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Author
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Topic: Apollo Earth-Moon-Earth travel time
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cspg
Member Posts: 6222
From: Geneva, Switzerland
Registered: May 2006
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posted 08-15-2009 12:36 AM
   
Someone asked me what was the travel time for Apollo missions between LM ascent to splashdown. At first, I thought, well, the time should be approximately the same than from lift-off to lunar landing. But I preferred to check the data to make sure. Although the Earth-to-Moon travel time is almost the same for all 6 Apollo lunar landing missions, the trip back shows a very different picture, much to my surprise (see data below). Anybody has an explanation for this? I probably should know the answer (and maybe I do) but right now, I don't have a clue...Earth to Moon travel time (from "Range zero" to LM lunar landing*):
Apollo 11: 4 days 6 hours 45 minutes
Apollo 12: 4 days 14 hours 32 minutes
Apollo 14: 4 days 12 hours 15 minutes
Apollo 15: 4 days 8 hours 42 minutes
Apollo 16: 4 days 8 hours 23 minutes
Apollo 17: 4 days 14 hours 22 minutes Moon to Earth travel time (from LM ascent stage ignition to splashdown*):
Apollo 11: 2 days 22 hours 56 minutes
Apollo 12: 4 days 6 hours 33 minutes
Apollo 14: 3 days 2 hours 17 minutes
Apollo 15: 5 days 3 hours 32 minutes
Apollo 16: 3 days 18 hours 20 minutes
Apollo 17: 4 days 20 hours 30 minutes *Apollo: The Definitive Sourcebook. Richard Orloff & David Harland. Springer-Praxis, 2006. |
ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 08-15-2009 08:17 AM
Great question! I don't have time for an exhaustive answer at the moment. However, some of the reasons included glitches along the way (e.g., Apollo 14-troubleshooting the LM's faulty abort switch prior to landing; Apollo 16-extra lunar orbit prior to landing due to trouble with Casper's SPS engine steering, and planned extra days in orbit after LM ascent cancelled for same reason). In other cases, there were scientific reasons (e.g., Apollo 15-extra time in lunar orbit following ascent for mapping and science). In Apollo 11's case, the short trip back following ascent was "get those guys home so we can check the 'mission accomplished' box!" |
Dietrich
Member Posts: 68
From:
Registered: Jul 2009
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posted 08-15-2009 05:06 PM
To my understanding the travel time should be the period between Earth lift-off (range zero) and Lunar arrival (shut-off of Lunar Orbit Insertion burn) and the trip back would be ignition for Transearth Injection burn until splash-down. The delays in lunar orbit before and after the LM landing and return to th CSM do not belong to the trip time from a trajectory point of view. Strictly speaking, also delays in earth orbit before TLI should not be counted, but there were none as far as I know. |
Obviousman
Member Posts: 438
From: NSW, Australia
Registered: May 2005
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posted 08-15-2009 06:23 PM
I agree with Dietrich. The times you want to consider are: - TLI burn to LOI burn;
- TEI burn to splashdown.
The missions often spent additional time in lunar orbit conducting photography, experiments, etc.
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ilbasso
Member Posts: 1522
From: Greensboro, NC USA
Registered: Feb 2006
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posted 08-15-2009 06:46 PM
With those limiting definitions, it should be possible to correlate travel time with the Earth-Moon distance (which varies between 225,000 and 252,000 miles every month). Also affecting time of LOI burn, although to a lesser extent, will be the longitude of the landing site. |
cspg
Member Posts: 6222
From: Geneva, Switzerland
Registered: May 2006
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posted 08-15-2009 11:43 PM
quote:
Originally posted by Dietrich:
To my understanding the travel time should be the period between Earth lift-off (range zero) and Lunar arrival (shut-off of Lunar Orbit Insertion burn) and the trip back would be ignition for Transearth Injection burn until splash-down.
