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Author
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Topic: Apollo command module landing g-forces
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NavyPilot
Member Posts: 80
From: USA
Registered: Nov 2015
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posted 08-10-2022 10:35 PM
  
Is there a listing of measured landing g-forces for Apollo missions? Frustratingly, there is nothing in "Apollo By The Numbers," which compiles so much operational data by mission.Trying to understand anecdotal assertions (based on film) that Apollo 15 "hit harder," when there may be environmental or operational factors beyond descent rate that can affect or influence resultant impact g-loads. Thanks! |
oly
Member Posts: 1407
From: Perth, Western Australia
Registered: Apr 2015
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posted 08-11-2022 07:24 AM
quote:
Originally posted by NavyPilot:
influence resultant impact g-loads.
Impact what? |
randy
Member Posts: 2602
From: West Jordan, Utah USA
Registered: Dec 1999
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posted 08-11-2022 07:53 AM
If memory serves, the 'hard impact' referred to was the fact that one of the parachutes had failed, so the water impact was going to be harder. |
NavyPilot
Member Posts: 80
From: USA
Registered: Nov 2015
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posted 08-11-2022 11:35 AM
Thanks all. I was referring to splashdown loads. The statements about Endeavour's landing forces appear to be anecdotal and mostly presumed from the higher descent rate. I was wondering if there was any factual data to determine if any other CM may have hit harder due to landing orientation dynamics and wave shape interaction. Cheers.
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SpaceAholic
Member Posts: 5124
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 08-11-2022 12:21 PM
IMU accelerometers would have captured; if telemetry was continuously recorded to the DSE through spashdown and subsequently readout then the data is "out there". |
LM-12
Member Posts: 3648
From: Ontario, Canada
Registered: Oct 2010
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posted 08-11-2022 03:51 PM
Pete Conrad described the Apollo 12 splashdown this way in the post-flight debriefing: We really hit flatter than a pancake, and it was a tremendous impact, much greater than anything I'd experienced in Gemini. The Mission Report has this: Sea-state conditions were fairly rough, and the landing impact was extremely hard. (Editors note: Later information indicates the command module did not enter the water at the nominal 27.5-degree angle, from which it hangs on the parachute system. Engineering judgement indicates that the command module entered the water at an angle of 20 to 22 degrees, which corresponds to an impact acceleration of about 15g. This off-nominal condition is attributed to a wind-induced swing of the command module while it was on the parachutes and to the existing wave slope at contact.) |
Blackarrow
Member Posts: 3492
From: Belfast, United Kingdom
Registered: Feb 2002
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posted 08-12-2022 12:21 PM
That reminds me that Apollo 12 arguably came closest to a flight fatality. The G-forces on splashdown tore a movie camera from its mounting and it struck Al Bean on his forehead, briefly knocking him out cold. My understanding is that if it had struck the middle of his forehead, it might well have killed him. That's why Bean was the only Apollo astronaut to return with a visible injury, as shown by the sticking plaster on his forehead. (OK, I suppose someone with an eagle eye might have spotted the blood-clots under Dave Scott's finger nails...) |
oly
Member Posts: 1407
From: Perth, Western Australia
Registered: Apr 2015
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posted 08-12-2022 10:22 PM
quote:
Originally posted by NavyPilot:
I was referring to splashdown loads.
