The Saturn V Launch Sequence

The Second by Second Details

The sequence of events here has been assembled from the official NASA Flight Journals of all ten manned Saturn V missions and appendix C of NASA Special Publication 4204 (“Moonport: A History of Apollo Launch Facilities and Operations”) The exact times of the events vary slightly from mission to mission, so they have been approximated here and should not be considered exact. Times are shown a Hours : Minutes: Seconds. T- means before launch and T+ means after launch.

 T-130:30:00 The Countdown sequence begins. Throughout the countdown, technicians will conduct a variety of tests to ensure all systems are nominal. 

T-130:00:00 – Command and Service Modules turned on for systems verification.

T-50:30:00 – F-1 Engine Hypergolic Cartridge Installed

T-48:00:00 – Oxygen and hydrogen from the service module tanks are fed into the fuel cells to provide internal power. 

T-36:30:00 – CSM Liquid Oxygen and Liquid Hydrogen Tanking

T-12:00:00 S-IC is loaded with 203,000 gallons of RP-1 Fuel

T-08:00:00 - Liquid oxygen is loaded into the S-IC, S-II, and S-IVB stages. This takes just over three hours. Heat will cause nearly a quarter of it to boil away, which is seen as the plumes of white vapor drifting away from the rocket. The tanks will be replenished closer to launch.

T-07:42:00 – Precooling of the S-II and S-IVB liquid hydrogen tanks begins. 

T-04:49:00 – The fueling of the S-II hydrogen tank begins. This is slow at first because the inside of the tank is still too warm. But it cools quickly as the LH₂ boils off. The entire process takes 46 minutes, and the tank will be replenished at various points before launch. When loading of the S-II is completed, the same process is carried out to fill the S-IVB hydrogen tank.

T-03:30:00 – Fueling of the S-IVB hydrogen tanks is complete. 

T-03:25:00 – The crew boards the spacecraft. The Commander enters first and sits in the left-hand couch. The Lunar Module Pilot enters and sits in the right-hand couch. Finally, the Command Module Pilot enters and takes the center couch. 

T-01:22:00 – The Command Module was pressurized and checked for leaks before the protective booster cover was closed. The Launch Control Center and Houston run through a series of checks to make sure they are receiving all the signals from the spacecraft, including the first motion signal that would indicate liftoff. The last weather balloon was released to determine wind direction.

T-01:14:00 – Closeout crew has secured the white room and begins clearing the pad area. Elevators are set at the 96-meter level in case they’re needed by the astronauts in an emergency.

T-01:01:00 – The Pad area has been cleared. 

T-00:56:00 – Swing Arm 9, which allowed access to the spacecraft, was retracted to a standby position.

T-00:50:00 Power transfer test. Up to this point, the spacecraft and the launch vehicle had been on external power. This test showed whether the internal electrical systems are functioning properly. The test would take about five minutes, and afterward, power was switched back to the external source. 

T-00:40:00 – The Launch Escape System was armed.

T-00:35:00 – The liquid hydrogen and liquid oxygen tanks were replenished as needed.

T-00:30:00 – The water system is ready to begin flooding the pad 2 seconds after liftoff. Final propulsion checks are completed. Reaction control systems on the service module are armed. Recovery helicopters are on station. 

T-00:25:00 – The Command Module pilot begins the process of arming and checking the Reaction Control System on the Service Module. 

T-00:20:00 – The second and third stage propulsion systems are chilled to prepare for the flow of the cryogenic propellants when they are ignited.

T-00:11:00 – The CSM is switched to full internal power. Communications between the astronauts and ground controllers are checked. 

T-00:05:00 - Swing Arm 9 is pulled back into its fully retracted position. Launch controllers give their Go/No-Go for launch. 

T-00:04:00 – The Launch Vehicle Test Conductor clears the launch vehicle for launch.

T-00:03:07 – Control of the countdown is switched to the automatic sequencer.

T-00:02:30 – The fuel and oxidizer tanks in all the stages are pressurized with helium to ensure a smooth flow down to the engine.

T-00:00:50 – Power for the launch vehicle stages is switched to their internal batteries.

T-00:00:45 – The Commander makes the final guidance alignment before launch.

Saturn V Launch Sequence Video

Harrison Schmitt, the lunar module pilot on Apollo 17, later described the last thirty seconds of the countdown this way: “Everything had come alive beneath us. The gimbals were moving and the rocket, you could feel it. You’re lying there on your back. You could feel the engines moving down a football field below you or more, as it prepared for ignition.”

T-00:00:8.9 The engine start sequence begins. LOX tank valves are opened, and LOX flows into the main thrust chambers of the F-1 engines. The F-1 gas generators and turbopumps are started. Ignition begins with the injection of a hypergolic solution into the main thrust chamber. Main fuel valves open, adding the RP-1 to the main thrust chamber. Thrust begins to build. The center engine was started first, and then the outboard engines were started in opposing pairs 300 milliseconds apart.

