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).
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."RL-10
Hydrogen Properties Package. TEMPERATURE RANGE: 13.8K TO 12,000K PRESSURE RANGE: 0.1 bar TO 10,000 bar
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