IMPULSE DRIVE

	The principal sublight propulsion of the ship and certain auxiliary 
power generating operations are handled by the impulse propulsion system 
(IPS). The total IPS consists of two sets of fusion-powered engines: the main 
impulse engine, and the Saucer Module impulse engines. During normal 
docked operations the main impulse engine is the active device, providing 
the necessary thrust for interplanetary and sublight interstellar flight. High 
impulse operations, specifically velocities above 0.75c, may require added 
power from the Saucer Module engines. These operations, while acceptable 
options during some missions, are often avoided due to relativistic 
considerations and their inherent time-based difficulties.
	During the early definition phase of the Ambassador class, it was 
determined that the combined vehicle mass of the prototype NX-10521 could 
reach at least 3.71 million metric tons. The propulsive force available from 
the highest specific-impulse (IĄ) fusion engines available or projected fell far 
short of being able to achieve the 10 km/sec® acceleration required. This 
necessitated the inclusion of a compact space-time driver coil, similar to 
those standard in warp engine nacelles, that would perform a low-level 
continuum distortion without driving the vehicle across the warp threshold. 
The driver coil was already into computer simulation trials during the 
Ambassador class engineering phase and it was determined that a fusion-
driven engine could move a larger mass than would normally be possible by 
reaction thrust alone, even with exhaust products accelerated to near 
lightspeed.
	Experimental results with exhaust products temporarily accelerated 
beyond lightspeed yielded disappointing results, due to the lack of return 
force coupling to the engine frame. The work in this area is continuing, 
however, in an effort to increase powerplant performance for future starship 
classes.
	In the time between the Ambassador and the Galaxy classes, 
improvements in the internal arrangement and construction of impulse 
engines proceeded, while continuing the practice of using a single impulse 
engine to perform both propulsion and power generation functions like its 
larger cousin, the warp engine. Magnetohydrodynamic (MHD) and electro 
plasma system (EPS) taps provide energy for all ship systems in a shared 
load arrangement with the warp reaction core.  Ę