Posted on 02/04/2003 1:34:19 AM PST by bonesmccoy
In recent days the popular media has been focusing their attention on an impact event during the launch of STS-107. The impact of External Tank insulation and/or ice with the Orbiter during ascent was initially judged by NASA to be unlikely to cause loss of the vehicle. Obviously, loss of the integrity of the orbiter Thermal Protection System occured in some manner. When Freepers posted the reports of these impacts on the site, I initially discounted the hypothesis. Orbiters had sustained multiple impacts in the past. However, the size of the plume in the last photo gives me pause.
I'd like to offer to FR a few observations on the photos.
1. In this image an object approximately 2-3 feet appears to be between the orbiter and the ET.
2. In this image the object appears to have rotated relative to both the camera and the orbiter. The change in image luminosity could also be due to a change in reflected light from the object. Nevertheless, it suggests that the object is tumbling and nearing the orbiter's leading edge.
It occurs to me that one may be able to estimate the size of the object and make an educated guess regarding the possible mass of the object. Using the data in the video, one can calculate the relative velocity of the object to the orbiter wing. Creating a test scenario is then possible. One can manufacture a test article and fire ET insulation at the right velocity to evaluate impact damage on the test article.
OV-101's port wing could be used as a test stand with RCC and tile attached to mimic the OV-102 design.
The color of the object seems inconsistent with ET insulation. One can judge the ET color by looking at the ET in the still frame. The color of the object seems more consistent with ice or ice covered ET insulation. Even when accounting for variant color hue/saturation in the video, the object clearly has a different color characteristic from ET insulation. If it is ice laden insulation, the mass of the object would be significantly different from ET insulation alone. Since the velocity of the object is constant in a comparison equation, estimating the mass of the object becomes paramount to understanding the kinetic energy involved in the impact with the TPS.
3. In this image the debris impact creates a plume. My observation is that if the plume was composed primarily of ET insulation, the plume should have the color characteristics of ET insulation. This plume has a white color.
Unfortunately, ET insulation is orange/brown in color.
In addition, if the relative density of the ET insulation is known, one can quantify the colorimetric properties of the plume to disintegrating ET insulation upon impact.
Using the test article experiment model, engineers should fire at the same velocity an estimated mass of ET insulation (similar to the object seen in the still frame) at the test article. The plume should be measured colorimetrically. By comparing this experimental plume to the photographic evidence from the launch, one may be able to quantify the amount of ET insulation in the photograph above.
4. In this photo, the plume spreads from the aft of the orbiter's port wing. This plume does not appear to be the color of ET insulation. It appears to be white.
This white color could be the color of ice particles at high altitude.
On the other hand, the composition of TPS tiles under the orbiter wings is primarily a low-density silica.
In the photo above, you can see a cross section of orbiter TPS tile. The black color of the tile is merely a coating. The interior of the tile is a white, low-density, silica ceramic.
Yes, I know. I can't guess how much it weighs yet, because I don't know the air density up there...>10 mi I'm sure. It was 81 secs into flight, but I don't have an acceleration curve for the ship. If I use sea level air density, I get ~8 slugs. That's too high by at least a factor of 6. If the true air density is known the object would weigh less proportionately to dwhere it's at/1.2g/l...(approximate weight) It also assumes 1Kmph ship velocity. Getting an est of the mass of that object requires knowing the air density and ship speed well. Getting an est. for the relative speed from the film isn't.
That 30fps frame speed only allows a resolution of 33.3msec for time anyway and also they are are creating an MPEG from a higher fps video. To do that they cut the spatial resolution and have the same frame appearing multiple times.
The best that I can do with these images is to find either 150fps, or200fps, as an average speed for the debris to travel the 60ft from the nose tip to the impact under the wing. Those translate to average speeds of 102, or 132mph. There's an initial speed when the debris passes though a plane tangent to the nose tip. That's around 50ft/sec, or 100ft/sec. If the average vel is 132mph, then the debris impacted when it was going 244mph and an average deceleration of 330mph/sec2 is obtained. Some of the decelaration numbers I got, because of the graininess ranged from 310 to 480 ft/sec2, or 210 to 325mph/sec2. The driving force for the acceleration is the relative wind velocity, so as the chuck decelerates, the decleration decreases proportionally, because it's following momentum transfer.
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That 30fps frame speed only allows a resolution of 33.3msec for time anyway and also they are are creating an MPEG from a higher fps video. To do that they cut the spatial resolution and have the same frame appearing multiple times.
"a flat piece of ice would likely begin coming apart just from the stresses when it turned perpendicular to the air-stream"
There were 2 pieces coming down. The bigger one, that hit the wing, was oblong with a length/dia of ~2.5. It had an angular vel of ~5rev/sec.
I believe that all analysis is helpful to either eliminate or include items as contributing factors.
Our analysis at FR on any subject is always a work in progress, due primarily to missing information.
As the information flows, the analysis get perfected.
Still working, still looking, still impressed by what has been done so far.
Also, still in a state of shock.
not an area I am familiar with, but discussers were pretty positive that it was mis labeled"
Do you think we'll ever get the complete story?
There are many web sites and news gathering organizations working on this ... it's all very intersting.
I agree, there doesn't seem to be any kind of cover up going on.
It has been discussed. As I watch the press conferences I am becoming more and more concerned with the references to maximizing "pay load"(that may not be the exact word). I am getting the feeling that the "Bean Counters" were demanding more paying customers. How much "income" was derived from those experiments on this flight ?
Yes, at least I have.
Research noted the tank was one of two remaining heavies in inventory(I have omitted all the terminology), and the craft was the first and heaviest, although they removed much weight during overhaul, I recall 6,600 lbs mentioned. Third, the payload was a whopper, but it fit the launch profile fine and no difficulties were even considered.
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