S-IVB
The deadline for proposals to build the upper stage of a new rocket was the 29th of February 1960. Eleven companies submitted bids to NASA with hopes of securing the contract. Douglas Aircraft Company won the award on April 19 after administrator T. Keith Glennan made his decision. Convair had finished second in the competition but lost out because Glennan did not want one company to dominate the liquid hydrogen market. Convair already built the Centaur stage for the Atlas-Centaur rocket and adding another major program would have been too much concentration of power. The Marshall Space Flight Center chose Douglas partly because their previous work on the S-IV stage showed strong similarities to what they needed now. This earlier stage used six RL-10 engines while the new design required only a single J-2 engine. The name S-IVB came from its evolution as an uprated version of the original S-IV stage. It became the first stage designed specifically for the C-5 rocket which later received the official name Saturn V.
Douglas built two distinct versions of this stage known as the 200 series and the 500 series. The 200 series flew on the Saturn IB vehicle and lacked a flared interstage found on the larger rockets. It carried less helium pressurization since it never needed to restart its main engine during flight. Three solid rockets separated the 200 series from the S-IB stage below it. The 500 series featured a flared interstage matching the diameter of the S-II stage on the Saturn V. Two small Auxiliary Propulsion System thruster modules replaced three solid rockets in the 500 configuration. These APS modules provided ullage motors for restarting the J-2 engine and attitude control during coast phases. Each module contained dinitrogen tetroxide and monomethyl hydrazine propellant tanks plus compressed helium. The stage itself held thousands of pounds of liquid oxygen and liquid hydrogen fuel. Empty mass measurements varied between configurations but remained substantial due to heavy tanking requirements.
Lunar missions required firing this stage twice during a single mission profile. The first ignition occurred after the second stage cutoff to achieve Earth orbit insertion. A second burn followed later to perform translunar injection toward the Moon. This dual firing sequence distinguished lunar flights from suborbital test missions. Apollo 4 marked the first time a 500 series stage restarted its J-2 engine successfully. That event placed both spacecraft and stage on an Earth-intersecting trajectory. Some early tests like AS-203 exploded in orbit while testing bulkhead behavior under weightlessness. Data from those failures validated whether the restart capability could work on future missions. The Auxiliary Propulsion System handled roll control during main engine firings and three-axis stability during long coast periods. Engineers used specific thruster sizes ranging from 150-pound-force units to larger propulsion modules for precise maneuvering.
A surplus tank with serial number 212 became the hull for Skylab, America's first space station. Douglas converted this empty vessel into a habitable module before launch. Skylab lifted off aboard a Saturn V rocket on the 14th of May 1973. It reentered Earth's atmosphere over the Pacific Ocean on the 11th of July 1979. Another unit, serial number 515, was modified as a backup Skylab but never flew into space. Stages numbered 206 through 210 were produced between 1966 and 1967 then stored at Huntington Beach until 1971. They underwent refurbishment and ground testing before shipping to Kennedy Space Center. Stage 209 served as an unflown rescue vehicle for Apollo Soyuz Test Project operations. These conversions demonstrated how engineers repurposed spent hardware rather than discarding it entirely.
Starting with Apollo 13 in April 1970, mission planners deliberately crashed spent stages into the Moon. The impact generated seismic waves that instruments measured to characterize the lunar interior. S-IVB-508 struck the surface on the 14th of April 1970 following its use in the Apollo 13 mission. Subsequent impacts occurred during Apollo 14, 15, 16, and 17 missions. Each crash provided data about moonquakes and internal structure beneath the surface. Some stages like 507 remained in heliocentric orbit while others impacted the lunar terrain. A 200 series stage from AS-201 impacted the Atlantic Ocean at coordinates 9.6621 South latitude and 10.0783 East longitude. These experiments turned discarded rocket parts into scientific tools for understanding planetary geology.
Twelve 200-series units and sixteen 500-series units were built alongside three test stages. Additional orders for four more 200-series stages canceled in August 1968 before assembly began. Two extra 500-series stages intended for rockets 516 and 517 also faced cancellation around the same time. Stage S-IVB-S known as Battleship was scrapped in 2024 after sitting atop another vehicle at Ardmore, Alabama. Facilities test stage F appears to have been destroyed in the 1990s. Dynamic test stage D now resides at the U.S. Space & Rocket Center in Huntsville. Unused unit 211 remains on display at the same facility. Several flight stages decayed naturally or impacted oceans during their missions. Backup vehicles like 515 converted to Skylab B never launched but sit preserved at the National Air and Space Museum today.
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Common questions
When was the deadline for proposals to build the S-IVB upper stage?
The deadline for proposals to build the upper stage of a new rocket was the 29th of February 1960. Eleven companies submitted bids to NASA with hopes of securing the contract.
Which company won the contract to build the S-IVB stage and why did they win it?
Douglas Aircraft Company won the award on April 19 after administrator T. Keith Glennan made his decision. The Marshall Space Flight Center chose Douglas partly because their previous work on the S-IV stage showed strong similarities to what they needed now.
What is the difference between the 200 series and 500 series versions of the S-IVB stage?
The 200 series flew on the Saturn IB vehicle and lacked a flared interstage found on the larger rockets. The 500 series featured a flared interstage matching the diameter of the S-II stage on the Saturn V and used Auxiliary Propulsion System thruster modules instead of three solid rockets.
How many times did the S-IVB stage fire during lunar missions and when did this begin?
Lunar missions required firing this stage twice during a single mission profile to achieve Earth orbit insertion and perform translunar injection toward the Moon. Apollo 4 marked the first time a 500 series stage restarted its J-2 engine successfully in April 1967.
When was Skylab launched and when did it reenter Earth's atmosphere?
Skylab lifted off aboard a Saturn V rocket on the 14th of May 1973. It reentered Earth's atmosphere over the Pacific Ocean on the 11th of July 1979.
Which S-IVB stages were crashed into the Moon for seismic experiments and what data did they provide?
Starting with Apollo 13 in April 1970, mission planners deliberately crashed spent stages into the Moon to generate seismic waves that instruments measured to characterize the lunar interior. Subsequent impacts occurred during Apollo 14, 15, 16, and 17 missions to provide data about moonquakes and internal structure beneath the surface.