Further on "Rockets not carrying fuel."

From: Robert Clark (rgregoryclark_at_yahoo.com)
Date: 10/29/04 

Date: 29 Oct 2004 11:06:46 -0700

During a web search I came upon a news article
describing a method of using water pressure at the bottom of the sea to launch
rockets (1). I had started a discussion last year on sci.astro about the
possibility of piping the fuel up to a rocket during ascent rather than
carrying the entire fuel load from the beginning of the trip (2).
  During this discussion, someone raised the possibility of just using the
momentum of the moving fuel alone to provide the propulsion (3). I wanted to get
 some input on the feasibility of this idea.
 I wanted to keep the fuel piped up gaseous to save weight. You can keep the
density low at high pressure by making the temperature high. See (4) to
calculate the density and other physical properties of hydrogen based on
pressure and temperature. For example, at 500 bars and 3000 K, the density is
only 4.1 kg/m^3.
 Carbon fibers already exist of sufficient strength to support their own
weight over 100 km (5). These fibers are also of high melting temperature. So
could probably withstand say 3000 k temperatures.
 As for pumping the gas up to 100 km heights at those pressures, I suggest
some type of "ram pump" (6). However, note that the Space Shuttle already uses
pumps for its liquid hydrogen and oxygen capable of hundreds of bars of
pressure (7).
 Some of the things I would like some feedback on are the feasibility of
moving gasous hydrogen through a 100km long pipe at 500 bar and 3000 K,
assuming we have a carbon fiber material that can withstand the temperatures,
and perhaps most importantly, what would be the aerodynamical effects of a 100
km long tube, say .1 meters wide, moving at hypersonic speeds.
 

     Bob Clark

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1.)HYdro Pneumatic ACCelerator.
http://www.hypacc.com/index.htm
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2.)From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Rockets not carrying fuel.
Newsgroups: sci.astro, sci.space.policy, sci.physics
Date: 2003-07-28 20:59:39 PST
http://groups.google.com/groups?th=7c7989d63883b7ce

_____________________________________________________________________

3.)From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Rockets not carrying fuel.
Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.mech.fluids,
sci.engr.mech
Date: 2003-08-18 09:45:46 PST

luciusone@chapter.net (Lucius Chiaraviglio) wrote in message
news:<3f39766c.22766206@news.charter.net>...
> rgregoryclark@yahoo.com (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/technology/sts-newsref/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?
>
> In addition to the problems others have mentioned, if you somehow
> did manage to pump fuel up to the shuttle fast enough through a hose of
> manageable size (assuming that you could keep the hose from getting burned
> up by the exhaust and air friction), pretty soon you will get to the point
> at which the kinetic energy of the fuel exceeds any chemical energy it could
> possibly have (same reason as why you need to carry so much chemical fuel
for
> each little bit of payload in the first place). At this point, you might as
> well select what you send up the hose for optimum pumping characteristics
and
> never mind about its fuel characteristics, because at this point the shuttle
> has become an Orbital Water Wiggle(tm).

 Your suggestion of just using the kinetic energy of the mass sent up
the hose suggests another possibility: you use the tether to provide
the propulsion for the lower portion of the trip then the rocket or
space plane would continue to orbit on its own power. This would then
be another method of assisted launch to orbit, instead of using
jet-powered craft to assist to high altitude for example.
 You could burn hydrogen on the ground using engines at least as
powerful as the shuttle main engines to send the gases up the pipe.
The result would be steam sent up to the rocket. You bend the pipe
around when at the rocket to direct the exhaust aft. On ignition on
the ground the exhaust velocity would be around 4400 m/s. The question
is how quickly would this be attenuated on the trip up the pipe?
 You could use the decrease in velocity due just to gravity to get a
rough estimate. Probably the gas could reach over 10km high before the
velocity is decresed by gravity alone by half.

