Why does the shuttle throttle on ascent?

"Brian Gaff" wrote in message
news
I don't think this is entirely true. I have some old stuff rattling around
in my mind from the 80s which put the rating at least twice this though of
course, only in the thrust direction. After all, the instantaneous
pressures on change can be rather less than subtle.

I agree. I recall that the dynamic air pressure on the shuttle is the
limiting factor, and that just happens to come out to the 3 G's that the
shuttle experiences.

Also, the attachment of the shuttle to the tank is a limiting factor.
--
Jim in NC

If you've got a few hours to kill:

http://spaceflight.nasa.gov/shuttle/...hutref/events/

Sounds like essentially what Dudley said:

To keep the dynamic pressure on the vehicle below a specified level, on
the order of 580 pounds per square foot (max q), the main engines are
throttled down at approximately 26 seconds and throttled back up at
approximately 60 seconds. This also reduces heating on the vehicle.

"Danny Deger" wrote in message
...

Why does the shuttle throttle to 3 Gs on ascent?


The 3 G throttling is done late in the flight (about 7:30)and has nothing to
do with dynamic pressure. It was designed in to allow "regular" people fly
the shuttle.

While in the atmosphere the main engines are throttled back to reduce the
maximum aerodynamic pressure. The grain in the SRB is also designed to have
them go through a period of reduced thrust at about the same time.

Danny Deger

"Danny Deger" wrote in message ...
:
: "Danny Deger" wrote in message
: ...
:
: Why does the shuttle throttle to 3 Gs on ascent?
:
:
: The 3 G throttling is done late in the flight (about 7:30)and has nothing to
: do with dynamic pressure. It was designed in to allow "regular" people fly
: the shuttle.
:
:

Yes, the aerodynamic loads are highest early in the flight so the engines are throttled then back up. The shuttle rolls
over on its back to fake the occupants into feeling 3 gs when in fact the vehicle is pushing 4 gs....

"Blueskies" wrote in message
. net...

"Danny Deger" wrote in message
...
:
: "Danny Deger" wrote in message
: ...
:
: Why does the shuttle throttle to 3 Gs on ascent?
:
:
: The 3 G throttling is done late in the flight (about 7:30)and has
nothing to
: do with dynamic pressure. It was designed in to allow "regular" people
fly
: the shuttle.
:
:

Yes, the aerodynamic loads are highest early in the flight so the engines
are throttled then back up. The shuttle rolls
over on its back to fake the occupants into feeling 3 gs when in fact the
vehicle is pushing 4 gs....

No.
The 3 Gs is at the backs of the occupants (and along that same axis for the
vehicle.) This is the same if they are heads up or heads down.
If you lie with your back on the floor, you feel the same 1 G if your head
is facing north or south.

Tim

"Tim Rogers" wrote in message ...
:
: "Blueskies" wrote in message
: . net...
:
: "Danny Deger" wrote in message
: ...
: :
: : "Danny Deger" wrote in message
: : ...
: :
: : Why does the shuttle throttle to 3 Gs on ascent?
: :
: :
: : The 3 G throttling is done late in the flight (about 7:30)and has
: nothing to
: : do with dynamic pressure. It was designed in to allow "regular" people
: fly
: : the shuttle.
: :
: :
:
: Yes, the aerodynamic loads are highest early in the flight so the engines
: are throttled then back up. The shuttle rolls
: over on its back to fake the occupants into feeling 3 gs when in fact the
: vehicle is pushing 4 gs....
:
: No.
: The 3 Gs is at the backs of the occupants (and along that same axis for the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your head
: is facing north or south.
:
: Tim
:
:

Not talking about facing north or south, they're talking about hanging from your feet or standing upright...

"Blueskies" wrote in message
et...

"Tim Rogers" wrote in message
...
:
: "Blueskies" wrote in message
: . net...
:
: "Danny Deger" wrote in message
: ...
: :
: : "Danny Deger" wrote in message
: : ...
: :
: : Why does the shuttle throttle to 3 Gs on ascent?
: :
: :
: : The 3 G throttling is done late in the flight (about 7:30)and has
: nothing to
: : do with dynamic pressure. It was designed in to allow "regular"
people
: fly
: : the shuttle.
: :
: :
:
: Yes, the aerodynamic loads are highest early in the flight so the
engines
: are throttled then back up. The shuttle rolls
: over on its back to fake the occupants into feeling 3 gs when in fact
the
: vehicle is pushing 4 gs....
:
: No.
: The 3 Gs is at the backs of the occupants (and along that same axis for
the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your
head
: is facing north or south.
:
: Tim
:
:

Not talking about facing north or south, they're talking about hanging
from your feet or standing upright...

Considering the velocity vector is forward, it still doesn't really matter
which way they are.

In article ,
Blueskies wrote:
: The 3 Gs is at the backs of the occupants (and along that same axis for the
: vehicle.) This is the same if they are heads up or heads down.
: If you lie with your back on the floor, you feel the same 1 G if your head
: is facing north or south.

Not talking about facing north or south, they're talking about hanging
from your feet or standing upright...

When all the forces (engine thrust and air drag) are from your back to
your chest or vice versa, being head-up or head-down is precisely the same
as being head-northward or head-southward while lying on your back on
Earth, i.e. it makes not the slightest difference in what you feel.

The shuttle in ascent is in free fall except for thrust and drag. The
ascent path, and the shuttle's orientation during ascent, are carefully
chosen to *avoid* having the wings generate lift. The wings are not
strong enough to provide any useful amount of lift during ascent, and
the dominant concern is to avoid tearing them off by overloading them.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"Blueskies" wrote in message
. net...


snip

Yes, the aerodynamic loads are highest early in the flight so the engines
are throttled then back up. The shuttle rolls
over on its back to fake the occupants into feeling 3 gs when in fact the
vehicle is pushing 4 gs....



For some time now the shuttle rolls to heads up well before 3 G throttling.
This is done so the antennas can communicate with the TDRS satellites.

Danny Deger

Blueskies wrote:
Yes, the aerodynamic loads are highest early in the flight so the engines are throttled then back up. The shuttle rolls
over on its back to fake the occupants into feeling 3 gs when in fact the vehicle is pushing 4 gs....



That also lowers stress on the wings; the Bomarc ramjet missile used to
roll belly-up on the bearing to its target after liftoff, then turn
right-side up once in basically horizontal flight.

Pat