Google Earth Community: Columbia Disaster Debris Field

Further reading-- Debris Field

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Approximately 84,000+ pieces of debris have been recovered, about 37% of the shuttle by weight. The factors affecting the trajectory of any given debris piece are the item's initial velocity, altitude and angle of descent as well as its weight and lift and drag coefficients. Knowing these variables will allow us to calculate the terminal velocity of any piece of debris and determine its travel time to impact. Many of the lighter flat panels that broke free from the main body stopped traveling forward almost immediately and fluttered to the ground within a few hundred yards of where they separated, most of these fell at the beginning of the debris field near Dallas. Other heavier pieces continued to travel along the flight path for hundreds of miles. The SSME Powerheads were by far the heaviest single items from the debris field and they traveled the furthest.

The SSME Powerheads are at the extreme end of the debris field near Fort Polk LA. The final report contains the velocity at which the SSME's impacted the ground as Mach 2 and the items weight as 800 lbs. A secondary debris item should be a theoretical piece of arbitrary debris that falls near the center of the debris field. By looking at the photos of debris on this page and on the Investigation page you can get some idea of the size and shape of typical debris in that area and to some extent the approximate weight of those items. Since the drag and lift coefficients are virtually impossible to determine accurately due to unknown attitude and tumble rate of the items as they fell, a value of 1 is very reasonable and will be used for both coefficients on any and all debris items. Because this calculation will be checking the conclusions stated in the official final report all of the initial values will come from that document, initial velocity is Mach 18 and initial altitude is 1200,767 Ft. Since the final report makes the case that the Columbia was flying within a nominal reentry envelope when it suddenly broke up, the nominal angle and rate of descent for that point in time of reentry will be used. For a nominal Space Shuttle reentry at EI+923 the angle of descent is 0.3960° and the rate of descent is 200 Ft./Sec.

Comparison of how debris from different ends of the size, shape and weight spectrum would have traveled to the ground based on the official location of "vehicle main body breakup" using the corresponding initial altitude and velocity values.

Some general assumptions have been made about the debris properties and the initial conditions.

The assumptions made for the calculation to the left is that the SSME Powerheads are pitched straight forward, initial vertical velocity equals 0, at their initial horizontal velocity of Mach 18. The parabolic trajectory is based on a free falling object with roughly equal vertical and horizontal velocities. However this trajectory may not be accurate for objects that have an initial very high forward momentum value such as the Powerheads. The trajectory may then be much straighter.

Trajectory Diagram 1 shows the questionable location of "vehicle main body breakup" discovered in the overlay analysis of Fig. OA-B1-1. This location for vehicle breakup in relation to the size and proximity of the debris field would require that a good portion of the debris travel in the opposite direction after breakup. Trajectory Diagram 2, Fig. OA-B1-4, shows a more likely location for the breakup of an aircraft traveling at high altitude and hypersonic velocity in relation to the debris field.

Conclusions:

Because there are a number of unknown factors affecting the trajectory of any given piece of debris, determining a terminal velocity due to gravity should give an approximate but acceptable time to impact.

Using known properties for debris items and some general assumptions as well as the initial conditions stated in the official final report, the following vertical travel times to impact have been calculated.

SSME Powerhead = 10.00 Min.

Arbitrary Debris Item = 14.36 Min.

Analysis of the Powerhead trajectory using Newtonian Mechanics. It assumes that the Powerheads continued on a more or less straight course during and after main body vehicle breakup occurred which is probably correct. The problem with this relationship is that with the very long horizontal distance and shallow angle involved it is unable to determine very much about the altitude.

It is simply the most probably method NASA used to calculate the impact time shown in the Ground Track documents. The distance of travel is the hypotenuse of a right triangle made of the altitude and the distance to main body vehicle breakup or where that altitude occurred along the Ground Track. The final velocity of Mach 2 is probably from a final radar image of the items mentioned on one of the debris maps.

If the initial altitude is cut in half from its present value or even down to one quarter the final answer is only changed by a few percent.

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Edited by danescombe (03/14/08 05:57 AM)