Why does the shuttle throttle on ascent?

Morgans wrote:

Of course, on some engines, that was grounds for grounding the aircraft to
inspect the engine, to see if it was damaged from exceeding 100% power.

On the P-51 Mustang, this was called "War Emergency Power"; it would
give some extra zip, but would also destroy the engine in around ten
minutes after engaging it. :-)

Pat

Stubby wrote:

There was a famous story of gold shippers that moved quantities of
gold from San Francisco to Anchorage in the 1800s. Of course they
carefully measured the gold before and after, presumably using a
spring scale rather than a balance. The bankers concluded a little
bit of gold was being lost from every shipment. After a lot of
finger-pointing, they identified the difference in gravity as the
source of the difference.
Shouldn't that be the other way around? the gold would weigh less as you
approached the equator due to the spinning of the Earth causing
centrifugal force on it.

Pat

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

On Sun, 07 Jan 2007 15:01:21 -0600, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:



Stubby wrote:

There was a famous story of gold shippers that moved quantities of
gold from San Francisco to Anchorage in the 1800s. Of course they
carefully measured the gold before and after, presumably using a
spring scale rather than a balance. The bankers concluded a little
bit of gold was being lost from every shipment. After a lot of
finger-pointing, they identified the difference in gravity as the
source of the difference.
Shouldn't that be the other way around? the gold would weigh less as you
approached the equator due to the spinning of the Earth causing
centrifugal force on it.

Plus the surface is a little farther from the center, reducing the
apparent weight further. Maybe he means from Anchorage to San
Francisco, perhaps from the Klondike.

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

Brian Thorn wrote:
No, throttling high performance rocket engines is still somewhat
difficult and risky, despite the Shuttle making it look easy. NASA has
always worried that the Mains won't throttle back up as they are
intended, which would mean the crew would be going for a swim.



And considering what those ditching model tests looked like, this would
be a real good opportunity to use the parachutes. :-)

Pat

Rand Simberg wrote:
Plus the surface is a little farther from the center, reducing the
apparent weight further. Maybe he means from Anchorage to San
Francisco, perhaps from the Klondike.


That's what I was thinking also; gold would be being shipped southwards
from Alaska, not to it.

Pat

"Pat Flannery" wrote

Shouldn't that be the other way around? the gold would weigh less as you
approached the equator due to the spinning of the Earth causing
centrifugal force on it.

Exactly what was intended. As it was weighed closer to the equator, it
would weigh less, thus making the people who owned the gold think that
someone had been taking some of it during shipment.
--
Jim in NC

Pat Flannery writes:

On the P-51 Mustang, this was called "War Emergency Power"; it would
give some extra zip, but would also destroy the engine in around ten
minutes after engaging it. :-)

One wonders what sort of emergency would justify running the engine a
bit faster for just ten minutes, and then replacing the entire
aircraft.

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

"Mxsmanic" wrote in message
...
Danny Deger writes:

Why does the shuttle throttle to 3 Gs on ascent?

The real Shuttle snip

As opposed to your world of simulation.

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DW