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  Mercury - Gemini - Apollo
  Apollo lunar module docking ports

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Author Topic:   Apollo lunar module docking ports
Jim_Voce
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posted 12-23-2018 03:20 AM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
If I have my facts right, then in the early design of the Apollo Lunar Module, the LM had two docking ports. The first was the overhead, rooftop docking port that the command module would dock with in order to extract the LM from the Saturn IVB stage. The second docking port was located at the front of the LM in between and just below the triangular windows of the LM. This docking port would be used when the LM was returning from the moon.

Why did Grumann Aircraft opt for having two docking ports when the LM already had enough maneuvering capability to use its rooftop docking port for all docking activities? Specifically, a simple blast of one of the LM reactive control system quads could rotate the LM so that its rooftop docking port was accessible to the CSM (thereby making only one docking port for the LM necessary).

Can anyone explain?

One Big Monkey
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From: West Yorkshire, UK
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posted 12-23-2018 04:11 AM     Click Here to See the Profile for One Big Monkey     Edit/Delete Message   Reply w/Quote
According to Thomas Kelly's excellent "Moon Lander," the initial design brief including two docking ports to give redundancy — if there was some sort of problem with one docking port they could use the other.

This was discarded when NAA developed the method they used: the removable drogue docking system. It was similar to the equipment used in mid-air refuelling, so not only was it proven technology it as something that the many pilots in the astronaut crews would recognise.

Repeated testing showed that it could work without any problems (although Apollo 14 made hard work of it!), so it was adopted.

Jim_Voce
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posted 12-23-2018 11:00 AM     Click Here to See the Profile for Jim_Voce   Click Here to Email Jim_Voce     Edit/Delete Message   Reply w/Quote
Thank you for that additional information. Redundancy sounds possible. Can anyone else confirm that as well?

Tom
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posted 12-23-2018 01:26 PM     Click Here to See the Profile for Tom   Click Here to Email Tom     Edit/Delete Message   Reply w/Quote
If I remember correctly, initially the lunar module was going to be the "active" spacecraft for rendezvous and docking operations. The docking port located between the two windows would make that maneuver a bit easier to perform. Later it was decided that the command module would be the "active" spacecraft.

oly
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From: Perth, Western Australia
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posted 12-23-2018 05:59 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
Given the requirements faced by Grumman in achieving the lunar module weight reductions needed, the mass of two structural docking ports and associated hardware were an early target for potential weight savings,

The mass of the structure for the overhead docking window is far less than a complete hatch, which would be a single use item.

Also remember that the procedures for performing rendezvous and docking had not been tried when the original lunar module designs were drawn up. As the Gemini program proceeded, and rendezvous and docking procedures were tested, the perceived difficulties were overcome and the technical information could be transferred to the Apollo application.

Jim Behling
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posted 12-24-2018 12:34 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Tom:
If I remember correctly, initially the lunar module was going to be the "active" spacecraft for rendezvous and docking operations.
That was it, they thought the crew needed visibility and eyes on the CSM and so the docking port was in front of them.

Ross Sackett
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From: Santa Fe, NM
Registered: Aug 2015

posted 12-26-2018 02:28 PM     Click Here to See the Profile for Ross Sackett   Click Here to Email Ross Sackett     Edit/Delete Message   Reply w/Quote
Tom Kelly's account of building the LM is excellent on how they had to modify the proposal design, but not as complete when it comes to the original design decisions on the five-leg LEM. The Grumman LEM proposal is a lot clearer, though.

The two hatches weren't needed so much for redundancy, but because they expected for extraction and lunar rendezvous to have rather different procedures. The top hatch was needed only to extract the LEM from the S-IVB. In the original proposal Grumman planned to link the CSM to the LEM with a trapeze-like harness so that initial alignment and docking would be nearly automatic. For rendezvous and docking in lunar orbit, as mentioned the LEM would be the active spacecraft, with four eyes in the CSM looking through large windows, with a laser beacon as a backup aid.

oly
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posted 12-28-2018 07:09 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
From memory, I believe that Kelly talks about the docking ports and landing gear designs during his oral history interview. The forward hatch docking requirement idea was quickly done away with.

This later turned out to be a good idea when the shape of the forward hatch was changed to accommodate the square shape backpack.

Kelly also talks about the landing gear design evolution, and the design requirements. How the solid energy absorbers came about, how the four leg design was chosen and what terrain criteria was considered for the feet design.

All times are CT (US)

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