S5.92
The S5.92 is a Russian rocket engine, currently used on the Fregat upper stage. It burns a hypergolic mixture of unsymmetrical dimethylhydrazine fuel with dinitrogen tetroxide oxidizer in a gas-generator cycle.
Design
The S5.92 has two throttle settings. The highest produces of thrust, a specific impulse of 327 seconds, and a 3-second ignition transient. The lower throttle level produces of thrust, specific impulse of 316 seconds, and a 2.5 second ignition transient. It is rated for 50 ignitions, and 300 days between ignitions.
History
It was originally designed by the famous A.M. Isayev Chemical Engineering Design Bureau, for the two spacecraft of the Phobos program. While the Mars missions were unsuccessful, the spacecraft manufacturer, NPO Lavochkin, found a market niche for the technology. Thus, the engine was adapted for use on the optional Fregat upper stage of the Soyuz and Zenit launch vehicles.