Legs
Topic Author
Posts: 246
Joined: Fri Jun 23, 2006 3:37 pm

Moon Landing Sites

Thu Oct 09, 2008 6:30 am

I was playing around on this site http://www.google.com/moon/ just now, and got to wondering, what are the reasons for all the landing sites being so close? (relatively speaking)

I realise orbital mechanics probably plays a big part, but was there other concerns such as terrain etc?

Any and all feedback would be greatly appreciated.

Legs
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Moon Landing Sites

Thu Oct 09, 2008 7:20 am

There were many constraints, terrain (flat - IOW a Mare) certainly being one. Then orbital issues due to the need to support a free (or nearly free) return to earth (which implied a lunar orbit pretty much in-plane to the moon’s orbit). Those limited the landing latitudes because of LEM range limitations and the need for observations from the CM.

Next there were issue with site lighting (they wanted the landing to occur with the Sun 5-13 degrees above the horizon to best illuminate/contrast obstacles on the surface), the site had to be on the earth side and in sunlight for the entire stay, and then there were technical issues with related to the navigation system that required a certain amount of time for alignment during the descent (during which the LEM had to be in communications with mission control, hence around the "edge") which basically ruled out anything further east than 40 degrees.

And I'm sure I'm forgetting some parameters.

Basically this left a section about 90 miles either side of the equator and about 1500 miles long. And the flat spots in that limited it further.

The parameters were planned to be relaxed a bit for later missions, but those never flew.

All of the missions had several possible landing sites, spaced in such a way that you could get several launch windows in during the right part of the lunar day cycle (spaced far enough apart to allow for the two day Apollo/Saturn recycle – IOW, about 12 degrees).
 
GDB
Posts: 12652
Joined: Wed May 23, 2001 6:25 pm

RE: Moon Landing Sites

Thu Oct 09, 2008 8:57 am

Later sites, were terrain wise, much more ambitious. Apollo 15 being a good example.
But, the Apollo/Saturn system was constrained from going too far off the Lunar equator.
Remember, from 15 onwards, they had a more capable LEM, for fuel, consumables.

Scientists wanted a landing at Tycho, in the Southern highlands, the terrain was tricky (though a Surveyor probe had landed there in 1968, which like Apollo 12, could have been the landing target).
But, NASA, in particular Apollo 9 commander Jim McDivitt, who after that flight was a senior manager, ruled it out due to the extra demands fuel wise of going so far off the equatorial region, he feared in an emergency, reserves could be too low.

Some wanted a Lunar North Pole landing, I'm unclear if the Apollo system as it was then, could do that without major modification (anyone on here know?).
 
Legs
Topic Author
Posts: 246
Joined: Fri Jun 23, 2006 3:37 pm

RE: Moon Landing Sites

Thu Oct 09, 2008 10:46 am

Thanks for the detailed responses, once again, this forum and its members have amazed me.

I kinda figured the list of constraints would be pretty hefty, but I got really curious about the actual technical details involved.

Legs
 
Thorny
Posts: 1508
Joined: Thu Jul 07, 2005 8:44 am

RE: Moon Landing Sites

Thu Oct 09, 2008 3:35 pm



Quoting Rwessel (Reply 1):
And I'm sure I'm forgetting some parameters.

The other big one was the need to keep the CSM flying over the target so they could rendezvous after lunar liftoff. Too far from the equator, and that would take more fuel than the CSM could accomodate, at least for the 2-3 day missions they were planning by then.

Quoting GDB (Reply 2):
I'm unclear if the Apollo system as it was then, could do that without major modification (anyone on here know?).

No, it couldn't. Later upgrades (with the F-1A engine, for example) probably would have allowed this.

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