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  Force of gravity during Apollo lunar liftoffs

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Author Topic:   Force of gravity during Apollo lunar liftoffs
Duke Of URL
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posted 12-27-2012 05:17 PM     Click Here to See the Profile for Duke Of URL   Click Here to Email Duke Of URL     Edit/Delete Message   Reply w/Quote
Does anybody know what the G forces of the liftoffs from the moon were?

ejectr
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posted 12-28-2012 06:43 PM     Click Here to See the Profile for ejectr   Click Here to Email ejectr     Edit/Delete Message   Reply w/Quote
Murdoc Online: May the (G) Force be with You
This is a simple graph of the G forces experienced during the trip from the launch pad to low earth orbit in a Saturn V.

Duke Of URL
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posted 12-28-2012 11:25 PM     Click Here to See the Profile for Duke Of URL   Click Here to Email Duke Of URL     Edit/Delete Message   Reply w/Quote
To be clear, I was interested about the G forces to which astronauts were subjected during a liftoff from the lunar surface. In other words, what G force did they get while leaving the lunar surface.

Once again for clarity, when the astronauts blasted off the surface of the Moon. (and only the surface of the moon, please) how many g's were they pulling?

Sorry for any confusion.

Robert Pearlman
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posted 12-28-2012 11:47 PM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
From the Apollo 15 Flight Journal, citing comments by David Scott:
"It was also very low g. The pictures show the thing popping off the ground. Pop? I think we went from 1/6th g to maybe a half or whatever. You weren't being pushed hard. We were standing up and you would think, boy, all those g's standing up. Not really. You could hardly tell."

Headshot
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posted 12-29-2012 07:38 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
This is a very good question.

About a half of a g is what I recall Pete Conrad estimating during an interview with Paris-Match back in late '69 or early '70.

I reviewed the Apollo XII Mission Report, but could not find an acceleration graph of the lunar liftoff, nor did I find any comments from Conrad or Bean in their Tech Debrief.

moorouge
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posted 12-29-2012 10:41 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
You may find this provides your answer.

Guillaume
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posted 12-29-2012 11:42 AM     Click Here to See the Profile for Guillaume   Click Here to Email Guillaume     Edit/Delete Message   Reply w/Quote
I remember Alan Bean saying that it felt like an elevator ride.

Blackarrow
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posted 12-29-2012 05:04 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
If the g-force on lunar liftoff is about 0.5g, that would be three times normal lunar gravity, the equivalent of 3g acceleration after liftoff from Earth.

However, I suspect that what matters is the difference rather than the multiplier. The difference is 2g lifting off from Earth, but from the moon it's a pretty modest .33g increase. I hope that makes sense.

moorouge
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posted 12-30-2012 02:04 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Which is basically what the Webber International University website said.

moonguyron
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posted 01-03-2013 08:15 PM     Click Here to See the Profile for moonguyron   Click Here to Email moonguyron     Edit/Delete Message   Reply w/Quote
Here is some simple math that will answer all your questions about "g" forces during any powered phase of flight. Stay with me a bit here and you will see it is simple high school math.

For any burn you need the change in velocity in feet/sec. For example the lunar liftoff went from zero to 6047 ft/sec. ( I get this from an Apollo 17 Flight Plan I have.) Now divide this change in velocity by the time in seconds of the burn. In this case 7 minutes 14 seconds equals 434 seconds. This yields 13.935 ft/sec squared. (That's the average acceleration during the burn). Now all we have to do is divide this 13.935 by 32 ft/sec squared (the acceleration of one "earth g') and you get .435 "g" average coming off the moon.

Another example: TLI: Change in velocity was 10375 ft/sec. Time of burn was 344 seconds. 10375 divided by 344 is 30.16 ft/sec squared average during the burn. Divide this by 32 ft/sec squared and average "g" is .94 for the burn.

I have done this for all burns for a flight to the moon and back just to get a feel for the "g" load they experienced. Except for launch all accelerations were quite benign. Launch on the other hand was quite different and was not nearly so linear as great gobs of propellant were used which changed dramatically the vehicle weight during boost which changed acceleration as it burned off. For that I would refer you to the Saturn V Manual where graphs show the "g" load during each stage to orbit.

