Rocket engines requires a tremendous amount of fuel high at high pressure .Often th pump costs more than the thrust chamber.One way to supply fuel is to use the expensive turbopump mentioned above,another way is to pressurize fuel tank. Pressurizing a large fuel tank requires a heavy , expensive tank. However suppose instead of pressurizing entire tank, the main tank is drained into a small pump chamber which is then pressurized. To achieve steady flow, the pump system consists of two pump chambers such that each one supplies fuel for ½ of each cycle. The pump is powered by pressurized gas which acts directly on fluid. For each half of the pump system, a chamber is filled from the main tank under low pressure and at a high flow rate, then the chamber is pressurized, and then the fluid is delivered to the engine at a moderate flow rate under high pressure. The chamber is then vented and cycle repeats.
The system is designed so that the inlet flow rate is higher than the outlet flow rate.This allows time for one chamber to be vented , refilled and pressurized while the other is being emptied.A bread board pump has been tested and it works great .A high version has been designed and built and is pumping at 20 gpm and 550psi.
Nearly all of the hardware in this pump consists of pressure vessels, so the weight is low.There are less than 10 moving parts , and no lubrication issues which might cause problems with other pumps. The design and constr. Of this pump is st, forward and no precision parts are required .This device has advantage over standard turbopumps in that the wt. is about the same, the unit,engg.and test costs are less and the chance for catastrophic failure is less.This pump has the advantage over pressure fed designs in that the wt. of the complete rocket is much less, and the rocket is much safer because the tanks of rocket fuel do not need to be at high pressure.The pump could be started after being stored for an extended period with high reliability.It can be used to replace turbopumps for rocket booster opn. or it can be used to replace high pressure tanks for deep space propulsion.It can also be used for satellite orbit changes and station keeping.
A calculation of the weight of this type of pump shows that the power to weight ratio would be dominated by the pressure chamber and that it would be of the order of 8-12 hp per lb., for a 5 second cycle using a composite chamber. This performance is similar to state of the art gas-generator turbopump technology. (The F1 turbopump on the Saturn V put out 20 hp/lb) This pump could be run until dry, so it would achieve better residual propellant scavenging than a turbopump. This system would require a supply of gaseous or liquid Helium which would be heated by a heat exchanger mounted on the combustion chamber before it was used to pressurize the fuel, as in the Ariane rocket.. The volume of gas required would be equivalent to a standard pressure fed design, with a small additional amount to account for ullage in the pump chambers. The rocket engine itself could be a primarily ablative design, as in the NASA Fastrac, scorpious rocket or in recent rocket engine tests.