Haze around shuttle during launch

[Gregory Fedor]

In article <89...@borg.cs.unc.edu>, le...@cs.unc.edu (Jon Leech) writes:
|>
|> I'm watching the Discovery launch, and saw an odd phenomenon. When
|> passing through about 20K feet, a band of (apparently) haze became
|> visible circling the orbiter around the cockpit. It gradually moved
|> about halfway down the fuselage over the span of a few seconds, then
|> disappeared. Any ideas what this might be?
|> --

If I am not mistaken (and I'm sure some aeromechanical engineer out there
will correct me if I'm not) what you observed is not haze, but a shock wave
generated by the shuttle stack as it passes through a point of maximum
dynamic pressure. For a computer engineer like myself, this means the
shuttle is moving at a high rate of speed relative to the dense atmosphere
it is in at the time. If you notice, they throttle back the engines at
around this point to help reduce the dynamic pressure. After that point
in the flight the now famous "Go at throttle up" call is made.

I have also often seen this effect on aircraft passing through moist (i.e.
dense) air. The aircraft (or shuttle in this case) causes an increase in
pressure in the air just in front of it. This increase in pressure
squeezes the air, and if it is fairly moist it will condense into a haze
like cloud.

Okay all you aero guys, how did I do? Please correct me if I'm wrong.
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[John Logajan]

smf...@endeavour.lerc.nasa.gov (Gregory Fedor) writes:
>I have also often seen this effect on aircraft passing through moist (i.e.
>dense) air. The aircraft (or shuttle in this case) causes an increase in
>pressure in the air just in front of it. This increase in pressure
>squeezes the air, and if it is fairly moist it will condense into a haze
>like cloud.

My guess is the condensation occurs in the decompression immediately following
the compression you just mentioned. You will often see such fog on the
top side and aft of winged aircraft but not on the bottom side. Cloud chambers
work by sudden decompression also.
--
- John Logajan MS010, Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- log...@network.com, 612-424-4888, Fax 612-424-2853

[Jon Leech]

I'm watching the Discovery launch, and saw an odd phenomenon. When
passing through about 20K feet, a band of (apparently) haze became
visible circling the orbiter around the cockpit. It gradually moved
about halfway down the fuselage over the span of a few seconds, then
disappeared. Any ideas what this might be?
--

Jon Leech (le...@cs.unc.edu) __@/
``Before I refuse to take your questions, I have an opening statement.''
- Ronald Reagan

[Gary Morris @wayward]

In <89...@borg.cs.unc.edu> le...@cs.unc.edu (Jon Leech) writes:
> I'm watching the Discovery launch, and saw an odd phenomenon. When
>passing through about 20K feet, a band of (apparently) haze became
>visible circling the orbiter around the cockpit. It gradually moved
>about halfway down the fuselage over the span of a few seconds, then
>disappeared. Any ideas what this might be?

There is an area of low pressure along the upper surface of any lifting
body or wing, and when air with moisture content near saturation enters
the low pressure, it is suddenly over saturated and the moisture
condenses into a cloud. This is what you were seeing.

It can also been seen above aircraft wings, under high wing loading,
such as landing and taking off, or during high-g turns. The higher the
pressure drop the more you will see this effect.
--GaryM
--
Gary Morris Internet: ga...@telesoft.com
KK6YB UUCP: ucsd!telesoft!garym
TeleSoft, San Diego, CA Phone: +1 619-457-2700

[William F. Hagen]

This phenomenom is always demonstrated
at fighter jet airshows by flying the
fighters at just below mach 1 right in
front of the audience. As sthe jet just pierces the sound barrier the
fog arount the plane is quite pronounced!

[Gavin Eadie]

> I'm watching the Discovery launch, and saw an odd phenomenon. When
>passing through about 20K feet, a band of (apparently) haze became
>visible circling the orbiter around the cockpit. It gradually moved
>about halfway down the fuselage over the span of a few seconds, then
>disappeared. Any ideas what this might be?

It's water in the air being condensed by the shock wave spreading
back from the shuttle.