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.
Active protection forcibly cools the hottest surfaces of the vehicle to reduce their temperature, allowing for more conventional materials to be used. Although an active system was deemed workable in a 1972 study, it was determined to be too heavy (Current Technology..., p. 292). In ablative cooling, a thin coating on the craft burns up upon reentry, dissipating some of the heat. Although this system had been used successfully for most of the history of the US Space Program, it did not satisfy the condition of extended reusability (Lucas, p. 569). This leaves radiative protection.
http://www.rose-hulman.edu/~stevenpc/RCC/selection1.jpg
(From Carbon-Carbon..., p.12) The superalloys of the day could not withstand the high temperatures at the leading edge. Ceramic tiles like those used on most of the shuttle could almost withstand the temperature, but were too weak for the leading edges. Carbon-carbon composites were known to have high strength at elevated temperatures and low coefficients of thermal expansion, but were extremely susceptible to burning up the presence of oxygen. RCC represents a compromise between a carbon-carbon composite and ceramics. It uses carbon-carbon for strength and a thin outer coating of silicon carbide to protect the carbon from the atmosphere. This produces a very strong, very heat resistant material with a low coefficient of thermal expansion that is well suited for reentry vehicles.
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Look at the drop in strength of the ceramics as the temperature increases.
The space shuttle wing leading edge and nose cap are composed of a carbon/carbon composite that is protected by silicon carbide. The coefficient of thermal expansion mismatch leads to cracks in the silicon carbide. The outer coating of the silicon carbide is a sodium-silicate-based glass that becomes fluid at the shuttles’ high reentry temperatures and fills these cracks.
Small pinholes roughly 0.1 mm in diameter have been observed on these materials after 12 or more flights. These pinholes have been investigated by researchers at the NASA Johnson Space Center, Rockwell International, the Boeing Company, Lockheed Martin Corporation, and the NASA Glenn Research Center at Lewis Field to determine the possible sources and the extent of damage.
Left: Pinhole from OV–102 wing leading-edge panel 12 RH; 15 flights. Right: Cross-sectional view (backscattered electron image).
A typical pinhole is illustrated in the preceding photomicrographs. These pinholes are found primarily on the wing leading edges and not on the nose cap, which is covered when the orbiter is on the launch pad. The pinholes are generally associated with a bead of zinc-rich glass. Examination of the orbiter and launch structure indicates that weathering paint on the launch structure leads to deposits of zinc-containing paint flakes on the wing leading edge. These may become embedded in the crevices of the wing leading edge and form the observed zinc-rich glass.
Laboratory experiments indicate that zinc oxide reacts vigorously with the glass coating on the silicon carbide. Thus, it is likely that this is the reaction that leads to pinhole formation (Christensen, S.V.: Reinforced Carbon/Carbon Pin Hole Formation Through Zinc Oxide Attack. Rockwell International Internal Letter, RDW–96–057, May 1996). Cross-sectional examination of pinholes suggests that they are enlarged thermal expansion mismatch cracks. This is illustrated in the following photomicrographs. A careful microstructural analysis indicates that the pinhole walls consist of layers of zinc-containing glass. Thus, pinholes are likely formed by zinc oxide particles lodging in crevices and forming a corrosive zinc-rich glass that enlarges existing cracks (ref. 1).
Left: Pinhole from OV-102 wing leading-edge panel; 12 RH, 15 flights. Right: Cross-sectional view with optical microscope.
Having established the likely source of the pinholes, we next needed to model the damage (ref. 2). Our concern was that if a pinhole went through the silicon carbide to the carbon/carbon substrate, oxygen would have a clear path to oxidize the carbon at high temperatures. This possibility was examined with studies in a laboratory furnace. An ultrasonic drill was used to make artificial pinholes in a sample of protected carbon/carbon. After exposure, the specimens were weighed and cross-sectioned to quantify the extent of oxidation below the pinhole.
The results at higher temperatures showed good agreement with a simple diffusion-control model. This model is based on the two-step oxidation of carbon to carbon monoxide and carbon dioxide. The fluxes are illustrated in the final figure. The model indicates a strong dependence on pinhole diameter. For smaller diameters and short times, the oxidation of carbon is very limited.
Model for the oxidation of a carbon/carbon composite at the bottom of a pinhole in a SiC coating.
