The Saturn rocket series’ biggest brother, the culmination of America’s efforts during the Cold War Space Race against the Russians, and the paragon of human spaceflight achievement, The Apollo program’s primary tool was the mighty Saturn V, the pride of American space exploration, and NASA’s poster child. Designed by Wehrner von Braun, the massive rocket took 24 astronauts beyond Earth’s orbit, 12 of which walked on the Moon.
The Saturn V dwarfed every previous rocket fielded by America in the Space Race, remaining to this day the tallest, heaviest, and most powerful rocket ever brought to operational status and still holds records for the heaviest payload launched and largest payload capacity. On the pad, she stood 363 feet (111m) tall, taller than the Statue of Liberty by 58 feet, with a diameter of 33 feet (10m), and weighed 6.5 million pounds fully fueled. Her designed payload capacity was rated at 261,000 pounds (118,000 kg) to Low Earth Orbit and 90,000 pounds (41,000 kg) to the Moon, but in later missions was able to carry about 310,000 pounds (140,000 kg) to LEO and sent up to 107,100 lb (48,600 kg) worth of spacecraft to the Moon.
The total launch vehicle was a 3 stage vehicle: the S-IC first stage, S-II second stage and the S-IVB third stage. The first stage used RP-1 for fuel, while the second and third stages used liquid hydrogen (LH2), with all three using liquid oxygen (LOX) for oxidizer.
The first stage of the Saturn V is the lower section of the rocket, producing the most thrust in order to get the vehicle off the pad and up to altitude for the second stage.
The Rocketdyne F-1 engine used to propel the rocket was designed for the U.S. Air Force by Rocketdyne for use on ICBM’s, but was dropped and picked up by NASA for use on their rockets. This engine still is the most powerful single combustion chamber engine ever produced, producing 1,522,000 lbf (6,770 kN) at sea level and 1,746,000 lbf (7,770 kN) in a vacuum. The S-IC has five F-1 engines. Total thrust on the pad, once fully throttled, was well over 7,600,000 lbf, consuming the RP-1 fuel and LOX oxidizer at a jaw-dropping 13 metric tonnes per second.
The launch sequence for the first stage begins at approx. T-minus 8.9 seconds, when the five F-1 engines are ignited to achieve full throttle on t-minus 0. The center engine ignited first, followed by opposing outboard pairs at 300-millisecond intervals to reduce the structural loads on the rocket. When thrust had been confirmed by the onboard computers, the rocket was “soft-released” in two stages: first, the hold-down arms released the rocket, and second, as the rocket began to accelerate upwards, it was slowed by tapered metal pins pulled through dies for half a second.
It took about 12 seconds for the rocket to clear the tower. During this time, it yawed 1.25 degrees away from the tower to ensure adequate clearance despite adverse winds. (This yaw, although small, can be seen in launch photos taken from the east or west.) At an altitude of 430 feet (130 m) the rocket rolled to the correct flight azimuth and then gradually pitched down until 38 seconds after second stage ignition. This pitch program was set according to the prevailing winds during the launch month. The four outboard engines also tilted toward the outside so that in the event of a premature outboard engine shutdown the remaining engines would thrust through the rocket’s center of gravity. At this point in the launch, forces exerted on the astronauts is about 1.25 g.
At about T+ 1 minute, the rocket has gone supersonic, at which point, shock collars form around the rocket’s second stage separator. At this point, the vehicle is between 3 and 4 nautical miles in altitude.
As the rocket ascends into thinner atmosphere and continues to burn fuel, the rocket becomes lighter, and the engine efficiency increases, accelerating the rocket at a tremendous rate. At about 80 seconds, the rocket experienced maximum dynamic pressure. Once maximum efficiency of the F-1 engines is achieved, the total thrust peaks at around 9,000,000 lbf. At T+ 135 seconds, astronaut strain has increased to a constant 4 g’s.
At around T+ 168 seconds, the engines cut off as all fuel in the first stage is expended. At this point in flight, the rocket is at an altitude of about 36 nautical miles (67 km), was downrange about 50 nautical miles (93 km), and was moving about 6,164 miles per hour (2,756 m/s). The first stage separates at a little less than 1 second following engine cutoff to allow for engine trail-off. Eight small solid fuel separation motors backs the S-IC from the rest of the vehicle, and the first stage continues ballistically to an altitude of about 59 nautical miles (109 km) and then falls in the Atlantic Ocean about 300 nautical miles (560 km) downrange. Contrary to the common misconception, the S-IC stage never leaves Earth’s atmosphere, making it, technically, an aircraft.
