Observation on TPS damage on Orbiter

NASA photos | 2-3-03 | BoneMccoy

[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.

[tubebender]

Could it be, that they plugged it, and the plug came loose?

I think if you go back and look at the video of the foam strike you will see a better view of that rectangular lighter spot. I noticed it the first time they showed the entire video.

[Resolute]

"If you're correct, and the TPS was previously breached completely by foam from the tank, it's the end of the discussion and heads will roll for allowing the program to continue. The reports from STS-87 look bad enough as it is."

Even if full breach of TPS has not occurred previously, the sight of 1920 cubic inch foam strike on STS-107 seems to have some people in the NASA community alarmed. For example, earlier in this thread were posted some comments from Mischoud where the external tanks are assembled:

"That big piece clearly de-bonded. That big chunk would eat the shuttle up.''

"This is clearly a de-bonding issue. The foam came undone because it had not adhered to the tank properly,'' Rogers said. "I worry that NASA will find some other cause because there is a lot at stake financially if it is the foam. It'll stop the whole program.'''

Last week Lawrence Mulloy was interviewed regarding STS-107. Here is an excerpt:

It also raises the same sort of questions about NASA's handling of safety issues heard in 1986. They echo especially loudly for Lawrence Mulloy, a former NASA engineer who made many of the key calls on Challenger's o-rings and was sharply criticized by a presidential commission investigating the catastrophe.

If - "a big if," he stresses - foam debris proves the trigger for Columbia's breakup minutes from landing in Florida, then he fears NASA forgot the lessons of its own history.

"If it turns out that's the case, you have a direct comparison to the acceptance of the o-rings," he said. As early as the second shuttle flight, he said, engineers found heavy damage on those critical seals.

"We saw the tests and analysis and convinced ourselves that the o-ring was doing the job," said Mulloy, who retired not long after Challenger and now lives outside Nashville, Tenn. "We convinced ourselves that this was an acceptable situation and it did not constitute a safety of flight risk."

Mulloy hears the same sort of rationalization he once employed coming again from NASA. Foam debris, though a problem from the very first tests of the shuttle, became less a safety concern as more flights returned safely, despite often heavy damage to the thermal tiles. After 113 flights, he said, foam would have moved far down the list of concerns.

"You build up a history and a database that says you can tolerate the deviance you're seeing again and again," he said. "That was the mistake on Challenger. I hope it was not the mistake on Columbia."

Mulloy, chief engineer for external tanks from 1973 to the first Columbia launch in 1981, says foam loss was always a worry.

Shuttle probe may reveal pattern of miscalculations

Nobody can truly say that there was no prior cause for alarm (regarding the foam). It just hadn't resulted in catastrophe before. It's like the teenager who didn't get pregnant all those other times . . . Human nature is simply to play with fire, until those bad consequences that Cassandra predicted finally come to pass. Then everyone who ignored (or worse reviled) Cassandra is shocked, simply shocked, that the evil day ever came to pass . . .

[Resolute]

The operative equation for kinetic energy is 0.5*m*v^2, where m is mass, and v is velocity. If we double the mass we get double the kinetic energy. If we double the speed, we get quadruple the kinetic energy. Therefore 0.5*2.67*500*500 is equal to 0.5*4000*12.9*12.9 (at least, to three significant figures it is).

[Resolute]

Here's another link quoting Lawrence Mulloy (designated scapegoat from 1986 Challenger disaster):

Engineer who took blame in '86 questions foam studies

Here Mulloy is quoted as follows: "It's almost a direct corollary to what happened to the O-rings," Mulloy said. "This deviant situation became an acceptable situation. Things were coming off the tank, and that had become an acceptable situation. Things are not supposed to come off the tank."

[Eastbound]

"... completely agree with Slipstick here. This thought was nagging at me but I couldn't articulate it earlier. Slipstick has found a possible cause of a double foam strike, first on the LESS and then on the underside of the wing."

