Development of A Light-Weight Regeneratively Cooled Thrust Chamber With Brazed Ribs and Brazed Outer Wire Trap

Design and fabrication procedures are discussed of a brazed-ribtype thrust chamber fabricated from stainless steel or inconel for a Sooo-lb thrust 20: 1 expansion-area-ratio regeneratively cooled liquidpropellant rocket engine which is designated as the JPL 6K Engine and operates at a chamber pressure of 150 psia. Hydrazine is used as the fuel and regenerative coolant and nitrogen tetroxide as the oxidizer. The nozzle-throat diameter is 5.42 in. The thrust chamber consists of a sheet-metal gas-side liner with longitudinal ribs spotwelded and brazed to the outer surface. Wire is wrapped over the
ribs circumferentially, spot-welded to the ribs, and brazed. The liner, ribs, and wire form the coolant-passage walls.

There are three basic advantages to this type of thrust chamber: light weight, ease of fabrication, and comparatively low cost. The total dry weight of a thrust chamber of this type and size made of 347 stainless steel is 46.2 lb, and the wet weight is 56.3 Ib.

A total of 87 static engine tests were made on 19 of 23 thrust chambers fabricated by this technique. Four of the chambers tested had an expansion-area ratio of 20:1, and 15, which were shorter but had the same throat diameter, had an expansion-area ratio of 3.5:l. Accumulated test time was 1926 sec, including 558 sec regenerative cooling with hydrazine and 1368 sec cooling with water. One 20:l thrust chamber was subjected to 16 separate engine tests, with an accumulated test time of 399 sec, and was still in very good operating condition after the tests were completed.

With water flowing through the coolant passages at 10 lb/sec, the measured nominal pressure drop between coolant manifolds of a 20:l thrust chamber wrapped with flat wire was 17.2 psi.