Тред №243758

Цитата: Gexagen от 04.08.2010 01:59:29
Покажите конкретно документ на английском (если мы неправильно перевели) из НАСА! а не Покровского в котором говорится о том что "трясся болезный на 6-ом апполончике" (ц)
в ваших ссылках я этого не нашел.

Цитата: Gexagen от 04.08.2010 01:59:29

 

Цитата
Unlike the near perfect flight of Apollo 4, Apollo 6 experienced problems right from the start. Two minutes into the flight, the rocket experienced severe Pogo oscillations for about 30 seconds. George Mueller explained the cause to a congressional hearing:
   Pogo arises fundamentally because you have thrust fluctuations in the engines. Those are normal characteristics of engines. All engines have what you might call noise in their output because the combustion is not quite uniform, so you have this fluctuation in thrust of the first stage as a normal characteristic of all engine burning.

   Now, in turn, the engine is fed through a pipe that takes the fuel out of the tanks and feeds it into the engine. That pipe's length is something like an organ pipe so it has a certain resonance frequency of its own and it really turns out that it will oscillate just like an organ pipe does.

   The structure of the vehicle is much like a tuning fork, so if you strike it right, it will oscillate up and down longitudinally. In a gross sense it is the interaction between the various frequencies that causes the vehicle to oscillate.

In part due to the pogo, the spacecraft adaptor that attached the CSM and mockup of the Lunar Module to the rocket started to have some structural problems. Airborne cameras recorded several pieces falling off it at T+133s.

After the first stage was jettisoned at the end of its task, the S-II second stage began to experience its own problems. Engine number two (of five) had performance problems from 225 seconds after liftoff, abruptly worsened at 319 seconds, and then at 412 seconds shut down altogether. Then two seconds later Engine Number Three shut down as well. The onboard computer was able to compensate and the stage burned for 58 seconds more than normal. Even so the S-IVB third stage also had to burn for 29 seconds longer than usual. The S-IVB also experienced a slight performance loss, the significance of which would only become evident later.[1]

Цитата
The cause of the pogo during the first stage of the flight was well known. However, it had been thought that the rocket had been 'detuned'. To further dampen pressure oscillations in the fuel and oxidizer pumps and feed lines, cavities in these systems were filled with helium gas from the propulsion system's pneumatic control system, which acted to attenuate the oscillations.

Цитата
Не помогло однако

The problems of the Apollo 6 test would have resulted in an abort of a manned Apollo flight. However, the booster rocket shakedown on this mission was invaluable, as none of the eleven subsequent Saturn V flights experienced any serious problems.

Цитата
There was little press coverage of the Apollo 6 mission mainly because on the same day as the launch, Martin Luther King, Jr. was shot and killed in Memphis, Tennessee, and President Johnson had announced he would not seek reelection only five days before.

Цитата
Pogo and Other Problems

The pogo bounce had been observed (although to a much smaller degree) on Apollo 4, so its appearance during Apollo 6 did not come as a complete surprise. Also, five years earlier, in 1963, pogo had threatened to end the Gemini program when the Titan II suffered this phenomenon on launch after launch. Its apparent cause was a partial vacuum created in the fuel and oxidizer suction lines by the pumping rocket engines. This condition produced a hydraulic resonance - more simply, the engine skipped when the bubbles caused by the partial vacuum reached the firing chamber. Sheldon Rubin of the Aerospace Corporation had finally suggested installing fuel accumulators and oxidizer standpipes, to ensure a steady flow of propellants through the lines. This had solved the Gemini launch vehicle problems, and NASA had this background experience to draw on when the Saturn V began having pogo troubles.* 39

Pogo on Apollo 4 had been measured at one-tenth g, much less than the one-fourth g set as the upper limit in Gemini. The lower oscillation was probably the result of carrying just "a hunk of junk," to simulate lunar module weight, on the earlier flight. But a test article flown on Apollo 6 had the shape and weight of a real lander in the adapter. This change in mass distribution coupled back into the fuel system problem and increased the pogo oscillations. The mission analysts later discovered that two of the Saturn engines had been inadvertently tuned to the same frequency, probably aggravating the problem. (Engines in the Saturn V cluster were to be tuned to different frequencies to prevent any two or more of them from pulling the booster off balance and changing its trajectory during powered flight.)

The rocketeers at Huntsville first wanted to know from Houston whether a crew could have withstood the vibration levels on Apollo 6. If so, the next Saturn V flight could be manned, even without a pogo cure. Low informed Saturn V Program Manager Arthur Rudolph that these levels could not be tolerated. Marshall also asked whether the emergency detection system could be used to abort the mission automatically if such high vibrations again occurred. During Apollo 6, the system had cast one vote for ending the mission. Had it cast a second vote, abort would have been mandatory. Low and chief astronaut Donald Slayton did not want to use the system in an automatic pogo abort mode. Low met with George H. Hage, Phillips' deputy, and they decided on the immediate development of a "pogo abort sensor," a self-contained unit that would monitor and display spacecraft oscillations. From what the sensor told him, a spacecraft commander could decide whether to continue or stop the mission.40

Marshall Space Flight Center pulled an S-IC stage out of Michoud Assembly Facility, brought it to Huntsville, and erected it in a test stand. By May, Huntsville, Houston, and Washington Apollo officials were ready to attack the pogo problem. Hage agreed to head the activity until Eberhard Rees could finish his task on the command module at Downey and take over. At one time during the pogo studies, Lee B. James (who had replaced Rudolph as the Huntsville Saturn V manager) said, 1,000 engineers from government and industry were working on the problem.41

