Saturn V: the body of the alloy.

Saturn V: the body of the alloy.

This article from the micro-channel public number: forever relentless tour phase of Miao Hon (ID: haibaraemily_planets), of: Genius Novo Lu Qi, Editor: haibaraemily, from the head of FIG: Eastern IC

Last time, under the high pressure of the Soviet Union, the engineers of Lockaine rose up and finally built the strong heart (engine) of the Saturn V rocket. And when the engineers at Lockayne were having a headache for the rocket's heart problems, Douglas (which is responsible for Saturn's fifth-core S-IVB) and Boeing (for Saturn V) were assigned to the rocket for bones, flesh and skin. Engineers of the core-level S-IC and North American Airlines (the Saturn's fifth-core S-II) also encountered a lot of trouble.

The size and structure of Saturn V. Source:National Air and SpaceMuseum and NASA, Adapted:haibarae.

That's-the rocket is too big. How do these companies build such a large shell of Saturn 5?

S-IVB: I'm going to have to lose weight in the dead.

In fact, for Douglas, the manufacturing of the above-mentioned S-IVB is a bit simpler. This aspect is because S-IVB is not so big after all, and it is still acceptable. On the other hand, we also said in the prequel. S-IV, the predecessor of S-IVB, has been basically mature and available, and as early as 1961, it has been sent to space by the C-1 carrier rocket... The rest is just some peeling, adapting to the J-2 engine. problem.

But even so, from S-IV to S-IVB is still a very tortuous road.

The SIV proposal dates back to 195859. At that time, the planning of Saturn series had not been determined. NASA put forward five versions of C1 to C5 in one breath. Of course, C2, C3, C4 was cut down to C5, namely Saturn 5. SIV was originally planned as the fourth stage of the C4 rocket.

As the first major component of the Saturn series of launch vehicles, NASA was cautious about the S-IV level, and it was not until the end of 1959 until the early 1960s that it was determined to determine the contractor. Of course, there is also a reason that von Braun and the Army Ballistic Missile Agency (ABMA, the predecessor of the Marshall Space Flight Center) have not been placed on NASA at that time, although both sides have been mad.

After a complex bidding-bidding process, Douglas won from more than 20 companies in May 1960 and officially became a S-IV contractor. In the prequel, we mentioned that since the formal determination of the configuration of C ≤ 5, the requirements of S-IV have been slightly increased, and S-IVB has been moved to the table as a modification. In order to test the S-IVB class, Saturn 1 was correspondingly transformed into Saturn-1B, and due to some progress problems with the JV 2 engine mentioned last time, the first launch of the Saturn-1B was completed nearly five years after the launch of the planet 1.

Structure of the S-IVB class. Source: NASA

Since the final S-IVB class has the task of rounding the orbit and launching the spacecraft directly into the Earth-Moon transfer orbit, it has the highest requirements and the research priority.

"launching a kilogram of load into a ground-moon transfer orbit requires a takeoff mass of 50 kilograms (that is, a load ratio of 2%), which means that if high-energy fuel is not used, it will not be able to carry such a heavy load. Not surprisingly, liquid oxygen-liquid hydrogen fuel has become a good choice because of its high specific impulse characteristics.

We can simply understand the specific impulse as 1 kilogram of some kind of fuel that produces 1 kilogram of acrylic (9. 8 newtons on Earth) for a time that lasts in seconds of (s). The specific impulse at different mixing ratios is slightly different, but the specific impulse of liquid hydrogen and liquid oxygen is too good compared with other common chemical fuels. The parameters of propellants are sorted out from: [3] and [4]

The initial moon landing program was Earth orbit rendezvous (EOR), so the initial design of the S-IVB was 5.6 m in diameter and could be anchored in Earth orbit for 30 days. Later, the berthing time was shortened to 4.5 days, and then it was decided to take a plan to return directly to the moon and return after the lunar orbital intersection. In this way, the S-IVB only needs to wait 4.5 hours in space.

Even so, the diameter of 5.6 meters has not been changed until the final dust of Saturn V is finalized, and the diameter of S-IVB is raised by 1 meter to 6.6 meters.

Although the S-IVB time is tight, it is not impossible for Douglas, an aerospace giant with a long history of aircraft design and designed and built the "Raytheon" launch vehicle some time ago. Many technologies, including machining, sheet metal, welding, and etching, are already in the know, and this is probably the reason for its final contract.

Based on the successful experience of the "Raytheon" launch vehicle, Douglas engineers quickly chose the aluminum alloy 2014 as the main material for the fuel tank, and designed the outer casing and bearing structure in a conventional way - just like them. Design the aircraft in general.

As a result, it was all called back soon-it was too heavy.

The field of aircraft itself is very sensitive to the weight of death. The aerospace industry, especially the request for landing on the moon, is more abnormal, so engineers have to follow the abnormal situation.

1. Start cutting from fuel tank….

For the inner casing of the fuel tank, the engineers quickly found a way to reduce weight – designing the original one-piece alloy plate as a surface mesh, and the more vivid statement is made into a waffle. However, such a plate is very difficult to do, and it has to be "carved" with special equipment. In this way, people get a 7.5 square meters, 1.9 cm thick sheet, which is the original material of the fuel tank inner casing.

Wait...1.9 cm thick? SIVB diameter is 6.6 meters. What's the concept? For example, if you hold a 330 milliliter Coke Easy Pull can with a diameter of 66 mm and a wall thickness of 0.11 mm, if you double the wall thickness, it's a 100-fold reduced SIVB fuel tank. It's called a sick weight loss.

