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Several nozzle concepts that promise a gain in performance over existing conventional nozzles are discussed in this paper. It is shown that signi cant performance gains result from the adaptation of the exhaust ow to the ambient pressure. Special attention is then given to altitude-adaptive nozzle concepts, which have recently received new interest in the space industry. Current research results are presented for dual-bell nozzles and other nozzles with devices for forced ow separation and for plug nozzles with external freestream expansion. In addition, results of former research on nozzles of dual-mode engines such as dual-throat and dual-expander engines and on expansionde ection nozzles are shown. In general, ow adaptation induces shocks and expansion waves, which result in exit pro les that are quite different from idealized one-dimensional assumptions. Flow phenomena observed in experiments and numerical simulations during different nozzle operations are highlighted, critical design aspects and operation conditions are discussed, and performance characteristics of selected nozzles are presented. The consideration of derived performance characteristics in launcher and trajectory optimization calculations reveal signi cant payload gains at least for some of these advanced nozzle concepts.

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Various technology programs in Europe are concerned, besides developing reliable and rugged, low‐cost, throwaway equipment, with preparing for future reusable propulsion technologies. One of the key roles for realizing reusable engine components is the use of modern and innovative materials. One of the key technologies that concerns various engine manufacturers worldwide is the development of fiber‐reinforced ceramics—CMCs (ceramic matrix composites). The advantages for the developers are obvious–the low specific weight, the high specific strength over a large temperature range, and their great damage tolerance compared with monolithic ceramics make this material class extremely interesting as a construction material. Over the past few years, the EADS‐ST Company (formerly DASA) has, together with various partners, worked intensively on developing components for hypersonic engines and liquid rocket propulsion systems. In the year 2000, various hot‐firing tests with subscale (scale 1:5) and full‐scale nozzle extensions were conducted. In this year, a further decisive milestone was achieved in the sector of small thrusters, and long‐term tests served to demonstrate the extraordinary stability of the C/SiC material. Besides developing and testing radiation‐cooled nozzle components and small‐thruster combustion chambers, EADS‐ST worked on the preliminary development of actively cooled structures for future reusable propulsion systems. In order to get one step nearer to this objective, the development of a new fiber composite was commenced within the framework of a regionally sponsored program. The objective here is to create multidirectional (3D) textile structures combined with a cost‐effective infiltration process. Besides material and process development, the project also encompasses the development of special metal/ceramic and ceramic/ceramic joining techniques as well as studying and verifying nondestructive investigation processes for the purpose of testing components.

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