Fig. OA-E1B-1 

Fig. OA-E1B-1 shows the directions of the positive X, Y and Z coordinates as they relate to the Space Shuttle.  The actual location of the axis would intersect the vehicle C.G. more towards the center of the shuttle.

Fig. OA-E1B-3 gives the approximate orientation of the shuttle at 82 seconds after launch.  Although most people would assume that the ascent velocity vector falls inline with the longitudinal X axis, flight parameters such as sideslip and angle of attack are important during ascent just as they are during reentry.  As the vehicle travels past Mach 1 shock waves form around all of the leading edge surfaces of the various components that make up the stack.

Fig. OA-E1B-7 shows two possible different trajectories for foam debris from the forward bipod attachment location.  Because there is no video that clearly shows debris impacting the WLE RCC Panel 8 or 9, it may have also hit the rear bipod.

Fig. OA-E1B-2 is a still from the debris impact video that reportedly showed exactly how and when the Columbia was damaged.  The first analysis done on the debris impact were based on the presumption that if debris hit the wing at all, the impact location would have been well onto the underside of the wing and not at the leading edge.  When viewing the video from this angle it's easy to understand why there was so much debate about the impact location.

Although the debris does appear to impact something under the left wing and break apart it is nearly impossible to determine exactly what.  The video close up seems to show the object moving past the leading edge and much further out towards the wing tip than RCC panels 6 through 9.  The aft bipod attachment is an excellent possibility for an impact location based on the initial trajectory.  However, even that is difficult to tell from the current angle.

View the Ascent Impact Video

An additional effect of the various shockwaves on the foam debris would be to help maintain its forward velocity and thereby reduce the difference in closing speed between the shuttle and the debris.  Right now the official investigation is assuming that the velocity of the debris went almost to zero just after it separated from the External Tank creating an impact velocity equal to that of the shuttle stack itself.  The boundary layers associated with the shockwaves are a source of friction and might help to maintain the forward velocity of the debris somewhat thereby decreasing the final impact velocity.

Velocity of Stack - Velocity of Debris = Final Impact Velocity.

Fig. OA-E1B-4

Fig. OA-E1B-4 is a photo of Columbia moving past the vertical structure of Launch Pad 39A during the launch of STS-107.  The forward and aft bipod attachments are clearly shown in this photo.  A schematic depiction of the bipod locations along with the possible alternate trajectory is shown in Fig. OA-E1B-7.

It is virtually always necessary to use statistics to determine failure trends for any mechanical or electronic systems.  However, statistics can almost always have a double meaning if not more.  In the case of foam debris damage to the Space Shuttle Fig. OA-E1B-5 and OA-E1B-6 would seem to show very little reason to worry about foam significantly damaging Wing Leading Edge RCC panels.

Summary / Conclusions:

Based on the analysis above, any piece of foam debris that breaks loose from the External Tank (ET) will not have a tendency to jump off the tank surface and immediately move towards other components of the stack.  The 2 to 3 G'^s holding the debris to the ET will cause it to slide down the length of the unit until it collides with another obstruction, such as the rear bipod attachments, and break up.  In order for the debris to come off the surface of the ET it must be acted on by other outside forces such as boundary layer flows from the other shockwaves that create vortexes.  The boundary layer flow from the nose of the shuttle itself would have been the dominant aerodynamic force in that area and would have had a tendency to move debris down between the shuttle and the ET but not back up towards the wings, especially debris that would need to be physically lifted away from the ET.

The official scenario that has been presented as a vehicle to explain how a 2.1 lbs. piece of foam created a 12" hole in a shuttle wing leading edge RCC panel requires that the piece of foam debris immediately leap from the ET, acquire a speed of 600 to 700 Mi. / Hr, (880 - 1027 Ft. / Sec.), and take on a trajectory that helps it avoid other obstacles and steers it right to the target.  Based on observing how the piece of foam would have to interact with the various items that make up the shuttle stack, that whole scenario seems very unlikely.

1. The piece of foam must be lifted from the ET by a vortex action, which if it exists at that point during ascent, would be the result of interactions from the other shock waves.  The vortex, if available, must fight a 2 to 3 G force, (4.2 - 6.3 lbs.), puling the debris back towards the ET.

2. The linear distance from the point where the foam breaks free to the #8 RCC Panel is approx. 58 Ft.  At the debris velocity of 600 to 700 Mi. / Hr the time of travel for the debris is only 0.0659 to 0.0565 Sec.  This is only the linear distance and does not account for any path adjustments.

3. The facts are that the debris had to make numerous course adjustments in order to impact the RCC panel at the precise angle to cause the damage shown in the official report.  In addition the debris had to be lifted against a force pushing it towards the ET and away from the shuttle.  Any change of direction the debris makes for any reason from its initial straight line trajectory causes it to lose some degree of its forward speed which again is one of the parameters listed in the official report for causing damage.  0.0659 Sec. is simply not enough time for a piece of foam to make that many course corrections and still maintain a large enough velocity to break through the RCC Panel.

Any piece of foam debris breaking away from the forward bipod area has at least three different factors working against its changing direction towards the leading edge of the wing.  

1. The starting position for the foam puts it well below the wing.  If the shuttle stack were flying straight and level with not other influences, the debris would never be able to reach any part of the wing.

2. Fig. OA-E1B-3 shows the Columbia with an inclination of about 25 to 30° with the vertical.  At the elapsed time of 82 seconds after launch the shuttle was at least beginning a roll maneuver that would put it into position for orbit.  When the shuttle is beginning to take on such a parabolic trajectory it is intuitively obvious that it would be traveling away from anything that fell off of the External Tank (ET) and setting up a source of centrifugal acceleration that forces any lose objects outward away from the shuttle.

3. The super sonic shockwave and resulting boundary layer flow around the wing would have at least a small effect on any object it encounters.  The effect would be to move the object around and below the wings surface.