Hope this helps.

xlsteve
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posted 01-04-2013 08:37 AM     Click Here to See the Profile for xlsteve   Click Here to Email xlsteve     Edit/Delete Message   Reply w/Quote
As a practical description, I've heard Alan Bean describe it as riding in one of those glass elevators in a mall or hotel.

moorouge
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posted 01-12-2013 10:37 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Now we've settled the 'g' at lift-off on the moon, what would have been the 'g' experienced by Stafford and Cernan when they fired up the ascent stage in lunar orbit? The same or more or less?

moonguyron
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posted 01-19-2013 09:23 PM     Click Here to See the Profile for moonguyron   Click Here to Email moonguyron     Edit/Delete Message   Reply w/Quote
Since I do not have access to the velocity change or time of acceleration we can not apply the above math. However we do know that all ascent engines are essentially the same in thrust, and,although the AP-10 LM was somewhat lighter they would experience very close to the same acceleration ("g" load) as all subsequent departing LM's, just not for as long a duration.

LM-12
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posted 01-19-2013 10:13 PM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
The Apollo 12 splashdown was a hard landing in choppy seas. Pete Conrad described the splashdown as "a tremendous impact". The post-flight Mission Report estimated that the impact acceleration was about 15g.

John Charles
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posted 03-03-2013 08:08 PM     Click Here to See the Profile for John Charles     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by moonguyron:
That's the average acceleration during the burn...
Good information, thanks! During lunar launch, the perceived g level was lower than the average and reached its maximum value at orbit insertion because the mass of the ascent stage decreased as propellants were used but the thrust of the engine remained constant. Have you looked at the final g level at burn out by dividing the empty weight of the ascent stage by the engine's thrust? (I haven't but it would be interesting.)

moonguyron
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posted 03-04-2013 02:21 PM     Click Here to See the Profile for moonguyron   Click Here to Email moonguyron     Edit/Delete Message   Reply w/Quote
John, I don't have access to the numbers (ascent stage weight and engine thrust) but if you can get them, let's do the math. I did mention that these are approx. numbers based on an average. And as mentioned, as in launch when vast quantities of propellant dramatically change the vehicle weight these accelerations change correspondingly.

Paul78zephyr
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posted 07-08-2014 06:59 PM     Click Here to See the Profile for Paul78zephyr     Edit/Delete Message   Reply w/Quote
I don't recall reading anything about what the astronauts felt during lunar liftoff/ascent in the LM ascent stage.

Unlike liftoff from the earth where they were laying on their backs on cushioned/contoured couches, lunar liftoff was done standing up. As was the landing but the landing rate was much less.

Is there anywhere that any of the CDRs/LMPs discussed the physical sensations/issues felt during lunar liftoff/ascent (other than 'boy I'm glad that engine worked', etc)? Anything about G forces - especially considering they had just been in a 1/6th G environment for some time.

Editor's note: Threads merged.

Headshot
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posted 07-09-2014 06:08 AM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
Lunar lift-off was comparable to a ride in an standard elevator. I believe it was thought to be about 1/4 g.

Greggy_D
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posted 07-09-2014 06:22 AM     Click Here to See the Profile for Greggy_D   Click Here to Email Greggy_D     Edit/Delete Message   Reply w/Quote
I asked Charlie Duke if the LM liftoff/ascent was a violent maneuver. His reply:

"Nah, it wasn't violent. It was real sporty though."

music_space
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posted 07-11-2014 06:00 AM     Click Here to See the Profile for music_space   Click Here to Email music_space     Edit/Delete Message   Reply w/Quote
"Smooth", "Like an elevator". I've read this, was it Buzz or Michael?

Besixdouze
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posted 07-11-2014 07:24 AM     Click Here to See the Profile for Besixdouze   Click Here to Email Besixdouze     Edit/Delete Message   Reply w/Quote
How would Michael have known? Perhaps you meant Neil.

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