Author Topic: Apollo landing sites vs targets  (Read 3117 times)

Offline Mr Fogbank

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Apollo landing sites vs targets
« on: 03/20/2018 11:45 pm »
Can anyone point me to a clear summary of the 6 Apollo landing sites versus their optimal targets?

Offline Archibald

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Re: Apollo landing sites vs targets
« Reply #1 on: 03/21/2018 09:21 am »
Well, Armstrong and Aldrin famously missed by 8 km, more exactly they found big boulders all over the place, and a crater, and then the radar went astray, and they landed with only 15 seconds of descent fuel left.

Apollo 12 by contrast landed right near the Surveyor.
« Last Edit: 03/21/2018 09:21 am by Archibald »
Han shot first and Gwynne Shotwell !

Offline MATTBLAK

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Re: Apollo landing sites vs targets
« Reply #2 on: 03/21/2018 10:35 am »
Does anyone know which one of the 6x Apollo landings got down with the most descent propellant remaining? We know Apollo 11 was the least, but the most..? :) My money would be on 12 or 15 17.

Edit: I meant to say 17 - and this was borne out by learned answers below :)
« Last Edit: 03/22/2018 02:20 am by MATTBLAK »
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Offline Mr Fogbank

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Re: Apollo landing sites vs targets
« Reply #3 on: 03/21/2018 03:15 pm »
I have read that Apollo 14 LM landed "just yards" from its target. I always wondered if this was due to Shepard's skill, or other factors such as a perfect descent profile.

I have also read that Apollo 11 landed long due to the initial descent burn commencing late. Anyone know if that is the case?

I would love to find maps (photos from orbit) showing the six targets vs the actual landing sites.

Offline Brian Mc

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Re: Apollo landing sites vs targets
« Reply #4 on: 03/21/2018 03:34 pm »
Hi Folks,
Answers to most of these questions can be found in Richard W. Orloff's excellent document "Apollo By The Numbers" located at:

https://history.nasa.gov/SP-4029.pdf

Looks like Apollo 17 had the most prop left (in terms of hover burn time remaining = 117 Sec).
« Last Edit: 03/21/2018 03:36 pm by Brian Mc »

Offline Mr Fogbank

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Re: Apollo landing sites vs targets
« Reply #5 on: 03/21/2018 03:46 pm »
Thanks, Brian!

Offline the_other_Doug

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Re: Apollo landing sites vs targets
« Reply #6 on: 03/21/2018 04:05 pm »
First off, except for bragging rights, the final three landings had rather relaxed constraints when it came to their exact landing spots.  When you had the Rover, it didn't matter if you were as much as a kilometer from your planned landing point; that just meant a few extra minutes (or fewer minutes) getting to your station stops on your traverses.

The landing in which the navigation state was the most off was the first, of course -- Apollo 11.  It landed almost outside of its targeting ellipse. This was based on a number of factors, including imperfect modeling of the lunar gravitational sphere, as well as cumulative effects from orbital maneuvering between the CSM and LM.  For all landings after the first, the Noun 69 adjustment to the targeted landing point brought the miss distances from the targeted landing points down from miles to less than 500 meters, normally.

Pete Conrad came the closest to landing spot-on at his previously selected landing point.  He only maneuvered past the "Pete Parking Lot" northeast of the Surveyor Crater because he liked the looks of the ground to the northwest of the crater better.  Had he chose, Conrad could have landed within a couple of feet of the planned landing point.  The navigational state during the approach phase of that landing was almost exactly perfect.

Al Shepard's landing was another matter.  On Apollo 14, the computer had a slight glitch in its programming.  While it believed it was targeting the correct landing point, roughly a third of the way between the Triplet and Doublet craters (and indicated this to Shepard in the Landing Point Designator numbers during the approach phase), it was actually targeting a point about 1200 feet short of the point it was supposed to be targeting.  Had they not touched the controls, their LM would have landed somewhere around Weird Crater in the valley between Triplet and Cone Ridge.

