The Washington Post just republished it's February 21, 1962 article covering the launch, Earth orbit, and safe re-entry and recovery of (Senator) John H. Glenn, in recognition of his service and recent passing.

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Parachute Drops Capsule, Flier Into the Atlantic By John G. Norris, Staff Reporter Wednesday, February 21, 1962; Page A1

It is worth taking time to read how spaceflight was described a half century ago. I was surprised to read how many Earth stations were involved, and that NASA astronauts were posted at several of them and if I understand correctly were in voice communication with him.

This must have been quite a network. Since things could change rapidly, it was probably a goal to keep in voice communication with the astronaut as continuously as possible. The netowrk itself deserves a separate question. Here I'm wondering:

How many of the Earth stations involved in receiving telemetry from the spacecraft while in orbit had astronauts stationed on site? Was this coincidental or was there intention to have a fellow astronaut 'on the other end of the line'? If intentional, what was the rationale?

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    $\begingroup$ The practice in the US human spaceflight program has always been for the crew in space to communicate only with an astronaut on the ground (Capcom). Before satellite communications networks were set up, this meant stationing astronaut Capcoms at the different ground stations. $\endgroup$ Commented Dec 9, 2016 at 4:12
  • $\begingroup$ @OrganicMarble Since this is NASA first-ever manned orbital mission, does "has always" have it's origin here, or with Allan Shepard's flight? $\endgroup$
    – uhoh
    Commented Dec 9, 2016 at 4:28
  • $\begingroup$ The first zivil communication satellite Telstar was started some month later, but in 1962 transatlantic telephone cables did exist, TAT-1 and TAT-2. Today the datarate of glas fiber communication cables between the continents is much greater than that of satellite communications networks. $\endgroup$
    – Uwe
    Commented Dec 9, 2016 at 10:00
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    $\begingroup$ Okay, I think I have an actual answer finally. $\endgroup$ Commented Dec 10, 2016 at 3:10
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    $\begingroup$ spacelog.org has Slayton rather than Cooper as CAPCOM on Shepard's flight. $\endgroup$ Commented Dec 10, 2016 at 4:34

3 Answers 3


According to NASA's mission report on Mercury-Atlas 6, the following ground stations in the Mercury network offered voice communication and spacecraft telemetry (in order of eastward travel):

  • Atlantic Missile Range (i.e. Cape Canaveral)
  • Bermuda
  • Mid-Atlantic Ship
  • Canary Islands
  • Kano, Nigeria
  • Zanzibar
  • Indian Ocean Ship
  • Muchea, Australia
  • Woomera, Australia
  • Canton Island
  • Hawaii
  • Southern California
  • Guaymas, Mexico
  • Corpus Christi, Texas

There are two additional stations with radar tracking capability but not communications.

Most of these stations made contact with Glenn on the first orbit, as you can determine by reading the transcripts.

With fourteen stations there obviously weren't enough astronauts for "CAPCOM is an astronaut" to be a hard rule. In addition, at several of the stations, the initial contact is made by a technician; e.g. the transcript shows call sign "Canton Com Tech" before the call sign "Canton CAPCOM" takes over. In a few cases the surgeon at the site addresses Glenn directly ("Friendship Seven, this is Surgeon Zanzibar") to discuss blood pressure tests and the like. Apart from Cooper I don't think any of the CAPCOMs are addressed by name.

According to The Space Race Encyclopedia, Cooper was at Muchea, Grissom at Bermuda, and Schirra at California. Shepard was CAPCOM at Canaveral according to The Right Stuff and other sources. As Carpenter was Glenn's backup crew, I assume he had to be at Canaveral as well. Slayton's autobiography places him at Canaveral ("sitting next to" Shepard), so I believe the answer is that there were four astronaut CAPCOMs at different sites on this particular flight.

Interestingly, after losing contact with Woomera on the first orbit, Glenn calls "broadcasting in the blind to the Mercury network", and gets replies from Canaveral, Kano, and Zanzibar -- saying they did not read the transmission! I infer from this that another ground station (Woomera or Canton?) did receive, and relayed to the others.

According to Wikipedia, "NASA believes that an astronaut is most able to understand the situation in the spacecraft and pass information in the clearest way."