And the production of such a "easy-to-pull can" needs 7 pieces of such aluminum alloy plate. In order to deal with these aluminum alloy plates, Douglas also specially found Giddings and Lewis to design a 3.6 × 12 meter large grinder, with two knife heads, each plate takes an average of 120 hours to process. The finished plate needs to be further bent, and Douglas has brought the bender that processes the DC-8 aircraft-the one that produces 2.53 GPa, the only guy in the factory who can process S-IVB.

In addition to the cylindrical shell in the middle of the rocket's fuel tank, there are upper and lower hemispheric tops / bottoms and internal ribs. The manufacture of hemispherical surface is still very complex, usually using multiple surface welding method to synthesize. S-IVB is no exception, each hemispherical surface is composed of 9 triangular surfaces (commonly known as "melon flap"), and because it is curved surface, mechanical grinding is no longer suitable, so it is necessary to use chemical methods to carry out surface treatment.

This operation is fine and fine—on the one hand, the surface-treated chemicals are consumed in whole barrels, and on the other hand, these chemicals need to be cleaned at specific times along specific routes. After that, in order not to pollute the surface, people will carefully transfer it to the automatic welding device, and the rest will let the machine solve it.

The bottom of the S-IVB tank. Source: NASA

This automatic welding machine is also very interesting, its welding head will weld along the gap from top to bottom, the advantage is that the melted solder will not accumulate too much, nor will it lead to defects such as bubbles and cracks in the weld. The more amazing thing, however, is that the automatic welding torch sometimes blows, and after a period of time, it is either welded off and off, or it is not welded at all according to the direction of the weld. What's even more amazing is that the melon flap is doing so well that the gap that needs to be welded is not big enough for the sensor to feel it. The final solution is to raise the sensitivity of the sensor on the one hand and open the seam of the splice a little so that the artificial mental retardation can know what to do. Engineer: everyone saw it. This is the first time I've heard of such a magical request.

Since the J-2 engine uses a dual-component fuel, it is necessary to separate the fuel from the oxidant, and the conventional approach is to store the two tanks separately, which means that there is a need for a fixed ring between the tanks to hold them, which in turn is part of the mass. NASA's weight-loss requirements for the upper level have reached a level of metamorphosis, so this routine is quickly rejected.

Since you can't make two separate tanks, you can only make one, and then add a partition to separate liquid hydrogen / liquid oxygen. The partition is a curved shell, but it consists of two layers of aluminum with a honeycomb fiberglass insulation, a total thickness of about 5 centimeters. The hydrogen tank and the oxygen tank share a hemispheric base (the huge hemisphere above), which is made up of a similar structure. This alternative design reduces quality at the S-IVB level by about 20 per cent, and NASA is satisfied.

But there is a reason why the partition and the base are designed with such sandwiches: the boiling point of liquid hydrogen is-253C, and the boiling point of liquid oxygen is-183C. In order to prevent liquid oxygen from freezing, it has to be insulated, and NASA's kind eyes are looking at the total mass of S-IVB, so it has to be very thin-the end result is that the aluminum plate at the top of the curved shell is only 0.8mm thick, and the aluminum plate at the bottom is only 1.4mm thick. And its diameter, as we said earlier, is 6.6 meters.

Such a thin thickness and such a large area have brought a lot of problems to Douglas engineers. It is too easy to make a glass fiber surface, but it is necessary to fit such a thin aluminum plate. Life.

Imagine if you want to save a piece of paper into a curved surface. Will this piece of paper become wrinkled? This is the case with aluminum panels, which adapt to the glass fiber side and become potholed. After many failures, Douglas engineers simply gave up the treatment-since folds are inevitable, let's just let the fiberglass fit the aluminum plate! After a lot of manual work, this problem has always been solved, although it feels like a violent aesthetic style.

This fiberglass insulation layer also has a story. Douglas started the construction of the aircraft and initially planned to use Balsa wood as insulation material. Those who have played airplane models know that Balsa Wood is also known as balsa wood, and there is also a special name called "Aircraft Wood". Because its density is only 0.05-0.1 grams per cubic centimeter, it is very suitable for aircraft model.

However, due to the impact of the reduction of Balsamu in the same year, okay, this is not the main reason, and the test report indicates that there are structurally significant defects. Finally, Douglas engineers had to reluctantly give up the material and use the glass as described above. fiber.

As a completed rocket stage, in addition to the fuel tank, S-IVB also includes upper and lower skirt rings, interstage segments, outer surrounding shells and so on. The skirt rings at the top and bottom are not only supporting the fuel tank, but also equipped with the rocket control system, which is used to connect with the ground before launch.

the interstage section is communicated with the S-IVB and the S-II level, an auxiliary propulsion module is also hidden in the middle, Therefore, a small boost rocket is needed to push the fuel to the bottom, so it is called a "bottom rocket", in addition, a number of recoil rockets are hidden, and the command/ service cabin is to be dragged out of the lunar boat to be started to be quickly separated from the airship system;

The outer casing not only protects the fuel tank, but also has various bearing structures in the middle, such as the engine, the supporting equipment, etc. These structures are mostly processed by a five-axis machine tool; There are also 9 helium gas tanks. When the liquid oxygen is gradually consumed, the helium gas is released by heating to maintain the pressure of the liquid oxygen tank (the liquid hydrogen tank is not used, because the liquid hydrogen is evaporating whenever it is, Just keep the pressure).

