On Sun, 02 Feb 2003 18:05:20 -0800, you (David Anderman <davida@cwo.com>) wrote: >This really creates the impression that all that unusual stuff flying off >the Shuttle over California may be more an artifact of these images getting >a lot more scrutiny than the "normal" flyover images. I wonder what kinds >of stuff would show up in videos of prior flyovers if they were subject to >the same scrutiny as yesterday's video. Not too much. As Dale has already pointed out, there shouldn't be any pieces falling behind, none at all. Any irregularities in the re-entry fireball brightness, that might occur due to a variety of reasons, ought to manifest themselves as singular flicker around the Shuttle, not as indivual objects or parts of any kind. The resulting plasma trail ought to be a fairly regular, steady arc in the sky, without any major variations in color or brightness until it starts to dissolve much later on. Unfortunately I've never witnessed a Shuttle re-entry myself, but there are enough pictures available -also fairly hires- that show what it's supposed to look like under normal conditions, apart from the laws of physics that govern its appearance anyway. At the risk of boring people who know this, but only to reiterate in an understandable manner how the heat shield works, for those who don't know. Corrections are welcome, I'm not a rocket scientist (I only play one on the Internet). You might have heard quotes from people who saw the Columbia breakup and at first attributed the multiple pieces and trails to the heat shield working in a regular fashion. This is not how the Shuttle heat shield works. The shield is designed to be heat resistant without conducting the heat through, that is it can be glowing fiery hot on one side and fairly cool on the other side of the material, and the latter is of course where the actual aluminium airframe of the Shuttle is, which needs to be protected from heat. The fireball that can be seen is ionized air, plasma that occurs as the Shuttle hits the thickening atmosphere at breakneck speed. Actually this plasma doesn't even really touch significant parts of the heat shield (the Shuttle's edges are more affected, obviously). This is a fundamentally different design from manned capsules, such as an Apollo or Soyuz capsule, which had and have an ablative heat shield that is supposed to burn (or melt) off to quite some extent during the entry phase, the burned off fiery parts of which is what people apparently had in mind when thinking of trailing pieces that "belong there". Lots of sample pictures of ablative shields dissolving are available from the Apollo era, and they were widely published back then. In case of the Shuttle, such trailing parts most definitely do not belong there, since, as I said, it's a completely different type of shield. (The point to make design-wise here is that the Shuttle is a winged craft that enters belly first and decelerates in the atmosphere more gradually and over a longer period of time, with lower G-loads and also at much lower temperatures, than a capsule with an ablative shield.) A loss of heat shield tiles doesn't necessarily equal major damage. Tile loss has occured before without much of a negative effect, actually this was a big issue early in the Shuttle program when the tile glue mixture was yet to be improved. There even were incidents where tile loss and/or damage resulted in plasma burning into the airframe structure and melting structural parts, even to the point of complete physical burnthrough on the exterior. This is obviously serious, but it didn't result in a loss of vehicle. When you today hear certain news media report that "experts think the cause of the STS-107 accident might be a failed heat shield", you ought to dismiss that as generally too simplistic news-agency food. The whole story must be much more intricate regarding what kind of damage occured where, when, and why. CU! Markus P.S.: Does anyone notice how I always include some remotely observational stuff to keep this halfway on-topic? :/ ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Sun Feb 02 2003 - 23:21:39 EST