500 mph?

[Ron Adair]

I have never seen an explanation of the calculation to arrive at 500 mph being
the velocity with which the foam hit the shuttle's wing. It seems to me that
the assertion that the foam would decelerate at such a huge rate that within 50
feet or so it was already travelling at 500 mph less than the shuttle itself
appears puzzling. Any comments. Just wanting to know. - Ron

[Mike Dennis]

It's not about physics. It's all about frame rates. They know the film's
frame rate and they know the size of the vehicle. All they do is measure
how far the debris moves from frame to frame. The can even nail down the
approximate direction (vector) of the debris based on how where it comes
from and what it hits. That's far more accurate than the physics B.S. that
some have been throwing around.

Columbia was traveling far faster than 500mph, so it's not that simple. The
physics calculations needed to come up with 500mph are incredibly
complex--and, IMHO, pointless in light of the visual evidence.


"Ron Adair" > wrote in message
...
> I have never seen an explanation of the calculation to arrive at 500 mph
being
> the velocity with which the foam hit the shuttle's wing. It seems to me
that
> the assertion that the foam would decelerate at such a huge rate that
within 50
> feet or so it was already travelling at 500 mph less than the shuttle
itself
> appears puzzling. Any comments. Just wanting to know. - Ron
>

[Mike Speegle]

In news:JazzMan > typed:
> Ron Adair wrote:
> >
> > I have never seen an explanation of the calculation to arrive at
> > 500 mph being the velocity with which the foam hit the shuttle's
> > wing. It seems to me that the assertion that the foam would
> > decelerate at such a huge rate that within 50 feet or so it was
> > already travelling at 500 mph less than the shuttle itself appears
> > puzzling. Any comments. Just wanting to know. - Ron
>
>
> Man, isn't this horse dead enough yet? Geez....

No!!! Keep beating the bejeezus out of it, over, and over, and....
--
Mike
__________________________________________________ ______
"Colorado Ski Country, USA" Come often, Ski hard,
Spend *lots* of money, Then leave as quickly as you can.

[Jon Berndt]

"Ron Adair" > wrote in message

> I have never seen an explanation of the calculation to arrive at 500 mph
being
> the velocity with which the foam hit the shuttle's wing. It seems to me
that
> the assertion that the foam would decelerate at such a huge rate that
within 50
> feet or so it was already travelling at 500 mph less than the shuttle
itself
> appears puzzling. Any comments. Just wanting to know. - Ron

The CAIB today posted an explanation:

http://www.caib.us/news/documents/impact_velocity.pdf

Jon

[Bruce Palmer]

JazzMan wrote:

> Ron Adair wrote:
>
>>I have never seen an explanation of the calculation to arrive at 500 mph being
>>the velocity with which the foam hit the shuttle's wing. It seems to me that
>>the assertion that the foam would decelerate at such a huge rate that within 50
>>feet or so it was already travelling at 500 mph less than the shuttle itself
>>appears puzzling. Any comments. Just wanting to know. - Ron
>
>
>
> Man, isn't this horse dead enough yet? Geez....

Apparently not. The CAIB put up a PDF document today that answers this
question. It's titled "Foam Impact Velocity Determination" and can be
found at: "http://www.caib.us/news/documents/impact_velocity.pdf"

--
bp
Proud Member of the Human O-Ring Society Since 2003

[hawk]

Well, the frame rates on the photos are what they used to determine the
speed. But, think about it this way. Drive down the road at 60 mph and
throw a napkin out the window. The 60 mpg wind blowing past the window
will rapidly accelerate the napkin to the rear. I imagine the shuttle
speed was well over 500 mph at the time of the incident.

hawk

Ron Adair wrote:
> I have never seen an explanation of the calculation to arrive at 500 mph being
> the velocity with which the foam hit the shuttle's wing. It seems to me that
> the assertion that the foam would decelerate at such a huge rate that within 50
> feet or so it was already traveling at 500 mph less than the shuttle itself
> appears puzzling. Any comments. Just wanting to know. - Ron
>

[Doug...]

In article >, says...
> Well, the frame rates on the photos are what they used to determine the
> speed. But, think about it this way. Drive down the road at 60 mph and
> throw a napkin out the window. The 60 mpg wind blowing past the window
> will rapidly accelerate the napkin to the rear. I imagine the shuttle
> speed was well over 500 mph at the time of the incident.

To be a little more accurate, your hypothetical napkin is already
accelerated to 60 mph. The air through which the car is traveling is at
an ambient speed relative to the ground -- let's assume for the moment
that it's a still day -- and there is a boundary layer around the car
where the air is being accelerated by the motion of the car. It's a very
thin boundary layer, though, and actually moves into the car if you have
a window open.

When you toss the napkin out the window, it becomes a separate system
from the car, which is of course maintaining its accelerated state with
its engine. As the napkin passes outside of the boundary layer, it is
*decelerated* from its original 60 mph speed by the still air. Because
it has little mass and a relatively large surface area, it is decelerated
*very* quickly. It quickly matches the acceleration state of the
surrounding air. From the point of view of the person who dropped the
napkin, it *seems* to have been accelerated away from him, but in fact
his accelerated car is moving *away* from it.

Now let's assume that another car is following the first car, also
traveling at 60 mph. If the napkin stays up in the air until the second
car arrives, the napkin will strike the second car at 60 mph. The napkin
has not been accelerated to strike the second car, it has assumed the
speed of the surrounding air. The napkin hits the second car at the same
speed that a dandelion seed hanging in the air would hit it.

Now, the situation on the ascending shuttle stack was somewhat different.
The stack was continuing to accelerate, not just maintaining a given
speed, so anything dropped into the airstream was not only going to
decelerate to the speed of the air around it, the stack was still adding
speed relative to that air. So while the debris was decelerating, the
stack was also accelerating. Also, the boundary layer is far more
complex around the ascending shuttle stack than around a car -- there is
turbulence in the airstream surrounding it, caused by the relatively non-
aerodynamic form of the attachment struts, by the lift generated by the
orbiter's wing, and by pressure from the rocket motors. The complex
nature of the boundary layer and its associated turbulence is why the
time measurement of the speed with which the foam moved from the bipod
ramp to the wing is the simplest way to calculate its impact speed. It's
not simple to model the complex airstream around the ascending stack.
There are many, many forces acting on the airstream, some of which are
variable from moment to moment.

I will say this -- I reviewed a lot of the existing tape and film of the
foam strike last night, and noticed once again that it *appears* that the
main piece of foam spends at least two frames (and possibly three)
tumbling at the level of the forward attach point before moving down the
stack to the wing. Perhaps it simply has not fully detached from the
bipod ramp at that point, but it definitely moves *forward* into the
airstream at least once. This would argue that there were turbulent
airflows around the bipod ramp area which were moving in directions other
than directly fore-to-aft. As soon as the foam moves away from the bipod
area, though, the time it takes to reach the wing proves definitely that
it decelerated to a relative speed differential of roughly 500 mph to
that of the orbiter. There's just no way to question it -- it's a matter
of physical laws.

--

It's not the pace of life I mind; | Doug Van Dorn
it's the sudden stop at the end... |