As the spacecraft descends under parachutes towards the ocean, the wave size, shape, wave amplitude, and the direction of travel of both the spacecraft and wave all play a part in the impact force.If the spacecraft has no drift and is descending vertically, its interaction with a wave will be different compared to a spacecraft with some horizontal drift (caused by wind). Also, if the spacecraft impacts a wave as it is rising compared to a wave that is falling, will influence the resulting impact force. A combination of a spacecraft with drift and a rising or falling wave will also influence the resulting impact force, as will the angle that the spacecraft “hangs” beneath the parachutes. In Apollo 15, one main parachute collapsed during descent, and AL Worden describes seeing a second parachute begin to collapse just before splashdown. This would significantly change the descent rate and resulting impact force, however, as the crew survived, it demonstrates that the impact force was survivable. Ocean wave patterns change. Anyone who has spent time on the ocean will recognise that while a wave frequency may be consistent for given conditions, wave size and pattern can change for many reasons including wind. The Apollo command module was tested in many different sea states and many drop tests were conducted to determine favorable landing angles and tolerances. Tests were also conducted for spacecraft rollover and self-righting. I seem to remember one episode of Moon Machines may have discussed an early water drop test where the command module boilerplate ruptured during the drop test and sunk as the engineers and scientists watched on. |
NavyPilot
Member Posts: 80
From: USA
Registered: Nov 2015
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posted 08-16-2022 07:12 PM
Still just looking for a written record tabulating any data. Thanks! |
Lou Chinal
Member Posts: 1378
From: Staten Island, NY
Registered: Jun 2007
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posted 08-17-2022 06:36 PM
In a conversion I had with Gene Cernan many years ago he stated "we hit like a grand piano on Apollo 10." |
Andy Anderson
Member Posts: 113
From: Perth, Australia
Registered: Dec 2009
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posted 08-17-2022 10:14 PM
quote:
Originally posted by NavyPilot:
Is there a listing of measured landing g-forces for Apollo missions?
I could not find any actual numbers of landing forces but this page from the NASA Apollo Recovery Ops Procedures Manual MSC-01856, June 1971 gives a clue as to what was expected in the splash down velocities. I am not sure if the listed 32ft/sec works out to 1g and 36ft/sec equals 1.12g. (The actual calculation is 1 ft/s2 = 0.031081 g; therefore 1 g = 32.174049 ft/s2 - with the velocity amount being "squared").In any case, even if those calculated "g" numbers based on the published expected splash down velocities are correct, as mentioned above, without consideration of the sea condition the actual numbers would have been very much different. EDIT. On reflection, my calculation of the 'g" is wrong - velocity and acceleration are different "beasts" of course.  |
MartinAir
Member Posts: 211
From:
Registered: Oct 2020
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posted 08-18-2022 07:07 AM
WOW, 32 ft/sec nominal splashdown velocity? No wonder they hit like a grand piano... |
Headshot
Member Posts: 1110
From: Vancouver, WA, USA
Registered: Feb 2012
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posted 08-18-2022 09:21 AM
An article discussing the landing of the Apollo 15 command module appeared in the 16 Aug 1971 issue of AWST (page 43). It gave some different figures.A three-parachute landing was estimated at 28 ft/sec, or a 8-10 g landing. The two-parachute landing that 15 experience was estimated at 32 ft/sec, or "... around 16 g or so." The command module was designed, according to the article, to withstand a 78 g landing. The crew probably would have received injuries from such a landing, but would have survived. |
Headshot
Member Posts: 1110
From: Vancouver, WA, USA
Registered: Feb 2012
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posted 08-18-2022 10:35 AM
According to Virtual Apollo by Sullivan, the crew's couch attenuation system was designed to absorb up to 40 g impacts. Anything higher would damage the system and probably injure the crew.Also, the 16 g estimate for the Apollo 15 landing was based on the fact that the couch attenuation system struts would start to stroke at around 16 g, but no evidence of stroking was initially observed upon inspection. |
Space Cadet Carl
Member Posts: 294
From: Lake Orion, MI
Registered: Feb 2006
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posted 08-18-2022 10:37 AM
quote:
Originally posted by Headshot:
An article discussing the landing of the Apollo 15 command module appeared in the 16 Aug 1971 issue of AWST (page 43).
Thanks for retrieving that information from the AW&ST archive. It really puts it in layman's terms! |
Lou Chinal
Member Posts: 1378
From: Staten Island, NY
Registered: Jun 2007
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posted 08-19-2022 05:46 AM
The normal rate of decent for a man carrying parachute is 18 FPS at sea level. That's a 28 ft. C9 canopy. |
NavyPilot
Member Posts: 80
From: USA
Registered: Nov 2015
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posted 08-21-2022 09:12 PM
Lou, the SJU-17 NACES uses a 21-foot canopy. Naval aviators accept that it's there to make landing survivable, if not enjoyable! |
Lou Chinal
Member Posts: 1378
From: Staten Island, NY
Registered: Jun 2007
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posted 08-21-2022 11:08 PM
Hey what can I tell you. My first jump was with a 24 ft. seat pack. I'll admit I'm living in the past! |
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