Eliminating turbopumps to simplify rocket engines and lower launch costs.

On another space list there was discussion on ideas for prizes that
could be offered to spur space access. Here's one that would be
important and could have a lot of entrants from many different fields,
since there are so many different ways it could be accomplished: a
simple, highly reliable, low cost method of moving the high pressure,
large volume amounts of propellant for high performance, high thrust
rockets rather than by using turbopumps.
The space shuttle main engine turbopumps for example are the most
complicated and expensive and maintenance intensive parts of the
engines. They have to be overhauled every few flights. Such turbopumps
are a big reason the high thrust, high performance rocket engines are
usually not reusable or have rather limited reusability like the SSME,
whose reusability is 100 flights of 500 seconds, or about 14
cumulative hours. Compare this to jet aircraft engines which might
last thousands of hours.
A simpler type of rocket engine is the pressure-fed engine:
Pressure-fed cycle (rocket).
formatting link
(rocket)
However, a problem with using a pressure-fed system for the high
performance engines is that you would need quite high pressure in the
propellant tanks to deliver the fuel at high pressure which would
require significantly heavier tanks to hold the propellant. The reason
the high performance engines operate at high pressures is that they
burn at high temperature and therefore high pressure in the combustion
chamber and you need to deliver the fuel at high pressure just for it
be able to enter the combustion chamber.
Here is a study on lower costs to space from 1989 that discusses the
problem of using pressure fed engines with the high performance
engines:
Big Dumb Boosters: A Low-Cost Space Transportation Option?
February 1989
"Launcher Reliability"
"Workshop participants disagreed on the reliability of low-cost
designs. Proponents of simplified designs argue that reducing the
number of moving parts and using heavier materials with conservative
design margins decreases the possibility of malfunctions. They note
that a pump-fed engine may have 15,000 parts compared with fewer than
100 in a pressure-fed
engine. Simple designs, that decrease possibilities for human error
and reduce special handling, would not only increase reliability, but
also simplify trouble-shooting. =93When a pump-fed engine fails you have
a research project on your hands,=94 said one workshop participant. In
the
words of the Shakers, =93Tis a gift to be simple.=94
Another workshop participant pointed to the Shuttle=92s complexity and
the Challenger accident: =93you can=92t be in a position where when you
have a failure you have to reconstitute the design team to figure out
what went wrong.=9425 Others disputed the view that simplicity equals
reliability. They argued that commercial jet aircraft are made
reliable by their very
sophistication. Still others drew attention to the high reliability of
the pump-fed engine used on the Atlas Centaur, the RL-10, which has
suffered no failures in over 150 flights and hundreds of ground tests
since its first test flight in 1962."
formatting link

This passage mentions the reliability of the RL-10 turbopumps dating
from the 1960's. But initially the RL-10 engine only operated at a
chamber pressure of 24 bar and with thrust of only 15,000 pounds.
Compare this to the SSME's which operate at a chamber pressure 200 bar
at a thrust of 500,000 pounds maximum.
Note also that with the RL-10 as time went on improved versions
increased its thrust requiring higher chamber pressures and higher
fuel flow rates. This necessitates much higher stress on the
turbopumps and undoubtedly higher costs:
RL-10
formatting link

If you were to use pressure-fed methods to replace turbopumps for the
high performance engines, one way this might be done for example would
be instead of having the entire propellant tanks be pressurized,
requiring heavy tank walls, have the propellant instead flow into a
smaller chamber first, either by gravity or a low pressure system,
then have only this smaller chamber be pressurized to the high
pressures required for the engine.
It doesn't have to be a pressure fed method though. The space shuttle
liquid hydrogen turbopumps pump 73 kg/sec of liquid hydrogen at 500
bar for each engine. By the Bernoulli principle this is equivalent to
pumping this amount of fuel at standard pressure but at about 1,100 m/
s. (By the Bernoulli principle, you can trade velocity for pressure
and vice versa in a (near)incompressible fluid just by varying the
pipe diameter.) Then any method that could move this large amount of
fuel at 1,100 m/s would work just as well. This is why I say you could
have many different entrants from many different fields for this. For
example, you could have a (electro)mechanical method that had the
hydrogen being carried by rotating buckets moving at this speed. This
could look similar to a garage-sized "launch loop" discussed as an
alternative launch method to rockets, except that it would be moving a
fluid and it wouldn't have to move nearly as fast as orbital velocity
but only at 1,100 m/s.
Another possibility might be just to heat the liquid hydrogen so that
it reached the pressure needed in gaseous form. Strictly speaking this
is not the same as a pressure-fed method since that uses some other
gas to provide the pressurization.
Liquid hydrogen has a density of about 72 kg/m^3 at a temperature of
20 K. Then we want to find the temperature and pressure at which this
same mass of liquid hydrogen will now be a gas at this density.
This page calculates properties of hydrogen given temperature and
pressure:
Hydrogen Properties Package.
TEMPERATURE RANGE: 13.8K TO 12,000K
PRESSURE RANGE: 0.1 bar TO 10,000 bar
formatting link

