Technical Article B1 Space Shuttle Reentry Sonic Boom Seismic Recordings

This section analyses seismographic data recorded at various seismic recording stations along the reentry flight path for STS-107.  Where similar data from previous shuttle missions is available comparisons are made between the graph produced by Columbia during STS-107 and the other missions.  Because all of the flight parameters have to be identical in order for the comparison to be valid, only missions with the same orbital inclination and landing area can be used such as STS-78 and STS-90.  In addition to the flight parameters listed, if the shuttle is at the same location when the data is recorded the graphs should be nearly identical.  Weather conditions may alter the data but the effects should be relatively minimal.

The map in Fig. TA-B1-1A is interactive and will go to a larger version of the graphed data when the thumbnails are clicked on.

Fig. TA-B1-1A

Typically there is very little seismic activity recorded due to Space Shuttle reentries until the orbiter approaches its landing area.  At that point, about 50 miles away from the runway, the shuttle's altitude has decreased enough that very low intensity sonic booms can be heard by local residents who are listening for them.  Those sonic booms in turn will be recorded by local seismographs.  See, SonicBoomsSeismic.pdf.

Fig. TA-B1-1B

Fig. TA-B1-1B diagrams the sequence of events resulting in a pressure disturbance from a sonic boom being converted into seismic waves recorded on a seismometer type device.  Based on the description of sonic boom formation presented in, Technical Article TA-A3; Shockwave Formation and Sonic Booms, the point where a sonic boom is felt and heard is where the surface of the sonic cone passes over a person or other object.  It stands to reason then that the point where the pressure waves are transferred to the Earth is where the sonic cone intersects the surface of the Earth.  The pressure waves then become seismic waves that radiate out from that point and diminish over the distance traveled by some rate that is dependent on the geological properties of the immediate area.  Seismic recording devices such as those at the TXAR infrasonic array record the pressure waves transmitted through the Earth from that point.

Both missions referenced on Fig. TA-B1-1B, STS-78 and STS-107, were flown by Columbia and had the same orbital inclination, 39˚, as well as the same landing point, KSC Runway 33.  According to the STS-107 official investigation the Columbia was still flying a normal reentry at that point as far as basic flight parameters such as altitude, velocity, attitude and flight path would indicate.  ¹The location where the seismic disturbance originated is the same for both recordings, (on Fig. TA-B1-1B Point 1 for STS-78 is the same as Point 1 for STS-107).  Therefore, based on all available information including Columbia's flight parameters during the STS-107 reentry, the two recordings from the TXAR Infrasonic array made during the reentries of STS-78 and STS-107 should be identical.  The two seismographs are analyzed below and compared for any differences that indicate what may have been happening to Columbia at that point during reentry.  See, Comparative Analysis of STS-78 and STS-107 TXAR Seismographs.

Fig. TA-B1-2

Back to Map

Fig. TA-B1-3A

Back to Map

Fig. TA-B1-3B

Back to Map

Fig. TA-B1-4

Back to Map

Fig. TA-B1-5A

Back to Map

Fig. TA-B1-5B

Back to Map

Comparative Analysis of STS-78 and STS-107 TXAR Seismographs

The two TXAR seismograms above, Fig. TA-B1-5A and Fig. TA-B1-5B, were both created by Columbia on different dates during different missions.  Both STS-78 and STS-107 had the same orbital parameters, (altitude = 280 km, orbital inclination = 39˚), and landed at the same location, KSC Runway 33.  ¹Therefore the assumption can be made that Columbia was in the same relative position and distance to the TXAR array when both seismographs were recorded during the respective missions.  Aside from some variations in the frequency, which would be expected considering Columbia's loss of control during STS-107, the major difference between the two charts is the ²amplitude.  It is observed that the amplitude for STS-107 is four times greater than that of STS-78.

The factors affecting the strength of the seismic waves as they travel over a given distance and through a given medium are unknown, (the dissipation rate over distance, the geology of the area in question etc.).  However, it may be assumed that during the 7 years which separate the two missions, no great geologic changes have occurred within the area.  ¹In addition the distance traveled by the seismic waves from the point of origin to the TXAR infrasonic array is the same for both STS-78 and STS-107.  Therefore, the size of the disturbance at that point must have been at least four times greater for STS-107 than for STS-78, or in other words the sonic boom was at least four times greater.

Fig. TA-B1-5C

Based on the diagram and calculations of Fig. TA-B1-5C it is possible to predict the amount of energy transferred to the ground from a sonic boom formed by the same aircraft traveling at the same velocity during different flights.  The calculation is based on the altitude of each flight as measured at the point of origin for the seismic disturbance with the difference in the energy transferred to the Earth being directly proportional to the difference between the altitudes.  The amplitude of the seismic disturbance measured at a given distance from the point of origin has a one to one relationship to the amount of sonic energy transferred.

The only explanation for the difference in the seismic amplitudes between the seismographs of Fig. TA-B1-5A and Fig. TA-B1-5B is the difference in the strength of their related sonic booms and by definition their individual altitudes.  Based on the Energy Density equation in Fig. TA-B1-5C the altitude of STS-107 must be significantly lower than the altitude of STS-78 resulting in a greater transfer of sonic energy as evidenced by the measured seismic amplitudes.

Altitude calculation for Columbia during the STS-107 reentry at the location where both of the seismic recordings for STS-78 and STS-107 were made, (Point 1).

This calculation is based on the format derived in Observational Analysis: OA-B1 (Altitude Calculations to Verify the Modified STS-107 Reentry Trajectory).

(q): 1° Horizontal distance (X): 2,895,393 Ft.  (Point 1): 33.8374, -101.875 End of Debris Field (Point 2): 31.0315, -93.0742

Fig. TA-B1-5D

Back to Map

Fig. TA-B1-6

Back to Map

1. Numerous papers published by the academic teams responsible for reporting on the various Infrasonic arrays state that the locations of Columbia during the two TXAR recordings from missions STS-78 and STS-107 were virtually the same.

2. The exact units used for the vertical axis are unknown, (most likely units of pressure), but they appear to be identical for both graphs.

Copyright © 2003, 2004 ColumbiasSacrifice.com