More than anyone else, the astronauts know each other and the interior of the spacecraft as seen by the pilot; they develop their own jargon. (If you've ever given technical support over the phone, you know how much easier it is to do so when the person you're talking to speaks the same technical jargon dialect that you do.) If communication is fragmented, the astronaut CAPCOM can piece it together. If the astronaut pilot is in the middle of a procedure and says "ah crud it's doing that thing again", the astronaut CAPCOM knows what he means. CAPCOM can then translate for the rest of mission control at leisure, as necessary.

Even for the very first American manned flight, it was considered important for Alan Shepard to be in communication with someone who had undergone the same training (Deke Slayton); for the second flight, Shepard was the natural choice for Grissom's CAPCOM because he was the only one who'd been through a flight.

Trust was also a factor. The Mercury 7 astronauts, while competitive, were a very close-knit group, and knowing that one of their own was in the comm loop reassured them that they had support in case of any disagreement between the crewman and mission control.

  • $\begingroup$ Excellent comprehensive answer, thanks for the research, the link, and taking care to summarize the key points clearly here as well. $\endgroup$
    – uhoh
    Commented Dec 10, 2016 at 3:07
  • $\begingroup$ The MA-6 post flight report on NASA's site has a good description of the comm network as well. I'll clean up links a bit once I get home. $\endgroup$ Commented Dec 10, 2016 at 3:13
  • $\begingroup$ What about the communication of the ground stations with the main station in Cape Canaveral? The mid-atlantic ship and the indian ocean ship could only use short wave radio. The existing transatlantic telefone cables may be used for Canary Islands, but not for Australia and Hawaii. Did they use relay radio transmission in a chain from station to station? The next Capcom should know what his colleagues said before. $\endgroup$
    – Uwe
    Commented Dec 13, 2016 at 9:53
  • $\begingroup$ The sites were networked via microwave and cable links, but I don't know the site by site details. long-lines.net/sources/BLR0362/BLR40(3)Mar1962.pdf $\endgroup$ Commented Dec 13, 2016 at 16:33
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    $\begingroup$ It looks like the blind transmission you mentioned was a scheduled test of the HF system, which I believe was a backup (the VHF being used normally in orbit). See the comment from CAPCOM at MET 01:02:08. It looks like those stations had it on the schedule to call out whether or not they received the capsule's transmission. Then a couple minutes later was normal VHF reacquisition at Canton. All three of those stations were below the capsule's horizon the way I figure it, so I think it was an HF propagation experiment. $\endgroup$
    – hobbs
    Commented Dec 16, 2016 at 21:35

I did some statistics with the data from http://mercury6.spacelog.org/original/144/

The first orbit was 1:32:47 with voice transmisson for a total of 1:25:01 and hand over gaps of 0:07:46. All time values in hours:minutes:seconds

The second orbit was 1:34:13, voice transmission for 1:26:32 and gaps for 0:07:41.

The third orbit was 1:33:18, communication for 1:25:02 and gaps for 0:08:16.

The longest gap was 0:04:54, a lot of gaps less than 30 seconds.

The times of telemetry data look a bit different, a total of 0:23:57 of the first orbit without telemetry, second orbit 0:23:40 and third orbit a total of 0:40:09. The longest gaps without telemetry were 0:14:30 and 0:15:30, both in the third orbit. But voice transmission was possible during this longer gaps without telemetry. There have been short phases with simultaneous reception of telemetry by two ground stations from 10 seconds up to 10 minutes.

Due to the low orbit with an inclination of 32.54 and the limited number of ground stations it was not possible to achieve a continous communication. Only during the second orbit all ground stations could communicate. A radio link was established even with Mercury 6 very low above or even below the horizon and a distance of up to 1100 nautical miles.


According to this article, there were 13 capcom stations, of which the most critical 6 had astronauts at them, and the other 7 were manned by "recent college graduates".

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    $\begingroup$ In addition to the flying astronaut, his backup crewman would be suited up and ready to step in right up to the launch, so wouldn't be available for Capcom duty at a different site. $\endgroup$ Commented Dec 9, 2016 at 19:12
  • $\begingroup$ That site seems kinda sketchy. They have some weird random image of the Capcom game, instead of anything to do with actual capcoms. $\endgroup$ Commented Dec 10, 2016 at 8:46

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