Good point! And the data becomes: Moon to Earth travel time (from TEI SPS ignition to splashdown):
Apollo 11: 2 days 11 hours 55 minutes
Apollo 12: 3 days 9 minutes
Apollo 14: 2 days 19 hours 26 minutes
Apollo 15: 2 days 23 hours 23 minutes
Apollo 16: 2 days 17 hours 30 minutes
Apollo 17: 2 days 19 hours 49 minutes |
Max Q
Member Posts: 399
From: Whyalla South Australia
Registered: Mar 2007
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posted 08-16-2009 03:53 AM
Giving the fact that TEI to Splashdown times should be used then Apollo's 8,10 & 13 could be in that list also. |
cspg
Member Posts: 6222
From: Geneva, Switzerland
Registered: May 2006
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posted 08-16-2009 04:05 AM
And another good point!Apollo 8: 2 days 9 hours 41 minutes
Apollo 10: 2 days 6 hours 27 minutes
Apollo 13: 2 days 15 hours 27 minutes |
randy
Member Posts: 2231
From: West Jordan, Utah USA
Registered: Dec 1999
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posted 08-16-2009 10:10 AM
Would another factor to consider be that on the way out, you're going against the pull of the earths gravity, and the other way, you're going with gravity? |
Lou Chinal
Member Posts: 1332
From: Staten Island, NY
Registered: Jun 2007
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posted 08-17-2009 06:12 AM
Going along with the distance which varies you would also have to take into account the entry interface speed.Good topic! |
Flyboy7077
New Member Posts: 8
From: Fremont, CA
Registered: Jul 2008
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posted 08-22-2009 12:06 AM
Apollo 13 went around the moon on a free return trajectory, they didn't do a TEI burn. They did do the PC+2 burn, but that was just to speed their return, not to start down the path home (they were already on the road). |
Max Q
Member Posts: 399
From: Whyalla South Australia
Registered: Mar 2007
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posted 08-22-2009 01:45 AM
Not trying to be picky but the Apollo 13 time line at the NASA site shows a TEI Burn at 79:27:38.95 which you are correct was the PC+2 Burn but as they left a free return trajectory wouldn't the burn at 61:29:43.49 GET using the LM been similar to a TEI? |
John Charles
Member Posts: 342
From: Houston, Texas, USA
Registered: Jun 2004
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posted 08-22-2009 09:59 PM
I don't think it is the same. "PC" means "pericynthion" or the time of closest approach to the moon. This is approximately when the SPS engine would have been fired for TEI, for an Apollo leaving lunar orbit. "+2" means 2 hours after pericynthion. Given that Apollo lunar orbits had periods of about 2 hours, the Apollo 13 PC+2 time was the equivalent of a full lunar orbit later than TEI would have been if it had been leaving lunar orbit. So Apollo 13's Earth-transit time is actually 2 hours longer than that given in the list upthread. |
Philip
Member Posts: 6002
From: Brussels, Belgium
Registered: Jan 2001
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posted 11-21-2009 10:29 AM
quote:
Originally posted by cspg:
Apollo: The Definitive Sourcebook. Richard Orloff & David Harland. Springer-Praxis, 2006.
Does the book also mention the total distances travelled during each mission? |
moorouge
Member Posts: 2458
From: U.K.
Registered: Jul 2009
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posted 11-21-2009 11:15 AM
As far as I can see one factor has not been mentioned - the position of the targeted landing point. This would affect transit times. |
cspg
Member Posts: 6222
From: Geneva, Switzerland
Registered: May 2006
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posted 11-21-2009 11:57 PM
quote:
Originally posted by Philip:
Does the book also mention the total distances travelled during each mission?
I've just looked at the tables!  There is so much data in this book that I can't be sure that such info exists.
But I guess you'll have to define "Total distances": broken down into different segments like, distance travelled in Earth orbit, in Moon orbit, Earth-Moon distance, distance on lunar surface, and by whom. Hard to tell if such info exists - distance on Moon, yes- for the others, I don't know. |
Apollo Redux
Member Posts: 346
From: Montreal, Quebec, Canada
Registered: Sep 2006
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posted 11-23-2009 11:45 AM
Jump'n! What's with Apollo 11's Earth transit.. did someone leave something in the oven?  |
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