the saturn s-ii

8/6/2019 The Saturn S-II

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SATURN

N O R T H A M E R I C A N A V IA T IO N , IN C . SPACE and INFORMATION SYSTEMS DIVISION


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THE S - l l

The S - l l is the second stage of NASA's Apol lo moon-landing rocket - he giantSaturn V. The most powerful hydrogen-fueled booster under production, the S - I l i sdestined for Apo llo manned lunar missions and w i l l help power three Americans to themoon. The S - l l is being developed and manufactured a t Seal Beach, Calif., byNo rth American's Space and Information Systems Division, Downey, Cali f., underthe technical direction of NASA's Ma nh al l Space Fli ght Center, Huntsville, Ala.


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The S - l l stands 81-1/2 feet high, has a 33-foot diameter, and weighs 80,000pounds empty and 1,025,000 pounds loaded. I t is constructed ~ r i m a r i l ~f an aluminumal lo y (2014-T6 aluminum). With its fi ve Rocketdyne J-2 engines of 200,000 poundsthrust each, the S - l l develops a total thrust of one mi ll ion pounds. Graphically, aPolaris missile could spin lengthwise on a string inside the S- l l , and a Minuteman missilewould reach the S - I l l s chest. (Figure 1 )

LIQUID HYDROGEN FUEL

The S - l l is powered by a combination of liquid hydrogen and liquid oxygen pro-pellants, Liqu id hydrogen i s a colorless, tasteless, odorless gas. Its atom i s the lightestknown. When reduced to a temperature of 423 degrees below zero Fahrenheit, i t becomesa liqu id . Because li qu id hydrogen offers a maximum amount of energy per pound, i tbecomes possible to l i f t payloads which would require three or more stages using otherfuels, In its li qui d state, hydrogen forms the newest of the nation's space fuels.

S - l l ASSEMBLY

Starting at the top is the forward skirt to which the upper S-IVB (thi rd stage)connects. Below it, occupying more than half the total length of the stage, i s the288,750-gallon li qu id hydrogen tank. The domed top of the tank i s called the forward(I quid hydrogen) bulkhead. The tank's cy lindrica l sides comprise the six l iq ui d hydrogencylinders. Below this tank i s the common or intermediate bulkhead that forms the bottomof the li qu id hydrogen tank and the top of the 93,750-gallon li qu id oxygen tank.Actually, i t i s two bulkheads in one: the af t common bulkhead and the forward commonbulkhead, The bottom of the li qu id oxygen tank i s called the af t (I quid oxygen)bulkhead. A bolting ring attaches the liquid oxygen tank to the S - l l structure. Belowthe af t bulkhead i s the thrust structure and the a f t sk ir t assembly. Then comes the heatshield, and the interstage which attaches to the bottom first stage (S-IC) of the SaturnV. (Figure 2)

NEW TECHNIQUES

The construction of a rocket so big, yet so delica te, ca lle d for revolutionarytool ing techniques. New and precise methods had to be devised, tested, and retested.


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~ i g a m, SATURN S-II CUTAWAY - mawing of the S-11.stage $hawsinterlor of the iquid oxygen tank (above engines) zlnd the liquidhydrogen tank. The five J-2 engine$ develop a thm of one millionponnb.


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One such new technique developed by North American specialists i s skate welding. Theautomatic skate welder is operated by an elect rical weld package that regulates andremembers every welding operation. This welder li te ra ll y skates over the part to bewelded on a track that i s held in position by vacuum-operated suction cups. An operatorfo llow ing the automatic welder can adjust the programed weld procedure. The trackis precisely positioned on the sheets to be welded and remains fixed throughout the trim,weld, and subsequent X-ray inspection. Each of these three procedures is accomplishedby mounting the respective head on the track.

A unique welding technique was introduced to prevent entrapped gas bubbles inthe fabrication of the S - l l . I t requires trimming, polishing, deburring and vacuumcleaning. Operaton may not touch a cleaned joint surface before welding, becausefingers deposit undesirable chemical particles on the edges to be welded whicheventually would dissolve in the molten weld metal. These bubbles would solidify in theweld metal, causing a defect in the weld bead.

