Why does the shuttle throttle on ascent?

Morgans writes:

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it hits
the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary atmosphere
slowing the foam so effectively and rapidly, that causes the relative
closing speeds of the now nearly stationary foam hitting the speeding
shuttle.

That's what he said.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic wrote:
The foam does the damage because of the high speed that it has when it hits
the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary atmosphere
slowing the foam so effectively and rapidly, that causes the relative
closing speeds of the now nearly stationary foam hitting the speeding
shuttle.


That's what he said.

Actually, even with no atmosphere around the foam would still move
rearwards- because the Shuttle is still accelerating after it falls off.

Pat

In article ,
says...

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it hits
the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary atmosphere
slowing the foam so effectively and rapidly, that causes the relative
closing speeds of the now nearly stationary foam hitting the speeding
shuttle.

Isn't that exactly what he said?

--
Duncan

"Morgans" wrote in message
...

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it
hits the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary
atmosphere slowing the foam so effectively and rapidly, that causes the
relative closing speeds of the now nearly stationary foam hitting the
speeding shuttle.
--
Jim in NC


OK, now I'm trying to figure out how to insert a magical, imaginary conveyor
belt into this scenario. :-)

TP in FL (Go Gators!)

"muff528" wrote in message
news:z4Coh.2414$%Q4.1156@trnddc06...

"Morgans" wrote in message
...

"Brian Gaff" wrote

Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Sorry, but you got that one wrong.

The foam does the damage because of the high speed that it has when it
hits the shuttle.

If there was no drag, the foam would not hit with any force; it would be
going the same speed as the shuttle.

When a chunk of foam falls off, it is the drag of the stationary
atmosphere slowing the foam so effectively and rapidly, that causes the
relative closing speeds of the now nearly stationary foam hitting the
speeding shuttle.
--
Jim in NC


OK, now I'm trying to figure out how to insert a magical, imaginary
conveyor
belt into this scenario. :-)

Please tell me you're not referring to that silly Straight Dope thing on a
plane on a conveyor belt.



TP in FL (Go Gators!)

Yes, and it is also why the shedding foam can only do serious damage within
the lower atmosphere, as the drag cannot decelerate the chunks enough to
strike with enough force to do harm at that altitude.

Uh... even with no atmosphere, the rocket is accelerating wrt the
detached foam. I'm not convinced this is insignificant.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Jose, if in space, the foam, when it detached, would be going the same
speed as the rocket, and the only incremental change in velocity would
be that cause by the rocket between the time it detached until it hit.
If the rocket was at say 3 Gs and the foam had 50 feet before it hit,
it would 'fall' for t = (2 * 50 / (3 * 32))^.5 or about a second.
Impact speed would be 100 feet a second or so or about 70 miles an
hour. It's light stuff, probably wouldn't hurt.

Because it's light stuff though, it probably had aerodyamic breaking to
about zero speed when it shed off in the atmosphere, and that would
mean a hypersonic impact. That would hurt -- and did.




On Jan 7, 10:35 am, Jose wrote:
Yes, and it is also why the shedding foam can only do serious damage within
the lower atmosphere, as the drag cannot decelerate the chunks enough to
strike with enough force to do harm at that altitude.Uh... even with no atmosphere, the rocket is accelerating wrt the
detached foam. I'm not convinced this is insignificant.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Jose wrote:
Yes, and it is also why the shedding foam can only do serious damage
within the lower atmosphere, as the drag cannot decelerate the chunks
enough to strike with enough force to do harm at that altitude.

Uh... even with no atmosphere, the rocket is accelerating wrt the
detached foam. I'm not convinced this is insignificant.

Jose

You could figure this out; if there is no air around when the foam sheds
then its velocity in relation to the Shuttle is based on the distance it
covers and how many Gs the Shuttle is accelerating at.
From the bipod ramp to the place where it hit Columbia was about fifty
feet.
Say the Shuttle was accelerating at 3 G's. At one G acceleration is 32
ft. sec/per sec, so at 3 G's it's three times that, or around 100 ft.
per second, so the foam takes around around 1/2 second to reach the wing
after release (actually a little more than 1/2 second, as it's picking
up more velocity in relation to the shuttle in the last 1/2 second than
the first 1/2 second, so let's call it .7 seconds) So, it travels 50
feet in .7 seconds, or around 80 feet per second at impact. That works
out to around 55 mph at impact for that hypothetical case. IIRC, the
piece that hit Columbia was doing around 400 mph, so velocity is around
1/8 of that that damaged Columbia's wing. Every time you double the
velocity of a impactor, you quadruple its energy, so something going 55
mph isn't going to pose much of a threat at all, as if I'm doing my math
right it only has around 1.6% of the energy of the Columbia impact.

Pat

"Danny Deger" wrote in message
...
Why does the shuttle throttle to 3 Gs on ascent?


The answer is:

So Navy Fighter pilots can fly the shuttle :-)

Danny Deger

P.S. I was an Air Force figher pilot.

"Danny Deger" wrote in message
...

"Danny Deger" wrote in message
...
Why does the shuttle throttle to 3 Gs on ascent?


The answer is:

So Navy Fighter pilots can fly the shuttle :-)

Ah, is this so that they can let the AF pilots catch up?

Danny Deger

P.S. I was an Air Force figher pilot.

I was wondering why you of all people was asking this. :-)