When these accessories are ready to stop, they can be assembled.

2. Finally can be assembled

The S-IVB assembly center is located in Huntington Beach. It has an assembly building, 36 meters high and 2,230 meters in circumference. The two cranes are responsible for feeding various spare parts into the assembly area.

Busy S-IVB assembly shop. Source: NASA

Assembling the rocket structure is also a big project -

The first is still big, it is very troublesome to install such a big thing;

The second is fragility. If you touch it a little, you may have problems. If you leak it, it will be scrapped. Especially the liquid hydrogen tank will have a slight gap. The unstable hydrogen molecule will dare to run for you.

As mentioned above, the liquid hydrogen tank shares a base with the liquid oxygen tank and is separated by a partition. In fact, the liquid oxygen tank is barely a ball. The liquid hydrogen tank is actually a oil drum lacking the base. Therefore, it is necessary to weld its cylindrical surface to the upper hemisphere of the liquid oxygen tank.

This process is also very tedious: in order to ensure air tightness, these two major accessories will interference fit at room temperature, so before formal welding, the liquid hydrogen tank part needs to be preheated a little to make it expand, and then the workers can weld it. And the fuel tank at this time can not bear the force, so you have to hang it all the time-yes, imagine a two-story behemoth hanging in front of you, as if the wind could paste your face, which gives a sense of pressure as much as the sword of DamoChris, so not only the engineer was a hero, but the frontline workers were also very brave.

After very careful welding, the fuel tank needs to be X-ray flawed, and it is supplemented with penetrant dyeing to check whether there are any flaws that are hard to find by the naked eye. After passing the verification, the static test can be carried out immediately and the design pressure is over 5%. A slight overload is a regular hydraulic test.

Douglas started the aircraft, and this test has been done many times. There is a complete hydraulic testing system, including an automatic control system and dazzling matching instruments. Everything is perfect, except that occasionally the improper control of excessive pressure causes the fuel tank to collapse.

Once again, the suffocating operation of artificial intelligence has forced people to embrace nature-if we make a super big vertical pipe and then inject it into it, it will overflow. Isn't that much more useful than any instrument? (remember the joke that the fan blew the box empty?) So next to Huntington Beach, a 43-meter-high water tower was quickly erected to replenish the water and complete the water pressure test. To prevent the plane from bumping into it, a lamp was added to the top to prevent birds from nesting on it, surrounded by bird cages.

What? Even birds interfere?

Of course, to know the height of the assembly workshop is 36 meters, and the top has a wide variety of supports to support, plus Huntington's beach climate, so soon the doves are making a nest on the beam. It's a little thing that a bird's shit falls on a man, and it's a big deal on the rocket structure.

In order to drive the pigeons, a high-decibel whistle was installed in the assembly workshop, and two sounds were called. But once people start working, the whistle has to be closed, and then the pigeons are back.

Several violent old brothers picked up the guns, but in addition to harvesting humanitarian criticism, they only harvested a few holes in the roof. Closing all the doors and windows that can be closed seems to be a great note, but there is a long transport track under the door of the assembly workshop. Yes, the familiar figure is coming in from the gap between the rail and the door. ! Although these white messengers are symbols of peace, they are here as enemies.

Finally, it is up to bird experts to come up with a solution. So you see, even an ornithologist, you can contribute to the cause of human moon landing.

3. Test... And then it's going to blow up again?

In such a harsh assembly environment, whether S-IVB is reliable or not, it naturally needs to be tested to verify.

Different rocket stages have different test methods, but generally follow the "ground test - static ignition test - flight test" process.

The Rocket level Test Link and content of Saturn 5. Source: NASA

Specifically, it can be subdivided into the following aspects:

Structural test, structural test. It includes the main body of Saturn V in addition to the F-1 engine, as well as the S-IU instrument unit. The engine is not tested because it is already at the bottom. This test is the most basic test used to verify that each unit component is qualified;

All system test, full system test, added the engine. This is used to communicate (and cross-spray) the engineers of each contractor. Each component needs to be jointly tested at this stage and put in place.

Dynamic test, dynamic test, this part simulates the rocket launch vibration and so on, not only to verify whether the rocket structure in the dynamic environment will fail, but also to verify whether the instrument will fail;

Battleship test, does not add S / IC here because S-IC class ignition has been started in dynamic testing. As the upper level, S-II and S-IVB need to carry out additional ignition test.

Facilitiescheckout, which is the final acceptance, is not far from the last flight test, once it is qualified.

From the last article, we know that Douglas has its own test center in Salamento, which has more perfect self-test and countdown facilities, and there is a certain distance from Huntington Beach to Salamento. S-IVB needs to fly to this stage, which is 6.6 meters in diameter. So Douglas called a transport plane called pregnant Rainbow Fish to complete the task.

S / IVB unloaded from pregnant Rainbow Fish. Source: NASA

The staff in the center seems to be quite vocal about the hot potato of S-IVB. After all, this is a jar filled with high-energy fuel! If hydrogen escapes due to leakage of the liquid hydrogen tank, it will mix with the air and ignite under appropriate conditions. However, considering that the concentration of dissolved hydrogen is high and the pressure is high, the flame is often stable and continuous. But the problem is that once the ignition command is issued, a large amount of hydrogen igniting will cause an explosion. Even worse, the small flames produced during the day will become invisible under the cover of the sun. Although there are many infrared cameras next to the liquid hydrogen tank, the dead ends still exist.