More than 2,500 feet o f seams on the S - l l must be welded. To accomplish this,revolutionary giant weld fixtures were designed to accommodate final assembly of thestage, bulkheads, and cylinders. Five bulkhead fixtures were required: one fo r theforward bulkhead, two for the forward common bulkhead, one for both the a f t commonbulkhead and the af t bulkhead, and one for the assembled common bulkhead to the l iq uidhydrogen cylinder. Bulkheads are made up of gores. (A gore i s shaped lik e a slice of pie.Twelve aluminum gores comprise one bulkhead.) One weld fixture - alled the "dollar"welder - s used to weld three-foot diameter domed sections, which resemble largesi lver dollars, a t the apex of the bulkheads. Another fix ture - alled the thick-to-thinwelder - s used to we ld the two segments of the af t common bulkhead together,

A l l of these welding fixtures, except the thick-to -thin section welders, are locatedin the bulkhead fabricat ion bui lding a t Seal Beach. The thick-to-thin welders, whichare required for certa in two-piece gores, were transferred to No rth American's Slausonfaci l i ty in Los Angeles because of space limitat ions. Some of these tools are shown inFigure 3. Figure 4 shows a welded aft common bulkhead on its welding fixture. Figure 5shows the a f t common bulkhead and the forward common bulkhead weld ing fixtures insidethe bulkhead fabrication building ,

FACILITIES

The bulkhead fabrication building i s a 154- by 300- by 50-foot-high structuredsteel frame building with a 30-foot wide staging area, Inside are two cab-operated,interlocking bridge cranes; an electrically-powered gantry crane to position the bulkheadsin the autoclave; sliding walls and roofs; and other massive tooling.

The autoclave is the largest pressure cooker in the world. Actually, i t is ahemispherical, covered, pressure vessel, 38 fee t in diameter by 20 fee t high, used tobond and cure the core insulation between the aft common and forward common bulkheads.


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S-I1 MAJOR ASSEMBLIESFWD SKIRT

-FWD BULKHEADI k - 1 ~ ~ YLINDERD SUBASSY (6)000lIlmmmmmmmm-BOLTING RING

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LH2 CYLINDER

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Figure 4. AF T COMMON BULKHEAD - T he first 6-11 bulkhead whichw i l l be used for sta tic tests is shown on the welding fix ture a t NorthAmerican's Seal Beach facility. Horizontal and vert ical l inesindicate the che mi ca l preparat ion used to protect the weld areas .Lines also indica te how the bulkhead was fabricated.


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The autoclave's bonding temperature is 340 degrees Fahrenheit and its pressure i s 50pounds per square inch, augmented by a 10-pound-per-square-inch vacuum pulledbetween the two bulkheads.

Nea r the bulkhead fabrication build ing i s the 120-foot-high ve rti ca l assemblybuilding. In this facil ity, the major components of the S - I l are welded together and itsflight systems are installed.

Th i s bu ild ing includes four ver tica l assembly stations, (each about 110 feet h ighand 35 feet i n diameter) opening i n floors for welding, insulation, system installat ion,and combined systems checkout. I t also includes two hydrostatic test stations for l iq uidoxygen tank and l iq ui d hydrogen tank h idrostatic (water-pressure) testing.

Another Seal Beach facility is the water condition ing plant which contains tanksand equipment to furnish demineralized water, heat detergent solution and trichloroethylenefor the hydrostatic testing and clean ing operation. I t includes water pumps and a storagetank for f ir e fight ing , and compressors and equipment to furnish a i r a t 100 pounds ofpressure per square inch.

The structural static test facility includes a test tower with hydraulic struts forstructural testing on an initial test stage. The tower, 138 fee t high, w i l l be enclosed onthree sides.

Other fac il it ie s include the service building, which houses supporting personnel,and andther bu ild ing for the pneumatic test, paint, and packaging operation.

A l l of these facilities contain revolutionary tooling to accommodate the variouscomponents of the S - l I. These components are described below.

THRUST STRUCTURE

The five J-2 engines are installed on the thrust structure, a riveted, skin-stringerand internal frame construction wh ich resembles a miniatu re amphitheater. Th is part isfabricated in four panels and has a machined cy lin dr ical ski rt. A heat shield atop thethrust structure protects the base area of the.stage against reci rculat ion of hot engineexhaust gases and heat from the exhaust. The heat shield is of lightweight constructionprotected by low-density abla tive material. This structure fits pa rt ia lly into the af tinterstage assembly and around combustion chamber of the engines; the assembly i sshown i n Figures 6 and 7.

INTERSTAGE

The interstage, fabricated at N or th American's Tulsa plant, i s of riveted, semi-monocoque, skin-s tringer construction. (Semimonocoque means tha t the S-11's skin is


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primarily without an internal framework). The interstage is 2 19 inches long with a 396-inch diameter and has a 30- by 30-inch access door. A master mating gauge i s used todr i l l the bolt pattern so that the interstage fits to the S-IC stage below. An af t skirt andthrust structure delivered to Seal Beach for use on the static test stage w i l l be used byengineering development laboratory personnel for stress-load testing.