Glenn contact: Dr. Nathan S. Jacobson, (216) 433–5498, Nathan.S.Jacobson@grc.nasa.gov
NASA Johnson contact: Dr. Donald M. Curry, (281) 483–8865, donald.m.curry1@jsc.nasa.gov
Author: Dr. Nathan S. Jacobson
Headquarters program office: OSF
Programs/Projects: Space Shuttle Leading Edge Structural Subsystem
Responsible NASA Official: Walter.S.Kim@grc.nasa.gov, 216-433-3742,
point of contact for NASA Glenn's Research & Technology reports
Web page curator: Nancy.Amman@grc.nasa.gov (InDyne, Inc.)
Last updated: April 2000
Can you explain the meaning of this word ?
http://www.nytimes.com/2003/03/13/national/nationalspecial/13SHUT.html?ex=1048136400&en=d2fedee0926ad954&ei=5006&partner=ALTAVISTA1
Shuttle Team Sought Satellite Assessment of Liftoff Damage
By EDWARD WONG
Two or three days after the space shuttle Columbia's liftoff, a group of NASA engineers asked the shuttle program manager to request the aid of United States spy satellites in determining the extent of debris damage to the shuttle's left wing, but the manager declined to do so, a senior NASA official said yesterday.
The official said the satellites would "absolutely" have helped the engineers measure any damage to the wing's protective heat tiles from debris slamming into them about 81 seconds after liftoff on Jan. 16.
He said Lambert Austin, an engineer at Johnson Space Center in Houston, had asked Ron D. Dittemore, the shuttle program manager, in a group meeting to obtain satellite images to help gauge the damage. Mr. Dittemore turned down the request, even though Mr. Austin was also speaking for several other engineers, the official said.
Mr. Austin and his colleagues were disappointed, the official said, especially because they believed Mr. Dittemore did not have the technical knowledge of imagery to determine whether the images would have been helpful.
Mr. Austin declined yesterday to comment.
Mr. Dittemore also would not comment, but a NASA spokesman said yesterday that Mr. Dittemore and other officials had decided that satellite images would not necessarily help determine damage.
It is unclear how Mr. Austin's request was related to another NASA request for imagery made around the same time to Defense Department officials, and later withdrawn via an e-mail message, which NASA publicly released last month.
The senior official also said some NASA engineers were now questioning whether the debris actually came from the large external fuel tank. The engineers are scrutinizing the solid rocket boosters to see whether the debris could have originated there, he said.
While the shuttle was in orbit, five Boeing engineers concluded in a report to NASA that the debris impact had not caused serious damage based on the assumption, now perhaps faulty, that the debris was a chunk of foam insulation from the external tank.
A central question in the investigation of the Columbia's break-up on Feb. 1 is whether the National Aeronautics and Space Agency and its contractors had enough information to accurately assess the tile damage. Many experts say damage from the debris may have weakened the wing and is the most obvious possible root cause of the accident, though there are many suspects.
A reconnaissance satellite could have been used to capture images of the tiles. Shortly after the Columbia accident, when aerospace experts outside NASA asked why the agency had not sought satellite assistance, Mr. Dittemore said such images might not have been sharp enough.
But the senior NASA official, who agreed to talk on the condition that his name not be used, said: "When a group of engineers puts forward a request, they're not doing it for grins and giggles. Within their minds, they thought that was a path that would resolve some final concerns. I don't know if it was a cost issue, a timing issue. I don't know if assets could not be arranged."
The official added, "If they had done that, we might know something."
It is unclear whether even a better determination of the tile damage would have helped NASA bring the astronauts home safely.
James Hartsfield, a NASA spokesman, said yesterday that there were discussions in the days after liftoff on whether to obtain satellite imagery. Officials decided not to, he said, because they were satisfied with the Boeing analysis and, as Mr. Dittemore indicated, they questioned the usefulness of the images that satellites would provide.
Mr. Hartsfield said someone at NASA did make an early request for imagery to the Defense Department. But he said that request, which "was not coordinated with the rest of the flight operations world," was withdrawn by another NASA official, Roger D. Simpson.
Mr. Hartsfield said he did not know who had made the request to the Defense Department. The National Reconnaissance Office, the government's main operator of spy satellites, is chartered under the Defense Department. The senior NASA official familiar with Mr. Austin's request said that as far as he knew, Mr. Austin did not contact a department official directly and dropped his request after Mr. Dittemore denied it.
