S-II

S II

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S-II

The S-II (pronounced "ess two") was the second stage of the Saturn V

Saturn V

The Saturn V was a multistage rocket liquid-fuel expendable launch system rocket used by NASA's Apollo program and Skylab programs from 1967 until 1973....
rocket. It was built by North American Aviation

North American Aviation

North American Aviation was a major United States aircraft manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter aircraft, the B-25 Mitchell bomber, the F-86 Sabre jet aircraft fighter, and the X-15 rocket plane, as well as Apollo Apollo spacecraft, the second stage of the Satu...
. Using liquid hydrogen (LH2) and liquid oxygen (LOX) it had five J-2 engines

J-2 (rocket engine)

Rocketdyne's J-2 was America's largest production liquid hydrogen fueled rocket engine before the Space Shuttle main engines , and is being revived in support of Project Constellation....
in a cross pattern. The second stage accelerated the Saturn V through the upper atmosphere with 5 MN of thrust.

beginning of the S-II came in December 1959 when a committee recommended the design and construction of a high-thrust, liquid hydrogen

Liquid hydrogen

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Encyclopedia

The S-II (pronounced "ess two") was the second stage of the Saturn V

Saturn V

North American Aviation

J-2 (rocket engine)

History

The beginning of the S-II came in December 1959 when a committee recommended the design and construction of a high-thrust, liquid hydrogen

Liquid hydrogen

Rocketdyne

Pratt & Whitney Rocketdyne is a United States company that designs and produces rocket engines that use liquid rocket propellants. Pratt & Whitney Rocketdyne is a division of Pratt & Whitney, itself a wholly owned subsidiary of United Technologies Corporation, headquartered in Canoga Park, California....
and it would be later called the J-2

J-2 (rocket engine)

Rocketdyne's J-2 was America's largest production liquid hydrogen fueled rocket engine before the Space Shuttle main engines , and is being revived in support of Project Constellation....
. At the same time the S-II stage design began to take shape. Initially it was to have four J-2 engines and be 22.5 meters in length and 6.5 meters in diameter.

In 1961 the Marshall Space Flight Center

Marshall Space Flight Center

The George C. Marshall Space Flight Center , the original home of NASA, is a lead center for Spacecraft propulsion, Space Shuttle propulsion, Space Shuttle external tank, crew training and payloads, International Space Station design and construction, for computers, networks, and information management....
began the process to find the contractor to build the stage. Out of the 30 aerospace companies invited to a conference where the initial requirements were laid out, only 7 submitted proposals a month later. Three of these were eliminated after their proposals had been investigated. However it was then decided that the initial specifications for the entire rocket were too small and so it was decided to increase the size of the stages used. This raised difficulties for the four remaining companies as NASA

NASA

The National Aeronautics and Space Administration is an agency of the Federal government of the United States, responsible for the nation's public list of space agencies....
had still not yet decided on various aspects of the stage including size, and the upper stages that would be placed on top.

In the end on 11 September 1961 the contract was awarded to North American Aviation

North American Aviation

North American Aviation was a major United States aircraft manufacturer, responsible for a number of historic aircraft, including the T-6 Texan trainer, the P-51 Mustang fighter aircraft, the B-25 Mitchell bomber, the F-86 Sabre jet aircraft fighter, and the X-15 rocket plane, as well as Apollo Apollo spacecraft, the second stage of the Satu...
(who were also awarded the contract for the Apollo Command/Service Module

Apollo Command/Service Module

The Command/Service Module was a spacecraft built for NASA by North American Aviation. It was one of the two spacecraft that were utilized for the Apollo program, along with the Apollo Lunar Module, to land astronauts on the Moon....
), with the manufacturing plant built by the government at Seal Beach, California

California

California is a U.S. state on the West Coast of the United States of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, Arizona to the southeast, and to the south the Mexico state of Baja California....
.

Configuration

When fully loaded with fuel, the S-II had a mass of about 500,000 kg. The hardware was only 3% of this—97% was liquid hydrogen and liquid oxygen.

At the bottom was the thrust structure supporting five J-2 engines. The center engine was fixed, while the other four were gimbal

Gimbal

A gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of two gimbals, one mounted on the other with pivot axes orthogonal, may be used to allow an object mounted on the innermost gimbal to remain immobile regardless of the motion of its support....
led.

Instead of using an intertank (empty container between tanks) like the S-IC

S-IC

The S-IC was the first Multistage rocket of the Saturn V rocket. The S-IC first stage was built by The Boeing Company. Like the first stages of most rockets, most of its mass of over two thousand metric tonnes at launch was propellant, in this case RP-1 rocket fuel and liquid oxygen oxidizer....
, the S-II used a common bulkhead that included both the top of the LOX tank and bottom of the LH2 tank. It consisted of two aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
sheets separated by a honeycomb structure made of phenol

Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
. It insulated a 70 °C (125 °F) temperature differential between the two tanks. The use of a common bulkhead saved 3.6 tonnes in weight.

