Apollo 6 near disaster
Discussion
Ineteresting writeup about how close Apollo 6 came to disaster. Apollo 6 was the second unmanned flight of the Saturn V
"Apollo 6, launched on April 4, 1968, nearly shook itself apart during launch. You may know about two J-2 engines going out on the second stage, but did you know that the SLA lost panels, the LES almost activated and the Service Module moved 3 inches on the SLA?
NASA's final report on the mission is rich with detail, but let's look at the one failure that never stops causing my mouth to drop: The failure of the Spacecraft LM Adapter, or SLA. Inside is a Lunar Module test article.
The SLA, designed by North American Aviation, was made of nearly 2 inches of aluminum honeycomb material. Now, the Saturn V's design was plagued by "pogo" oscillations that threatened to shake the vehicle apart. Pogo oscillations shook Apollo 6 early on, as the Launch Escape System was wildly vibrating at 1 min 28 sec into the flight.
At about 2 min 13 sec, several SLA panels began to bend, inward, and eventually buckle entirely, falling from the vehicle as the photos below show. If this event occurred earlier when the atmosphere was thicker, drag forces would have certainly caused the vehicle to break apart further. The report suggests that there were fears corrosion damage to the SLA aluminum (the things sat around in the Florida salty sea air).
What you may not know is that, at the same time, one of the three wires that control the Emergency Detection System (EDS) lost power. There are three such wires throughout the length of the Saturn. If two of them lost power, the Launch Escape System would've activated, pulling the Block I CSM-020 Command Module away and ending the mission.
("Apollo 13" film fans hear Lovell say "EDS to manual, inboard" during their launch, just prior to their first staging. Basically, he's turned off the EDS because they're near the end of the LES's usefulness and will jettison the LES just after staging.)
For the next mission (Apollo 7, the first manned mission) and later, some vent holes were made to check for corrosion and later for Apollo 8 to equalize any pressure differential. Also for 8, cork paneling covered the SLA to aid in temperature variations, and a type of ultrasonic inspection was done to all future adapters to check for voids in the aluminum.
The distance between the Service Module and the SLA apparently moved at least 3 inches in flight because of the SLA damage as well.
Read the report at your leisure. (This material may be too sensitive for younger space enthusiasts.)
https://ntrs.nasa.gov/search.jsp?R=19700025117
( in this last image the text at the top indicates the camera locations which gave the data used for the diagram )
"Apollo 6, launched on April 4, 1968, nearly shook itself apart during launch. You may know about two J-2 engines going out on the second stage, but did you know that the SLA lost panels, the LES almost activated and the Service Module moved 3 inches on the SLA?
NASA's final report on the mission is rich with detail, but let's look at the one failure that never stops causing my mouth to drop: The failure of the Spacecraft LM Adapter, or SLA. Inside is a Lunar Module test article.
The SLA, designed by North American Aviation, was made of nearly 2 inches of aluminum honeycomb material. Now, the Saturn V's design was plagued by "pogo" oscillations that threatened to shake the vehicle apart. Pogo oscillations shook Apollo 6 early on, as the Launch Escape System was wildly vibrating at 1 min 28 sec into the flight.
At about 2 min 13 sec, several SLA panels began to bend, inward, and eventually buckle entirely, falling from the vehicle as the photos below show. If this event occurred earlier when the atmosphere was thicker, drag forces would have certainly caused the vehicle to break apart further. The report suggests that there were fears corrosion damage to the SLA aluminum (the things sat around in the Florida salty sea air).
What you may not know is that, at the same time, one of the three wires that control the Emergency Detection System (EDS) lost power. There are three such wires throughout the length of the Saturn. If two of them lost power, the Launch Escape System would've activated, pulling the Block I CSM-020 Command Module away and ending the mission.
("Apollo 13" film fans hear Lovell say "EDS to manual, inboard" during their launch, just prior to their first staging. Basically, he's turned off the EDS because they're near the end of the LES's usefulness and will jettison the LES just after staging.)
For the next mission (Apollo 7, the first manned mission) and later, some vent holes were made to check for corrosion and later for Apollo 8 to equalize any pressure differential. Also for 8, cork paneling covered the SLA to aid in temperature variations, and a type of ultrasonic inspection was done to all future adapters to check for voids in the aluminum.
The distance between the Service Module and the SLA apparently moved at least 3 inches in flight because of the SLA damage as well.
Read the report at your leisure. (This material may be too sensitive for younger space enthusiasts.)
https://ntrs.nasa.gov/search.jsp?R=19700025117
( in this last image the text at the top indicates the camera locations which gave the data used for the diagram )
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