Why does the shuttle throttle on ascent?

Why does the shuttle throttle to 3 Gs on ascent?

Danny Deger

Danny Deger writes:

Why does the shuttle throttle to 3 Gs on ascent?

The real Shuttle throttles back during ascent at a certain point in
order to reduce aerodynamic stresses as it rises through the
atmosphere.

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Danny Deger wrote:
Why does the shuttle throttle to 3 Gs on ascent?

I don't know about G's but the shuttle adjust the engine thrust
up and down at various times in the launch based on the dynamic
pressures involved.

Danny Deger wrote:
Why does the shuttle throttle to 3 Gs on ascent?

As the fuel is burned/jettisoned the engines have a smaller vehicle mass
to accelerate. So to maintain an acceptable acceleration level, you
throttle back engines.

Also, as you leave the atmopsphere, there is less and less air resistance,
so you also need less power to maintain the desired acceleration level.

And early in the ascent, they throttle back to ensure the shuttle's air
speed isn't too great as it travels through the still dense atmosphere
since it would create too much aerodynamic drag.

"Ron Natalie" wrote in message
m

I don't know about G's but the shuttle adjust the engine thrust
up and down at various times in the launch based on the dynamic
pressures involved.

"'Go' for throttle up."

My generation's equivalent of "Where were you when Kennedy got shot?"

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

Danny Deger

As the shuttle ascends, the dynamic pressure (in slugs/sq.in) increases as
the square of the velocity. The shuttle is throttled back to 65% thrust to
avoid over stress at a speed computed under what is called critical q.
As the shuttle ascends, it is ascending into lower air density (which of
course transfers into a lowering dynamic pressure). The throttling back
takes the shuttle through a transition area during the ascent that ends as
the lowering air density meets the parameters that allow throttle up. This I
believe occurs at about 35 to 37K.
The point where lowering air density meets the ability to throttle up again
is the max q for the shuttle. (Max q meaning maximum dynamic pressure)
After reaching max q, the shuttle is go for throttle up as the increasing
velocity past max q will never exceed the structural limitations of the
shuttle due to it's entrance into lower air density that doesn't have the
ability to overstress the structure.
Hope this helps a bit.
Dudley Henriques

In article ,
Danny Deger wrote:
Why does the shuttle throttle to 3 Gs on ascent?

This is partly for the benefit of the passengers -- it's thought that a
healthy adult can be expected to take about 3G without testing -- and
partly to limit structural loads. (The Saturn V first stage shut down
its center engine early for the latter reason.)

There is also an earlier bit of throttle reduction, during the SRB burn,
done to keep speed down until the shuttle is out of the thickest air.
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On the way;

DH

"Richard Riley" wrote in message
...
On Sat, 6 Jan 2007 22:10:34 -0500, "Dudley Henriques"
wrote:


Hope this helps a bit.
Dudley Henriques

Dudley, would you email me off list? (not on this topic)

Richard at riley dot net

Dudley:

Isn't dynamic pressure expressed in pressure units, pounds per
square inch (or SI, Pascals: newtons/sq. meter)? Mass density, which
you mention later, is in slugs/cu.in or cu.ft (or SI, Kg/cu.meter).

Thanks for all your good posts, I've learned a lot from them over
the years.

David

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

Danny Deger

As the shuttle ascends, the dynamic pressure (in slugs/sq.in) increases as
the square of the velocity. The shuttle is throttled back to 65% thrust to
avoid over stress at a speed computed under what is called critical q.
As the shuttle ascends, it is ascending into lower air density (which of
course transfers into a lowering dynamic pressure). The throttling back
takes the shuttle through a transition area during the ascent that ends as
the lowering air density meets the parameters that allow throttle up. This I
believe occurs at about 35 to 37K.
The point where lowering air density meets the ability to throttle up again
is the max q for the shuttle. (Max q meaning maximum dynamic pressure)
After reaching max q, the shuttle is go for throttle up as the increasing
velocity past max q will never exceed the structural limitations of the
shuttle due to it's entrance into lower air density that doesn't have the
ability to overstress the structure.
Hope this helps a bit.
Dudley Henriques

"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.