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Apollo 6 Mission 1968 NASA; Second Saturn V Flight Test
🕑 Added 2020-11-22 21:26:31 +0000 UTCmore at http://quickfound.net/
Silent (soundtrack missing).
Originally a public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
https://en.wikipedia.org/wiki/Apollo_6
Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/
Apollo 6 (also known as AS-502), launched on April 4, 1968, was the second A-type mission of the United States Apollo program, an uncrewed test of the Saturn V launch vehicle. It was also the final uncrewed Apollo test mission.
The objectives of the flight test were to demonstrate trans-lunar injection capability of the Saturn V with a simulated payload equal to about 80% of a full Apollo spacecraft, and to repeat demonstration of the command module's (CM) heat shield capability to withstand a lunar re-entry. The flight plan called for following trans-lunar injection with a direct return abort using the command and service module's (CSM) main engine, with a total flight time of about 10 hours.
A phenomenon known as pogo oscillation damaged some of the Rocketdyne J-2 engines in the second and third stages by rupturing internal fuel lines, causing two second-stage engines to shut down early. The vehicle's onboard guidance system was able to compensate by burning the second and third stages longer, though the resulting parking orbit was more elliptical than planned. The damaged third-stage engine also failed to restart for trans-lunar injection. Flight controllers elected to repeat the flight profile of the previous Apollo 4 test, achieving a high orbit and high-speed return using the service module (SM) engine. Despite the engine failures, the flight provided NASA with enough confidence to use the Saturn V for crewed launches. Since Apollo 4 had already demonstrated S-IVB restart and tested the heat shield at full lunar re-entry velocity, a potential third uncrewed flight was cancelled...
Unlike the virtually 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...
In part due to the vibrations, the spacecraft adapter that attached the CSM to the rocket and housed the mockup LM started to have some structural problems. Airborne cameras recorded several pieces falling off it at T+133 seconds.
After the first stage was jettisoned, the S-II second stage began to experience its own problems. Engine number two had performance problems from 225 seconds after liftoff, which abruptly worsened at T+319 seconds, and then at T+412 seconds the Instrument Unit shut it down altogether. Then two seconds later, engine number three shut down as well. The Instrument Unit was able to compensate, and the remaining three engines burned for 58 seconds longer than normal. The S-IVB third stage also had to burn for 29 seconds longer than usual. The S-IVB also experienced a slight performance loss...
Due to the less than nominal launch, the CSM and S-IVB were inserted into a 93.49-nautical-mile (173.14 km) by 194.44-nautical-mile (360.10 km) parking orbit, instead of the planned 100-nautical-mile (190 km) circular orbit.[2] Then, after the standard two parking orbits to check out the vehicle's readiness for Trans Lunar Injection (TLI), the S-IVB failed to restart.
It was decided to use the SM engine to raise the spacecraft into a high orbit, as had been done in Apollo 4, in order to complete some of the mission objectives. It burned for 442 seconds (longer than it would ever fire on a nominal lunar mission) to get to the planned 11,989-nautical-mile (22,204 km) apogee. There was now however, not enough fuel to speed up the atmospheric reentry and the spacecraft only entered the atmosphere at a speed of 33,000 feet per second (10,000 m/s) instead of the planned 37,000 feet per second (11,000 m/s) of a lunar return. However, this had been demonstrated on Apollo 4.
Ten hours after launch, it landed 43 nautical miles (80 km) from the planned touchdown point in the North Pacific Ocean north of Hawaii, and was lifted on board the USS Okinawa...
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 damp 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 like a shock absorber...
