Metal working – Method of mechanical manufacture – Rocket or jet device making
Reexamination Certificate
1998-08-31
2001-06-26
Rosenbaum, I Cuda (Department: 3726)
Metal working
Method of mechanical manufacture
Rocket or jet device making
C029S428000
Reexamination Certificate
active
06249967
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to he fabrication of a liquid-fueled rocket engine, and, more particularly, to the attachment of the injector to the combustion chamber.
A typical liquid-fueled rocket engine includes a generally cylindrical combustion chamber, with an injector attached to its injector end and a flared nozzle attached to its nozzle end A liquid propellant including fuel and an oxidizer flows through injector ports in the injector and into the combustion chamber. The propellant is mixed and ignited in the combustion chamber. The hot gas resulting from the combustion expands through the nozzle and drives the rocket eggine and the attached rocket structure in the direction opposite to that in which the nozzle is pointed.
In order to achieve maximum efficiency of the rocket engine in terms of thrust per weight of propellant and maximum specific impulse, the mixing (if any) of the propellant components must be complete to encourage complete combustion. An internal step structure at the injector end of the combustion chamber is under development to promote the complete mixing and combustion. The step structure also protects the injector end of the combustion chamber wall from the highest of the tp es developed inside of the combustion chamber.
The injector is normally welded or bolted to the injector end of the combustion chamber to achieve two main objectives, structural attachment and sealing against leakage of hot gas during engine firing. However, because of the high heating rates and thermal expansion mismatches associated with the rocket engine having a step strucre, welding and bolting have not proved feasible with this combination of different materials. A more complex attachment structure involving several different materials is required at the injector end.
Thus, while the rocket engine with internal step structure in the combustion chamber offers important potential benefits in terms of improved efficiency and specific impulse, those benefits have not been fully realized in initial forms of the rocket engine in part because of fabrication difficulties. There is a need for a fabrication approach which provides the necessary strength and sealing against hot gas leakage, and also allows the step design to function without damaging the combustion chamber. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a fabrication approach for a rocket engine having an internal step structure at the injector end. The fabrication approach allows the step structure to be present to improve performance, but provides the necessary indirect attachment so that the step structure does not damage the wall of the combustion chamber by expansion during firing. The attachment of the step structure to the injector and to the wall of the combustion chamber is selected to achieve sufficient structural strength and sealing against leakage of hot gas, and also to prevent damage to the combustion chamber wall. The resulting rocket engine has high efficiency and also good reliability.
In accordance with the invention, a method for fabricating a rocket engine comprises the steps of providing an annular step collar having an outer diameter, providing an annular transition joint, and first brazing, at a first-brazing temperature, the step collar to the transition joint to form a first subassembly. The method further includes providing a combustion chamber, and second brazing, at a second-brazing temperature, the transition joint of the first subassembly to the combustion chamber to form a second subassembly. An annular adaptor is provided and third brazed, at a third brazing temperature, to the step collar of the second subassembly to form a third subassembly. An injector is provided and welded to the annular adaptor of the third subassembly.
The injector, step collar, and combustion chamber must be joined together at the injector end of the combustion chamber by the attachment which provides sufficient strength, seals agalnst the leakage of hot combustion gas from the interior of the combustion chamber, and prevents damage due to the large dimensional changes experienced during the firing of the rocket engine. In the preferred approach of the present invention as described herein, the attachment includes a step collar/injector joint structure joining the step collar and the injector, and a clip structure joining the combustion chamber and the step collar. The clip structure comprises a C-shaped annular clip having a first leg extending parallel to the chamber length and with an inner diameter of about that of the outer diameter of the combustion chamber and affixed thereto, a second leg extending parallel to the chamber length and with an outer diameter of no greater than that of the outer diameter of the step collar and affixed thereto, and a web extending between the first leg and the second leg. This C-clip provides the necessary strength by acting in the manner of a circumferential rib to withstand hoop stresses produced during the manufacturing and the firing of the rocket engine and also the thermal expansion stresses. It seals the injector end, and also allows the step collar to differentially expand without loading excessive additional stress into the wall of the combustion chamber. The clip is preferably made from a gold-plated molybdenum alloy, most preferably an alloy of 50 weight percent molybdenum, 50 weight percent rhenium.
The present invention thus provides a rocket engine which has improved efficiency of operation and improved specific impulse due to the presence of the internal step within the combustion chamber. It also has good reliability because its structure withands the combustion temperatures to which it is exposed, and accounts for additional stresses caused by the presence of the step collar. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
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Jassowski, Donald M. et al., “Advanced Small Rocket Chambers Option 1-14 Lbf Ir-Re Rocket”, NASA Contract 191014, Aug. 1992.
Bronson David
Kreiner Kurt B.
Neiderman Joel M.
Stechman Carl R.
Woll Peter E.
Cuda Rosenbaum I
Gudmestad T.
Hughes Electronics Corporation
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