[HN Gopher] Talking with the Moon: Inside Apollo's premodulation...
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       Talking with the Moon: Inside Apollo's premodulation processor
        
       Author : picture
       Score  : 71 points
       Date   : 2022-05-13 15:14 UTC (7 hours ago)
        
 (HTM) web link (www.righto.com)
 (TXT) w3m dump (www.righto.com)
        
       | evgen wrote:
       | A great write-up, but for me the cherry on top is footnote #7
       | that describes exactly what "SCE to AUX" actually did and how it
       | managed to reset the telemetry when Apollo 12 was struck by
       | lightning. Very cool to finally understand what happened.
        
       | the__alchemist wrote:
       | This is really cool! I wonder if nowadays those collections of
       | passives would be replaced not with a PCB, but with a single IC.
        
         | zw123456 wrote:
         | The amazing thing is now days an entire WIFI AP, RF section and
         | all is on a single chip. https://en.wikipedia.org/wiki/ESP32
         | 
         | I was 14 when Neil Armstrong set foot on the Moon, it was one
         | of the inspirations for me to become and engineer, and no doubt
         | had that effect on generations.
         | 
         | I love seeing this old Apollo gear. I know the Apollo AGC has
         | been posted here a million times but this RF stuff was really
         | cool to get a look at!
        
         | kens wrote:
         | Yes, I expect you could put the whole premodulation processor
         | on a single IC nowadays. Even in the late 1960s, an op amp IC
         | could have replaced the amplifiers built from discrete
         | components.
        
       | kens wrote:
       | Author here if anyone has questions about obscure Apollo
       | hardware...
        
         | mzs wrote:
         | Do you have a guess?
         | 
         | >The unusual feature of this module is the encapsulated module
         | in the upper left. This module appears to contain three
         | transistors and five capacitors. It's unclear why these
         | components are encased in plastic. The block diagram for this
         | module doesn't show any special circuitry that would motivate
         | encapsulation. I hope to reverse-engineer this module to figure
         | this out.
        
           | atoav wrote:
           | I'd also say thermal coupling to ensure these components
           | drift with some common average temperature. One thing where
           | this would be done is e.g. an exponential converter or an
           | antilog-amplifier, although there one would need only two
           | transistors (one PNP and one NPN).
        
           | jmole wrote:
           | temperature consistency across all the parts, probably. It's
           | the reason things like discrete current sources use dual
           | transistor packages: important transistor parameters track
           | strongly with temperature, and if you want them to match, the
           | temperatures need to be the same.
        
         | ThinkingGuy wrote:
         | I was interested to see how communication between and from the
         | individual astronauts was handled via VHF and then relayed by
         | the lunar lander.
         | 
         | Did the lunar rover used on Apollo 15-17 have the same
         | equipment as the lunar lander, to transmit back to Earth?
        
           | kens wrote:
           | The Lunar Communications Relay Unit (LCRU) on the rover
           | provided S-band communication to Earth (MSFN) for voice,
           | telemetry and TV.
        
         | zw123456 wrote:
         | Fascinating as usual Ken, thank you. I am still absorbing the
         | tech, but one thing that struck me in the very detailed photos
         | (thanks for that) it does not appear that the components,
         | resistors, capacitors etc. were soldered to the binding posts,
         | it looks almost as if they were welded or fused?
         | 
         | I am wondering if that was for reliability due to vibrations of
         | launch ?
         | 
         | oops never mind, i see your comment on one photo.
        
           | kens wrote:
           | Yes, the components were spot-welded. This was common in the
           | Apollo electronics. I think it was more reliable than
           | soldering.
        
             | zw123456 wrote:
             | Right, it had to survive the vibration of the mighty Saturn
             | V. But even so, that construction, the insulating tubes and
             | hot glue, I am not sure I would risk my life on that!
        
               | Koshkin wrote:
               | I am sure it (the construction) was extensively tested.
        
               | HPsquared wrote:
               | It's unlikely the astronauts would trust their life to
               | this processor alone. There would be at least one backup,
               | and probably a plan in the event of total communication
               | failure. System design!
        
         | urda wrote:
         | What's your favorite bit of obscure Apollo hardware?
        
       | hsnewman wrote:
       | Was this featured on Curious Marc?
        
         | kens wrote:
         | He's done a bunch of videos on the S-band transponder that is
         | connected to the premodulation processor, but hasn't covered
         | the premodulation processor yet.
        
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       (page generated 2022-05-13 23:01 UTC)