     Bob Clark
_____________________________________________________________________

4.)Hydrogen Properties Package
http://www.inspi.ufl.edu/data/h_prop_package.html

_____________________________________________________________________

5.)Carbon fiber (Dani Eder)
http://yarchive.net/space/exotic/carbon_fiber.html

_____________________________________________________________________

6.)From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Rockets not carrying fuel.
Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.mech.fluids,
sci.engr.mech
Date: 2003-07-30 22:03:44 PST

The total weight of the fuel and pipe would only have to be carried
near the end of the trip. For the lowest part of the trip where
typically according to the rocket equation most of the fuel gets
burned, little mass for the fuel and pipe would have to be carried.
 What I wanted to see was how the rocket equation would be changed
when for the great majority of the trip there is little fuel "cost"
for the fuel weight itself.
 As for the pipe, I'm estimating according to the strength vs.
lightness characteristics of carbon nanotubes that a thin walled pipe
composed of nanotube material even a hundred kilometers long whould
only weigh in the range of a few thousand kilos. The question then
would be the mass of the fuel that needed to be carried or supported
by the rocket.
 The first thing to notice is that when you don't have that huge 1.6
million pound mass attached that needs to be accelerated you might not
need the high efficiency that a liquid hydrogen/liquid oxygen engine
offers. Then in that case you might be able to do with just gaseous
hydrogen and without an additional liquid oxygen oxidizer. This page
suggests hydrogen is used in liquid form to save weight and bulk:

Spaceflight :Principles of Rocketry
"Hydrogen and oxygen are gases at ordinary temperatures. But it is not
possible to store them as gases for use in a rocket. They would have
to be compressed to carry them in quantity, and these compressed gases
would have to be held in thick-walled tanks to withstand their
pressure. These tanks would add weight, which is a rocket designer's
enemy, for rocket builders always seek the lightest possible weight.
When these gases are liquefied at low temperatures, the rocket can
carry the largest possible quantities, and the tanks are light in
weight."
http://www.centennialofflight.gov/essay/SPACEFLIGHT/rockets/SP6.htm

 Hydrogen gas is quite light at 1 atm pressure, about .08 kg/m^3. So
even if the pipe were 100km long and .1m wide giving it a volume on
the order of 1000 m^3, the mass of the hydrogen in the pipe would be
only 80 kg. But even liquid hydrogen is not very massive at about 71
kg/m^3 so it's mass within this 100km pipe would be only 71,000 kg,
still quite a difference from 1.6 million pounds.
 But what if the rocket never even had to support the mass of the
fuel? This page gives an example of a type of pump known as a ram pump
that works from gravity alone and can raise liquids many times higher
than the distance of the fall of a gravity driven stream:

Contents for the pulser pump section of Gaiatech.
http://members.tripod.com/~nxtwave/gaiatech/pulser/index.htm

 This page gives a more general discussion of ram pumps:

Designing a Hydraulic Ram Pump.
http://www.lifewater.org/wfw/rws4/rws4d5.htm

 This method may also be adaptable to work for pumping gases.
For a quite large fluid reservoir on the ground the force for raising
the fuel to the rocket would be provided by the pump on the ground not
the rocket. So the rocket would only be supporting the mass of the
fuel pipe itself. In this case you might even be able to use both
liquid hydrogen and liquid oxygen if the rocket did not have to
support the weight of these liquids.
 Another possibility for pumping the fuel to the rocket might be to
use the principle of a hydraulic lift. As shown on this page a large
diameter piston moving a short distance can move a thin diameter
piston a long distance via an incompressible fluid:

How Hydraulic Machines Work
http://science.howstuffworks.com/hydraulic1.htm

(though in this case in order to drive the liquid 100km, the weight
you might need to apply to the large piston might be that of a
battleship.)
 As for the speed of the fuel and whether it would have to be
accelerated to supersonic speeds. Note that what matters is its speed
with respect to the *pipe*. So you could have the pipe being
accelerated to high speed by the rocket while the fuel is moving at a
rather slow speed *with respect to the pipe*, this speed being
determined by the rocket's fuel requirements.
 As for cryogenic requirements, if it turns out you wanted to use a
cryogenic fuel you might be able to insulate the fuel line with a
vacuum jacket and move the fuel fast enough to limit the loss due to
evaporation.