FORWARD AND AFT SKIRTS

The forward skirt also i s a riveted, semimonocoque, skin-stringer structure. I t is137 inches long and has a 30- by 30-inch access door. I t is fabricated in four panelswit h external longerons and subassembled internal frames. The af t skirt, similar inconstruction, is 88 inches long.

A master mating gauge i s used to d r i ll the bo lt pattern to ensure that the skirts mateprecisely to the upper and lower stages.

BOLTING RING

The bolting ring supports the liq uid oxygen tank by attaching i t to the S - I lstructure wi th 600 bolts, A top flange of the ring connects to the first li qu id hydrogentank cy linder and a bottom flange connects to the af t skirt. The "J" section of thecommon bulkhead is welded to the first cylinder.

CYLINDERS

Each of the six liquid hydrogen cylinders comprises four panels welded together.Five of the cylinder panels are 8.3 feet high and 27 feet long, the other panel i s 28inches high. Longitud inal and circumferential stiffeners are machine-milled on theinside surface to a rectangular grid pattern. The or iginal thickness of the panel i s twoinches. I t i s mi lled to approximately a quarter-inch thickness between the stiffeners.

In order to prevent bo il -o ff of the -423 degree Fahrenheit liqu id hydrogen,insulation is bonded to the external surface of each cylinder. Th is insulation i s made ofphenolic honeycomb f i ll ed wi th isocyanate foam. Two laminate nylon external sealingskins are bonded to the honeycomb insulation.

These cylinders are welded together during final assembly of the S - l l in the verticalassembly bu ilding. Figures 8 and 9 show these cylinders.


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BULKHEADS

A l l of the bulkheads (Figure 10) are the same size wi th one exception. The forwardcommon bulkhead i s sli ghtly larger since i t must f i t over the aft common bulkhead. The12 gores that comprise each bulkhead are approximately 20 feet long and 103 inches wide.They vary in thickness along the we ld land (longitudinal area where the gores are weldedtogether) from one-half inch to one-eighth inch. They are welded together on anelect ric al ly control ed, hydraulic bulkhead weld fixture.

The common bulkhead may be likened to two giant domes, one placed inside theother, open end down, wit h a layer of insula tion (of varying thickness) sandwichedbetween them (Figures 1 1 and 12). The top dome i s the forward common bulkhead andthe bottom dome the a f t common bulkhead. The af t common bulkhead gore i s differentfrom the other bulkhead gores in that each of its gores i s composed of a thick section(resembling a waffle) a t the wide end and a thin section. These are welded together onthe thick-to-th in welding fixture,

The forward common bulkhead (sometimes called the lower LH2 bulkhead, Figure13) consists of a thin dome wi th a J-section on its periphery that allows for expansionof the bulkhead when i t is fi ll ed with liqu id hydrogen. The section resembles a "J, " andthe lower l i p is welded to the li qu id hydrogen cylinder.

In order to bond the phenolic honeycomb insulation to the aft common and forwardcommon bulkheads, several operations are performed. The a f t common bulkhead i s placedfirst on the bonding fixture, a dome-shaped tool resembling the bulkhead, Then thehoneycomb core insulation, in numerous sections, i s fit ted to the bulkhead. The sectionsare then tapered to exact thickness specifications b y machining, the thickest par t being4.75 inches. They are then bonded and cured in the autoclave. The cured insulation i sremoved and stored so the bulkhead can be l if te d by the huge 50-ton gantry crane,inverted, and transferred to the processing room. The bulkhead is inverted by amechanical and pneumatic turn-over sling.

In the processing room, which resembles a huge sunken bath, the bulkhead i sli fte d onto a circular wa ll and receives a spray bath with a solution of 24 percentsulfuric acid, detergent, and water. This prepares i t for receiving the adhesive whichholds the honeycomb. After the adhesive i s put on the bulkhead, insulation cores areplaced over it. The entire assembly i s li ft ed onto the autoclave which pressurizes andcures the adhesives. Fu ll pressure and heat i s applied by the autoclave for an hour only,although several hours are required before and after full pressure and heat to prevent toorapid a temperature change, which could cause buckling of the bulkhead.

When the aft common bulkhead i s removed from the autoclave and placed on thebonding fix ture again, the forward common bulkhead i s mated to it . To ensure a perfectfi t, several impression checks are taken. Then the forward common bulkhead receives a

the saturn s-ii

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