So the most suffocating operation came: there was always a warrior holding a broom and walking around the liquid hydrogen tank. Once the broom was lit, there was a leak.

However, even with this kind of inspection work, the bombing will still blow up.

On January 24, 1964, during the whole system ignition test of the S-IV class, there was an earth-shaking big bang, and the TNT equivalent was no longer tested. Just as the launch of SA-5 No. 1 coincided with the launch, a team of 11 people organized by W. R. Lucas and J. B. Gayle of (MSFC), the Marshal Space Flight Center, began to zero. according to tape records, it was found that the bottom of the liquid oxygen tank (also the bottom of the liquid hydrogen tank) had cracks caused by overpressure, which in turn led to a fire in which the entire S-IV class was turned into a fire within milliseconds.

After an assessment, the Carp staff let SA-5 continue on the grounds that "since the liquid oxygen tank will explode when it is overpressurized, let's just keep an eye on the pressure of the liquid oxygen tank," the reason is that "since the liquid oxygen tank is overpressurized and explodes, let's just keep an eye on the liquid oxygen tank pressure." Fortunately, the January 29 th launch was a success, otherwise a few more people would have to be added to the thank-you list.

With the S-IV accident, the S-IVB test became very cautious, but it was still hidden. In January 1967, the S-IVB also exploded.

The wreckage after the explosion. Source: NASA

The explosion occurred with S-IVB-503, which was the test No. 3 machine for the acceptance test. This incident is quite strange. When the countdown was 150 seconds, the arrow computer reported a mistake, but it was quickly solved. In the 11 seconds before the simulated ignition, the test machine was smouldering in another big bang. The explosion smashed the roof and windows of a nearby house, and also stopped the acceptance test of the test No. 2 machine.

The investigation results of the accident quickly pointed to the problem of welding the helium tank: due to the use of pure titanium instead of special alloy solder for welding, the helium tank could not be under pressure and damaged, and the fragment finally led to the J-2 engine fuel mixing pipeline. Damage, which in turn caused a detonation, and finally exploded.

Fortunately, the problem of S-IVB-503 is a thorough man-made problem, and after strengthening the management of the production process, in May of the same year, S-IVB-503N (formerly S-IVB-504) finally passed the acceptance test, which is also a hurry. On the progress.

S-IVB started early, the diameter is small, all R & D have to stumble, that S-IC and S-II level face a pair of light scenes again?

S-IC level: delay and delay

Boeing officially obtained the S-IC development contract on December 15, 1961, and soon received instructions from the Marshall Space Flight Center (MSFC) to build a first stage with a diameter of 10 meters, using liquid oxygen - Kerosene fuel system.

The reason for not using high-energy liquid-liquid-hydrogen fuel is simple: the density of liquid hydrogen is less than 1/10 of that of kerosene, and the fuel tank of the first stage cannot be made too big (again, look back at the table in the previous table). The density ratio is known.)

1. How many engines?

And how many engines S-IC had to install at first also pulled the skin for a long time. At the end of 1960, when the configuration of C ≤ 5 began to be demonstrated, the design of the core stage was four F ≤ 1 engines in parallel. Many people don't like the plan and feel unstable enough.

In particular, Rosen (Milton Rosen), then director of manned space vehicles and power systems, and his immediate supervisor, Holmes (the last one who intended to land on the moon with a backup plan), formed a discussion group and discussed the first level configuration of Saturn 5 for two weeks in a conference room in Huntsville.

According to Rosen later, one of the discussions was open for five days! In these two weeks, supporters of five engines thought that one more engine would have one more thrust, and the load design would be more relaxed; the supporters of the four engines said that the design of von Braun is now. The team has already drawn the picture according to the design of the four engines, and you will drag the progress. Finally, von Braun asked the design team's opinion, and the design team said: What the hell! We can't wait for five engines!

The reason is simple: because the launch mass of the Saturn V is very large, the first stage needs to bear a lot of force. Since there is no previous design experience of the main structure of the rocket with such a large diameter, the design team adopted a more conservative structure-using two intersecting beams to realize the bearing force, the four engines are divided at the four ends of the crossbeam, while in the actual material accounting, The design team found that the mass of the two beams exceeded the pre-estimated quality, and if one more engine was added to the support point of the two beams, the existing design would not be changed, but the limit would be reduced because of the increase in capacity.

Rosen later had to say: "conservative design is also good, it saved Apollo program."

In the process of assembling S-IC 's rice repair factory production line, you can see that the fifth engine has been added directly to the support point of the two intersecting beams, and no changes have been made to the existing design. Source: NASA

However, as the project progressed, the opponents had to accept five engines. Every time the rocket team went to Houston to discuss the business, they would find that the spacecraft system was fat, and the four-engine solution could not be quickly suit one's needs.

On December 21, 1961, the S-IC class engine configuration dust settled, as we see today-five engines.

Von Braun's team made an initial design for the S-IC level and a further refinement was made to the MSFC, and the MSFC soon found that the contractor was not enough to let the contractor boeing to assist in the design. These foreign aid forces have made the MSFC room moose.

By the summer of 1962, the number of engineers who worked on the MSFC and the Boeing work card reached 500. Not only that, Boeing had another 600 people at the Huntsville Industrial Center, a waste cotton mill in Huntsville. "jobs.

This is not all. There are 450 Boeing employees in the Mishuo factory in New Orleans who will be involved in the processing and assembly of S-IC. In addition, Boeing's test center in Seattle has also freed up wind tunnels and test equipment. The heavy-duty processing equipment in Wichita is also ready to be sent to Mi Xiu for assembly.

