is 1.4 atm., the ignition monitor valve directs fluid pressure to the main fuel valves.
  • Main fuel valves are opened.
  • Fuel enters thrust chamber.
  • Pressure inside the thrust chamber increases, transition to mainstage is accomplished.
  • If the "Thrust OK" pressure switch senses a fuel injection pressure of 73 atm., a THRUST OK signal is sent to the IU (the Instrument Unit, the electronic heart of the launch vehicle).

Copyright 2011 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.