Everything you never knew you wanted to know about the Mercury Project
Did Aurora 7 have an earth path indicator
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Documentation
This section summarizes some of the official documentation which specifically says that there was no EPI in SC/18.
In a development project like Mercury, the documentation often has a hard time keeping up with the changes, but the paper trail seems to show this effect in a way which argues against an EPI in Spacecraft 18 during MA-7. At one time, SC18 apparently had or was supposed to have had an EPI. Early documents indicate this, but later documentation indicated that it did not.
NASA TN D-3814, "Second United States Manned Three-Pass Orbital Mission (Mercury-Atlas 7, Spacecraft 18) Description andPerformance Analysis" available here in pdf form has this to say on page 5 (page 17 in the pdf doc).
The spacecraft 18 configuration differed from that of spacecraft 13 in the following ways:
...
3. The earth-path indicator and oxygen partial-pressure indicator were
deleted, since they were not necessary to accomplish the mission.
This report was clearly written quite some time after the flight, since it mentions that Cape Canaveral had been renamed Cape Kennedy, which dates it after the Kennedy assassination.
The February 1962 edition of SEDR-104_Mercury_familiarization_manual has it as having one, but the instrument panel drawings in the May 1962 edition which covers Spacecraft 18 as well as Spacecraft 16 and Spacecraft 20 shows the door covering the hole left by the removal of the EPI. The same IP drawing has an inset which shows the switch to control the balloon experiment on MA-7 which replaced the Cabin O2 gauge. The text of this manual, on the other hand has a description of the EPI, so it would appear that in this case, so it looks like the writting documentation hadn't kept up with the changes, but the change in question was the removal of the EPI.
Fig IP-1 shows the instrument panel in the February 1962 edition, while Fig IP-2 shows the same diagram in the May 1962 edition. Fig IP-3 was created by changing Fig IP-2 to reflect the insets so as to depict the configuration for Spacecraft 18
So, in summary, it would appear that the documentation supports a conclusion that the EPI was originally planned for (and perhaps installed in) Spacecraft 18, but it was either never actually installed, or later removed. The post-flight documentatin clearly indicates that it wasn't there, and the intermediate May 1962 edition of SEDR-104 shows an updated drawing of the main instrument panel without an EPI, although the text describing it had not yet been removed.
This just in
Barry Ferguson just (March 28, 2006) provided this photo of an object in a museum which is labeled as a door used to cover the compartment left when the earth path indicator was removed from the instrument panel of spacecraft 18.
Note that this door is very similar to that in the photo of the instrument panel of the MA-8 spacecraft shown in the bottom photo, but has a checklist attached. Note also the exposure recommendations on the camera checklist for "FIREFLYS" (sic). The "fireflies" seen by John Glenn were of interest on Scott Carpenter's MA-7 flight.
Here's some pretty definite word
From "This New Ocean" page 445:
- A number of technical changes based on MA-6 mission results were made for MA-7, mostly involving deletions of certain equipment from the spacecraft to reduce weight. Kleinknecht's office eliminated the sofar bombs and radar chaff recovery aids, which seemed unnecessary in view of the effectiveness that had been demonstrated by the sarah beacon and dye markers. Other deletions included the knee and chest straps on the couch, which had bothered Grissom; the red filter in the window; the moderately heavy Earth-path indicator; and the instrument panel camera, which had already gathered sufficient data.
Conclusion, temporary at least
It appears pretty certain now, that not only did Aurora 7 not have the earth path indicator but none of the capsules which flew after Friendship 7 did.
This gives a lesson in reading the official documentation. The capsules were subject to constant change and the documentation had a hard time keeping up. It also turns out that the right edition of the Mercury Familiarization Manual SEDR-104 is often more accurate in describing a particular capsule than the configuration manual for that capsule because of when they were issued, but one can't count on that.
See the article on Mercury Official Documentation for more about all of this.
Original Question
I've managed to collect a number of versions of the Mercury familiarization manual. I'm going through them trying to pick out the difference between the various capsules.
In reading the edition from February 1962, I noticed a comment that Capsule 18 which was used for the Aurora 7 mission did not have an earth path indicator installed. The Earth Path Indicator was the instrument which was mounted above the left side of the periscope display, and which had a moving earth globe inside.
I was a little surprised by this. I knew that Faith 7 lacked this instrument, and the photo which Peter Johnson supplied for the article on Was there a transparent cover over the periscope shows that Sigma 7 also lacked this instrument.
Update
I did find some evidence that the SEDR might be correct. Here is a link to a photo in the Field Guide to American Spacecraft Aurora 7 Instrument Panel in Chicago Museum which shows a hole where the EPI should be.
Here's another similar picture from Sven Knudson's web site. Note that there is a gaping hole where the EPI would be. I'm becoming convinced!
Sigma 7 Update
Here is a photograph of Sigma 7's instrument panel as displayed at the Astronaut Hall of Fame. The satellite clock is in the center of the photo. The EPI would be directly to the left of the clock. It is absent, and the hole is covered with an access door. The door latch matches the style of ring latch elsewhere in the capsule. The door is hinged on the left side.