This Mi Xiu factory used to be the first grade of Saturn No. 1 by Chrysler. Since the diameter of S-IB is only 60% of the S-IC, the workers had to remove some of the plants. The high bracket and air conditioning system freed up a net height of 12.2 meters, so that the S-IC can enter and exit smoothly.

Boeing's close ties to MSFC quickly benefited both: MSFC received a lot of new content from industry, new methods, and found a way to work with contractors; and Boeing learned a lot of space experience, laying the foundation for later expansion in space. Today, Boeing accounts for a large share of the, ULA (Joint launch Alliance.

2. S-IC level structure

S-IC class includes kerosene tank, liquid oxygen tank, and main structure.

SIC level structure with the aforementioned cross beam visible at the bottom. Source:NASA.

Since it is the first stage of the rocket, the requirement of S-IC on the weight is less than that of the upper level, so a more secure double-tank design is adopted, the upper liquid oxygen tank and the lower layer are coal oil tanks. In the liquid oxygen tank, a total of 1204 cubic meters of liquid oxygen is stored, and 730 cubic meters of kerosene are stored in the coal oil tank.

In order to ensure that liquid oxygen can reach the engine at a rate of 7.3 cubic meters per second, the pipeline of the liquid oxygen tank also passes through the coal tank, which is distributed to five transmitters by 10 different pipelines, transporting 4.9 cubic meters of kerosene per second.

There is a bearing structure between the tanks, in which there is a fuel filler port, which can infuse liquid oxygen at a rate of 5.5 cubic meters per minute, and inject kerosene at a rate of 7.3 cubic meters per minute. The top of the S-IC has a skirt ring connected to the S-II, which also includes a part of the control system to ensure the normal operation of the S-IC.

In order to adapt to the layout of five engines, the bottom slightly protrudes a part of the engine, and uses a half cone for pneumatic modification, and several recoil rockets are hidden in the interior, which are quickly far away from each other after the separation of S-II. The four stable tail wings ensure its stable flight in the atmosphere, especially considering the high temperature of more than 1100 ℃ produced by the engine, which is made of titanium alloy.

In the flight test, the S-IC has several cameras to observe the operation of the mechanism in the fuel tank. There are also two top-top color cameras to take the S-II-separated scene, which is also preserved when Apollo's formal manned flight-they splattered to the South Atlantic after it was separated and could enjoy a great image after the fishing.

The S-IC level is bound to have some problems in the process of design and construction. After all, the S-IVB has the previous technology base, and the S-IC is almost brand new, which has become an obstacle in front of the engineers.

Like the S-IVB, the design of the S-IC tank is also made up of several curved sheets, but for S-IC, this quantity and size are different from S-IVB.

The top of the fuel tank and the semi-spherical shell at the bottom are respectively made up of 8 aluminum alloy 2219 triangular plates, which are made into aluminum plate base material under the largest 50,000-ton press in the United States, and then ground by the upper grinding machine, and finally bent to a proper angle by using a water-expanding hydraulic machine.

On the other hand, the cylindrical surface is based on an aluminum plate of about 3 × 4.8 meters, and the tank is manufactured by a similar process. These parts are heat-treated in the electric furnace to make the surface firm. After completing these processes at the Boeing Wichita plant, 90% of the work has been done, and the rest can be shipped to the Mixiu plant for welding.

3. Finally can be welded and tested

Before welding, various parts need to be cleaned, especially the liquid oxygen tank, which is not as violent as liquid hydrogen, but is not stable as an oxidant. In theory, even a fingerprint on the inner wall of the tank can cause an explosion.

The aluminum plate generally has a layer of oil on the surface, so it is first degreased with a chemical reagent, then eluted with deionized water, then an anti-oxidation layer is formed on the surface of the aluminum alloy with nitric acid, and then eluted with water for the second time. Finally, it can be sent to the hot air box for drying. The steps of washing with clean water were carried out in a stainless steel pool with a height of 6.7 meters and a height of 6.7 meters. It was also the "largest dishwasher in the United States" by the workers of the Mi Xiu factory.

After that, it is welded, but the welding is heated and the heating is deformed. For this kind of thin shell tank, the deformation is even worse. In order to reduce the temperature, the engineers set the ambient temperature below 25 degrees and the relative humidity below 50%. However, it is clear that this operation does not cure the root cause, Boeing engineers have used the "tungsten inert gas shielded welding" (TIG) method to ensure the smooth welding process.

Welds like this have a total length of about 10 km, and each of them needs to be reliable, so a 15-person welding team needs to work 8 hours in a row.

By soldering the S-IC, it can be seen that substantially automated soldering is achieved. Source: NASA

After the welding, the tank needs to be subjected to a 105% water pressure slight overload test. The diameter of 10 meters makes it impossible to use the power of nature and can only re-engage the artificial mental retardation. This water pressure is so great that the tank will expand 1.3 cm after the test.

In order not to allow artificial mental retardation to lead to the tragedy of abandonment, a lot of cameras have been installed to monitor closely. Deionized water will be added to the specially treated dye, once there is a leak, people can see it in time.

A slight overload test like this is only part of a test, large and small, but after all the 10-week test process, S-IC can finally begin formal testing. The two S-IC were sent to Huntsville and the Mississippi test device (MTF), respectively. Although the first static ignition test was completed in Huntsville in 1965, most of the ignition tests were carried out there after the MTF was completed, because the MTF has two such test platforms.