The second stage is responsible with propelling the vehicle to orbital altitude and velocity. Already up to speed and altitude, the second stage doesn’t require as much Delta-V to achieve it’s operation.
For the first two unmanned launches, eight solid-fuel ullage motors ignited for four seconds to give positive acceleration to the S-II stage, followed by start of the five Rocketdyne J-2 engines. For the first seven manned Apollo missions only four ullage motors were used on the S-II, and they were eliminated completely for the final four launches.
About 30 seconds after first stage separation, the interstage ring dropped from the second stage. This was done with an inertially fixed attitude so that the interstage, only 1 meter from the outboard J-2 engines, would fall cleanly without contacting them. Shortly after interstage separation the Launch Escape System was also jettisoned.
About 38 seconds after the second stage ignition the Saturn V switched from a preprogrammed trajectory to a “closed loop” or Iterative Guidance Mode. The Instrument Unit now computed in real time the most fuel-efficient trajectory toward its target orbit. If the Instrument Unit failed, the crew could switch control of the Saturn to the Command Module’s computer, take manual control, or abort the flight.
About 90 seconds before the second stage cutoff, the center engine shut down to reduce longitudinal pogo oscillations (a forward/backward oscillation caused by the unstable combustion of propellant). At around this time, the LOX flow rate decreases, changing the mix ratio of the two propellants, ensuring that there would be as little propellant as possible left in the tanks at the end of second stage flight. This was done at a predetermined Delta-V.
Five level sensors in the bottom of each S-II propellant tank are armed during S-II flight, allowing any two to trigger S-II cutoff and staging when they were uncovered. One second after the second stage cut off it separates and several seconds later the third stage ignited. Solid fuel retro-rockets mounted on the interstage at the top of the S-II fires to back it away from the S-IVB. The S-II impacts about 2,300 nautical miles (4,200 km) from the launch site.
The S-II would burn for 6 minutes to propel the vehicle to 109 miles (175km) and 15,647 mph, close to orbital velocity.
Now in space, the third stage, the S-IVB’s sole purpose is to prepare and push the Command, Service, and Lunar Modules to the Moon via TLI.
Unlike the two-plane separation of the S-IC and S-II, the S-II and S-IVB stages separated with a single step. Although it was constructed as part of the third stage, the interstage remained attached to the second stage.
During Apollo 11, a typical lunar mission, the third stage burned for about 2.5 minutes until first cutoff at 11 minutes 40 seconds. At this point it was 1,430 nautical miles (2,650 km) downrange and in a parking orbit at an altitude of 103.2 nautical miles (191.1 km) and velocity of 17,432 mph (7,793 m/s). The third stage remained attached to the spacecraft while it orbited the Earth one and a half times while astronauts and mission controllers prepared for translunar injection.
This parking orbit is quite low, and would eventually succumb to aerodynamic drag if maintained, but on lunar missions, this can be gotten away with because the vehicle is not intended to stay in said orbit for long. The S-IVB also continued to thrust at a low level by venting gaseous hydrogen, to keep propellants settled in their tanks and prevent gaseous cavities from forming in propellant feed lines. This venting also maintained safe pressures as liquid hydrogen boiled off in the fuel tank. This venting thrust easily exceeded aerodynamic drag.
On Apollo 11, TLI came at 2 hours and 44 minutes after launch. The S-IVB burned for almost six minutes giving the spacecraft a velocity close to the Earth’s escape velocity of 25,053 mph (11,200 m/s). This gave an energy-efficient transfer to lunar orbit, with the Moon helping to capture the spacecraft with a minimum of CSM fuel consumption.
After the TLI, the Saturn V has fullfilled its purpose of getting the Apollo crew and modules on their way to the Moon. At around 40 minutes after TLI, the Command Service module (the conjoined Command module and Service Module) separate from the LM adapter, turns 180 degrees, and docks with the exposed Lunar Module. After 50 minutes, the 3 modules separate from the spent S-IVC, in a process known as Transposition, docking and extraction.
