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A spacecraft needs multiple receiving stations to prevent its radio signals from being blocked by Earth. Wikipedia has a map of the ground stations used for the Mercury missions.

The Right Stuff describes Mercury Atlas 6 being handed off between different CAPCOMs as the capsule flew across different parts of the planet. From listening to Apollo tapes, I know they centralized communications with the spacecraft in Houston. How was NASA able to do that for Apollo and what prevented them from doing it for Mercury?

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    $\begingroup$ There were 3 tracking stations during apollo. One in Honyeysuckle, Australia, Goldstone, California, and Madrid, Spain. Depending where the astronauts were, the signal from the tracking station was transferred to mission control in Houston. So only 1 CAPCOM was needed. $\endgroup$ – StarMan Aug 13 at 21:42
  • $\begingroup$ Apollo did use multiple capcoms: Mission control worked in shifts, and each shift had its own capcom. $\endgroup$ – Hobbes Aug 14 at 7:30
  • $\begingroup$ Good point, @Hobbes. I meant to say Apollo only had one CAPCOM at a time. $\endgroup$ – user16338 Aug 14 at 12:12
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During Project Mercury, NASA's communication network was new, and many of the ground stations did not have dedicated voice communications links back to Houston, so each site needed its own CAPCOM, as described in this QA. During Gemini the network was upgraded; many of the ground stations could provide direct voice links to Houston, but others could not, as described here.

During Apollo, all the ground stations had voice links to Houston, so there was generally only one CAPCOM. As StarMan notes, once the spacecraft was sufficiently far from Earth, only three ground stations were needed to stay in contact with it.

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  • $\begingroup$ Thanks! That makes sense to me. I appreciate the quick and detailed answer. $\endgroup$ – user16338 Aug 13 at 21:58

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