The Saturn V launch vehicle (SA-508) assigned to the Apollo 13 mission was developed at the Marshall Space Flight Center, Huntsville, Ala. The vehicle is almost identical to those used in the missions of Apollo 8 through 12.

The Saturn V rocket for Apollo 13 is illuminated by flood lights during pre-launch countdown demonstration test. Photo: NASA/KSC

First Stage
The first stage (S-IC) of the Saturn V is built by the Boeing Company at NASA's Michoud Assembly Facility, New Orleans, La. The stages five F-1 engines develop a total of about 7.6 million pounds of thrust at launch. Major components of the stage are the forward skirt, oxidizer tank, intertank structure, fuel tank, and thrust structure. Propellant to the five engines normally flows at a rate of 29,364.5 pounds (3,400 gallons) each second. One engine is rigidly mounted on the stage's centerline; the other four engines are mounted on a ring at 90 degree angles around the center engine. These four outer engines are gimbaled to control the vehicle's attitude during flight.

Second Stage
The second stage (S-II) is built by the Space-Division of the North American Rockwell Corporation at Seal Beach, Calif. Five J-2 engines develop a total of about 1.16 million pounds of thrust during light. Major structural components are the forward skirt, liquid hydrogen and liquid oxygen tanks (separated by an insulated common bulkhead), a thrust structure, and an interstage section that connects the first and second stages. The five engines are mounted and used in the same way as the first stage's F-1 engines: four outer engines can be gimbaled; the center one is rigid.

Third Stage
The third stage (S-IVB) is built by the McDonnell Douglas Astronautics Company at Huntington Beach, Calif. Major components are the aft interstage and skirt, thrust structure, two propellant tanks with a common bulkhead, a forward skirt, and a single J-2 engine. The gimbaled engine has a maximum thrust of 230,000 pounds, and can be shut off and restarted.

Instrument Unit
The instrument unit (IU), built by the International Business Machines Corp., at Huntsville, Ala., contains navigation, guidance and control equipment to steer the launch vehicle into its Earth orbit and into translunar trajectory. The six major systems are structural, thermal control, guidance and control, measuring and telemetry, radio frequency, and electric.

The instrument unit provides a path-adaptive guidance scheme where in a programmed trajectory is used during first stage boost with guidance beginning during second stage burn. This scheme prevents movements that could cause the vehicle to break up while attempting to compensate for winds or jet streams in the atmosphere.

The instrument unit's inertial platform (heart of the navigation, guidance and control system) provides space-fixed reference coordinates and measures acceleration along three mutually perpendicular axes of a coordinate system. If the platform fails during boost, systems in the Apollo spacecraft are programmed to provide guidance for the launch vehicle. After second stage ignition, the spacecraft commander could manually steer the vehicle in the event of loss of the launch vehicle inertial platform.

Propulsion
The Saturn V has 37 propulsive units, with thrust ratings ranging from 70 pounds to more than 1.5 million pounds. The large main engines burn liquid propellants; the smaller units use solid or hypergolic propellants.

The first stage separates during an earlier Saturn V rocket launch. Photo: NASA/KSC

The five F-1 engines on the first stage burn a combination of RP-1 (kerosene) as fuel and liquid oxygen as oxidizer. Each engine develops approximately 1,516,918 pounds of thrust at liftoff, building to about 1,799,022 pounds before cutoff. The five-engine cluster gives the first stage a thrust range of from 7,584,593 pounds at liftoff to 8,995,108 pounds just before center engine cutoff. The F-1 engine weighs almost 10 tons, is more than 18 feet long and has a nozzle exit diameter of nearly 14 feet. The engine consumes almost three tons of propellant every second.

The first stage also has eight solid-fuel retrorockets that fire to separate the first and second stages. Each retrorocket produces a thrust of 87,900 pounds for 0.6 seconds.

The second and third stages are powered by J-2 engines that burn liquid hydrogen (fuel) and liquid oxygen (oxidizer). J-2 engine thrust varies from 184,841 to 232,263 pounds during flight. The 3,500-pound J-2 engine is considered more efficient than the F-1 engine because the J-2 burns high-energy liquid hydrogen. F-1 and J-2 engines are built by the Rocketdyne Division of the North American Rockwell Corp.

The second stage also has four 21,000-pound-thrust solid fuel ullage rockets that settle liquid propellant in the bottom of the main tanks and help attain a "clean' separation from the first stage. Four retrorockets, located in the S-IVB's aft interstage (which never separates from the S-II), separate the S-II from the S-IVB. There are two jettisonable ullage rockets for propellant settling before engine ignition. Eight smaller engines in the two auxiliary propulsion system modules on the S-IVB stage provide three-axis attitude control.