Of course, if the S-IVC were to remain on the same course (in other words, if they leave it right there unattended), due to the physics of zero gravity environments, the third stage would present a collision hazard for the Apollo modules. To prevent this, its remaining propellants were vented and the auxiliary propulsion system fired to move it away. Before Apollo 13, the S-IVB was directed to slingshot around the Moon into a solar orbit, but from 13 onward, the S-IVB was directed to actually impact the Moon. The reason for this was for existing probes to register the impacts on their seismic sensors, giving valuable data on the internals and structure of the Moon.
Launch Escape System
The Saturn V carries a frightening amount of potential energy (the Saturn V on the pad, if launch failed and the rocket ruptured and exploded, would have released an energy equivalent to 2 kilotons of TNT, a force shy of the smallest atomic weapons), which luckily was unleashed as planned without incident. However, this being NASA, precautions were made to save the crew in event of a catastrophic failure.
The LES (Launch Escape System) has been around since the Mercury Program as a way to get the crew capsule away from a potential explosion on the pad or in early launch. The idea is that a small rocket would take the capsule far enough away from the rocket that parachutes could be deployed.
The LES included three wires that ran down the exterior of the launch vehicle. If the signals from any two of the wires were lost, the LES would activate automatically. Alternatively, the Commander could activate the system manually using one of two translation controller handles, which were switched to a special abort mode for launch. When activated, the LES would fire a solid fuel escape rocket, and open a canard system to direct the Command Module away from, and off the path of, a launch vehicle in trouble. The LES would then jettison and the Command Module would land with its parachute recovery system.
If the emergency happened on the launch pad, the LES would lift the Command Module to a sufficient height to allow the recovery parachutes to deploy safely before coming in contact with the ground.
An interesting factoid is how much power the LES possesses; in fact, the LES rocket produces more thrust (147,000 pounds-force (650 kN) sea level thrust) than the Mercury-Redstone rocket (78,000 pounds-force (350 kN)) used to launch Freedom-7 during the Mercury program.
After budget cuts necessitated mission cancellations and the end of the Apollo program, NASA still had at least one Saturn V rocket intended for Apollo 18/19. Luckily, in 1965, the Apollo Applications Program was established to find a use for the Saturn V rocket following the Apollo program. Much of the research conducted in this program revolved around sending up a space station. This station (now known as Skylab) would be built on the ground from a surplus Saturn IB second stage and launched on the first two live stages of a Saturn V.
The only significant changes to the Saturn V from the Apollo configurations involved some modification to the S-II to act as the terminal stage for inserting the Skylab payload into Earth orbit, and to vent excess propellant after engine cutoff so the spent stage would not rupture in orbit. The S-II remained in orbit for almost two years, and made an uncontrolled re-entry on January 11, 1975.
This would be NASA’s only Saturn V launch not associated with the Apollo program, and unfortunately, would prove to be the Saturn V’s last one. There were other concepts for Saturn V’s as launch vehicles, including a space shuttle design, but none of these ever came to fruition.
From 1964 until 1973, a total of $6.417 billion ($41.4 billion in 2016) was appropriated for the Saturn V, with the maximum being in 1966 with $1.2 billion ($8.75 billion in 2016).
Displays and Survivors
There are several displays of Saturn V rockets around the United States, including a few test rockets and unused ones intended for flight. The list below details what and where they are.
- Two at the U.S. Space & Rocket Center in Huntsville:
SA-500D is on horizontal display made up of S-IC-D, S-II-F/D and S-IVB-D. These were all test stages not meant for flight. This vehicle was displayed outdoors from 1969 to 2007, was restored, and is now displayed in the Davidson Center for Space Exploration. The second display here is a vertical display (replica) built in 1999 located in an adjacent area.
- One at the Johnson Space Center made up of first stage from SA-514, the second stage from SA-515 and the third stage from SA-513 (replaced for flight by the Skylab workshop). With stages arriving between 1977 and 1979, this was displayed in the open until its 2005 restoration when a structure was built around it for protection. This is the only display Saturn consisting entirely of stages intended to be launched.
- One at the Kennedy Space Center Visitor Complex, made up of S-IC-T (test stage) and the second and third stages from SA-514. It was displayed outdoors for decades, then in 1996 was enclosed for protection from the elements in the Apollo/Saturn V Center.
- The S-IC stage from SA-515 is on display at the Michoud Assembly Facility in New Orleans, Louisiana.
- The S-IVB stage from SA-515 was converted for use as a backup for Skylab, and is on display at the National Air and Space Museum in Washington, D.C.