Probably we won't need as high a pressure as the shuttle turbopumps of
500 bar but just somewhat more than that of SSME combustion chamber
pressure of 200 bar. At 50 K and 300 bar that page gives these
results:
Hydrogen Properties Package.
Results
Pressure =3D 3.000e+02 bar
Temperature =3D 5.000e+01 K
Enthalpy =3D 3.345e+02 kJ/kg
Entropy =3D 1.341e+01 kJ/kg.K
Vel.of sound =3D 1.591e+03 m/s
Density =3D 7.324e+01 kg/m**3
Them. cond. =3D 1.598e-01 W/m.K
Viscosity =3D 1.272e-05 N.s/m**2
Spec. heat =3D 1.182e+01 kJ/Kg.K
Gamma =3D 1.642e+00
We need though to calculate the power requirements for raising the
liquid at 20 K hydrogen to this temperature. You need to include also
the heat of vaporization to first change the liquid to a gas. Then use
the specific heat of hydrogen to calculate how much energy is needed
to raise the temperature of the gas from 20 K to 50 K. Taking into
account you want to do this for 73 kg/sec, you calculate how much
power is needed to do this for each SSME. It turns out it's comparable
to the power used for each liquid hydrogen turbopump. The purpose of
the exercise is not to save power, the turbopumps use up only a small
proportion of the SSME power output anyway, but to do it in a simple,
highly reliable, low maintenance, low cost way.
For this large amount of mass of 73 kg/sec you would need a rapid
means of transferring the large amount of heat to raise the
temperature. One method might be to use a highly heat conducting
material around the combustion chamber exterior that we will then
extend into the liquid hydrogen that needed to be heated at one time.
Also, since we don't need the turbopump we might be able to just use
the hydrogen sent around the combustion chamber and the engine nozzle
with the regenerative cooling method. I don't know though if this
would provide the sufficient mass of hydrogen rapidly that we need.
Still another possibility might be to use a microwave generator to
heat the hydrogen.
Bob Clark
Reply to
Robert Clark
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On another space list there was discussion on ideas for prizes that could be offered to spur space access. Here's one that would be important and could have a lot of entrants from many different fields, since there are so many different ways it could be accomplished: a simple, highly reliable, low cost method of moving the high pressure, large volume amounts of propellant for high performance, high thrust rockets rather than by using turbopumps. The space shuttle main engine turbopumps for example are the most complicated and expensive and maintenance intensive parts of the engines. They have to be overhauled every few flights. Such turbopumps are a big reason the high thrust, high performance rocket engines are usually not reusable or have rather limited reusability like the SSME, whose reusability is 100 flights of 500 seconds, or about 14 cumulative hours. Compare this to jet aircraft engines which might last thousands of hours. A simpler type of rocket engine is the pressure-fed engine:
Pressure-fed cycle (rocket).
formatting link
(rocket) However, a problem with using a pressure-fed system for the high performance engines is that you would need quite high pressure in the propellant tanks to deliver the fuel at high pressure which would require significantly heavier tanks to hold the propellant. The reason the high performance engines operate at high pressures is that they burn at high temperature and therefore high pressure in the combustion chamber and you need to deliver the fuel at high pressure just for it be able to enter the combustion chamber. Here is a study on lower costs to space from 1989 that discusses the problem of using pressure fed engines with the high performance engines:
Big Dumb Boosters: A Low-Cost Space Transportation Option? February 1989 "Launcher Reliability" "Workshop participants disagreed on the reliability of low-cost designs. Proponents of simplified designs argue that reducing the number of moving parts and using heavier materials with conservative design margins decreases the possibility of malfunctions. They note that a pump-fed engine may have 15,000 parts compared with fewer than 100 in a pressure-fed engine. Simple designs, that decrease possibilities for human error and reduce special handling, would not only increase reliability, but also simplify trouble-shooting. ?When a pump-fed engine fails you have a research project on your hands,? said one workshop participant. In the words of the Shakers, ?Tis a gift to be simple.? Another workshop participant pointed to the Shuttle?s complexity and the Challenger accident: ?you can?t be in a position where when you have a failure you have to reconstitute the design team to figure out what went wrong.?25 Others disputed the view that simplicity equals reliability. They argued that commercial jet aircraft are made reliable by their very sophistication. Still others drew attention to the high reliability of the pump-fed engine used on the Atlas Centaur, the RL-10, which has suffered no failures in over 150 flights and hundreds of ground tests since its first test flight in 1962."
formatting link
