LOX tank on top?

I read that the much denser LOX is on the top[*] of the ET, with the
LH below it. This seems counter-intuitive. I would think from a
structural point of view, you would want the heavier stuff on the
bottom, and it would also move the vehicle's CG aft, which I would
think would improve aerodynamic stability.

I assume NASA didn't just flip a coin to decide which goes on top, so
there must be more to it that that. What's the real answer?
[*] I'm not sure what the coordinate system is here. Is the pointy
end the top or the front?

(Roy Smith) writes:
I assume NASA didn't just flip a coin to decide which goes on top, so
there must be more to it that that. What's the real answer?

I think it's due to center-of-mass considerations. The loaded LOX tank is
heavier than the loaded LH2 tank, and you need to be able to be sure
that the center of mass of the combined Shuttle/ET is located far
enough forward that the thrust line from the SSMEs can pass through it.

--
Richard W Kaszeta

http://www.kaszeta.org/rich

Roy Smith wrote:
I read that the much denser LOX is on the top[*] of the ET, with the
LH below it. This seems counter-intuitive. I would think from a
structural point of view, you would want the heavier stuff on the
bottom, and it would also move the vehicle's CG aft, which I would
think would improve aerodynamic stability.


To make a missile (a rocket or an arrow, etc)
stable in the atmosphere, the center of gravity
should be forward of the center of pressure, so
mass forward actually increases stability.
Model rocketeers often find themselves adding
mass to the nose of their rockets (or adding fin
area) to improve stability.

- Ed Kyle

So true Ed,

If the center of gravity is behind the center of pressure during
subsonic flight - all anomalous aerodynamic events add up to a spiraling
"out of control" situation.

AFIK, France is the only nation that launches over downstream populations.

I don't think they will launch many things from Europe anymre - since
they have bought a launch territory in "BRAZIL" Sadly, so many islands
are being scarffed up by sons of global hyper-capitalists that no-one is
immune from Karl Rove.'s machinations.

iThanks,

Rick





ed kyle wrote:
Roy Smith wrote:

I read that the much denser LOX is on the top[*] of the ET, with the
LH below it. This seems counter-intuitive. I would think from a
structural point of view, you would want the heavier stuff on the
bottom, and it would also move the vehicle's CG aft, which I would
think would improve aerodynamic stability.



To make a missile (a rocket or an arrow, etc)
stable in the atmosphere, the center of gravity
should be forward of the center of pressure, so
mass forward actually increases stability.
Model rocketeers often find themselves adding
mass to the nose of their rockets (or adding fin
area) to improve stability.

- Ed Kyle

"Richard Kaszeta" wrote in message
...
(Roy Smith) writes:
I assume NASA didn't just flip a coin to decide which goes on top, so
there must be more to it that that. What's the real answer?

I think it's due to center-of-mass considerations. The loaded LOX tank
is
heavier than the loaded LH2 tank, and you need to be able to be sure
that the center of mass of the combined Shuttle/ET is located far
enough forward that the thrust line from the SSMEs can pass through it.

--
Richard W Kaszeta

http://www.kaszeta.org/rich

But isn't the LH2 tank twice as big as the LOX tank?

" George" wrote in news:TOfGe.218743
$nG6.143310@attbi_s22:


"Richard Kaszeta" wrote in message
...
(Roy Smith) writes:
I assume NASA didn't just flip a coin to decide which goes on top, so
there must be more to it that that. What's the real answer?

I think it's due to center-of-mass considerations. The loaded LOX tank
is
heavier than the loaded LH2 tank, and you need to be able to be sure
that the center of mass of the combined Shuttle/ET is located far
enough forward that the thrust line from the SSMEs can pass through it.

But isn't the LH2 tank twice as big as the LOX tank?

Yes. And LOX is eight times as dense as LH2. Your point is?

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

"Jorge R. Frank" wrote in message
...
" George" wrote in news:TOfGe.218743
$nG6.143310@attbi_s22:


"Richard Kaszeta" wrote in message
...
(Roy Smith) writes:
I assume NASA didn't just flip a coin to decide which goes on top, so
there must be more to it that that. What's the real answer?

I think it's due to center-of-mass considerations. The loaded LOX tank
is
heavier than the loaded LH2 tank, and you need to be able to be sure
that the center of mass of the combined Shuttle/ET is located far
enough forward that the thrust line from the SSMEs can pass through it.

But isn't the LH2 tank twice as big as the LOX tank?

Yes. And LOX is eight times as dense as LH2. Your point is?

--
JRF

Just pointing out a fact is all.

Rick Nelson wrote:

AFIK, France is the only nation that launches over downstream populations.

I don't think they will launch many things from Europe anymre - since
they have bought a launch territory in "BRAZIL" Sadly, so many islands
are being scarffed up by sons of global hyper-capitalists that no-one is
immune from Karl Rove.'s machinations.

France?

ESA launch from French Guiana but not over downstream populations
(unless you are counting seabirds)


--

France?

ESA launch from French Guiana but not over downstream populations
(unless you are counting seabirds)

yes, ESA launches from a spot with ocean in the north and east so
either for polar or obital launches , the rockets fly other the sea for
thousands of miles