Nozzle extension

As of 2009, the search for various schemes to achieve higher area ratios for rocket nozzles remains an active field of research and patenting.

This scheme assumes the outer skirt of the bell is extended while the engine is functioning and its installation to working position happens in the upper layers of the atmosphere.

[3] For example, application of nozzle extension for liquid rocket engine NK-33 improves the value of specific impulse up to 15-20 sec for near-space conditions.

This makes the nozzles a very sizable part of the engine, which must be completely enclosed below the nose cone of a rocket.

Consequently, the use of an outer expandable skirt in this case allows the size of the upper stage and payload fairing to be minimized, which in turn decreases the total mass of the nose cone.