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  Mercury - Gemini - Apollo
  Apollo: Lunar vs Earth Orbit Rendezvous

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Author Topic:   Apollo: Lunar vs Earth Orbit Rendezvous
Jim_Voce
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Posts: 119
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Registered: Jul 2016

posted 11-19-2017 11:50 AM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
In 1961 when the Apollo missions planning committee began working out the details of how to get a manned mission to the moon, two approaches were considered — direct ascent and earth orbit rendezvous (EOR). The final choice of course was the lunar orbit rendezvous (LOR) method using the CSM and the LM and this was adopted in 1962. But the planning group for the Apollo missions seemed to really resist the idea of LOR and LOR didn't seem to be given any serious consideration until John Houbolt came along and made some convincing arguments for it.

Conversely, the planning group didn't seem to be too intimidated by the idea of developing rendezvous and docking in earth orbit. So they gave serious consideration to the EOR method.

What made rendezvous and docking in lunar orbit fundamentally so much more intimidating than doing it in earth orbit? What were the extra technical challenges of LOR over EOR?

Jim Behling
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Posts: 1174
From: Cape Canaveral, FL
Registered: Mar 2010

posted 11-19-2017 09:08 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
Rendezvous and docking had yet to be done at the time and EOR had a safe haven in case of problems — reentry.

oly
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Posts: 225
From: Perth, Western Australia
Registered: Apr 2015

posted 11-20-2017 01:00 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
Until the Gemini program, NASA had not conducted rendezvous, EVA, controlled re-entry, long duration space flight and just about every other test conducted during the program so the risks, procedures, capability and chance of rendezvous in earth orbit was unknown. The performance of the Saturn V was unknown and the best method for lunar landing had not been established.

The best way to consider the lunar missions is to work backwards from splashdown and consider each requirement. If you know how much mass you want to bring back you can figure how much mass you need to fly from the moon back to earth. If you know what mass you want to lift off the moon you can then work out the mass of the lunar lander. Knowing this mass you can work out what requirements for launching this mass into earth orbit and so you can work out the launch mass and lift requirements.

Von Braun took some convincing that LOR resulted in the lowest mass at launch. Once the decision was made for LOR, then the Saturn lift requirements could be defined. There is an old interview online of von Braun describing how LOR was decided upon that I can't find again and there is also this video of Hubolt describing LOR.

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