Rockets not carrying fuel.

In article ,
Rand Simberg wrote:
Those numbers don't look right. Shouldn't the LOX be about 8
times the LH?

Yes, if the propellant were burned stoichiometrically. But for
reasons of propulsion efficiency, it's not.
6:1 turns out to be about the best mixture ratio, because the value of
more low-mass molecules (hydrogen) turns out to provide a higher
specific impulse than getting the maximum energy from the reaction.

In fact, it's a bit more complicated than that. Hydrogen improves the
exhaust properties so much, at so little cost in mass, that about 4:1
would yield the highest specific impulse.

But hydrogen is so bulky that you would pay a significant price for this,
first at the engine level and then at the vehicle level. At the engine
level, the hardware gets bigger and the required pump power goes up a lot
(pumps pump volume, not mass). At the vehicle level, the huge tanks are a
problem in several ways, not least being mass.

So the bottom line is that while you get maximum specific impulse at 4:1,
this costs you so much in extra hardware mass that it's not worth it --
you get maximum *vehicle* performance at leaner mixture ratios. Some
early hydrogen stages, designed before hydrogen's problems were well
understood, ran at 5:1, but modern belief is that 6:1 is about optimal.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

On Tue, 29 Jul 2003 15:49:56 GMT, in a place far, far away,
(Henry Spencer) made the phosphor on my monitor
glow in such a way as to indicate that:

In article ,
Rand Simberg wrote:
Those numbers don't look right. Shouldn't the LOX be about 8
times the LH?

Yes, if the propellant were burned stoichiometrically. But for
reasons of propulsion efficiency, it's not.
6:1 turns out to be about the best mixture ratio, because the value of
more low-mass molecules (hydrogen) turns out to provide a higher
specific impulse than getting the maximum energy from the reaction.

In fact, it's a bit more complicated than that.

Isn't it always? ;-)

Some
early hydrogen stages, designed before hydrogen's problems were well
understood, ran at 5:1, but modern belief is that 6:1 is about optimal.

Of course, unlike the bonding energy and mass of hydrogen and oxygen,
structural techniques are subject to change and improvement...

--
simberg.interglobal.org * 310 372-7963 (CA) 307 739-1296 (Jackson Hole)
interglobal space lines * 307 733-1715 (Fax) http://www.interglobal.org

"Extraordinary launch vehicles require extraordinary markets..."
Swap the first . and @ and throw out the ".trash" to email me.
Here's my email address for autospammers:

"Rene Tschaggelar" wrote ...
Doug Ellison wrote:

I believe it's only possible to pump fluids to a certain height - after
which you just cant push any more

Since nanotubes are being proposed, isn't the liqid being pulled up
by itself, by kapillary forces presumed the surface is wettable ?

That would be fun.

How many nano tubes "hundreds of kilometers long" would you need
to ensure your rocket is getting fuel fast enough to accelerate upwards
if it's depending on capillary action? ;-)

In article ,
Robert Clark wrote:
From this web page, the weight of the shuttle external tank with the
liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds
per second and the amount of hydrogen 465 pounds per second.

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?
What would be the fuel requirements for a rocket that did not carry
its own fuel? Say a rocket with the payload capacity of the shuttle
and with engines of the efficiency of the shuttle main engines?



Bob Clark

Practical considerations aside, I think it's a neat idea.

--
"A good plan executed right now is far better than a perfect plan
executed next week."
-Gen. George S. Patton

In article , Rene Tschaggelar writes:
Doug Ellison wrote:

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?


I believe it's only possible to pump fluids to a certain height - after
which you just cant push any more

Since nanotubes are being proposed, isn't the liqid being pulled up
by itself, by kapillary forces presumed the surface is wettable ?

At a rate of few tons per second, with hypersonic velocity. Suuuure.



Rene


Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

In article , (Gregory L. Hansen) writes:
In article ,
Robert Clark wrote:
From this web page, the weight of the shuttle external tank with the
liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds
per second and the amount of hydrogen 465 pounds per second.

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?
What would be the fuel requirements for a rocket that did not carry
its own fuel? Say a rocket with the payload capacity of the shuttle
and with engines of the efficiency of the shuttle main engines?



Bob Clark

Practical considerations aside, I think it's a neat idea.