Shepard actually had to level off and extend his approach to gain that extra 1200 feet downrange.  In doing so, he manually flew his LM downrange farther than Neil Armstrong did during the first landing.  But he ended up landing about 60 to 80 feet away from his pre-mission target point, after designating south of track and then back to the original trajectory line.  In fact, he mostly landed short, barely past the western rim of North Triplet.

Of the J missions, Dave Scott on Apollo 15 landed the farthest away from his pre-planned landing point.  This was due to a few factors -- first off, aiming for the landing site farthest from the lunar equator attempted during Apollo, the 15 crew found that their orbit was being perturbed more significantly by the Serenitatis and Imbrium mascons than other flights, so as they approached they were on a heading that started, at pitchover, from about 3000 feet south of their normal groundtrack.  It was converging to the correct landing point, but angling in from a point slightly south of what they had normally seen in training.  It wasn't well communicated to the crew, though, and Scott was under the impression that the computer's landing point was in error by 3000 feet to the south.

Part of the reason why Scott had a hard time evaluating and manually steering to the planned landing spot was because of the misunderstanding as to where he thought he was, but also because the terrain model they used in the simulator was based on 22-meter-resolution Lunar Orbiter photo coverage of the site, and was made with more relief than the actual plain at Hadley actually had.  Therefore, the landmarks Scott used to judge his approach --specifically, a string of four craters they named Matthew, Mark, Luke and Index, didn't stand out as they did in the simulator, so Scott failed to recognize them.  Thus, he used the relative locations of Hadley Rille and the Appenine front as his location guides, and ended up landing about 800 meters (IIRC) south and 300 meters west of his planned site.  Nearly a kilometer away.

In fact, Scott thought he had landed close to a crater they had named Salyut, which lies about halfway between their original planned landing point and the Appenine front.  What he thought was Salyut was instead a crater called Last, quite a bit further north than Salyut.

But, as I said, on the J missions with the rovers, a kilometer was something like ten minutes' driving time at worst, so the landing error meant very little.

On the final two landings, the LMs were landed within 200 meters of their planned landing spots.  In the case of Apollo 16, John Young lucked into landing on the only relatively flat patch of ground within the whole landing ellipse, and had Gene Cernan landed his LM exactly at the pre-planned spot, it would have landed on top of what was later dubbed Geophone Rock and toppled over... ;)

Basically, within the capabilities of the systems, only Apollo 11 had a truly significant miss distance.  The Noun 69 redesignation of the landing spot within the computer's simple model of the lunar surface reduced that error to being almost meaningless on the later landings.

For future lunar operations, all we'll really need is a series of radar beams installed on the surface; that will allow tweaking during descent to landing to ensure that the descending vehicle lands at the exact pre-planned spot --which will be important when they start up with cargo deliveries and landing on improved surfaces like concrete landing pads... ;)
-Doug  (With my shield, not yet upon it)

Offline Kansan52

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Re: Apollo landing sites vs targets
« Reply #7 on: 03/21/2018 04:12 pm »
A story I've heard repeated but never vetted (which isn't in Apollo by the Numbers) was the atmosphere in the tunnel between the LM and CM was not vented before the undocking. That small impulse helped create the LM being downrange prompting the manual landing.

Offline the_other_Doug

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Re: Apollo landing sites vs targets
« Reply #8 on: 03/21/2018 04:53 pm »
A story I've heard repeated but never vetted (which isn't in Apollo by the Numbers) was the atmosphere in the tunnel between the LM and CM was not vented before the undocking. That small impulse helped create the LM being downrange prompting the manual landing.

And I keep thinking that this is a conflation of events across two missions.  On Apollo 10, the outer layer of an insulation blanket on the CM tunnel hatch ripped open, liberating a lot of fiberglass material from within the insulation sandwich.  It got everywhere and tended to clog up the LM and CM air filters (as well as sticking to the crewmen's hair).  It also clogged up the CM/LM tunnel vent, which didn't have a filter covering over it.

When it came time to undock Snoopy from Charlie Brown, the vent clogged and the tunnel couldn't be brought below around 3.5 psi.  There was concern that undocking with that much pressure could damage the docking clamps, but they decided to go ahead and do it.  The docking hardware was undamaged, but there was acceleration imparted to both the LM and the CSM.  This was one reason why 10's LM, Snoopy, passed at pericynthion a good five miles south of its planned groundtrack.

