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.
Nice post. Thanks for the ping.
4420-" I think it's just bad engineering to rely on foam as an exposed structural member in supersonic flight. "
My argument all along - it is a really dumb idea to expose large chunks of un-reinforced foam to supersonic flight - really really dumb.
4421 - "Nice post. Thanks for the ping."
Thanks - just trying to keep this thread, in particular, professional. There is too much junk already on the internet.
From your post #4,413 above:
"...NASA and Lockheed Martin Space Systems Co. admit they will never completely eliminate the decades-old problem of foam popping off the tank during shuttle launches..."
... and that's because it's *always been* a bad idea and poor engineering.
An idea I had for repair of critical TPS; (and maybe snopercod or XBob, could forward this to your friends at NASA) it is to develop a plan to perform an EVA(s) for the purpose of harvesting less critical TPS and re-assembling them at the site of the critical damage.
Since the loss of some TPS isn't essential to the shuttle's survivability, various HRSI could be gathered during an EVA (if at least some of the tiles were pre-designed to be capable of being removed in-orbit), brought into the shuttle and reassembled into an appropriate configuration to be re-installed at the damaged area.
There are also various permutations of this idea that could provide a more robust repair solution to RCC damage.
TPS harvesting could reduce the weight burden of carrying a variety of TPS repair components/solutions in order to perform appropriate on-orbit repair.
I think they are removed on earth by attaching a suction cup to the tile and pulling it off (They're glued on with red RTV). The suction cup wouldn't work in space, of course, but you could use epoxy or something to glue a handle on the tile to pull it off.
I see no reason why a tile fabrication station couldn't be set up on the ISS, though.
BTTT
Yes, I know each is unique, but could be cut (or broken) to size. It wouldn't be perfect, but a *lot better* than some of the bizarre stuff I've heard about filling plastic bags with water and misc junk into the hole in the RCC - IMO pretty useless protection against a ~3000 degree arc-jet.
Also one of the "permutations" I alluded to - might have some pre-selected tiles more available for removal by attachment via some other method, easier for harvesting in space. Another permutation is to re-engineer the harvestable tiles (size shape, etc) to accomodate this type of repair procedure.
keep on thinking - CM.
There are really too many problems and you need a TPS expert to give a better explanation.
But - as Snopercod said, each tile is individually carved and shaped. Any slight irregularity will provide a gap to either pull off the whole tile, or allow hot plazma to leak through or between.
2. It took years to perfect techniques on the ground to keep the tiles on the orbiter, let alone in the vacume and heat/cold of space. And you must figure out a way to keep them sticking to the surface of the orbiter at 15,000 mph, through variations of thousands of degrees of heat and cold.
4. Tiles are made of foam, yes, but, it is very unique, and granual, and something more like a very light sugar cube, which turns to granular silicon crystals (about the size of sugar crystals, and it has almost no structural integrity. So the foam tiles on the orbiter are totally unlike anything you are familiar with, unlike the urethane foam on the external tank. And most of the pieces are lost on liftoff, so there is nothing to 'harvest'. Better a gouged tile than a space replacement, period. Just touching a broken tile with your finger will cause granules to cling to your finger.
5. Most of the damages to the oribter tiles are of 2 types - either 2 - gouges/chips - like a rock hitting your windshield, or 2 - the whole tile coming off.
6. And between each tile you need a special 'gap filler', exact thickness and perfectly trimmed. This is one of the keys to the process (the Russians copied our whole shuttle, but couldn't make it safely back from space basically because of 'gap filler' problems - and cockpit temps rose to 700 degrees.)
The only real way to solve the problem, is to prevent it, basically by assuring that foam and ice do not peel off the external tank.
Thanks for the suggestions and keep your thinking cap on.
4428 - "not perfect" is a recipe for disaster, and the aerodynamics and heat/cold would rip the 'not perfect' tile replacement right off, leaving a really dangerous big gap in the TPS, rather than a small gouge in the tile.
I don't know a lot about tiles, but I know that before OPF rollover they do a "step and gap" on each tile. They use some laser thingie to measure the gap between each tile and it's neighbors, and the difference in height. What a massive job that would be.
I'm sorry, from reading your replies I think I'm not explaining this very well to you all. I think we are agreed that landing the shuttle with an approximately 6" x 6" hole in the leading edge RCC is not desirable, no?
Sorry, I missed your reference to RCC.
There is no way to 'repair' RCC, period, on the ground or in space. It is like trying to put a broken egg (eg Humpty Dumpty) back together.
And there is no way to replace the RCC, even if you did carry a whole stock of them all into space. Like carrying a spare windshield on an aircraft.
RCC - a whole nother story than tile. Tile repair can be contemplated. RCC - not. And there is no way to secure any repairs to the wing structure.
And how are we going to get a 6" hole in the RCC - only from something falling off the external tank. So, only way to repair this is to make sure nothing falls off to begin with.
Take a look at the earlier posts, with pictures and links. Each piece of RCC. Each one is a work of high tech art, very very different from the other, and it takes months to make. In fact, the RCC is never changed.
Hadn't you seen this yet?
From http://msnbc.msn.com/id/3077565/
"NASA also studied the option of an in-flight repair of the damage, now believed to be a hole punched in one of the leading-edge reinforced panels. “Anything that had heat-absorbing properties” would be stuffed into the hole, Gehman reported, including flexible thermal blankets from the upper surface of the shuttle. Heavy metal objects such as stainless steel tools would be jammed into the breach, as well as bags of water that would be left to freeze. Teflon tape would cover the hole, and be cooled initially by the water ice behind it."
I would think that starting the repair with harvested HRSI would gain more controlled-reentry, flight-time than this weak NASA plan. And again, I repeat, I am *not* saying that this would result in a perfect repair - only in trying to maximize controlled re-entry time.
"Not perfect" *may* be a recipe for disaster, but leaving the RCC hole with repairs unattempted *was certain* disaster.
...life support supplies could well have been stretched to last about 30 days, if an immediate and severe slowdown of crew activities had been ordered. That in turn would have provided just barely enough time, “if all went well,” for the next-in-line shuttle, Atlantis, to launch on a rescue mission around Feb. 12.The rescue mission was “rehearsed with different sets of astronauts, and they all said it could be done,” Gehman reported. “They were standing out in the hallways to volunteer.”
New Moon Rising
http://www.amazon.com/exec/obidos/tg/detail/-/1894959124/ref=pm_dp_ln_b_6/102-6428063-8787311?v=glance&s=books&vi=reviews
NASA says it’s fixed shuttle foam problem
http://msnbc.msn.com/id/5831547/
NASA details defect in shuttle's fatal foam
http://msnbc.msn.com/id/5707670/
Improved how? Until I hear that the solvent used to prep the tank for foaming has been changed, I won't believe that the foam-shedding problem has been solved.
4434 - "Heavy metal objects such as stainless steel tools would be jammed into the breach, as well as bags of water that would be left to freeze. Teflon tape would cover the hole, and be cooled initially by the water ice behind it."
Wow - an interesting way to make a steam boiler shrapnel bomb.
4438 - "Improved how? Until I hear that the solvent used to prep the tank for foaming has been changed, I won't believe that the foam-shedding problem has been solved."
I agree, but at least they have removed the large chunks of unreinforced foam, which are my major bitch.
Read both stories - they are very interesting, very current, and perhaps should be posted here on this thread before they disappear.
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