This passage mentions the reliability of the RL-10 turbopumps dating from the 1960's. But initially the RL-10 engine only operated at a chamber pressure of 24 bar and with thrust of only 15,000 pounds. Compare this to the SSME's which operate at a chamber pressure 200 bar at a thrust of 500,000 pounds maximum. Note also that with the RL-10 as time went on improved versions increased its thrust requiring higher chamber pressures and higher fuel flow rates. This necessitates much higher stress on the turbopumps and undoubtedly higher costs:
RL-10
formatting link
If you were to use pressure-fed methods to replace turbopumps for the high performance engines, one way this might be done for example would be instead of having the entire propellant tanks be pressurized, requiring heavy tank walls, have the propellant instead flow into a smaller chamber first, either by gravity or a low pressure system, then have only this smaller chamber be pressurized to the high pressures required for the engine. It doesn't have to be a pressure fed method though. The space shuttle liquid hydrogen turbopumps pump 73 kg/sec of liquid hydrogen at 500 bar for each engine. By the Bernoulli principle this is equivalent to pumping this amount of fuel at standard pressure but at about 1,100 m/ s. (By the Bernoulli principle, you can trade velocity for pressure and vice versa in a (near)incompressible fluid just by varying the pipe diameter.) Then any method that could move this large amount of fuel at 1,100 m/s would work just as well. This is why I say you could have many different entrants from many different fields for this. For example, you could have a (electro)mechanical method that had the hydrogen being carried by rotating buckets moving at this speed. This could look similar to a garage-sized "launch loop" discussed as an alternative launch method to rockets, except that it would be moving a fluid and it wouldn't have to move nearly as fast as orbital velocity but only at 1,100 m/s. Another possibility might be just to heat the liquid hydrogen so that it reached the pressure needed in gaseous form. Strictly speaking this is not the same as a pressure-fed method since that uses some other gas to provide the pressurization. Liquid hydrogen has a density of about 72 kg/m^3 at a temperature of 20 K. Then we want to find the temperature and pressure at which this same mass of liquid hydrogen will now be a gas at this density. This page calculates properties of hydrogen given temperature and pressure:
Hydrogen Properties Package. TEMPERATURE RANGE: 13.8K TO 12,000K PRESSURE RANGE: 0.1 bar TO 10,000 bar
formatting link
Probably we won't need as high a pressure as the shuttle turbopumps of 500 bar but just somewhat more than that of SSME combustion chamber pressure of 200 bar. At 50 K and 300 bar that page gives these results:
Hydrogen Properties Package. Results Pressure = 3.000e+02 bar Temperature = 5.000e+01 K Enthalpy = 3.345e+02 kJ/kg Entropy = 1.341e+01 kJ/kg.K Vel.of sound = 1.591e+03 m/s Density = 7.324e+01 kg/m**3 Them. cond. = 1.598e-01 W/m.K Viscosity = 1.272e-05 N.s/m**2 Spec. heat = 1.182e+01 kJ/Kg.K Gamma = 1.642e+00
We need though to calculate the power requirements for raising the liquid at 20 K hydrogen to this temperature. You need to include also the heat of vaporization to first change the liquid to a gas. Then use the specific heat of hydrogen to calculate how much energy is needed to raise the temperature of the gas from 20 K to 50 K. Taking into account you want to do this for 73 kg/sec, you calculate how much power is needed to do this for each SSME. It turns out it's comparable to the power used for each liquid hydrogen turbopump. The purpose of the exercise is not to save power, the turbopumps use up only a small proportion of the SSME power output anyway, but to do it in a simple, highly reliable, low maintenance, low cost way. For this large amount of mass of 73 kg/sec you would need a rapid means of transferring the large amount of heat to raise the temperature. One method might be to use a highly heat conducting material around the combustion chamber exterior that we will then extend into the liquid hydrogen that needed to be heated at one time. Also, since we don't need the turbopump we might be able to just use the hydrogen sent around the combustion chamber and the engine nozzle with the regenerative cooling method. I don't know though if this would provide the sufficient mass of hydrogen rapidly that we need. Still another possibility might be to use a microwave generator to heat the hydrogen.
Bob Clark ================================
HAHAHA!
If you saw those jerks with an electric 18"-long torque nut driver counting turns on the swing bolt of the Hubble Space Telescope bay door you'd soon see NASA doesn't have a clue how to design ANYTHING efficiently.
formatting link
If you need two bottle rockets to lift the fuel tank why not lift the shuttle with no external tank and two bottle rockets? The entire mess looks like it was designed by Harley Davidson, stick a lump on as an after-thought.
Reply to
Androcles
=3D=3D=3D=3D=3D=3D=3D=3D
Well if they knew anything about propulsion design or efficieny, they wouldn't even build bays. Which is why the people who do build GPS, Digital-Terrain Mapping, AUVs, Optical Computers, Microcomputers, Distributed Processing, Post-Spock DSP, HDTV Debuggers, Pv Cell Energy, Cell Phones, Fiber Optics, On-Line Banking, On-Line Publishing, Self-Replicating Machines, Self-Assembling Robots, and Drones.
Reply to
zzbunker
...
Abuse of newsgroup charter reported.
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N:dlzc D:aol T:com (dlzc)

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