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.
I believe you caught a mistake in the writing of that piece.
The verbal explanation that I heard stated that it was a yaw and the thrusters were compensating. Finally the thrusters could not help anymore and the vehicle yawed left breached and rolled.
Who was that idiot!
I look at it like this.......You do not replace the car for the simple reason that you hit a deer with it and therefore the car is a deer hitter and dangerous to operate.
What you do is try not to hit any more deer and if you do, you carry a butcher knife and some duct tape, fix the car, dress out the deer, and go home and eat.
A bit of sarcasm there, but the point is the same.
I do not know enough about the characteristics of the shuttle while flying at over 15,000 MPH when the stuff started happening. My gut tells me that aero surfaces could likely start to degrade without much, if any, sensation or warning. Not until the degradation exceeded the ability of the shuttles control computers.
That is the point when it rolled and came apart. I would think that the last minute or so of flight, the crew was thinking that something was wrong, but in those suits, now mandated, they could not look about or see anything much. The computer was also executing the roll reversal program at the time which must be like riding a roller coaster.
If you read the time line I put on the previous page you will see the warnings they did receive.
If that is so, there are no tiles on that surface. It is special high temp carbon stuff.
The searing heat would have been directed into the wing instead of over the tops of the tiles. The tiles would be stripped off as the foundation the sit on got hot and released the adhesive holding them on.
The wings structural skin would melt and that drag that they reported would become very evident as this occurred.
The main reason I am thinking about his particular subject is the possible suggestion that a crew be able to jettison the cargo in case of a suspected tile failure. I suspect they had no way to do this, or tools available, even if it made sense to do so.
The leading edge is a dense carbon structure with a substantial, >1/8" layer of Silicon carbide formed over the surface. It's held in place by bolted metal framing components and the junctions to aluminum wing skin is ~ 2' back from the edge. The ragged appearance would be skin damage behind the edge structure. That edge structure is solid, if it lost it's support the whole edge section would fall out and the wing would disintergrate. The edge is madeup of reletively short, overlapped, solid sections held in place by a vise like grip from metal wing structure further back.
Also, I don't think tiles ever fall off, as some folks say. They only lose that outer layer of silica, thus lowering their insulation value. Under the silica is Nomex, bonded to a primered skin with that RTV silicone. That is a very tough bond. Unless the silicone is burned, it will not fail. The aluminum it's bonded to will become soft like putty, before the silicone is destroyed. The silicone/Nomex would keep the skin intact a lot longer than it would otherwise.
Back later
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