Usage of OEX Data in the Final Report

Observational Analysis F1
11/18/2003

The Case for the Final Report was Made Using OEX Data

It seems that the C.A.I.B. was unable to make the case for a wing breach using only the sensor data that was downloaded during reentry via the TDRS system. Perhaps this data was too random in both location and sensor readings to be of much use. Fortunately the OEX data recorder found in the debris field had enough data on the large magnetic tapes to help put together what happened after LOS as well as fill in some of the holes where data was lost during reentry due to the many intermittent communication blackouts with the S-Band antennas. However, the existence of the OEX recorder itself is questionable.

The sensors that Mission Control didn't see:

Sensors for the MADS/OEX were originally located near RCC panel #8/9 location because that is the 55% point on the wing. Sensors were also located at other strategic points along the length of the wing.

Fig. OA-F1-1

V09T9910A - Wing Leading Edge Clevis Temperature
V09T9895A - Wing Leading Edge Spar Temperature
V12G9921A - Wing Leading Edge Spar Strain
V07T9666A - Aft Panel Lower Surface Temperature

Fig. OA-F1-2

There are three temperature sensors and one strain gauge that are cited as being the source of the data that made the strongest case for the RCC panel #8/9 breach scenario. This side view, (above Fig. OA-F1-2), and the plan view, (near left Fig. OA-F1-1), shows the location of the sensors as stated in the STS-107 Accident Investigation Final Report Vol. I.

Fig. OA-F1-3

The above photo, Fig. OA-F1-3, is used in both the STS-107 Accident Investigation Working Scenario and Final Report Volume 1. It is a closeout photo that should have been taken after repair work on Columbia's left wing or after an overhaul. It is unknown where or when the closeout photo was taken.

The sensor labels have been altered from the original documents to show the correct MSID's.

Because these four particular sensors are listed as sending data to the OEX recorder, they and their associated wiring are the type of items that should have been removed during Columbia's last overhaul in Palmdale, see Columbia's most recent overhaul. They were installed when Columbia was new as part of a suite of sensors designed to aid in post flight engineering analysis. As can be seen in the cutaway view of the wing there are many sensors for taking temperature, pressure and structural measurements located throughout the wing. Those feed real-time data to the crew of the shuttle as well as mission control about the health of the shuttle.

Of the temperature sensors listed above there are serious discrepancies as to what the MSID's actually are within both the Working Scenario document and the Final Report. Some pages show the sensors as having MSID's beginning with V09T while other pages show the same sensor as being V07T. After carefully reading through technical reports from the Dryden Technical Report Server it has been determined that sensors with MSID's that are V07T####A usually take temperature readings near the surface of the TPS material while those that are V09T####A are generally located on the inside of the shuttles skin.

Further research indicates that the current MSID's applied to the sensors here are correct and the sensors will be referred to as such from this point on within this site. The MSID's may still appear incorrect in the Working Scenario and Final Report documents.

All the graphs below are from STS-107 Accident Investigation Final Report Volume I.

Fig. OA-F1-4

Fig. OA-F1-4 is reported to be data from the strain gauge MSID V12G9921A that is shown in Fig. OA-F1-1, OA-F1-2 and OA-F1-3. What the graph appears to show is a slight increase in strain during the period from approximately the 250 second mark to the 400 second mark. After that there is another small increase followed by a sharp downward movement which indicates negative strain or that there is compression on this member.
There is strange data at the 500 second point that seems to show reading that are nearly off scale hi and low. After that the strain goes back to zero until sometime after the 900 second point where another hi/low reading occurs. The reading then stop at LOS.

Fig. OA-F1-5

Fig. OA-F1-5 is temperature data from the sensor with MSID V09T9910A which is located on the outside of the wing spar and inside the cavity created by the RCC panel. It also shows a slight increase in its reading just as the strain gauge did with the same hi/low occurrence at the 500 second mark.

This sensor indicates a 50°F temperature increase over 200 seconds with a momentary temperature increase to 650°F at EI+487. The temperature then drops to -200°F which is effectively off scale.