Mike Collins was quite descriptive of every little oddity and "funny" that happened on Apollo 11 in his excellent autobiography, Carrying the Fire.  He goes into scary levels of detail about the attitude excursions that occurred during docking with the LM after its return from the surface, and blames it on his own inability to understand what each vehicle was trying to do right then.

And he says nothing about there being a problem getting the tunnel vented in time for undocking.  Plus, the insulation that had caused problems on 10 was removed on 11 and all subsequent flights.

I really believe that Eagle's trajectory dispersions had more to do with the fact that, on 11, they had the LM perform the CSM/LM separation maneuver.  Also, the LM's control system was in unbalanced jets mode during LM inspection, meaning that just changing attitude was capable of actually imparting translational energy, changing the orbit enough to cause a significant overshoot.

If there was a small amount of pressure in the tunnel at undocking, it wasn't something that Collins mentioned in his book, and none of the crew mentioned anything of the sort in the crew debriefings.  There's no hint of it in the transcripts of the onboard recordings during undocking, either.

So, like I say, I tend to think this got conflated between the two missions somewhere.
-Doug  (With my shield, not yet upon it)

Offline Mr Fogbank

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Re: Apollo landing sites vs targets
« Reply #9 on: 03/21/2018 05:09 pm »
Excellent info, folks. Thanks much!

Offline Apollo-phill

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Re: Apollo landing sites vs targets
« Reply #10 on: 03/21/2018 05:19 pm »
Look up Apollo Lunar Surface Journal ( ALSJ) on NASA History web site.

I'm sure everything you are looking/searching for will be in there including timings, charts,Mao's,diagrams,photos etc etc......😀

Apollo Phill
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Offline Apollo-phill

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Re: Apollo landing sites vs targets
« Reply #11 on: 03/21/2018 05:22 pm »
Not "Mao" 😈

S/be Maps .😃

Predictive text at it gain 😬

Apollo Phill
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Offline Mr Fogbank

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Re: Apollo landing sites vs targets
« Reply #12 on: 03/21/2018 05:24 pm »
Not "Mao" 😈

S/be Maps .😃

I was looking forward to Mao's artist's depiction of the landing sites!

Offline Kansan52

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Re: Apollo landing sites vs targets
« Reply #13 on: 03/21/2018 05:48 pm »
So, like I say, I tend to think this got conflated between the two missions somewhere.

Thanks for that. It explains the reason for not be able to vet the story. Your explanation makes so much sense to me.

Thanks again!!

Offline Lar

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Re: Apollo landing sites vs targets
« Reply #14 on: 03/21/2018 07:35 pm »
Awesome detail but the LM that missed the targeted landing spot by the most? You guys got it wrong, it was 13 :)

Hope that helps. (I'll get my coat)
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Offline MATTBLAK

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Re: Apollo landing sites vs targets
« Reply #15 on: 03/22/2018 02:22 am »
Ve make zee jokes round here!... We're supposed to make the funnies - then you moderators tell us to behave! ;) But seriously - that made me laugh. Nice one...
« Last Edit: 03/22/2018 02:23 am by MATTBLAK »
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Offline Archibald

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Re: Apollo landing sites vs targets
« Reply #16 on: 03/22/2018 06:01 am »
Awesome detail but the LM that missed the targeted landing spot by the most? You guys got it wrong, it was 13 :)

Hope that helps. (I'll get my coat)

Yeah, and Apollo 10, too (although it tried to correct its mistake by rushing to the surface spinning  uncontrollably, to John Young great dismay)

and by the way, you are wrong !

Quote
the LM that missed the targeted landing spot by the most? You guys got it wrong, it was 13

 Indeed the original Apollo 15 H-mission, Apollo 19 and Apollo 20 Lunar Modules very badly missed their landing spots - by 200 000 miles or so, landing in Earth museums instead of landing on the Moon.  ::)
« Last Edit: 03/22/2018 06:07 am by Archibald »
Han shot first and Gwynne Shotwell !

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