Skip to comments.Observation on TPS damage on Orbiter
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.
Another freeper noted that the orientation of the insulation/ice object changes the impact force based upon the surface area of the impact. The individual made the observation that if the object had impacted "edge" on, the damage would be greater than if the object impacted flatly on the leading edge.
The white plume seen in this frame may be partly composed of silica particles from pulverized tiles. Given the substantial size of the plume when compared to the relatively small size of the object, one wonders if the plume size is actually the density and size one would expect from an insulation approximately 2 feet in diameter.
Once it is established that ET insulation alone can not create the plume seen (via the colorimetric test), it should be possible to create a second test scenario. A mixture of ice and ET insulation can be created to mimic estimated launch conditions. That mixture should be fired at the test article and the plume colorimetrics studied.
The resulting data could be compared to the photographic evidence and permit the composition of the plume to be evaluated in a scientific manner.
It is my contention that if one compares the plume from a 2' piece of ET insulation to the plume in the photo: 1. The photo has a plume with greater white tones 2. The photo has a plume in greater size than expected. 3. The differences in size of plume and tone are accounted for by silica pulverized by the impact.
Knowing hindsight is always 20/20, I welcome discussion and criticism. This posting is meant to contribute to the scientific process and only suggests one scientific method to approach the accident investigation.
Thanks... God bless and rest the crew of STS-107 and 51-L.
I wonder though, whether or if ice was invoved, would the plume not have some prismatic effect as light reflected off of it?
In all photos but that above point 4, the ET has a reddish-looking thing near the bottom of the picture. The highlighting does not occur in this area.
In the picture above point 4, where the highlighter does cover that area, the previously reddish-looking thing is now white, yet the plume does not appear to have extended far enough to have produced that white color.
I'm neither disputing nor defending the tile theory because I simply don't understand enough science to argue for one or the other. I'm just pointing out what I see :)
I have a slow connect to the web, so these are the first real close-ups I've seen. What type of camera/film are these images made with? It seems they are not 'normal' but are IR enhanced [much like 'night-vision' rectifiers] and therefor the colors would be warped. Having seen someone hit and sliced open with a less than 1/2inch slab of ice from a building, I think your synopsis is right on the money. Thank you.
SHUTTLE INFRARED LEESIDE TEMPERATURE SENSING
The SILTS experiment will obtain high-resolution infrared imagery of the upper (leeward) surface of the orbiter fuselage and left wing during atmospheric entry. This information will increase understanding of leeside aeroheating phenomena and will be used to design a less conservative thermal protection system.
SILTS provides the opportunity to obtain data under flight conditions for comparison with data obtained in ground-based facilities. Six primary components make up the SILTS experiment system:
(1) an infrared camera,
(2) infrared-transparent windows,
(3) a temper ature-reference surface,
(4) a data and control electronics module,
(5) a pressurized nitrogen module and (6) window protection plugs. These components are installed in a pod that is mounted atop the vertical stabilizer and capped at the leading edge by a hemispherical dome. (The SILTS pod replaces the top 24 inches of the vertical stabilizer.)
Within this dome, the infrared camera system is mounted in such a way that it rotates to view the orbiter leeside surfaces through either of two windows-one offering a view of the orbiter fuselage and the other a view of the left wing. The camera is sensitive to heat sources from 200 to 1,000 F.
The camera's indium-antimonide detector is cooled to cryogenic temperatures by a Joule-Thompson cryostat. The camera's field of view is 40 by 40 degrees. Its rotating prism system scans four 100-line fields each second, with a 4-1 interlace, resulting in a 400-line image.
Each of the two infrared-transparent window assemblies consists of dual silicone windows constrained within a carbon-phenolic window mount. The windows and window mount assemblies are designed to withstand the entry thermal environment to which they would be subjected without active cooling. They are, however, transpiration cooled with gaseous nitrogen during experiment operation so that they do not reach temperatures at which they would become significant radiators in the infrared. A small thermostatically controlled surface between the two window assemblies provides an in-flight temperature reference source for the infrared camera.
The pressurized nitrogen system comprises two 3,000-psi gaseous nitrogen bottles and all associated valves and plumbing. The pressure system supplies gaseous nitrogen to the cryostat for camera detector cooling, to the external window cavities for window transpiration cooling, and to pin pullers that initiate the ejection of the advanced flexible reusable surface insulation window protection plugs upon SILTS activation to expose the viewing ports and camera.
The information obtained by the camera is recorded on the OEX tape recorder. The data, when reduced and analyzed, will produce a thermal map of the viewed areas.
The SILTS experiment is initiated by the onboard computers approximately five minutes before entry interface, which occurs at an altitude of approximately 400,000 feet. The camera operates for approximately 18 minutes through the forward-facing window and left-facing window, alternating evenly between the two about every five seconds.
After the six planned SILTS missions, an analysis of structural loads will determine whether the SILTS pod should be removed and replaced with the original structure or remain in position for other uses. The pod thermal protection system is high-temperature reusable surface insulation black tiles, whose density is 22 pounds per cubic foot.
This system was only on the Columbia......
When was this started? Did NASA cut it back to 2 or 3 flights to save funds?
IF they had it, and find it, it could be invaluable. Thanks.
They were attempting to find out why.
The hue of the dust was definately redish. I have no doubt.
NBC also verified the voracity of the reported tile loss over California. They said the guy was a astronomer with a telescope.
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