DAY 1 - July 16, 1969

The Launch

F-1 ignition sequence

Labelled diagram of the F-1 engine.

A large combustion chamber and bell have an injector plate at the top, through which RP-1 fuel and LOX are injected at high pressure through 2,816 holes. Above the injector is the LOX dome which also transmits the force of the thrust from the engine to the rocket's structure. A single-shaft turbopump is mounted beside the combustion chamber. The turbine section of this turbopump is at the bottom and is driven by the exhaust gas from burning RP-1 and LOX in a fuel-rich mixture in a chamber called the gas generator. After they power the turbine, these gases pass through a heat exchanger, then to a wrap-around exhaust manifold which feeds them into the periphery of the engine bell. The final task for these hot gases is to cool and protect the nozzle extension from the far hotter exhaust of the main engine itself.

Directly above the turbine, on the same shaft, is the fuel pump with two inlets from the fuel tank and two outlets that feed high pressure fuel, via shut-off valves, to the injector plate. A line from one of these feeds supplies the gas generator with fuel. Fuel is also used within the engine as a lubricant and as a hydraulic working fluid, though before launch, RJ-1 ramjet fuel is supplied from the ground, it being more suited for this purpose. At the top of the turbopump shaft is the LOX pump with a single, large inlet in-line with the turboshaft axis. This pump also has two outlet lines, with valves, to feed the injector plate. One line also supplies LOX to the gas generator

The interior lining of the combustion chamber and engine bell consists of a myriad of pipework through which a large portion of the fuel supply is fed. This cools the chamber and bell structure while also pre-warming the fuel. To ensure ignition, a cartridge of fluid sits in a branch of the high pressure fuel circuit. It has burst diaphragms at either end and its own inject points on the face of the injector plate. This fluid is triethylboron with 10-15 per cent triethylaluminium (known as TEA/TEB) and it is pyrophoric (i.e. self igniting) in the presence of liquid oxygen. Older documents refer to this substance as being hypergolic.

Graph of engine thrust rise during F-1 startup.

At about T minus 8.9 seconds, a signal from the automatic sequencer initiates a number of automatic operations in the engine which includes the firing of four pyrotechnic devices. Two of them are mounted inside the nozzle extension and cause the fuel-rich turbine exhaust gas to ignite when it enters. Another two initiate combustion within the gas generator. Links are burned away by these igniters to generate an electrical signal to move the start solenoid. The start solenoid directs hydraulic pressure from the ground supply to open the main LOX valves. LOX begins to flow through the LOX pump, causing it to begin slowly rotating' The LOX then flows through the injector into the combustion chamber. The opening of both LOX valves also causes another valve to allow fuel and LOX into the gas generator, where they ignite and their exhaust gas cause the turbine to accelerate. Fuel and LOX pressures rise as the turbine gains speed. The fuel-rich exhaust from the gas generator ignites in the engine bell to prevent backfiring and burping of the engine. The increasing pressure in the fuel lines opens a valve, the igniter fuel valve, which lets fuel pressure reach the igniter cartridge which promptly ruptures. TEA/TEB fluid, followed by fuel, enters the chamber through its ports where it spontaneously ignites on contact with the LOX already in the chamber.

Earth Orbit and Translunar Injection

Now safely in orbit, Apollo 11 circles Earth just over one-and-half times while still attached the S-IVB third stage of the Saturn launch vehicle. The crew remove their helmets and gloves, and for a while are free to move around the cabin. They unstow equipment, take some photographs, check the spacecraft systems and make star sightings to refine the alignment of their guidance platform. When over Hawaii for the second time, the S-IVB stage re-ignites to perform the Translunar Injection burn that will send them on their way to the Moon

At 000:18:54 a P52 is peformed (P52' refers to a program within the onboard computer with which Mike Collins will realign the spacecraft's inertial platform.)

Before launch, the platform at the centre of the Inertial Measurement Unit (IMU) was aligned to match the orientation of the launch pad at the moment of launch. For mechanical reasons, the orientation of this platform is prone to drifting away from the intended orientation so at regular points throughout the flight, it is realigned. This tendency to drift is normally very small but the intense vibration and shock that is present during launch and ascent tend to exacerbate it. Controllers can see this misalignment by comparison with the Saturn's own platform so prior to the first P52 realignment of the flight, they pass up a rough estimate of how much misalignment the CMP can expect to compensate for. This is the 'delta azimuth correction' figure.

