Structures and Mechanisms
Section 4.3.7.
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Trunnion Pin and Scuff Plate Positioning

We will have to have trunnions on the Lunar Transfer Vehicle's propulsion stage. We need to carry through some sort of structural attachment to the carrier.

One option is to put trunnion pins and scuff plates at each end of the service module and one in the middle; and then one at the front of the crew module where it normally is on the SPACEHAB module. That might be over-designing a bit, but we'd have to balance the weight of the trunnion pins against additional weight to make the service module's structure more rigid.

In the 2-module configuration, SPACEHAB has one trunnion pin at the front and back of the forward module, and then one at the back of the second module. For the Lunar Habitat, the 3-module configuration, there would be a trunnion pin at the back of the third module, as well. Their function is to support the relatively weak joint between the modules from bending loads, so only one trunnion pin is needed at each inter-module joint.

This is looking at the TLI stack from the "top" (that is, looking toward the side with the windows), I imagine it like this:

   ||           ||                        ||           ||           ||
  ----         ----       =====          ----         ----         ----
  -----------------      |     |    -----------------------------------
       ~ 30 ft     |     |     |         |   ~ 10 ft    |   ~ 30 ft
                   |-----       ------  -|              |
       Lunar       ||   Airlock       || |     LTV      | Tanks
       Base        ||                 || |     Crew     | Engines
       Habitat     |------------------  -|     Module   | External Equipment
                   |                  *  |              |
  -----------------                 ------------------------------------
  ----         ----                      ----         ----         ----
   ||           ||                        ||           ||           ||

Those are trunnion pins and scuff plates sticking out on the diagram. They're not even close to scale, of course.

Structures and Mechanisms

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