Practical considerations aside, I think that teleportation is a neater
idea:-)

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

In article ,
wrote:
In article ,
(Gregory L. Hansen) writes:
In article ,
Robert Clark wrote:
From this web page, the weight of the shuttle external tank with the
liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds
per second and the amount of hydrogen 465 pounds per second.

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?
What would be the fuel requirements for a rocket that did not carry
its own fuel? Say a rocket with the payload capacity of the shuttle
and with engines of the efficiency of the shuttle main engines?



Bob Clark

Practical considerations aside, I think it's a neat idea.

Practical considerations aside, I think that teleportation is a neater
idea:-)

Nah... the hose to the gas tank has sort of a Jules Verne quality to it.
It's cute, it's quaint. It has sort of the same quality as a torpedo
powered by an internal combustion engine.


--
"A good plan executed right now is far better than a perfect plan
executed next week."
-Gen. George S. Patton

Paul Blay wrote:
"Rene Tschaggelar" wrote ...

Doug Ellison wrote:


I believe it's only possible to pump fluids to a certain height - after
which you just cant push any more

Since nanotubes are being proposed, isn't the liqid being pulled up
by itself, by kapillary forces presumed the surface is wettable ?


That would be fun.

How many nano tubes "hundreds of kilometers long" would you need
to ensure your rocket is getting fuel fast enough to accelerate upwards
if it's depending on capillary action? ;-)


The quantity per unit time is a matter of the cross section
area covered with nanotubes. It'd work like a tree.
But as said somewhere else, climing up this tree'd be easier.

Rene

In sci.physics,

wrote
on Wed, 30 Jul 2003 18:15:28 GMT
:
In article , (Gregory L. Hansen) writes:
In article ,
wrote:
In article ,
(Gregory L. Hansen) writes:
In article ,
Robert Clark wrote:
From this web page, the weight of the shuttle external tank with the
liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds
per second and the amount of hydrogen 465 pounds per second.

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?
What would be the fuel requirements for a rocket that did not carry
its own fuel? Say a rocket with the payload capacity of the shuttle
and with engines of the efficiency of the shuttle main engines?



Bob Clark

Practical considerations aside, I think it's a neat idea.

Practical considerations aside, I think that teleportation is a neater
idea:-)

Nah... the hose to the gas tank has sort of a Jules Verne quality to it.
It's cute, it's quaint. It has sort of the same quality as a torpedo
powered by an internal combustion engine.

:-))

This thread is beginning to remind me of the movie "Wild Wild West"
for some reason... :-) (The 1999 variant with Will Smith.)

But yeah, one could use an ICE for a torpedo; just remember to
fill that oxygen tank, too.... :-)

[.sigsnip]

--
#191,
It's still legal to go .sigless.

In article , The Ghost In The Machine writes:
In sci.physics,

wrote
on Wed, 30 Jul 2003 18:15:28 GMT
:
In article , (Gregory L. Hansen) writes:
In article ,
wrote:
In article ,
(Gregory L. Hansen) writes:
In article ,
Robert Clark wrote:
From this web page, the weight of the shuttle external tank with the
liquid oxygen and hydrogen is 1.6 million pounds:

EXTERNAL TANK
http://science.ksc.nasa.gov/shuttle/...ewsref/et.html

But the amount of liquid oxygen that is burned is only 2,787 pounds
per second and the amount of hydrogen 465 pounds per second.

Nanotube productions methods are advancing quickly. Suppose it is
possible to make a fuel line of carbon nanotube material hundreds of
kilometers long. Could fuel be pumped up to a rocket accelerating to
orbital velocity?
What would be the fuel requirements for a rocket that did not carry
its own fuel? Say a rocket with the payload capacity of the shuttle
and with engines of the efficiency of the shuttle main engines?



Bob Clark

Practical considerations aside, I think it's a neat idea.

Practical considerations aside, I think that teleportation is a neater
idea:-)

Nah... the hose to the gas tank has sort of a Jules Verne quality to it.
It's cute, it's quaint. It has sort of the same quality as a torpedo
powered by an internal combustion engine.

:-))

This thread is beginning to remind me of the movie "Wild Wild West"
for some reason... :-) (The 1999 variant with Will Smith.)

You mean in the sense of being divorced from reality?:-)

But yeah, one could use an ICE for a torpedo; just remember to
fill that oxygen tank, too.... :-)

Sure.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"