At the moment that Apollo 11 was inserted into its parking orbit around Earth, an effort began to determine the shape of that orbit. In the first place, controllers wanted to be sure the stack had enough momentum to continue around Earth and was not about to re-enter the atmosphere. Then from an operational standpoint, a good understanding of the orbit was a necessary starting point when calculating the burn that will take the spacecraft to the Moon. Initial indications came from the spacecraft's computer and ground estimations. But as the spacecraft passes over tracking stations, each will add further data points, especially those in Australia which are essentially on the opposite side of the world and which will provide an antinode determination of the orbit.

hasselblad 500c with a dark slide

The crew have a number of Hasselblad 70-mm (film width) stills cameras on board. These have detachable film magazines that can be changed part way through a roll. To prevent the film from being fogged upon removal from the camera, each has a 'dark slide', a thin metal plate that must be inserted to cover the film gate before the magazine can be detached.

At 000:39:40 Collins jettisoned the optics dust cover (The side of the spacecraft opposite the hatch has two orifices through which the spacecraft's two optical instruments can peer. These are the telescope, a one-power, wide-field device intended to permit a star to be located within a constellation. It's field of view is ganged to one of the two lines of sight of the other instrument, a 28-power sextant with which angular measurements can be made. During ascent, the optics were protected by covers which Mike removes by pushing the optics control lever hard to the right.)

The Apollo Star code list

Coded into the computer's fixed rope memory are the positions of 37 stars, the Apollo star code list. Each has a numerical designation in octal (base eight). The computer therefore knows where these stars really are in the celestial sphere. With Mike's sightings, it now knows where they appear to be based on the current orientation of the guidance platform. Comparison of the two sets of data allows the error in the platform's orientation to be calculated and therefore be corrected. This is achieved by 'torquing' or rotating the platform by the required amount using the motors in the supporting gimbals.

At 001:09:22 Buzz Aldrin turns to his left and takes a somewhat blurred color photo of Neil with the Hasselblad camera Buzz then turns towards Mike and photographs him also, along with the TV camera which they have just been discussing.

AS11-36-5291 - Buzz Aldrin's photo of Neil Armstrong during the Earth orbit phase of the mission
AS11-36-5292 - Buzz Aldrin's photo of Mike Collins with TV camera during the Earth orbit phase of the mission.

At approx 001:25:10 Colins, Having lost the camera 5 minutes earlier, he has missed a sunrise photo, but he captures the glaring sun in the sky above the ocean, rising rapidly as a result of their orbital motion. He takes a further 8 photos at this point, through to AS11-36-5301. AS11-36-5298 is the best one showing the low pressure cell.

AS11-36-5293 - Sunrise over Earth - image by LPI
AS11-36-5294 - Earth shortly after sunrise - image by LPI
AS11-36-5295 - Earth shortly after sunrise - image by LPI
AS11-36-5296 - Earth shortly after sunrise - image by LPI
AS11-36-5297 - Earth shortly after sunrise - image by LPI
AS11-36-5298 - Earth shortly after sunrise - image by LPI
AS11-36-5299 - Earth shortly after sunrise - image by LPI
AS11-36-5300 - Earth shortly after sunrise - image by LPI


Standard form in which crews copy abort PAD data. This is the version in Flight Plan.

The PAD is interpreted as follows:
Purpose: This PAD is a contingency in case of abort for a return to Earth with an ignition time approximately 90 minutes after TLI.
Systems: The burn would be made using the large SPS (Service Propulsion System) engine at the rear of the Service Module, under the control of the Guidance and Navigation system.
CSM Weight (Noun 47): 63,481 pounds (28,794 kg). Strictly speaking, a more appropriate term to use would be "mass" rather than "weight". Weight is defined as the force an object exerts when acted upon by gravity whereas mass is a measure of the quantity of matter an object contains. A 1-kg mass exerts 9.81 Newtons on Earth but we would tend to measure that force with a spring balance and call it 1 kilogram. On the Moon, it exerts 1.62 Newtons but its mass is still 1 kilogram so spring balances would have to be recalibrated to read properly. In space, without engines running (i.e. during coast), it exerts essentially no force at all yet still has 1 kilogram of mass.
Pitch and yaw trim (Noun 48): -1.53° and +1.32°. The SPS engine is mounted on gimbals and can be aimed so that its thrust vector (the direction in which it pushes) acts through the spacecraft's centre of mass. These angles represent a calculated direction for these gimbals. They will only be used if the crew need to control the burn manually using the Stabilization Control System (SCS). In a normal automatic burn, the TVC (Thrust Vector Control) system automatically adjusts these angles for shifts in the stack's centre of mass.
Time of ignition (Noun 33): 4 hours, 10 minutes, 25.38 seconds. This is about 90 minutes after TLI.
Change in velocity (Noun 81), fps (m/s): x, -476.1 (-145.1); y, +0.1 (+0.03); z, +5,336.1 (+1,626.4). The change in velocity is resolved into three components which are quoted relative to the LVLH (Local Vertical/Local Horizontal).
LVLH is a frame of reference that is relative to a line drawn from the spacecraft to the centre of the body it is orbiting, or whose sphere of influence it is in.

