[meteorite-list] Shuttle Down

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 22 10:18:24 2004
Message-ID: <3E3C192F.9EED323A_at_bhil.com>

Dear List,

    With the caveat that the following is based on the original
flight procedures manual for the orbiter which have been modified
in detail over the years, here's the sequence of significant
flight events after leaving orbit.
    After the OMS de-orbit burn, the hypergolic propellants
(monomethyl hydrazine and nitrogen tetroxide) in the forward RCS
(reaction control system) are dumped. Doing so shifts the
orbiter's central balance point and assists in maintaining entry
attitude (28 to 38 degrees up-pitch). This is done very early in
the descent orbit (about ten minutes before first atmospheric
contact).
    Atmospheric contact begins at around 400,000 feet. Velocity
has increased to about 17,100 mph by the descent (conversion of
potential energy).
    LOS (loss of signal) begins at 312,000 feet. Velocity is
about 16,700 mph. RCS roll thrusters deactivate at exterior
pressure of about 10 psi. Aerodynamic surfaces on wings (elevons)
now control roll. At 20 psi exterior pressure RCS pitch thrusters
deactivate. Aerodynamic surfaces on wings (elevons) now control
pitch.
    Both these events occur before the point of maximum external
heating at 230,000 feet altitude. Velocity is about 15,200 mph to
15,000 mph at this point.
    At about 205,000 feet, the first roll-reversal maneuver
occurs. This is a banking maneuver to control re-entry. A second
and third roll-reversal maneuver are scheduled for about 4
minutes later and five minutes after that. The second would be
below 180,000 feet and the third at about 100,000 feet.
    If the shuttle was lost at 203,000 feet, that would place the
disaster during this first roll-reversal maneuver. The first
thought that comes to mind would almost certainly be catastrophic
wing failure.
    In the earliest portion of the re-entry films, at a point
where re-entry has been nominal, one can see the separation of a
single large component from the shuttle, probably a wing.
    The heaviest, densest and strongest section of the orbiter is
the crew compartment, originally reinforced to withstand up to 20
gee's and strenthened further after the Challender disaster. In
the many telephoto shots of the failed re-entry we're seeing on
TV right now, the central forward "main mass" is almost certainly
the crew compartment.


Sterling K. Webb
Received on Sat 01 Feb 2003 02:00:00 PM PST