S-IC is being lifted to the Mississippi test device. Source: NASA

The 124-meter-high test device became the tallest building in Mississippi at the time, with 1600 30-meter-long pile foundations at the bottom and four 12-meter-long cranes that could slowly lift the S-IC. From a distance, the building is a reinforced concrete monster with teeth and claws.

In its concrete structure, components such as offices, data centers, machinery rooms, elevators, etc. are gathered. Of course, in order to prevent the fire from burning the MTF, there is a huge reservoir at the bottom and a water supply system of 782 cubic meters per minute. The flow of water is supplied inward. After the ignition test starts, the second set of water supply system will be sprayed evenly on the bottom of the engine through a densely packed pipeline at a flow rate of 1,100 cubic meters per minute to ensure that the S-IC will not overheat. Next experiment. In a static ignition test lasting 5 minutes, the two water systems were able to meet the water needs of a small city of 10,000 people a day.

The welding problem of S-IC has always affected the progress of this level. In 1963-64, the problem of unreliable fuel tank quality caused by welding problems caused the S-IC-T system-wide test component to be delayed for 6 weeks. In October of the same year, the welding problem of liquid oxygen storage tanks led to S-IC-S was also postponed, and S-IC-T was postponed for another 19 weeks. The other small conditions that continue to occur are also dragging down the progress of the entire project. For example, the flight test of S-IC-1 has been delayed for three months.

But it doesn't matter, these problems are finally solved, and, anyway, it is not only S-IC, but also S-II.

S-II level... is also a disaster

The S-II is the second level of Saturn V and the most difficult part of the entire rocket system. The difficulty of the first-stage S-IC is its large size. The difficulty of the third-stage S-IVB lies in the liquid hydrogen system. Unfortunately, the S-II in the middle brought these two difficulties together.

S-II originated from the large hydrogen and oxygen fire arrow level plan in December 1959, including the J / 2 rocket engine and the suitable S-II rocket class plan. The project began with a committee led by (Abe Silverstein), director of the NASA space flight program, who is in fact a very experienced scholar of his own.

The air-dynamics study was carried out in 1943 by the Lewis Research Center, which helped his fellow Americans into the air-jet era. When NASA was founded in 1959, when he was 51, he quickly put forward a series of ideas that had to be said to be forward-looking.

In 1969, he retired from his job, but in the same year Apollo 11 must have achieved the goal of manned landing on the moon, and he must have been very happy. The old man died in 2001 and then joined the American Airlines Hall of Fame in 2014.

The frontal image of Hilferstein, this deep eye is the yearning for the universe. Source: NASA

Just a week after Hilfstein finished the report, NASA started the research, spent a year combing all kinds of serious and difficult problems, and finally carried out a preliminary design of S-II. By January 1961, NASA believed that the C / 1 carrier rocket could only be used as a beginning and would not last long. The C-2 rocket needed to be developed on a priority basis, so S-II was needed as the second stage.

In the initial design, the S-II is 6.5 meters in diameter and 22 meters in height, powered by four J 2 engines. In June, the idea of C ≤ 2 proved unfeasible, unable to get the spacecraft into lunar orbit, resulting in the design of C ≤ 3. Its primary S ≤ I was powered by two F ≤ 1 engines, the S-II became a little thicker, with a diameter of 8.13 meters, and soon MSFC suggested further expanding the diameter to 9.14 meters.

Frequent project changes delayed the bidding process by six weeks, after NASA decided on November 11, 1961 to hand over S-II to North American Airlines and set up an assembly workshop at Panther Beach.

And this coming back and forth seems to suggest that the S-II is a thorn in the way to build.

S-II structure. Source: NASA

The fuel tank structure of S-II is similar to that of S-IVB. In order to reduce the quality of the first stage and above, the fuel tank of S-II is also made into the common bottom of hydrogen tank / oxygen tank, with a spacer shell in the middle. The tank, which has taken on 426.4 tons of liquid fuel, accounts for only 3% of the fuel mass. It can be imagined what kind of "easy-to-pull tank" this tank will be, and this tank is still 10 meters in diameter.

The S-II is designed to accept S-IC and S-IVB structures, as well as skirt rings, interstage segments, and recoil rockets. In fact, the construction method of S-II can refer to S-IVB and S-IC, because the routines for making large-volume fuel tanks are the same.

However, it can be seen from the figure that the liquid oxygen tank does not seem to be spherical. In fact, the height of the oxygen chamber is only 6.7 meters, which is smaller than the diameter, so it looks like a short pier. Such a low-pitched tank can be difficult to do. It is made of 12 pieces of large and complex surfaced melons. S-IVB can be folded because of its small size, and the shape of the S-IC's tank is not so complicated.

The helpless North American aviation engineers actually imaginatively came up with the "underwater blasting" method, using the explosion to generate shock waves in the water, and the water is difficult to be compressed and evenly distributed, as long as the explosive position and detonation time are properly arranged. , you can get the results you want. Soon, the North American Airlines Los Angeles Division looked for the El Torro Marine Corps base next door to help, built a 211 cubic meter pool and the appropriate "energetic materials" began the test, the results were very successful, the only shortcoming is Each time a piece of suitable melon is made, it will be blasted 3 times.

The middle partition shell is also very troublesome to manufacture: first, the top of the oxygen box is molded, and then the top is covered with a honeycomb phenolic resin insulation layer, which is not the same as the glass fiber used for S-IVB. This is followed by a coarse alignment of the upper shell (also the bottom of the liquid hydrogen tank), which is then mechanically modified on the surface to remove the excess.

