"Rockets not carrying fuel" and the space tower.

From: Robert Clark (rgregoryclark_at_yahoo.com)
Date: 03/28/05 

Date: 28 Mar 2005 12:52:00 -0800

 I copied below a proposal for space access where the propulsion is
provided by a highly pressurized fluid piped up from the ground [you
may need to use a fixed-width font such as Courier New to properly view
the diagram.]
  A key aspect of the proposal as desccribed below is that the material
forming the pipeline does not have to be especially strong as for
example to support its own weight. The force for supporting each
portion of the pipeline is provided by the thrust produced by
pressurized fluid vented along the entire length of the pipeline.
 Note that this also would provide a means of producing a space tower
or space elevator (to low Earth orbit). You really wouldn't need to
attach a rocket to the end of the rocket itself. You would use the
pipeline to *slowly* raise the payload to the required altitude for
LEO. Then you could use a rocket attached to the payload only to give
the payload the required tangential orbital velocity. Note that the
fuel and rocket that would need to be attached to the payload would be
significantly less since this fuel would not be used for getting it up
to altitude.
 You could have this "space fountain" raised only when you wanted to
launch a payload, or you could have it permanently raised in the air.
This would work if you located the fountain next to a large permanently
flowing source of water such as a river. Then for example a ram pump,
which requires no moving parts, could be used to raise the water in the
fountain:

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

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

   Bob Clark

**********************************************************************************
Newsgroups: sci.astro, sci.physics, sci.mech.fluids, sci.engr.mech,
sci.space.policy
From: rgregorycl...@yahoo.com (Robert Clark)
Date: 20 Nov 2004 17:04:01 -0800
Local: Sat, Nov 20 2004 5:04 pm
Subject: Re: "Rockets not carrying fuel" for orbital transfer.

"George Dishman" <george.dish...@clara.co.uk> wrote in message
<news:1100550828.8114.0@damia.uk.clara.net>...
> "Robert Clark" <rgregorycl...@yahoo.com> wrote in message
> news:832ea96d.0411141957.1a521553@posting.google.com...
> >...

> > I came up with two other ideas for reducing the weight of the fluid

> > that had to be supported by the rocket as the tube trails behind
the
> > rocket.
> > Firstly, I wanted to investigate both the possibilities of using
> > gaseous hydrogen or liquid hydrogen for the fluid carried by the
tube.

> That drops the density so you need much higher
> speeds for the same flow rate so makes everything
> more difficult.

> > However, the liquid hydrogen scenario just gave too much weight.
But
> > suppose the rocket didn't have to provide the propulsion for the
fluid
> > in the tube? This is what I envision:

> <Snip pictures>

> All you have done is use a compound engine. The
> same mass is being accelerated to the same speed
> so will need the same fuel. You are forgetting
> the engines not only lift the craft but also the
> fuel needed to lift themselves. In fact with more
> engines, you have greatly increased the mass and
> the fuel needed, and all these schemes create a
> huge drag with air friction on the tube which also
> needs more fuel.

> Instead, imagine using a nearly rigid pipe as the
> arm of a trebuchet to pump fuel only over the first
> few seconds. That might be practical though the
> risks during disconnection are significant.

> George

 I'm also investigating the possibility of using a rigid structure to
reach into LEO. However, I think the efficiency of the tube method is
better than you suggest.
 Let's go back to the case of launch from Earth to LEO. I'm still
considering here that you're not using engines to combust fuel but are
only conducting a high pressure fluid up the tube to provide
propulsion. So the weight of the exhaust ports is quite small, not
that of a full blown engine.
 Let's estimate the the size of these exhaust ports.

          ^
          |
          |
Towards the rocket.

       | |
       | |<----Fluid carrying tube.
       | |
       | |
       | |
       |___ ___|
       /__ | | __\
      // || || \\
     //| |\\
    // | | \\
       | |
       | |
       | |
       | |
       | |
       | |
       |___ ___|
       /__ | | __\
      // || || \\
     //| |\\<---Exhaust ports directed aft.
    // | | \\
       | |
       | |
       | |
       | |
       | |
       | |
       |___ ___|
       /__ | | __\
      // || || \\
     //| |\\
    // | | \\
       | |
       | |
       | |

 Let's say you put a pair of these ports every 100 meters. Then each
pair of ports would only have to provide the thrust to support the
weight of 100 meters of the tube and fluid. Let's use liquid hydrogen
now. Its density is 71 kg/m^3. The volume of a 100 m tube, .3m wide is
Pi*(.15)^2*100 = 7.07 m^3. So the mass is 71 kg/m^3 times this or
about 502 kg, 1104 lbs.
 We're still using the presumption that we can communicate, say, a
pressure like the 6400 psi pressure produced by the shuttle liquid
hydrogen turbopumps up the tube. (Whatever type of pumps we use would
be located on the ground not the rocket so can be quite large.) Now we
want two exhaust ports to support 1104 lbs., or 552 lbs. each. So 552
lbs = (pressure)*(square area of ports) = 6400 * Pi * (1/4)*(diameter
of ports)^2 . We get a diameter of .33 in or 8 millimeters. Actually
they might even be smaller than this by using convergent-divergent
type nozzles used with rockets.
 Now remember the entire tubes weight is supported by these exhaust
ports so the great majority of the fluid that reaches the rocket will
be driving only the payload and rocket. For a .3m = 12in wide tube
this could be a thrust of 6400 * Pi * 6^2 = 723,824 lbs. that is
solely used to loft the payload and (engineless) rocket, and again we
can probably do better than this using the nozzles normally used on
rockets.
 Note that we can get even more thrust from the exhaust ports by
making them wider or by using more than 2 at each level. This is
important since we can also solve the hypersonic drag problem. These
exhaust ports are not engines but it would be a simple (and light
weight matter) to give them directional ability. Then you could have
them automatically direct their thrust to counteract the drag caused
by each portion of the tube.

    Bob Clark
**********************************************************************************

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