Shuttle Team Sought Satellite Assessment of Liftoff Damage
(Page 2 of 2)
But in an e-mail message dated Jan. 29 and sent from one NASA official to another in Houston, Mr. Austin was mentioned as the person who might have initiated the request to the Defense Department. The author of the e-mail message, J. Steven Stich, wrote that Mr. Austin's involvement was a "rumor."
That e-mail message was released last month by NASA, along with one written by Mr. Simpson on Jan. 23 in which he thanked officials at the United States Strategic Command for considering a request to observe the Columbia for damage but criticized the request as not having gone through proper channels
Mr. Simpson apologized for any "inconvenience the cancellation of the request may have caused" and said that it had served only to "spin the community up about potential problems." He added that the shuttle was "in excellent shape."
The retraction of that request is now part of the investigation into the Columbia's break-up, said Laura J. Brown, a spokeswoman for the independent investigative panel.
The request Mr. Austin made of Mr. Dittemore was to get satellites from the National Reconnaissance Office to look at the shuttle's tiles. Richard Oborn, a spokesman for the office, declined to talk about the satellites' operations and capabilities, saying such information is classified.
Though NASA did not ask the reconnaissance office for the use of the satellites in assessing the Columbia's tile damage, it requested the agency's help after the accident to try and determine whether the shuttle was hit by space debris.
An expert on tile damage, Paul S. Fischbeck of Carnegie Mellon University, said NASA had made a mistake by not using satellites, ground telescopes or both to obtain images of the wing tiles while the Columbia was still in orbit.
"It would have made the decision-making process a lot clearer, and that's the goal," said Professor Fischbeck, who has co-written two NASA studies on tile damage. "They classified this as not a problem, I think, prematurely."
The senior NASA official briefed on Mr. Austin's request also said some engineers working on the Columbia investigation were now not certain at all that the debris that hit the tiles had come from the external tank. Last month, several NASA officials said the debris was probably hardened foam insulation from the area near two metal struts that connect the tank to the shuttle. In four other shuttle launchings, foam had broken off from the area and damaged the orbiter.
But a close look at the video of the launching does not show beyond a doubt that that was the case with the Columbia, even though the Boeing engineers clearly made that assumption, the senior official said. The only thing the video shows, he said, is that debris from the right side of the orbiter floated beneath the nose and re-emerged on the orbiter's left side. It then slammed into the left wing.
Engineers specializing in the solid rocket boosters are checking to see whether the debris could have broken off from one of the boosters, the official said. They are looking at any material that could have come loose, including a silicone-based heat shield called superlightweight ablator that covered two structures on the boosters called bolt catchers.
Each bolt catcher is the size of two large stacked cans. There is a catcher on each rocket booster near the forward area of the external tank. They catch explosive bolts that come loose when the rocket boosters separate from the external tank as the shuttle shoots into orbit.
The official said NASA engineers recently determined that the amount of loads and stresses they had thought the bolt catchers could handle had been exceeded during their actual uses. During manufacturing, the bolt catchers were tested without the ablator on them.
The consequences of the bolt catchers' exceeding their load and stress limits are unknown right now, and engineers will have to run more tests, the official said.
During a launching in 1988, the shuttle Atlantis sustained serious tile damage from debris flying off a solid rocket booster. In that case, the debris came from the nose cone of a rocket booster and knocked out most of one tile below the crew compartment, said Professor Fischbeck. The shuttle's aluminum skin experienced high heating, he said, but a steel frame around an access hatch in the area absorbed most of the heat.
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Why are they so intent on avoiding testing and checking for the obvious - the impact of a 2.5 lb, suitcase sized block of foam on the tile? So far, the biggest they have tested, as far as I can tell, is about 1 cubic inch.
There has been a lot of discussion about space suits (how many or were there any aboard and EVA's) and yet we have seen no EVA hatch on STS-107.
Your drawing would be useful.
If you send it to Budge via e-mail at
budge
he can put it up for posting here.
Many thanks.
NASA Planning Space Return by Fall
WASHINGTON -
NASA (news - web sites) is making plans to return the space shuttle to orbit as early has this fall and has instructed engineers to be prepared to make any "corrective actions" recommended by the board now investigating the Columbia tragedy.
William F. Readdy, NASA's associate administrator for space flight, issued a memo this week instructing agency officials to organize a team to plan for quickly making changes in the space shuttle — or its operations — so that the craft would be quickly ready to fly.
"The team will prepare for a safe return to flight as soon as practicable," the March 12 memo said. "As a goal, the SSP (Space Shuttle Program) shall plan for corrective actions and reviews which support a launch opportunity as early as the fall of 2003."