And finally, the ultrasonic wave is used for flaw detection so as to ensure that no space exists in the middle of the sandwich. Similar to S-IVB, the top aluminum plate of this surface shell has a thickness of only 0.79 mm, a bottom end of only 1.3 mm, and even thinner than S-IVB. While the total thickness of the separator liquid hydrogen liquid oxygen is 13 cm.

The top of the liquid hydrogen tank is also made up of 12 pieces of melon, which is similar to the liquid oxygen tank. And the cylindrical part of the liquid hydrogen tank is divided into five groups of circular rings, each group of circular rings is formed by bending four aluminum plates, and in addition to the most lower layer of the cylinder with a height of 69 cm, in order to adapt the skirt ring to be fixed with the outer wall, the remaining four layer cylinders are high 2.4 meters. There are 636 high-strength pins on the skirt to ensure that the fuel tank is securely fixed.

It is clear, however, that as S-II uses liquid hydrogen as the fuel, the heat-insulating problem on S-IVB also has to make the engineers flexible on the S-II.

At first they chose a simple external insulation measure, first wrapped with a layer of polyfluoroethylene film, and then a ring of phenolic ester. However, one of the disadvantages is that once there is a hole in the surface of the undercooled material, the air in it will be liquefied, and the heat will be absorbed by liquid oxygen and vaporized again near the liquid oxygen tank, which will lead to the formation of bubbles between the adhesive and the surface of the material, which will peel off the insulation layer in a large area in the long run. North American Airlines' plan is to use the superfluency of liquid Helium to flow through these possible caverns and squeeze out the gas from the beginning of the liquid hydrogen infusion until it is launched.

The ideal is very good, but the reality is very ruthless. Not to mention the problem of high liquidity, in fact, the effect of this operation is very unstable. After continuing to fail N times, North American aviation engineers have to find another way. Since it is not used, it is easy to spray the insulation material directly to repair it, which is convenient and economical, and can reduce weight.

After all the materials have been prepared, S-II can load the fuel tank into the outer structure after routine operations such as vertical assembly, welding, hydrostatic testing and X-ray flaw detection similar to those of S-IVB. After the assembly, five J / 2 engines are arranged, and as long as they have passed a series of MTF tests, they can be officially put on the shelves and ready for launch.

It sounds beautiful, but in fact there is a problem in the soldering step.

The fuel tank material is aluminum alloy 2014 T6, the same choice as Douglas, but this material is not very suitable for welding, but there is no choice, because the material is still strong enough at low temperatures. In such a diameter of 10 meters, a single weld length of 31.4 meters, welding error requirements less than 0.33 mm, is not very suitable for welding materials, that is really artistic. The heat of welding and the deformation of materials also haunted S-II engineers, and then Norm Wilson, director of the S-II Panther Beach plant, said in an interview in 1968: "at first I didn't have many white hair. Look at me now." (pointing to his head full of silver silk)

This full silver is made up by a lot of experiments. These experiments, including the shape, size, thickness of the weld, and the parameters that the aluminum alloy can think of, were taken into account, and then an experiment, thickness from 16 mm all the way to less than 6 mm, then back to 13 mm, but not all. The constant failure made the engineers' temper gradually violent, especially the welding engineers.

So more parameters were included in the experiment: welding speed, arc voltage, welding path, working environment conditions, and even the addition of accessories in the solder should be taken into account! Everyone's experiment is for one thing only - welding the perfect weld.

This is, however, bound to be a bitter journey. The cylindrical surface of the hydrogen tank is formed by bending and welding different plates, and the different plates are in different positions, and the force is different. In the first welding attempt, the cylindrical part has finished 80%, and finally, due to the sudden release of the stress of the plate, the whole cylinder is deformed and has to be discarded. The welding process of the spherical shell of the curved surface is also very hard, and the welding is very good, but it is found that the tolerance is too large, and the welding seam has to be re-cut...

At a time when other factories adopted automated welding technology, Panther Beach workers were still doing what seemed to have passed-all holding welding guns, as if they were holding a torch, and the welding fire blew up in front of their eyes and spread out into starfires. And they use experience, and they use uninterrupted attempts to turn them into parameters, into lines of code, and enter them into tapes-yes, the programs of that era were burned into tapes. These codes contain a variety of details: precise current, arc temperature, the path of the welding head, the speed of movement, and even different welding tools.

By 1966, it was a crucial year for the development of Saturn 5, within which all problems needed to be solved. Engineers from various contractors and representatives of NASA,MSFC came to Panther Beach, and they also came to help further improve SI.

After inspecting the site, they proposed a number of improvements: reducing the ambient humidity to less than 30%; isolating a clean area, which filters out clean air with canvas curtains, all welders need to pass through the airlock compartment when entering and leaving the clean area Then, put on the white overalls - just like the bio-PhDs that raise cells; the new welding technology is also used.

These operations were finally implemented on the product: until 1968, all S-II had a more or less minor problem, and since S-II9, none of these problems existed and was a perfect product.

In the S-II unloaded by the MSFC, the large transporter looks like a toy in front of it. Source: NASA

Of course, things are not finished yet. After all, S-II is more difficult.

Remember the S-II thickness is thinner than S-IVB? Remember when we're designing S-ICs, are the ships fat every time we meet? The ship is also getting fat and the ship is 1 kg each, and it needs to save 1 kg from the S-IVB or 5 kg from the S-II or 14 kg from the S-IC. It's a pity that S-IVB has started to mass production, and S-IC is not so much less realistic, so it's only for S-II. And that's the next disaster.