I can easily visualize that. Last week a bird struck my car from the side, first hitting my right rear view mirror, then hitting the middle of my curved windshield hard enough to knock off the inside rear view mirror, then struck the upper right corner of the windshield, leaving ample evidence of hard impact in all three locations, as though it cartwheeled.

[XBob]

I never saw a skin breach personally, except once, when tile, on the aft of the wing, immediately above the elevon came off and the heat penetrated the elevon enough to burn through 2" of the 3" diameter elevon control shaft. It was as if someone had taken a cutting torch to the shaft and burned out a semi-circle about 6-8 inches wide and about 2" deep at the deepest point. It was essentially 'hanging by a thread'. So somehow, the burning stopped in time and the remaining portion of the shaft was strong enough to hold together until landing. Apparently only seconds more of high heat would have severed the shaft, and lost the elevon and orbiter itself.

I saw numbers of dings and chips 1"-3" and at most about 1 1/2" deep on various tiles, on various returned orbiters, but none of these dings penetrated through the tile.

Now, this proposed 'penetration, as far the falling 'block' is on 107 only. I talked to one NASA engineer who reviewed the falling 'block' video, did some calcs (un-officially) and his opinion was that the block would penetrate the tile, by 2 inches. (Official NASA at that particular time (we have had various 'official' answers NO penetration possible) - that's why he did the calcs himself. It wasn't his job. He also said he realized this didn't jive with everyone elses theories, but he checked his calcs, and didn't know what to make of it, himself.

I discarded the idea, initially, as 'interesting' but....

Then, I found the info about the aluminum honey comb panels, which until this time I didn't even know existed, (under the tiles and on top of the skin) in certain areas of the shuttle, especially in the area where we feel the 'block' hit. I have no debth on these aluminum honeycomb panels, except that they vary in thickness from approximately 1/6" to 3". It stands to reason that the thicker honeycomb panels would be located more inboard, on the thicker parts of the wing (why wouldn't they be part of the tapering wing thickness?). So, assuming this, 2 inches below the tile, would penetrate the aluminum honey comb, yet not penetrate the skin and into the interior cavity, leaving 1" of aluminum honeycomb to spare.

If this happened, and the tile was compromised all the way through into the honeycomb, theoretically, the honeycomb under the tile could perhaps start burning under the tile, yet not in the cavity, moving like a fire in a wall in a house, in unsensored areas, burning the honeycomb.

Does that explain my theory satisfactorily? Take a look at the wing section drawing budge posted for me, showing the aluminum honeycomb locations.

[Budge]

2380 - No tinfoil hat here. It is my understanding that the telemetry is so garbeled they are getting little to nothing from it.

What I really thought interesting in that is the matching of the various videos to the timeline.

I cannot vouch for the accuracy, but it sure seems to be darn close.

[XBob]

2377 - Sorry, this is out of my area of expertice. If you want to know about sensor design and implementation, you need to check with snopercod.

[XBob]

2378-"Yet, unless I'm wrong on the timeline, Columbia flew for a full minute after the Left Side gear sensors were torched unresponsive. That has me doubting my own scenario ."

check back on my most recent timeline, not too long back, and you will see that many sensors in the wheel well were near normal ranges at LOS.

[Budge]

2386 - You explained it very well.

[tubebender]

It would really help me if I knew what the shuttle speed was at 80 seconds into launch and what the altitude was. I have seen 1000 mph. I just don't understand how the foam could hit the wing at 500mph when the time was almost in milliseconds from loss of foam to impact if it was only 1000 mph.

[halfbubbleofflevel]

I wanted to mention two things.

I am using this as a reference: http://spacelink.nasa.gov/Instructional.Materials/NASA.Educational.Products/Space.Shuttle.Endeavour.Lifts.Off/Space.Shuttle.Endeavour.pdf

1) regarding the white patch on the external tank that some people spotted

The web link shown was on an Endeavor launch. The external fuel tank has the same white patch? Either this is the same tank or that spot is common to more than one tank.

2) Somebody mentioned "... not only did the tank shrink 6" in height on being loaded, it also swelled 3 feet in circumference. I have no verification of this and only heard it once."

