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Apollo 17 Flight Journal - Anomalies

Edited by Eric Hartwell - from the Apollo 17 Mission Report. Last updated March 20, 2006


15.1.1 Spurious Master Alarms

page 15-1

Several spurious master alarms without the accompanying caution warning lights were reported after earth orbit insertion. The alarms could be initiated by tapping on panel 2, indicating a short circuit to ground in that panel.

Figure 15-1- Main bus A undervoltage warning circuit.
Figure 15-2 - Cryogenic oxygen pressure monitoring circuit.

The main bus A undervoltage warning light flickered coincident with one alarm. Several times, the alarm occurred coincident with the crew switching of the cryogenic pressure indicator switch from position surge/3 to position 1/2. However, no alarms occurred when the switch was  transferred from position 1/2 to position surge/3.

The spurious master alarms are indicative of an intermittent grounding of the circuit which is possible in various locations in the system.

An intermittent short-to-ground in the main bus A undervoltage warning circuit (fig. 15-1) would cause the alarm and the main bus A undervoltage
warning light to flicker. The short could be in the wiring or could be conductive contamination in the main A reset switch. Postflight inspection of all wiring on panel 2 revealed no problems. Also, the main A reset switch located on panel 3 was disassembled and no contamination was found.

An intermittent ground in either the cryogenic pressure indicator switch, or in the wiring from the switch, or in the cryogenic oxygen pressure meter (fig. 15-2) would cause the alarms that occurred when the switch was placed to position 1/2. The switch and the meter were disassembled, but no contamination or problems were found. The wiring was also inspected for shorts to ground without success.

The alarms must have been caused by some intermittent ground on panel 2 which depended upon zero-g conditions to occur. The spurious warnings were only a nuisance and valid warnings could not be inhibited by this type of grounding problem. There is not a safety hazard associated with grounding the circuit because of the inherent current-limiting characteristics of the lamp (see fig. 15-1). Corrective action is not necessary for the Skylab or Apollo-Soyuz spacecraft.

This anomaly is closed.

15.1.2 Mission Timer Slow

page 15-3

The mission timer in the lower equipment bay was 15 seconds slow at 1 hour and 58 minutes after lift-off. The timer was reset and worked properly for the remainder of the mission.

Postflight testing has been performed on the timer and it operated normally. The circuitry has been analyzed to determine possible causes of the time loss with the result that the most probable cause was an intermittent in one of the integrated circuits within the timer. This condition may have been caused by mechanical imperfections within the construction of the circuit.

There is another mission timer on panel 2 and event timers in the lower equipment bay as well as on panel 1. Consequently, the loss of one timer is not critical for Skylab or the Apollo-Soyuz missions, and corrective action is not necessary.

This anomaly is closed.


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Source: Apollo 17 Command Module Onboard Voice Transcription Recorded on the Data Storage Equipment (DSE) MSC-07633, January 1973, 746 pages. http://www.jsc.nasa.gov/history/mission_trans/AS17_CM.PDF
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