I read about the mechanism of "docking" of Command Modules & Lunar Modules of the Apollo missions (the probe & drouge). It seems it was far too complex & had too many parts. I felt it is in principle similar to that of the mechanism for "Opening & Closing" of an umbrella. Can anyone explain the need for so many parts used on the actual docking mechanism on LMs & CMs? Could it have been as simple as that of an umbrella - may be with multiple latches, unlike the umbrella which typically has only one latch?
There were issues with the docking system so it possibly it needed to be more complex. Docking is always a trade off of mechanism simplicity VS event simplicity. Just using pipe flange with bolt holes would be mechanically simple but makes each event complicated with a space walk, spanner and lots of free floating fasteners, or you can make it involve a set of robot arms.
The docking process needs to handle several conflicting objectives:
- Be airtight when separated
- Handle collisions during docking process, at least without leaking
- Allow soft dock with as much misalignment as possible (target may be rotating)
- For Apollo, bring 40 tonnes to a stop in a couple of cm
- Mechanically rotate so latches align
- Bring into lateral alignment
- Pull the two parts together and hold
- Mechanically lock the outer rings (need a latch every 10cm or so)
- Test and then equalise pressure
- Allow the hatch hardware to be dismounted and moved out of the way.
- Be as light as possible.
- Support undocking.
- And pretty much any failure mode prevents the mission and/or kills the crew
There are many ways to solve that combined problem, and notably different methods have been used for other craft but none of them are simple.
So yes the Apollo docking probably could have been simpler, it was however the first of it's kind, mission critical and coming after some lessons learned on Gemini docking. It certainly did need to be more complex than an umbrella (see mechanical alignment requirements above)
One thing to note when comparing Apollo hardware part count with current is that it was mostly hand built so there was a tendency to make multiple parts and bolt them together to final form, and deal with tolerances through adjustable elements, where current tendency would be to CNC an element from a single block and just re-make it if out of tolerance or needing a change.
The Soviets designed a super-simple docking mechanism for their failed lunar program.
Of course, the price was that you had to EVA-transfer from craft to craft.
It was never used.
A standard umbrella requires a very complicated arm and hand mechanism to close it. This will not work in space.
In addition, an umbrella is not airtight, does not allow crewmembers to pass through it, and does not align and hold together two vehicles with a mass of many tens of tons.