Readdy said that NASA will be guided by the recommendations of the Columbia Accident Investigation Board, which is studying the factors involved in the Feb. 1 destruction of Columbia in which the seven crew members perished.
The space shuttle disintegrated while returning to Earth, scattering debris across wide areas of Texas and Louisiana.
The memo instructed engineers to review specific problems that already are being investigation by the CAIB. These issues include foam insulation that peeled off the shuttle's external fuel tank and smashed into the craft's left wing and may have damaged the thermal protection tiles on that wing.
The return-to-flight team also is to review ways to inspect and repair damaged tiles while the shuttle is in orbit. Other issues to be studied are how the spacecraft is prepared for orbit, the policies on granting safety waivers and the methods used to identify in-flight safety problems and how those issues are relayed to top NASA management.
Readdy said NASA will not "prejudge" the conclusions of the accident review board, but will concentrate efforts on problems that the board has already publicly discussed, such as the foam insulation debris and possible broken tiles on the wing.
"That's the elephant in the room," said Readdy. "We can't ignore those."
NASA's plans call for the first mission to be directed toward continuing the construction of the International Space Station (news - web sites). The mission also would be used to rotate crew members now in the station.
Three crew members now on the station, Expedition 6, will be replaced by next month by two crew members to be flown to the space station aboard a Russian Soyuz spacecraft. The Expedition 6 crew will return to Earth on a Soyuz now docked at the station.
Readdy also explained how he came to turn down an offer from the Department of Defense (news - web sites) to take pictures of Columbia while the spacecraft was in orbit.
NASA engineers knew that foam insulation had smashed Columbia's left wing during its Jan. 16 launch, but an evaluation had concluded that the incident represented no risk to the spacecraft or the crew and it was expected the craft could land safely.
Readdy said that someone "from another agency" had offered to use "assets", presumably high resolution cameras on spy satellites, to examine the space shuttle. But Readdy said he turned down the offer because NASA engineers had already concluded there were no safety issues involved.
"This was a routine offer for support using a national asset," said Readdy. He said he turned it down because he knew the capabilities of the "asset" and did not think it would add to the understanding of any possible damage to Columbia.
"If I thought for a second that there was anything that would be added to the discussion, that safety of flight issues were involved, I would not have hesitated" to accept the offer, Readdy said.
Readdy said he knew about the capabilities of the "assets" and concluded that the pictures would not be beneficial to NASA.
"In my judgment, I didn't think that would have added to the (engineering) discussion," he said.
NASA Administrator Sean O'Keefe said that such judgments are among the issues now being considered by the investigative panel.
___
On the Net:
NASA: www.nasa.gov
CAIB: http://www.caib.us/
Back to the STS assy, I found the pic at right of Atlantis. (There are some larger graphics there too.) As I mentioned somewhere earlier, the foam block starts off well above the orbiter's forward connect point on the ET. This shot also shows that block (at the right in the pic) with the white splat below that XBob said he thinks is an antennae connector. If that block were to come loose, the slipstream would carry it into the path of the left nose/wing chine, as the video from 'Florida Today' shows.
A note on the seeming differences between the Atlantis wing leading edge and the one's I've seen of Columbia's:
The RCC appears to extend deeper onto the wing at the juncture to the glove area. Is it also 'dished', as in a hollow (concave) grind on a knife-blade at that knee joint, or is that just a trick of the light and rendition? If so, I expect it was done to channel/adjust the vortex flow during re-entry.
Someone else said that the CAIB was looking at some foam exiting the boosters; there is a patch near the top outer side -- the one on the right is more noticeable. (Could that be the "six-inch block" you questioned, Bob?) That too could be a source, as the slipstream would again steer it into the path of the orbiter.
Much as I want to see NASA return to flight; not at the expense of a rushed investigation or misapplied scientific principles. Man will never make a space vehicle that is 100% safe; but that's not to say that Six-Sigma should not be strived for.
I also think that standard SOP should include a close inspection of the craft on orbit, even if it only provides peace of mind that nothing seems amiss.
Also, I didn't post it, but the William Harwood at CBSNews has an Updated Timeline - Rev.H; nothing new, just refinements of some timings.
Thanks. One can never have too many bookmarks. The GRIN website at NASA .. I like it!
This is one of the great things about a forum like this. It is as technical as you want to make it or not.
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