Why does the shuttle throttle on ascent?

Pat Flannery wrote:

http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld053.htm

A 747 with an SSME in the tail...

[Note to r.a.p. - that's a Space Shuttle Main Engine]

Mary Pegg wrote:
A 747 with an SSME in the tail...
The _New_ Boeing SST proposal! ;-)
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.

Pat

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. |

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