Everything you never knew you wanted to know about the Mercury Project
Earth path indicator
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Contents |
Introduction
Official Specifications
The following descriptions are taken from the various editions of the Mercury Familiarization Manual SEDR-104 in which the description changed in any way.
December 1959
In its initial specification the
Specification
from the December 1959 edition of SEDR-104
See Figure 12-3. The earth path indicator consists of a spherical map (globe) of the earth gimballed and rotating in a manner to indicate ground position under the capsule and approximate touchdown point when retrograde is initiated at indicated ground position. The indicator is spring motor powerered and is capable of running 48 hours without re-winding. The globe, which is approximately 4.38 inches in diameter, will display the following geographical features:
(1) All continents.
(2) All bodies of water having major dimensions of 300 statute miles.
(3) All political boundaries where bordering countries have major dimensions of 300 statute miles.
(4) The sixteen largest rivers of the world.
(5) All islands having major dimensions of 500 statute miles.
(6) All known islands or island clusters separated from continents by 300 statute miles and having major dimensions less than 500 statute miles shall be identified by an .020 diameter circle.
(7) The fifty largest cities of the world are identified by .020 dots.
(8) 15° latitude and longitude lines are presented and numbered.
Controls are provided on the face of the indicator to wind the spring motor and to adjust the orbit time, orbit inclination, to slew the globe about the earth and the orbital axes.
Changes for Test Capsules
The December 1959 edition of SEDR-104 notes no changes for any of the test capsules in regards to the earth path indicator
November 1961
Details of the earth path indicator changed in the November 1961 edition of SEDR-104
Specification
The earth path indicator (see Figure 12-5) consists of a spherical map (globe) of the earth gimballed and rotating in a manner to indicate ground position under the capsule. The indicator is spring motor powered and is capable of running 20 hours without re-winding. The globe, which is approximately 3.85 inches in diameter, will display the following geographical features:
(1) All continents
(2) All bodies of water having major dimensions of 300 statute miles
(3) The sixteen largest rivers of the world
(4) All islands having major dimensions of 500 statute miles
(5) All known islands or island clusters separated from continents by 300 statute miles and having major dimensions less than 500 statute miles shall be identified by an .020 diameter circle.
(6) The fifty largest cities of the world are identified by .020 dots.
(7) 15° latitude and longitude lines are presented and numbered.
Controls are provided on the face of the indicator to wind the spring motor and to adjust the orbit time, adjust orbit inclination and to slew the globe about the earth and the orbital axis. The touchdown area is displayed as a rectangle and the luminous dot inside of the rectangle being the point of impact. The landing area is 3040 nautical miles ahead of instantaneous orbital position above the earth as indicated by the four ring bullseye. The instrument is externally lighted by cabin floodlights.
Changes From Previous Specification
The size of the globe has been slightly reduced. The requirement to display political boundaries has been removed. They probably wouldn't have been very useful anyway. The indication of the touchdown area has been added.
Changes for Test Capsules
The November 1961 edition of SEDR-104 notes no specification changes in regards to the earth path indicator for any of the test capsules
February 1962
The specification of the earth path indicator in the February 1962 edition of SEDR-104 was unchanged from that in the November 1961 edition of SEDR-104
Changes for Test Capsules
The February 1962 edition of SEDR-104 states that [[spacecraft 18|] will not have the earth path indicator installed. There were no specification changes in regards to the earth path indicator for any of the other test capsules
May 1962
The specification of the earth path indicator in the May 1962 edition of SEDR-104was unchanged from that in the November 1961 edition of SEDR-104
Changes For Test Capsules
The May 1962 edition of SEDR-104 notes no specification changes in regards to the earth path indicator for any of the test capsules
December 1962
The earth path indicator has been dropped from the December 1962 edition of SEDR-104