Fig. OA-F1-6

Fig. OA-F1-6 is data from a temperature sensor, MSID V09T9895A, on the inside of the wing spar. The data from this sensor, inside the wing cavity, is similar to that shown in Fig. OA-F1-5.

This graph shows a similar temperature increase as the one above, about 125°F increase over 100 seconds or less with a very small amount of data at 450°F for only a brief moment at EI+522. Then a constant reading of -200°F which is also the off scale low for this sensor.

For this sensor a heat transfer analysis should be done to check the period of time required for the inside edge of the wing spar to reach the stated temperatures, (a transient conduction analysis).

Fig. OA-F1-7

Fig. OA-F1-7 is TPS temperature data from a sensor MSID, V07T9666A, on the underside of the wing near the leading edge. Again anomalous readings occur at the same times as the other sensors. The erratic data from the sensor shown as the sharp peaks and valleys of the graph along with an odd spattering of data points in those areas would tend to indicate something other than overheating.

Something like this might be expected in the event of an explosion that destroyed the sensor. It's also possible that the particular tile this sensor was attached to was destroyed or fell off the wing at this point.

It is unknown what relationship this sensor data has to a breach in the WLE RCC panel.

The effects of the strain reading, Fig. OA-F1-4, of -100 micro in./in., a negative strain says that a member is in compression, on the shuttle wing spar is unknown but based on earlier flights is appears the member is easily capable of handling that much strain in the positive direction. The temperatures in the other graphs are not capable of harming the shuttles components.

The temperature data shown in Fig. OA-F1-5 and OA-F1-6 would be an example of steady state thermal conduction through a flat plate which is the wing spar. The temperature on the outside of the spar that is exposed to the super heated plasma Fig. OA-F1-5 should start rising earlier and rise faster and higher than the temperature taken from the inside of the flat plate or wing spar. The outside temperature does start earlier but, when compared to the inside temperature, does not rise high enough or fast enough to be part of a steady state thermal conduction circuit. Therefore it is unlikely that this temperature data has anything to do with a wing breach and thermal heating of the wing spar.

Summary / Conclusions:

If the data from the graphs in Fig. OA-F1-4, OA-F1-5, OA-F1-6, OA-F1-7 is actual data from from the reentry of STS-107 and not fabricated, it definitely indicates that something significant happened between EI+250 and EI+500 but exactly what is unclear. Because these sensors reported directly to the OEX recorder, Mission Control would not have seen any of this data during reentry. This site has already reasonably shown that the OEX recorder was not on Columbia during STS-107 and was planted in the debris field later to guide the investigation to a predetermined conclusion. Because the discovery of the OEX was a reasonable explanation for the introduction of new data, it makes it extremely convenient that nobody else besides C.A.I.B. members would have seen it and would be able to question the data's authenticity. Whether the data actually came from anytime during reentry of STS-107 or if it was simply fabricated is unknown.

It has also been noted previously that areas of the shuttle left unprotected due to the loss of a thermal tile or in this case a large section of RCC material have remained undamaged. From the document, "Risk Management for the Tiles of the Space Shuttle";1994; Interfaces 24:1; Pg. 72, the following observation was made,

It is interesting to note, that in the two cases in which tiles have been lost in the past, burn-through did not occur (in one case, the tile was lost over a service hatch and the extra structure in the shuttle's frame was able to distribute the increased heating).

Another document assessing the risk probability to the shuttle in the event that the TPS is damaged, "Safety of the Thermal Protection System of the Space Shuttle Orbiter", gives the statistical probabilities that the aluminum skin of the orbiter will burn-through if the TPS is damaged as well as the probability that the shuttle will be lost if that happens. These values are based on both program flight history and engineering analysis of different locations on the shuttle. These values may be added to get the total probability for loss of the Space Shuttle from a foam strike but the individual probabilities are 0.25 for a burn through and 0.05 that the shuttle will be lost due to a burn through at the leading edge of the left wing. Here is a breakdown of some of the information from that document, Probabilities for Loss of the Space Shuttle.