Mitchell Report on Tavis and Temperature Drop
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See Annex G of our report for a full discussion of this topic.
Figure 9 (Below) – Temp. Malfunction During Cruise Environment (taken from Figure 20 in NASE Report No. NASA TM X-X-74020 by Michael Mitchell)
Looking at Figure 9, the top graph Y axis is labeled SENSOR OUTPUT (VOLTS). S/N 1591 started with about 0.49 VOLTS. As the temperature drop ensued, the voltage climbed (according to the graph) to about 0.54 VOLTS and then fell to about 0.41 VOLTs. So, overall, it fell from 0.49 to 0.41, a drop of 0.08 – but not mV unless the y Axis is labeled wrong. It probably should read a drop of 0.049 to 0.041. So there is an apparent one order of one magnitude in error here someplace. Is the error on the write up, or on the graph? One order of magnitude in error for a Viking pressure reading, depending on which way it were to go, could on the low side convert 10 mbar to 1 mbar, and on the high side convert 10 mbar to 100 mbar. Given all the weather seen there, 1 mbar seems implausible.
Looking at Figure 9, the top graph Y axis is (again) labeled SENSOR OUTPUT (VOLTS). S/N 1583 started with about 0.53 VOLTS. We'll ignore the decimal place for now as it's already addressed in the previous paragraph. As the temperature drop ensued, the voltage climbed (according to the graph) to about 0.61 VOLTS and then fell to about 0.45 VOLTs. So, overall, it fell from 0.53 to 0.45, a drop of 0.08 volts. This does not line up well with the drop of 41 mV as specified in the write up. It looks like the person generating the graph might have confused the minimum voltage there of 0.41 (or, really, 0.041) for sensor 1591 with the drop in voltage for sensor 1583.
Finally, the difference in voltage AFTER the temperature climbed back up to almost the right temperature was only about one sixth of what it was BEFORE the temperature drop. What might this indicate? Perhaps after the Viking Tavis pressure sensors experienced the REAL cold temperature on Mars, they would spit out essentially identical, but meaningless pressure readings. In-other-words, they were ruined. The area in red on Figure 9 represents the difference in mV between the two sensors tested.