Why does the shuttle throttle on ascent?

On Sat, 13 Jan 2007 16:28:30 -0600, Pat Flannery
wrote:

Coincidentally, History Channel this morning ran a show about the ICBM
Race and included Polaris launch footage. That roll was damned
impressive!

Is this the show that has the footage of the solid-fueled Minuteman
launch identified as a Titan II?

Yep. They show nearly identical footage a moment later and correctly
identify the Minuteman II.

Brian

"Jason A. Ciastko" wrote:

IIRC (I'll check with my co-worker that was on boomers), but I believe the
vertical launch tubes the hold the ICBMs are "tilted" slightly outboard and
are not truly vertical.

Nope.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

(Henry Spencer) wrote:

Could be an engine-startup transient that the guidance system then sorted
out (in particular, transient flow separation during startup is not at all
rare, and can briefly produce large unwanted thrust vectoring), some sort
of guidance/control-startup transient, or a deliberate "get a bit of
horizontal distance from the sub immediately" maneuver.

Possibly, no, somewhat.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

In article ,
Pat Flannery wrote:
A 747 with an SSME in the tail...

...It makes sense though... since you're storing LOX and LH2 on the 747
anyway for pumping into the ET at altitude, you might get some use out
of them to up its maximum release altitude at the same time.

If memory serves, Boeing eventually concluded that this wasn't a good way
to do it -- too much structural strengthening needed? They looked instead
at injecting fuel into the bypass ducts of the turbofans (!), and
concluded that they could get a very large thrust increase that way, and
that it wouldn't hurt the engines if you kept the duration short.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"Derek Lyons" wrote in message "Jason A. Ciastko"
wrote:

IIRC (I'll check with my co-worker that was on boomers), but I believe the
vertical launch tubes the hold the ICBMs are "tilted" slightly outboard
and
are not truly vertical.

Nope.

D.

Getting old is h*ll...

Thanks Derek. I'll stay with my swing wings now....


--
Jason A. Ciastko
Referee's are the only guys who can rob you
and then get a police escort out of the stadium.

Brian Thorn wrote:

Yep. They show nearly identical footage a moment later and correctly
identify the Minuteman II.


Then, right at the end of the show, they had footage of a Titan II
taking off.
Editors should know more about their subject.
My all-time favorite in this regard is still the Discovery Wings episode
on the B-17, where we learn that it's armed with ten _50 mm_ machine
guns. How would you like to be in a FW-190 coming into a squadron of
those? On the way home from a mission they could descend to low altitude
and engage in tank busting.
Still if nothing else it did have some interesting footage of Soviet
missiles, including that loopy Scud launcher that rises up to the top of
the submarine's conning tower.

Pat

Henry Spencer wrote:
If memory serves, Boeing eventually concluded that this wasn't a good way
to do it -- too much structural strengthening needed? They looked instead
at injecting fuel into the bypass ducts of the turbofans (!), and
concluded that they could get a very large thrust increase that way, and
that it wouldn't hurt the engines if you kept the duration short.

Somewhat similar to the way NASA looked into upping their SR-71's
performance via H2O2 injection into the afterburners.
But in that case the improvement in performance was pretty marginal.
Borrowing a page from the D-21/M-12 program, I wonder if you could use
the mini-shuttle's engines for the final climb, while constantly topping
the ET up from the internal tankage till release.

Pat

Pat Flannery wrote:

My all-time favorite in this regard is still the Discovery Wings
episode on the B-17, where we learn that it's armed with ten _50
mm_ machine guns.

Surely you (or Discovery Wings) meant ten 12.7 mm (0.5") machine
guns?

Jim Davis

Jim Davis wrote:

Surely you (or Discovery Wings) meant ten 12.7 mm (0.5") machine
guns?



That's what they obviously meant, but the narrator called them "50 mm
machine guns".
How would you like to be a waist gunner with one of those.... that would
be empowerment, wouldn't it?
The Germans did take after bombers with Me-410s armed with a single 50
mm cannon though.
They also shoehorned one of those into a prototype Me-262 jet's nose:
http://www.warbirdsresourcegroup.org...es/lrg0208.jpg

Pat

The shuttle actually throttles back twice during ascent. The first time
is at max Q. This is not a 3 G situation for the vehicle. After the
solids are dropped, the shuttle again throttles back in the last 30
seconds or so before main engine cut-off, so as to not exceed 3 G's of
forward acceleration when the fuel is almost gone. Whether this is due
to a structural or other reason, I'm not sure. But structural makes the
most sense for several reasons, weight being the primary one.

Bud


Jim wrote:
Thanks Danny, I had a good belly laugh from that one.
Jim
wrote in message
ps.com...

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

Danny Deger

Because structurally the shuttle vehicle is only stressed for 3 g's. If
they didn't throttle back in the late stages of the ascent when the
fuel is almost gone and the vehicle is light, it would exceed this
level of acceleration. Since the engines are liquid fueled, they can
hold full thrust until the fuel is gone.

Bud