At full thrust, the restraining hold down arms were released. As the rocket begins to ascend, it is slowed by the by 12 restraining pins, which have to be pulled through dies mounted on the rocket. This lasts for about 150 milliseconds.

In a 1973 debriefing, Apollo 17 Commander Gene Cernan offered his memories of the launch. “You could feel the ignition. You could feel the engines come up to speed. Just prior to lift-off and during the first few seconds of lift-off when we were near the pad, both the CMP and I could see the reflection of the engine ignition out the left-hand window and the hatch window in the BPC. We could not see the fire but could see a red glow through the windows reflecting apparently off the surface. Ignition was like a big old freight train sort of starting to rumble and shake and rattle and as she lifted off."

When the rocket has moved two centimeters, the umbilical connector plates in the side of the rocket are released, and the five remaining service arms are automatically swung out of the way.

T+00:00:01.35 – The stack yaws 1.25° away from the launch tower. Witnesses often were concerned that something was going wrong, but it was a normal procedure to avoid a collision that might be caused by wind.

T+00:00:13 – The Saturn V has risen 430 feet, clearing the launch tower structure. The rocket begins its pitch and roll maneuver, which will take between fifteen seconds and twenty-one seconds, and put the stack on course. This was accomplished by gimbaling the outboard F-1 engines. At this point, control of the mission shifts from the Launch Control Center at Kennedy to Mission Control in Houston. 

Gemini veteran Jim Lovell, described the launch of the Saturn V on Apollo 8 this way: “I don't think that the vibrations were any greater than they were in the Titan. Although there were a lot of small separate vibrations and a lot of noise, I think the flight itself was very smooth.”

“It is like an elevator slowly lifting off,” said Apollo 16 Lunar Module Pilot Charlie Duke. “At ignition, I had the lateral frequency of something or other. It just kept shaking at the same frequency throughout the whole S-IC burn. You felt yourself going faster and faster. I had the feeling it was a runaway freight train on a crooked track, swaying from side to side. That was all the way through the first stage.”

For the first forty-two seconds, Abort Mode 1a would involve the Command Module being separated from the Service Module and pulled away by the Launch Escape Tower. A small motor atop the LET would cause the Command Module to pitch over to the east toward the Atlantic Ocean. After firing for fourteen seconds, the LET would be jettisoned. The hypergolic fuels from the Reaction Control System would be vented. And the Command Module would then parachute to splashdown. After forty-two seconds, Abort Mode 1B would be used. The stack would already be pitched over. A set of canards would be deployed that would turn the Command Module so that its base and heat shield were facing in the direction of travel, and the parachutes would be deployed. 

T+00:00:56 – The atmosphere inside the Command Module was vented to lower the pressure from the level at launch. During this process, the oxygen/nitrogen mixture is slowly replaced by pure oxygen, which had the lower pressure, would be safe. 

T+00:01:23 – The stack passes through maximum dynamic pressure, where the drag caused by the atmosphere reaches its peak. This was experienced by the astronauts as a period of violent shaking and loud noise.

T+00:01:58 – The Aboard Mode now switches to 1C. The atmosphere at this point is too thin for the canards to have an effect, so the orientation of the Command Module after an abort would be controlled by the Reaction Control system until the canards become effective again. 

T+00:02:17 The center F-1 engine is shut down.

T+00:02:44 The outboard engines are shutdown. The astronauts felt this as if it was a physical blow. The acceleration of the S-IC would reach up to 4gs, driving the rocket forward and the astronauts backward into their couches. The stack in between them was physically compressed, but when the S-IC shut down, that tension was suddenly released. “When the outboards cut-off, as we had previously been briefed and as previous crews had discussed, there was a sharp unloading,” reported Apollo 12 Lunar Module Pilot Edgar Mitchell. “I expected to be thrown against the instrument panel, and I had my hands out to brace against it. But it was not as much as I expected. I do recall feeling the unloading reverberate through the spacecraft in several pulses.”

“It was what I'd call violent when the S-IC shuts down and everything recoils there,” recalled Apollo 15 Commander Dave Scott, who had also flown on Apollo 9. “It was really just a big bang.”

600 milliseconds after the S-IC shutdown, eight retrorockets fire to the pull the spent stage away from the S-II. The S-IC would continue to climb, reaching an altitude of about 366,000 feet before falling back to the Atlantic Ocean about 350 miles downrange. Eight ullage motors on the aft interstage at the bottom of the S-II fire for four seconds to settle the LH2 and LOX tanks. Then the S-II’s five J-2 engines are ignited. At this point, the astronauts were driven back into their couches again. 

T+00:03:13 - The S-II aft interstage is jettisoned. This was delayed after S-IC jettison to make sure there wasn’t a collision. 

T+00:03:17 - Escape tower and boost protection cover jettisoned. At this point, a launch abort would no longer involve the tower. Also, the Command Module windows would be completely uncovered for the first time.

T+00:09:09 - Second stage shutdown and separation

T+00:09:15 Third stage ignition

T+00:11:45 Third stage first shutdown, spacecraft now in Earth Orbit.