Re: STS-107 from Mt. Hamilton pictures posted

From: Markus Mehring (
Date: Sun Feb 02 2003 - 22:56:41 EST

  • Next message: Ted Molczan: "RE: Shuttle Reentry Observations"

    On Sun, 02 Feb 2003 18:05:20 -0800, you (David Anderman <>)
    >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
    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

    This archive was generated by hypermail 2b29 : Sun Feb 02 2003 - 23:21:39 EST