Everything you never knew you wanted to know about the Mercury Project
Satellite clock
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Introduction
Roger, Lift-off and the clock is operating!
The satellite clock provided the Astronaut and certain systems in the spacecraft with timing information.
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 satellite clock provided the Astronaut with both the time of day, mission elapsed time and two countdown timers. One countdown timer was assigned to the retro de-orbit burn, which was initiated by this instrument, the other could be used for whatever purpose was desired.
Specification
from the December 1959 Edition of SEDR-104 --- The satellite clock is a manually wound spring motor driven device located in approximately the center of the main instrument panel (see Section I). This unit indicates TIME OF DAY, ELAPSED TIME FROM LAUNCH, TIME OF RETROGRADE (with respect to time of launch), RETROGRADE TIME-TO-GO and an arbitrary time-to-go called "EVENT #1". Upon reaching "time-of-retrograde" a set of contacts within the clock close, initiating the retrograde sequence. The time of retrograde is normally computed and set prior to flight, but the time can be manually changed by the astronaut or remotely set electrically through the command receivers. Elapsed time and time of retrograde indicators provide outputs for telemetering. In addition to the time displays, the satellite clock visually indicates 5 minutes before retrograde event or 5 minutes before EVENT #l by lighting the specific indicator face yellow. Similarly, the clock initiates an aural signal to the astronaut's headset 30 seconds prior to either of the two events. Finally, ten minutes prior to retrograde time the clock transmits a signal to the ASCS to start rate gyro operation, etc., in preparation for retro operation. The satellite clock is automatically started by 28 V DC power at liftoff (8 inches off pad). Should this not occur, a push button switch has been provided above and adjacent to the clock to allow the Astronaut to energize the clock (and altitude sensor) manually.
Changes for Test Capsules
The December 1959 Edition of SEDR-104 notes no changes for any of the test capsules in regards to the satellite clock.
November 1961
Details of the satellite clock changed in the November 1961 Edition of SEDR-104
Specification
The specification satellite clock is an electro-mechanical timing device located above and to the right of the periscope display assembly. The satellite clock will indicate time of day, TIME FROM LAUNCH, TIME TO RETROGRADE and RETROGRADE TIME (see Figure 12-5). The time of day will be reflected by a manually wound spring-driven movement watch. The manually wound watch is located in the upper left-hand corner of the satellite clock. Time From Launch, Time To Retrograde, and Retrograde Time will be displayed on drum counters (digidial). The drum counters will indicate time in hours, minutes and seconds. The time elements will move in one step increments. The Time To Retrograde digidial will be supplemented by a telelight, located in the upper right-hand corner of the satellite clock, which will illuminate 5 minutes prior to retrograde time; in addition to the telelight, an aural signal to the Astronaut's headset is initiated 10 seconds prior to retrograde time. The satellite clock is automatically started by 28V d-c power at liftoff. Should this not occur, a push button switch is provided above and adjacent to the clock to allow the Astronaut to energize the clock (aud maximum altitude sensor) manually. The retrograde time is normally computed and set prior to flight, but the retrograde time can be manually changed by the Astronaut (retrograde time reset handle) or remotely set through the command receivers. Ten minutes prior to retrograde time, the satellite clock transmits a signal to the ASCS to start horizon scanners operating continuously and assures rate gyro operation in preparation for retro sequence. Upon reaching retrograde time, a set of contact points within the clock close, initiating the retrograde sequence. Time From Launch and Retrograde Time digidials provide outputs for telemetering.
Changes From Previous Specification
- The second countdown timer has been removed
- The clock now commands horizon scanner continuous activation and rate gyro operation in preparation for retro sequence.
Changes for Test Capsules
The November 1961 Edition of SEDR-104 notes no specification changes in regards to the satellite clock for any of the test capsules.
February 1962
The specification of the satellite clock 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 notes no specification changes in regards to the satellite clock for any of the test capsules.
May 1962
The specification of the satellite clock in the May 1962 Edition of SEDR-104was unchanged from that in the November 1961 edition
Changes For Test Capsules
The May 1962 Edition of SEDR-104 notes no specification changes in regards to the satellite clock for any of the test capsules.
December 1962
The description of the satellite clock changed slightly in the December 1962 Edition of SEDR-104
Specification
The satellite clock is an electro-mechanical timing device located on the upper right of the main instrument panel . The satellite clock indicates time of day, TIME FROM LAUNCH, TIME TO RETROGRADE and RETROGRADE TIME (see Figure 13-1). The time of day will be reflected by a manually wound spring-driven movement watch. The manually wound watch is located in the upper left-hand corner of the satellite clock. TIME FROM LAUNCH, TIME TO RETROGRADE, and RETROGRADE TIME will be displayed on digidial drum counters. The drum counters will indicate time in HRS, MIN, and SEC. The time elements will move in one step increments. The TIME TO RETROGRADE digidial is supplemented by a telelight. The telelight is located in the upper right-hand corner of the satellite clock and illuminates five minutes prior to retrograde time; in addition to the telelight, an aural signal to the astronaut's headset is initiated ten seconds prior to retrograde time. The satellite clock is automatically started by 28V d-c power at liftoff. Should this not occur, a push button switch is provided above and adjacent to the clock to allow the Astronaut to energize the clock (and maximum altitude sensor). The retrograde time is normally computed and set prior to flight, but the retrograde time can be manually changed by the astronaut with the use of the retrograde time reset handle located on the lower right of the satellite clock or remotely set through the command receivers. Ten minutes prior to retrograde time, the satellite clock transmits a signal to the ASCS to start horizon scanners operating continuously and assures rate gyro operation in preparation for retro sequence. When retrograde time is obtained, a set of contact points within the clock close, initiating the retrograde sequence. TIME FROM LAUNCH and RETROGRADE TIME digidials provide outputs for telemetering. The main instrument panel is lighted externally by the cabin flood lights.
Changes From Previous Specification
The changes appear to be editorial in nature. The change in the description of location is due to the lack of the earth path indicator in spacecraft 20. The figure number has changed.
Changes For Test Capsules
The December 1962 Edition of SEDR-104 applied solely to spacecraft 20 there were no test capsules in this specification.
