IMPULSE ENGINE CONFIGURATION

	The main impulse engine (MIE) is located on Deck 23 and thrusts 
along the centerline of the docked spacecraft. During separated flight mode, 
the engine thrust vectors are adjusted slightly in the +Y direction; that is, 
pointed slightly up from center to allow for proper center-of-mass motions. 
The Saucer Module impulse engines are located on Deck 10 on the vehicle 
XZ plane and thrust parallel to the vehicle centerline.
	Four individual impulse engines are grouped together to form the 
MIE, and two groups of two engines form the Saucer Module impulse 
engines. Each impulse engine consists of three basic components: impulse 
reaction chamber (IRC, three per impulse engine), accelerator/generator 
(A/G), driver coil assembly (DCA), and vectored exhaust director (VED). The 
IRC is an armored sphere six meters in diameter, designed to contain the 
energy released in a conventional proton-proton fusion reaction. It is 
constructed of eight layers of dispersion-strengthened hafnium excelinide 
with a total wall thickness of 674 cm. A replaceable inner liner of crystalline 
gulium fluoride 40 cm thick protects the structural sphere from reaction and 
radiation effects. Penetrations are made into the sphere for reaction 
exhaust, pellet injectors, standard fusion initiators, and sensors.
	The Galaxy class normally carries four additional IRC modules 
primarily as backup power generation devices, though these modules may 
be channeled through the main system exhaust paths to provide backup 
propulsion.
	Slush deuterium from the main cryo tank is heated and fed to interim 
supply tanks on Deck 9, where the heat energy is removed, bringing the 
deuterium down to a frozen state as it is formed into pellets. Pellets can 
range in size from 0.5 cm to 5 cm, depending on the desired energy output 
per unit time. A standing pulsed fusion shock front is created by the standard 
initiators ranged about the forward inner surface of the sphere. The total 
instantaneous output of the IRC is throttleable from 10Þ to 10¹ megawatts.
	High-energy plasma created during engine operation is exhausted 
through a central opening in the sphere to the accelerator/generator. This 
stage is generally cylindrical, 3.1 meters long and 5.8 meters in diameter, 
constructed of an integral single-crystal polyduranium frame and pyrovunide 
exhaust accelerator. During propulsion operations, the accelerator is active, 
raising the velocity of the plasma and passing it on to the third stage, the 
space-time driver coils. If the engine is commanded to generate power only, 
the accelerator is shut down and the energy is diverted by the EPS to the 
shipÕs overall power distribution net. Excess exhaust products can be vented 
nonpropulsively. The combined mode, power generation during propulsion, 
allows the exhaust plasma to pass through, and a portion of the energy is 
tapped by the MHD system to be sent to the power net.
	The third stage of the engine is the driver coil assembly (DCA). The 
DCA is 6.5 meters long and 5.8 meters in diameter and consists of a series of 
six split toroids, each manufactured from cast verterium cortenide 934. 
Energy from the accelerated plasma, when driven through the toroids, 
creates the necessary combined field effect that (1) reduces the apparent 
mass of the spacecraft at its inner surface, and (2) facilitates the slippage of 
the continuum past the spacecraft at its outer surface.
	The final stage is the vectored exhaust director (VED). The VED 
consists of a series of moveable vanes and channels designed to expel 
exhaust products in a controlled manner. The VED is capable of steerable 
propulsive and nonpropulsive modes (simple venting).  Æ