I think something is wrong here. Here is my reasoning:

External Tank Length: 47 meters
Diameter: 8.4 meters

That's probably the outside dimensions but close enough...

Now, using my rusty maths knowledge:
The tank shrinks 6" in length. That's easy to calculate: 6" is 0.15 meters
The circumerence increases 3 ft? That would be: 3 ft = 0.91 meters
New diameter = OldDiameter + 0.91 / pi which calculates out to 0.29 meters increase in the diameter.

The volume would be: length * pi * diameter * diameter / 4
Original volume would be: 2604.6 cubic meters
Volume after filling: 2778.7 cubic meters

This means the tank expands under the influence of the fuel: an increase of about 6.7% - which I can't believe is the case! I was under the assumption that the cold temperatures would shrink the tank.

Shrinking or expanding - both would stress the insulation. Regarding verification - I just am not sure if those figures were accurate.

[Resolute]

Foam has high ratio of surface area to weight. Aero engineers sometimes refer to this as a low ballistic coefficient: Beta = Mass/(drag_coefficient*reference_area). What this means in layman's terms is that some stuff slows down faster than other stuff, when cast into the atmosphere or wind. For example, one can throw a handful of metal BB's a lot further than one can throw a handful of paper confetti. In terms of drag, the foam is more like paper confetti than it is like metal BB's. Some discussion of this issue occurred on another thread:

(NASA Claims) Foam Probably Not Cause of Shuttle Disaster

[Resolute]

Here's one post from previous thread, quoting Mr. Dittenmore about estimated speed of debris and shuttle at time of strike . . .

Mr. Dittemore said . . .

[tubebender]

Foam has high ratio of surface area to weight. Aero engineers sometimes refer to this as a low ballistic coefficient:

I think I understand that but how did it slow to 500mph in a couple of miliseconds. Now I know the shuttle is accelerating also but if it was a 1000mph at 80 seconds what is it at 80 seconds plus a few miliseconds and what was the altitude.

[Resolute]

In the reference, Dittenmore says that the shuttle was traveling 1570 mph at the time when the 1920 cubic inch piece of foam struck the left wing.

And the deceleration interval was not a couple of milliseconds. The debris clearly required several video frames to transverse from point of detachment to point of impact. From the links that I saw here on FR, the frame rate was 30 frames/s. (I advanced the video one frame per step, and counted 30 per each 1 second advance of the movie clock). This translates to 33-1/3 milliseconds between video frames, not a "couple of milliseconds."

I have not seen the altitude enumerated anywhere. However, we can do a trapezoidal integration of the 1570 mph speed stated by Dittenmore. Altitude = 1/2*1570*(80/3600) = 34.9 miles. This is a very crude approximation, as it assumes (A) constant boost acceleration and (B) purely vertical ascent.

[Resolute]

Forgot to divide by 2, again. The crude estimate of altitude is 17.4 miles, with same caveats as before.

[John Jamieson]

I emailed you a photo of the RCC damage to STS45 to the right leading edge, panel 10.

I think that STS45 could have suffered the same fate as Columbia, if this damage had been on the lower side, instead of the upper side of the leading edge. NASA said this was due to "MOD" (meteorite/orbital debris), but it could have been ET foam too. It was on the left side, so yellow ice is not likely.

It's really hard to understand that the air is not hot until it is forced to change direction very quickly against it's will. The jet coming through the hole would actually be cold until it hit something, then the burning begins on that surface. Once the hole is there, the edges of the carbon should burn away slowly because the silicon carbide is only a very thin surface coating and carbon burns very well. The hole would slowly grow as the airjet also starts to penatrate any insulation and aluminum and copper wires in it's way. I suspect the defect in Columbia started this small or maybe even smaller. The jet would be very well defined and would just start eating away, much like water jets can be used to cut steel.

John

[John Jamieson]

I believe that both the tank "shrink" (not expand) and the foam "shrink" are well understood by the ET engineers and designers. They understood that when the tank was designed. I don't see this as a cause. (The amounts we've been talking about also seem way off.)

[John Jamieson]

Sorry, right side, NOT left side.