Сатурн V ракетының екінші сатысы: S II құрылысы және ерекшеліктері

Second stage of the Saturn V, built by North American Aviationthe functionally defined brain region

The S II (pronounced "S two") was the second stage of the Saturn V rocket. It was built by North American Aviation. Using liquid hydrogen (LH2) and liquid oxygen (LOX) it had five J 2 engines in a quincunx pattern. The second stage accelerated the Saturn V through the upper atmosphere with of thrust.

The beginning of the S II came in December 1959 when a committee recommended the design and construction of a high thrust, liquid hydrogen fueled engine. The contract for this engine was given to Rocketdyne and it would be later called the J 2. At the same time the S II stage design began to take shape. Initially it was to have four J 2 engines and be 74 feet (23 m) in length and in diameter. In 1961 the Marshall Space Flight Center 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 seven 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 had still not yet decided on various aspects of the stage including size, and the upper stages that would be placed on top. On September 11, 1961, the contract was awarded to North American Aviation (who were also awarded the contract for the Apollo Command/Service Module), with the manufacturing plant built by the government at Seal Beach, California. 15 flight stages were to be produced. Plans were also developed to build 10 follow on stages, S II 16 through 25, but funding to assemble them never materialized. These stages would have supported later Apollo missions, including those of the Apollo Applications Program.

When fully loaded with propellant, the S II had a mass of about The hardware was only 7.6% of this—92.4% was liquid hydrogen and liquid oxygen. At the bottom was the thrust structure supporting five J 2 engines in a quincunx arrangement. The center engine was fixed, while the other four were gimballed, similar to the engines on the S IC stage below. Instead of using an intertank (empty container between tanks) like the S IC, the S II used a common bulkhead (similar to that of the S IV and S IVB stages) that included both the top of the LOX tank and bottom of the LH2 tank. It consisted of two aluminum sheets separated by a honeycomb structure made of phenolic resin. It insulated a temperature differential between the two tanks. The use of a common bulkhead saved 3.6 tonnes in weight, both by eliminating one bulkhead and by reducing the overall length of the stage. The S II's common bulkhead design was tested in 1965 on the subscale Common Bulkhead Test Tank (CBTT), made of only 2 LH2 tank cylinders. It was formed by welding 12 gores (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 explosions to shape each gore. The LH2 tank was constructed of six cylinders: five were 2.4 meters high and the sixth was 0.69 meters high. The biggest challenge was the insulation. Liquid hydrogen must be kept colder than about 20 °C above absolute zero so good insulation is very important. Initial attempts did not work well: there were bonding issues and air pockets. Initially, the stage was insulated with a honeycomb material. These panels had grooves milled in the back which were purged with helium during filling. The final method was to spray insulation on by hand and trim the excess. This change saved both weight and time and avoided the issues with air pockets entirely. The LH2 tank volume was for storing of liquid hydrogen. The S II was constructed vertically to aid welding and keep the large circular sections in the correct shape.

Serial number Use Launch date Current location NotesCommon Bulkhead Test Tank (CBTT)Demonstrated S II's common bulkhead on a subscale tankUnknownSubscale S II tank assembly composed of two LH2 tank cylinders, a standard forward bulkhead, common dome, and aft skirt with a modified aft bulkhead. Tested in 1965. S II FUsed as Dynamic Test Stage replacement after destruction of S II S/D and S II TAt the U. S. Space & Rocket Center, Huntsville, Alabama Completed facilities checkouts and propellant load tests at Kennedy Space Center in 1966 as part of the SA 500F stack. Interstage failed to separate due to payload damage during launch. S II 14Apollo 18 (cancelled)N/AApollo Saturn V Center, Kennedy Space Center From the cancelled Apollo 18 mission. S II 15Apollo 19, later Skylab 1 backup (not flown)N/AJohnson Space Center From SA 515 the Skylab backup vehicle which NASA did not use. Also earmarked for Apollo 19.