Author Topic: Recover ship proximity to Apollo splash down  (Read 359 times)

Offline Willoughby

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Recover ship proximity to Apollo splash down
« on: July 12, 2017, 11:35:46 AM »
Could someone give a good source that would detail the distance between the Apollo splash down locations and their respective recovery ships?  I found something on Wikipedia that had a column called "mass distance", and I'm not sure what that means.  The numbers are very low - for the Apollo missions they really go no higher than about 3 km.  Is this really how accurately they were able to predict the splash down locations of Apollo - and if so, this was just from known trajectories, rotation of Earth, etc.?  In other words, are these numbers the ones I'm looking for?  I'm not suggesting fakery or any nonsense like that.  I was just wondering.

Here's the link to the Wikipedia page I am referring to :

https://en.wikipedia.org/wiki/Splashdown

Offline QuietElite

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Re: Recover ship proximity to Apollo splash down
« Reply #1 on: July 12, 2017, 12:10:53 PM »
The location and distance to the recovery ships for the Apollo missions can be found here:
https://history.nasa.gov/SP-4029/Apollo_18-40_Entry_Splashdown_and_Recovery.htm

I think you mean the Miss distance  ;)
Comparing the numbers it looks like that it is the distance to the preplanned target and not to the recovery ships (however the first digit for Apollo 16 in the Wikipedia article seems to be wrong).

No the high accuracy didnt just come from the known trajectory. The command module had a off center Center of Gravity so that it can change its lift by rolling the spacecraft and therefore gave them crossrange capabilities. Their guidance system constantly adjusted their attitude so that they would hit the preplanned splashdown target with high accuracy. You can look for reports about the EMS (Entry Monitoring System) for more details about the entry targeting for Apollo.

Offline Willoughby

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Re: Recover ship proximity to Apollo splash down
« Reply #2 on: July 12, 2017, 12:24:31 PM »
Yep, I totally misread that.  It is miss distance.  Thanks for this information.  That looks like something that would be available in the "Apollo by the Numbers" source that I have, but I must have overlooked it. 


When you say "preplanned" target, do you happen to know at what point these targets were calculated?  I find it hard to understand how they could know with any reasonable certainty where they should splashdown if this target was calculated pre-mission.  Any delays along the way would result in being far off that target simply from the Earth rotating more or less than originally planned.  Also, a mission like Apollo 13 surely would not have hit any pre-mission splashdown target for obvious reasons other than by coincidence.  It makes me think that the "target" location was something that wasn't calculated until well into the return trip from the moon.  Please correct me if I am mistaken.

Offline QuietElite

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Re: Recover ship proximity to Apollo splash down
« Reply #3 on: July 12, 2017, 12:59:45 PM »
Well the locations were certainly preplanned already before the mission and probably didnt change that much if the mission followed the exact flight plan.
After the TEI burn it should have been very clear since the midcourse corrections were very small and just made sure that the spacecraft stayed on its proper trajectory. Unless there were bad weather conditions at the primary recovery zone (which happened on some Apollo missions) it should be already known at the departure of the moon.
But yeah it wasnt absolutely clear until a few hours before reentry if it would splashdown at the primary target or downrange in the area that was accessible for the CM by its crossrange capability to avoid weather conditions.

Offline Zakalwe

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Re: Recover ship proximity to Apollo splash down
« Reply #4 on: July 12, 2017, 05:20:07 PM »
Didn't they alter the position of the ships to move them away from the predicted splashdown location after one Command Module came very, very close to ship?
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Offline bknight

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Re: Recover ship proximity to Apollo splash down
« Reply #5 on: July 13, 2017, 08:32:02 AM »
Didn't they alter the position of the ships to move them away from the predicted splashdown location after one Command Module came very, very close to ship?

That may be correct, but I thought it was a Gemini mission that came close and procedures were changed to move the ships further away.
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Offline Count Zero

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Re: Recover ship proximity to Apollo splash down
« Reply #6 on: July 16, 2017, 12:21:26 AM »
Didn't they alter the position of the ships to move them away from the predicted splashdown location after one Command Module came very, very close to ship?

Iirc, that was Apollo 8, which flew over the recovery ship.
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Offline Zakalwe

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Re: Recover ship proximity to Apollo splash down
« Reply #7 on: July 17, 2017, 08:34:01 AM »
Didn't they alter the position of the ships to move them away from the predicted splashdown location after one Command Module came very, very close to ship?

Iirc, that was Apollo 8, which flew over the recovery ship.

Thanks...I did think that it was an Apollo mission.
"Quod gratis asseritur, gratis negatur"
“That which can be asserted without evidence, can be dismissed without evidence.” – Christopher Hitchens.

Offline Count Zero

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Re: Recover ship proximity to Apollo splash down
« Reply #8 on: July 17, 2017, 10:13:02 AM »
I found it in a Tindallgram:

Date:  January 7, 1969
69-PA-T-1A
To:  FL/Chief, Landing and Recovery Division
From:  PA/Chief, Apollo Data Priority Coordination
Subject:  Let's move the recovery force a little

Jerry, I've done a lot of joking about the spacecraft hitting the aircraft carrier, but the more I think about it, the less I feel it is a joke.  There are reports that the C Prime command module came down right over the aircraft carrier and drifted on its chute to land 5,000 yards away.  This really strikes me as being too close.  In other words, I realize the probability of the spacecraft hitting the aircraft carrier is very low but there is absolutely no advantage in having the ship within five or ten miles of the aim point - with the possible exception of the PAO [illegible] for good commercial TV.  It certainly does not improve the recovery operation at all.  And, the consequence of the spacecraft hitting the carrier is truly catastrophic.
In summary, I seriously recommend relocating the recovery force at least five or ten miles from the target point.

Howard W. Tindall Jr.


http://www.collectspace.com/resources/tindallgrams/1969_tindallgrams.pdf
Page 153
"What makes one step a giant leap is all the steps before."

Offline Zakalwe

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Re: Recover ship proximity to Apollo splash down
« Reply #9 on: July 20, 2017, 03:59:54 AM »
Brilliant work there. Top sleuthing!
"Quod gratis asseritur, gratis negatur"
“That which can be asserted without evidence, can be dismissed without evidence.” – Christopher Hitchens.