On September 29, 1965, S-II-S/D (S ≤ D indicated that it needed to carry out structural test and dynamic test) to simulate the installation of S-IC, it broke down and broke into slag.

Due to the sensitive time of the accident, the MSFC quickly started the point-to-point docking. After collecting the debris for analysis, it was confirmed that the bottom skirt was damaged due to the 144% ultimate pressure of the defect. As a last resort, the next structural test can only be replaced by the S-II-T (T indicates a full-system experimental test) that was originally sent to Huntsville. As for the subsequent experiments, all queued.

S-II-S/D 's loss is not only a drag on S-II 's follow-up testing, but also a drag on the progress of the entire project. "the progress of S-II is out of control," (Brigadier General Edmund F.L. O'Connor, director of MSFC Industry, told von Braun. "they still have a lot of problems to solve." It is for this reason that in his October briefing, Conner bluntly said, "S-II is the most worrisome part at the moment." I think North American Airlines seems to have institutional deficiencies in the manufacture of S-II. " He also wrote to Thomas (Harrison Storms), director of space information systems (Space and Information Systems Division,S&ID), asking for his assistance.

The accident was so sensitive that it even shocked Lieutenant General (Major General Samuel C. Phillips), Apollo mission manager, on December 19, 1965, when he took a team of air force personnel directly to the North American aviation plant in Haibao Beach and met J.L. Atwood), North American aviation president, who said in person: "I'm not satisfied with the progress now."

The second accident occurred on May 28, 1966, and the S-II-T fell. Although it had previously completed a hot test of about 350 seconds, on the 25th three days ago, it burned near the liquid hydrogen valve, and it was not a problem because it was extinguished in time. But even so, engineers still need to find out why. At the same time as they were in a hurry, S-II also conducted a pre-experiment of dynamic testing in order to keep up with the progress. The empty liquid hydrogen tank was blown into the helium gas for cleaning, and at this time, the pressure sensor was off-line.

It is said that this is not a big problem. The next operation is coming: an unnamed staff member started the stress test. As a result, only one sound was heard, and the liquid hydrogen tank was overwhelmed by a large pressure, and five people were injured. Two of them were hospitalized.

The large gap created by S-II. Source: NASA

On Saturday, when the accident happened, on Saturday, von Braun was resting on a lake, and Stomstwind was in the world looking for him, and eventually called directly to his house, and, of course, he certainly couldn't find the father, and he could only find the wife of Braun. When they met on Tuesday, Braun said the "My love says you're on the phone with a crying.", but he said, '"It's a mistake to change so many times.",' he said.

The damage to S-II-T directly delayed the AS-501 test flight, and the already built S-II-2 (S-II for the second flight test) had to return to the factory for refurbishment because of other problems. When Lieutenant General Phillips heard that, he said even more angrily, "Why can't these people do this little thing well?" For North American Airlines employees, that day was undoubtedly a Black Saturday.

But the problem still has to be solved. In January 1967, the dissatisfied Lieutenant General asked the MSFC to organize a group of experts to go to the Seal Beach Factory to solve problems on the spot and teach new technical methods. Before the end of the month, new welding techniques have been widely used.

On January 27 th, three Apollo 1 astronauts died in the line of duty in a fire. The flight test of Saturn 5 was delayed, which gave S-II-1 a little time to repair it. At the joint request of a group of spaceflight giants, the S-II-1, which has been installed on Saturn 5, has been taken back for comprehensive and detailed testing for only one purpose: to ensure the safety of the S-II.

Several small defects of S-II-1 were found during the inspection, and these repairs lasted for 3 months. Until November 9, 1967, Saturn V finally began the AS-501 flight test mission, a complete success.

How many people will shed tears at the moment of successful launch? Source: NASA

The door to the moon finally opened

The main structure of rocket, like rocket engine, requires a lot of complicated and meticulous work. According to Tsiolkovsky formula, the lighter the rocket structure (dead weight), the better, which makes the development of the main part of the rocket become a "dance on the tip of the knife", and a little carelessness will cause big problems.

Whether it's S-IC, S-II, S-IVB, from the engine to the outer casing, every part of the Saturn V. Rocket is carrying the wisdom and sweat of thousands of engineers and front-line workers.

The size and structure of Saturn V. Source:National Air and SpaceMuseum and NASA, Adapted:haibarae.

From 1959 to 1967, Saturn 5 went through eight years of rough development. In the past eight years, people have achieved a great transformation from sketches to objects, which has never been completed before.

Exploring the unknown journey is a glorious road of thorns, and the road is long and long, and it is destined not to be smooth. But only this courage is the eternal glory that illuminates the short history of mankind.

So far, the engine is already in preparation, and the gate of the moon is finally opened to the human.

I wish to mark the great rocket engineers that the launch rocket section is almost over, and we'll see you later.


[1] SP-4206 Stages to Saturn

[2] SATURN | ILLUSTRATED CHRONOLOGY - Saturn's First Eleven Years: April 1957 through April 1968


[4] Haidn, O. J. (2008). Advanced rocket engines. Advances on Propulsion Technology for High-Speed ​​Aircraft, 1, 6-1.

This article from the micro-channel public number: forever relentless tour phase of Miao Wan Hon (ID: haibaraemily_planets), Author: Qi Lu promise genius edit: haibaraemily

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