The LOX

Liquid oxygen

Liquid oxygen is a form of the element oxygen. It has a pale blue color and is strongly paramagnetism. Liquid oxygen has a density of 1.141 g/cm? and is moderately cryogenics ...
tank was an ellipsoid

Ellipsoid

An ellipsoid is a type of Quadric that is a higher dimensional analogue of an ellipse. The equation of a standard axis-aligned ellipsoid body in an xyz-Cartesian coordinate system is...
al container of 10 meters diameter and 6.7 meters high. It was formed by welding 12 gores

Gore (segment)

A gore is a segment of a three-dimensional space shape fabricated from a two-dimensional material. The term was originally used to describe triangular shapes, but is now extended to any shape that can be used to create the third dimension....
(large triangular sections) and two circular pieces for the top and bottom. The gores were shaped by positioning in a 211,000 liter tank of water with three carefully orchestrated sets of underwater explosion

Underwater explosion

An underwater explosion, also known as an UNDEX, is an explosion beneath the surface of water. The type of explosion may be Explosive material or Nuclear explosive....
s to shape each gore.

The LH2

Liquid hydrogen

Liquid hydrogen is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecule H2 form.To exist as a liquid, H2 must be pressurized and cooled to a very low temperature, 20.28 K ....
tank was constructed of six cylinders: five were 2.4 meters high and the sixth 0.69 meter high. The biggest challenge was the insulation. Liquid hydrogen must be kept colder than about 20 °C above absolute zero (20 K or −252 °C or −423 °F) so good insulation is very important. Initial attempts did not work well: there were bonding issues and air pockets. The final method was to spray insulation on by hand and trim the excess.

The S-II was constructed vertically to aid welding and keep the large circular sections in the correct shape.

Stages Built

} |Carried "Camera Targets" spaced around the forward skirt and carried cameras to record first stage separation |- |S-II-2 |Apollo 6

Apollo 6

Apollo 8

Apollo 8 was the first manned space voyage to achieve a velocity sufficient to allow escape from the gravitational field of planet Earth; the first to escape from the gravitational field of another celestial body; and the first manned voyage to return to planet Earth from another celestial body....
|December 21, 1968 | | |- |S-II-4 |Apollo 9

Apollo 9

Apollo 9 was the first manned flight of the Apollo Command/Service Module along with the Apollo Lunar Module . Its three-person crew of Mission Commander Jim McDivitt, Command Module Pilot David Scott, and Lunar Module Pilot Rusty Schweickart tested several aspects critical to landing on the moon including the LM engines, backpack life suppo...
|March 3, 1969 | |1800 kg lighter allowing 600 kg more payload, more powerful engines and carried more LOX |- |S-II-5 |Apollo 10

Apollo 10

Apollo 10 was the fourth manned mission in the Apollo program. The mission included the second crew to orbit the Moon and an all-up test of the Apollo Lunar Module in lunar orbit....
|May 18, 1969 | | |- |S-II-6 |Apollo 11

Apollo 11

Apollo 12

Apollo 13

Apollo 13 was the third manned lunar-landing mission, part of Project Apollo under NASA in the United States. The crew members were Commander Jim Lovell, Command Module pilot Jack Swigert, and Lunar Module pilot Fred W....
|April 11, 1970 | |Inboard engine failed during ascent due to pogo oscillations. |- |S-II-9 |Apollo 14

Apollo 14

Apollo 14 was the eighth manned mission in the Apollo program and the third mission to land on the Moon. The 9 day mission was launched on January 31 1971, with lunar touch down on February 5....
|January 31, 1971 | | |- |S-II-10 |Apollo 15

Apollo 15

Apollo 15 was the ninth manned mission in the Apollo program and the fourth mission to land on the Moon. It was the first of what were termed "J missions", long duration stays on the Moon with a greater focus on science than had been possible on previous missions....
|July 26, 1971 | | |- |S-II-11 |Apollo 16

Apollo 16

Apollo 17

Apollo 17 was the eleventh Human spaceflight in the NASA Apollo program. It was the first night launch of a United States human spaceflight and the sixth and final lunar landing mission of the Apollo program....
|December 7, 1972 | | |- |S-II-13 |Skylab 1 |May 14, 1973 | |Modified to act as the terminal stage |- |S-II-14 |Apollo 18 (cancelled) |N/A |Apollo-Saturn V Center, Kennedy Space Center

Kennedy Space Center

The John F. Kennedy Space Center is the NASA space vehicle launch facility and Launch Control Center on Merritt Island, Florida, Brevard County, Florida, United States....
|From the cancelled Apollo 18 mission. |- |S-II-15 |Skylab 1 backup (not flown) |N/A |Johnson Space Center |From SA-515 the Skylab backup vehicle which NASA did not use. |}