Diagram to explain the Local Vertical/Local Horizontal frame of reference.

Imagine the point where this line intersects the planet's surface. We can further imagine a flat plane at this point parallel to the horizontal. Obviously, as the spacecraft moves across the planet, the absolute orientation of this plane keeps changing but it provides a useful reference for orbital velocity computation. In this arrangement, the plus-Z axis is along the vertical line towards the planetary centre, the plus-X axis is in the direction of orbital motion parallel to the local horizontal and the plus-Y axis is perpendicular to the orbital plane.
Spacecraft attitude: Roll, 180°; Pitch, 193°; Yaw, 000°. The desired spacecraft attitude is measured relative to the alignment of the guidance platform. At this point, it would be aligned per the launch REFSMMAT. In other words, the platform's axes match the orientation in space of the launch pad at the tie of launch.
HA, expected apogee of resulting orbit (Noun 44): Not applicable. If this abort burn were to be made, the apogee of the resulting orbit would be over 9999.9 nautical miles, beyond the limit of the computer's display.
HP, expected perigee of resulting orbit (Noun 44): 20.3 nautical miles (37.6 km). The perigee distance is so low, it intersects the Earth's atmosphere. What this really means is that the spacecraft will re-enter.
Delta-VT: 5,357.3 fps (1,632.9 m/s). This is the total change in velocity the spacecraft would experience and is a vector sum of the three components given above.
Burn duration or burn time: 6 minutes, 33 seconds.
Delta-VC: 5,334.9 fps. Delta-VC is really about giving the crew another method of controlling their engine. If all goes well, the Guidance and Navigation system will monitor the burn and, taking into account the extra thrust imparted by the engine after it is shut down, it will stop the burn at the right time to give the required total Delta-V. Should the G&N system fail to shut down the engine, the Entry Monitor System (EMS) can do it as it contains an accelerometer that measures Delta-V along the X-axis. This accelerometer drives a counter (hence 'C') that decrements towards zero, at which point it would send a signal to stop the engine. However, the EMS does not take into account the tail-off thrust. For this reason, the figure for Delta-VC is slightly lower than Delta-VT. The crew would enter it into the EMS Delta-V display prior to the burn.
Sextant star: Star 33 (Antares, Alpha Scorpius) visible in sextant when shaft and trunnion angles are 157.8° and 12.2° respectively. This is part of an attitude check.
Boresight star: Not available. This is a second attitude check which is made by sighting on another celestial object with the COAS (Crew Optical Alignment Sight). In this case, no suitable object would be available on that side of the spacecraft.
The next five parameters all relate to re-entry, during which an important milestone is "Entry Interface," defined as being 400,000 feet (121.92 km) altitude. Another important point is when atmospheric drag on the spacecraft imparts a deceleration of 0.05 g.
Expected splashdown point (Noun 61): 2.52° south, 25.8° west; in the mid-Atlantic.
Range to go: 1,188.7 nautical miles (2 201.5 km). To set up their EMS (Entry Monitor System) before re-entry, the crew need to know the expected distance the CM would travel after Entry Interface.
Expected velocity at Entry Interface: 34,345 fps (10,468 m/s).
Time of Entry Interface: 16 hours, 3 minutes and 50 seconds GET. This is the predicted time at which the spacecraft would be at 400,000 feet (121.92 km) altitude.
GDC align stars: The stars to be used for GDC align purposes are the north set, Vega and Deneb. The align angles are roll, 71°; pitch, 291°; yaw, 341°.
The PAD includes some additional notes. The SPS propellant tanks are full, so there would be no need to perform an ullage burn to settle their contents. If it were to be made, the crew should not be docked to the LM.

At 002:53:03 Armstrong praises the launch vehicle "Hey, Houston, Apollo 11. That Saturn gave us a magnificent ride."

Apollo 11 is now safely out of Earth orbit and on its trans-lunar trajectory. Next, it must separate from the final stage of the Saturn launch vehicle and extract the Lunar Module.