"Charles Buckley" wrote in message
...
Jim Oberg wrote:
Did anybody capture good views of the 'ring of fire' effect (with
apologies to Eric Flint) just prior to MECO? Since the ring collapsed
at MECO I'm presuming it was the shock wave of the engine plume and
the upper atmosphere. Even though shot backwards at 3000 meters/sec,
the combustion productions were impacting ambient upper atmosphere at
about that same speed because the stack was nearly at orbital velocity
(8000 meters/sec).

The light was not the plume -- LH2/LO2 flame is essentially invisible.

Why it should be green is a bigger question -- I wonder about color
imbalance
in the low light level situation. Ground observers were seeing orange and
yellow-orange colors, not green -- and that's the proper wavelength for
the
source of the light, atomic oxygen recombination immediately following O2
dissociation from molecular impacts.

Ground observers (I was one) are looking usually at low elevations through
thick atmospheric attenuation, so only red-yellow gets through. Green is
associated with excited (not ionized) oxygen beginning at altitudes above 60
km (similar to aurora) so it is not unreasonable for what was seen around
the orbiter. Incidentally the same glow was seen on the leading edges of
the OMS pods.