Out on the West Coast, at the rocket engine test site at Edwards Air Force Base, Rocketdyne started testing its F-1 engine in late May. In the first six tests, helium was injected into the liquid-oxygen feed lines in an attempt to interrupt the resonating frequencies that had caused the unacceptable vibration levels. In four of the six tests, the cure was worse than the disease, producing even more pronounced oscillations. The Saturn V people at Marshall also tried helium injection, but their results were decidedly different. No oscillations whatsover were observed. Tests using the S-IC stage's prevalves as helium accumulators were then conducted at both Edwards and Marshall. The prevalves were in the liquid-oxygen ducts just above the firing chambers of the five engines and were used to hold up the flow of oxygen in the fuel lines until late in the countdown, when the fluid was admitted to the main liquid-oxygen valves in preparation for engine ignition. The prevalves were modified to allow the injection of helium into the cavity about 10 minutes before liftoff; the helium would then serve as a shock absorber against any liquid-oxygen pressure surges.

What had happened to the S-II and S-IVB stages, with two of the five J-2 engines shutting down in one case and the single J-2 engine refusing to start in the other, was more of a mystery than pogo. During tests at Arnold Engineering Development Center, at Tullahoma, Tennessee, engineers discovered that frost forming on propellant lines when the engines were fired at ground temperatures served as an extra protection against lines burning through. But frosting did not take place in the vacuum of space; the lines could have failed because of this. Also, in the line leading to each of the engines was an augmented spark igniter. Next to the igniter was a bellows. During ground tests, liquid air, sprayed over the exterior to cool it, damped out any vibrations. Vacuum testing revealed that the bellows vibrated furiously and failed immediately after peak-fuel-flow rates began. These lines were strengthened and modified to eliminate the bellows.42

Another item noticed by the flight control monitors during the boosted flight of Apollo 6 (and later confirmed by photographs) was that a panel section of the adapter that housed the lander had fallen away just after the Saturn V started bouncing. The controllers had been amazed that the structural integrity was sufficient to carry the payload into orbit. James Chamberlin in Houston discovered that thermal pressure (and therefore moisture) had built up in the honeycomb panels during launch; with no venting to allow the extra pressure to escape, the panel had blown out. A layer of cork was applied to the exterior of the adapter to keep it cooler and to absorb the moisture, and holes were drilled in the adapter panels to relieve the internal pressure if heat did build up inside on future launches.43

Although Marshall was responsible for stability and dynamic structural integrity throughout the boost phase, the Manned Spacecraft Center could not afford to sit on the sidelines and watch while its sister center wrestled with these problems. Houston had to get an Apollo payload stack together for structural testing. On 16 May 1968, Low and James decided to use a "short stack" (the S-IC stage would be left out at this time but could be incorporated later).** Astronaut Charles Duke was sent to Huntsville to keep information flowing between the centers, and Rolf Lanzkron was assigned by Low to manage the spacecraft dynamic integrity testing, which was satisfactorily completed on 27 August with no major hardware changes found necessary.44

Цитата
Phillips and Hage arrived in Houston on 17 August and met with Gilruth, Low, Kraft, and Slayton. The Apollo program leader from Washington said that Webb had given him clear authority to prepare for a 6 December launch, to designate it as a C-prime mission, and to call it Apollo 8. He then ticked off what else had been authorized: they could assign Borman's crew to the flight, equip and train it to meet the 6 December launch, and speak of the flight as earth-orbital while continuing to plan for a lunar orbit. The plotters were well aware, and Phillips reemphasized it, that a successful command module qualification flight in earth orbit by Apollo 7 was the key to the first lunar flight's being approved for 1968.12 Now Houston had to train crews to fly that mission, as well as the others that would follow.

Цитата
Инженеры даже не смогли найти причины многочисленных проблем, каждая из которых привела бы к невыполнению миссии и весьма вероятной смерти экипажа.

Далее администраторы НАСА [Program Office] начали записывать разговоры между собой, и договариваться кому и что говорить, вести записи друг на друга и [Off record].  Многие вспомнили молодость и пошли в парашютисты.
А решение об аполлончике-8 (декабрь 1968) было принято в Вашингтоне (угадайте какое); в ноябре и вашингтонский ЦК сменился кстати, там тренированные парашютисты.

Цитата
In what was termed the October surprise, Johnson announced to the nation on October 31, 1968, that he had ordered a complete cessation of "all air, naval and artillery bombardment of North Vietnam", effective November 1, should the Hanoi Government be willing to negotiate and citing progress with the Paris peace talks. In the end, the divided Democratic Party crumbled enabling Republican Richard Nixon to win the election.

Johnson was not disqualified from running for a second full term under the provisions of the 22nd Amendment; he had served less than 24 months of President Kennedy's term. Had he stayed in the race and won and served out the new term, he would have been president for 9 years and 2 months, second only to Franklin Delano Roosevelt. Coincidentally, Johnson died just two days after what would have been the end of his second full term.

Цитата
"Военное дело просто и вполне доступно здравому уму человека. Но воевать сложно."
К.Клаузевиц

"Политика штука тонкая. А митинговать все могут."  
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