Apollo Discussions > The Reality of Apollo

Apollo 11 Fuel Level at touchdown

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Zakalwe:
It's an oft-repeated "fact" that the Eagle had only about 20 seconds fuel remaining when it touched down. It certainly adds to the tension of the story and adds a little of the "spice" that journalists so love.  However, I am sure that I have seen it somewhere that the fuel level was later re-calculated and they had a lot more to spare. The design of the anti-slosh baffles allowed the fuel to slosh around and casued the instruments to under-read. I also seem to remember seeing that the anti-slosh baffles were later re-designed.

Is my recollection correct or did I dream this? If my recollection is correct, do you have a verifiable source for it?

Thanks in advance.

BertL:
I think I heard this from In the Shadow of the Moon, but the "20 seconds left" was an indicator that if they couldn't find a landing spot in that time the mission was aborted and Aldrin and Armstrong were to rendezvous with the CSM again.

Zakalwe:
Arrgghh...as luck would have it...20 seconds after I hit "Post" I found the information here: http://www.hq.nasa.gov/alsj/a11/a11.landing.html

"Post-flight analysis indicated that Neil landed with about 770 pounds of fuel remaining. Of this total, about 100 pounds would have been unusable. As indicated in an unnumbered figure ( 63k ) from page 9-24 in the Apollo 11 Mission Report ( 5.7 Mb ), the remainder would have been enough for about 45 seconds, including about 20 seconds for an abort."

". Slosh uncovered the Quantity Gauge, latching the light early, losing the crew half a minute of flight time. It also made the LPD unreliable. Apollo 12 flew with the same configuration and its Quantity light came on early"

Grumman redesigned the baffles to prevent the problem:


The engineers were able to demonstrate retro-fitting the new design through a 2"  Quantity System hole (maybe they missed their calling as gynaecologists!)

Echnaton:
I have wondered how precise was the knowledge the controllers had about the error in their readings.  They could have gotten information from the earth and lunar orbit testing, but there was no way to look into the tank to see how much gas was really left, so to speak.  As disciplined as Armstrong was, I also wonder if he would have ignored an abort order under circumstances where he was almost there.  IIRC Aldrin said that he thought Armstrong would have and it is hard to tell a test pilot how to fly his craft from a quarter of a million miles away. 

These were guys of great skill with nerves of steel.  I still feel a sadness with the loss of Armstrong.  The world seems a little less bright. 

Zakalwe:

--- Quote from: BertL on September 03, 2012, 12:10:26 PM ---I think I heard this from In the Shadow of the Moon, but the "20 seconds left" was an indicator that if they couldn't find a landing spot in that time the mission was aborted and Aldrin and Armstrong were to rendezvous with the CSM again.

--- End quote ---

From the same source that I linked to:

"The quantity light latched at 102:44:31, and indicated that 5.6% of the original propellant load remained. This event started a 94-second countdown to a 'Bingo' fuel call which meant 'land in 20 seconds or abort.' So if the count gets down to zero, Neil will have 20 seconds to land, if he thinks he can get down in time. Otherwise, he will have to abort immediately. If you're 50 feet up at 'bingo fuel' with all of your horizontal rates nulled and are coming down to a good spot, you could certainly continue to land. With your horizontal rates nulled at 70 to 100 feet, it would be risky to land - perhaps giving you a landing at the limiting load of the landing gear. At anything over 100 feet, you'd punch the abort button, say goodbye to the moon, and stew for the rest of your life!"

The Contact Light came on 55 seconds after the Fuel Quantity light, which lit at 102:44:45. CAPCOM called 60 seconds to the "bingo" call at 102:45:02. But  the lamp lit early and the post-flight analysis showed that they had enough for 45 seconds of flight after they had touched down.

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