        Bob Clark

_____________________________________________________________________

7.)From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: Rockets not carrying fuel.
Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.mech.fluids,
sci.engr.mech
Date: 2003-07-31 20:04:41 PST
 

"Jonathan Barnes" <jbarnes@ATnetcomuk.co.uk> wrote in message
news:<bgblu8$2fm$1@taliesin2.netcom.net.uk>...
> > Hydrogen gas is quite light at 1 atm pressure, about .08 kg/m^3. So
> > even if the pipe were 100km long and .1m wide giving it a volume on
> > the order of 1000 m^3, the mass of the hydrogen in the pipe would be
> > only 80 kg. But even liquid hydrogen is not very massive at about 71
> > kg/m^3 so it's mass within this 100km pipe would be only 71,000 kg,
> > still quite a difference from 1.6 million pounds.
>
> so lets assume we can pump liquid hydrogen down this pipe ( what does the
> temperature do to the tube ? )
>
> at 5 m/s flow speed, with an ID of 0.1 m the tube delivers 2.8 Kg /s of fuel
> to the engine..... TINY engine in rocket terms... and the oxygen is a lot
> worse.
>
>
> If the pipe and it's fuel accelerate with the rocket the pressure at the
> base of the tube is HUGE.
> just standing up the static pressure on the base is 71 x 9.81 x 100,000
> N/m^2 = 700 atmospheres ( bar )
> Add a pumping pressure to force the liquid through 100 Km of pipe...?? 100
> bar more.
>
> The pipe will be very thick walled to resist the huge pressure at it's base
>
> This is not going to work.

 I found on this page that the shuttle fuel lines are actually 12
inches or 30 cm wide:

Hunt for cracks moves to shuttle Endeavour
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 9, 2002
"The cracks detected in Atlantis and Discovery are located where the
flow liners cross over the gimbal joints closest to the point where
the incoming 12-inch hydrogen lines enter the main engines."
http://spaceflightnow.com/news/n0207/09cracks/

 At a flow rate for the liquid hydrogen of 465 lbs/s, that's 211 kg/s.
With liquid hydrogen density of 71 kg/m^3, that's about 3 m^3. So for
a .3m diameter pipe that comes to about 3/(.3 x .3) or 33 m/s.
 This larger size pipe would cause a problem as for the mass of the
fuel IF you did want to use cryogenic propellants. If the propellant
were gaseous hydrogen that would still only be 720 kg for the fuel in
the 100 km long pipe.

 Surprisingly the huge pressure you mentioned is in fact comparable to
the pressures already generated by the shuttle engine's turbopumps.
According to this page the pressure generated by the liquid hydrogen
turbopump is 6,400psi or 441 bar and for the liquid oxygen turbopump,
7,250psi or 500 bar:

Space Shuttle Turbopumps.
http://www.pratt-whitney.com/3a/html/products_ss_main.html

 Even more telling is the turbopumps have enough power to send a
stream of liquid hydrogen 36 miles or 58 km into the air:

Atlantis Crew to Test Fly New, Safer Shuttle Main Engine
By Jim Banke
Senior Producer,
Cape Canaveral Bureau
posted: 07:00 am ET
10 July 2001
"NASA wound up with the most powerful rocket engine for its size in
history. Together, the three shuttle engines generate more than a
million pounds of thrust -- the energy equivalent of 23 Hoover Dams.
And just one of the high pressure fuel turbopumps, barely larger than
a typical automobile engine, has the power to send a column of liquid
hydrogen 36 miles into the air."
http://www.space.com/missionlaunches/missions/sts104_pump_010710-1.html

 IF liquid fuel were to be used you would want to use the method of
pumping the fuel to the rocket using power on the ground, so that the
rocket would not have to support the weight of the fuel. You could use
either the ram pump method or scaled up versions of the turbopumps
already used on the shuttle.

        Bob Clark
________________________________________

Relevant Pages

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  • Re: Further on "Rockets not carrying fuel."
    ... > possibility of piping the fuel up to a rocket during ascent rather than ... > carrying the entire fuel load from the beginning of the trip. ... > density low at high pressure by making the temperature high. ... > need the high efficiency that a liquid hydrogen/liquid oxygen engine ...
    (sci.physics)
  • Re: Further on "Rockets not carrying fuel."
    ... > possibility of piping the fuel up to a rocket during ascent rather than ... > carrying the entire fuel load from the beginning of the trip. ... > density low at high pressure by making the temperature high. ... > need the high efficiency that a liquid hydrogen/liquid oxygen engine ...
    (sci.astro)