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 auxiliary power 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 0.9c, may require added power from the auxiliary power engines. These operations while acceptable options during some missions, are often avoided due to relativistic considerations end their inherent time-based difficulties.

During the early definition phase of the Gabriel class, it was determined that the combined vehicle mass of the prototype could exceed the impulse performance of the current maximum rating on current designs rated for at least 540,000 metric tons. The propulsive force available from the highest specific impulse (Isp) fusion engines available fell short of being able to achieve the 10-km/sec2 acceleration required. This necessitated the inclusion of a compact space-time driver coil, similar to that standard in warp nacelles, which would perform a low-level continuum without driving the vehicle across the warp threshold. The advanced driver coil was already into computer simulation trials during the Galaxy 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.

In the time between the Gabriel and the Matrix, 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.

The four SBX (FYX-9000) Impulse Drive Units are standard for all Gabriel Class Starships. The main impulse engine (MIE) is located on Deck 8 and thrusts along the centerline of the spacecraft. Four individual impulse engines are grouped together to form the MIE with two groups of two engines to each and form the port and starboard impulse drives. 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 Gabriel class normally carries four additional IRC modules as power generation devices, though these modules may be channeled through the main system exhaust paths to provide backup propulsion.

Normal Operation

For normal function, the Main Matter/Antimatter Reactor acts as power source. The Main Reactor feeds a small amount of energy in the form of a photon beam via the Impulse Energy Conduit to the Impulse Deflection Crystal. The Crystal heats up under this bombardment until the interior of the Reaction Chamber is at an operational temperature of 5000° C. After operational temperature is achieved, the Injection Nozzles feed deuterium pellets from the deuterium fuel tank into the Reaction Chamber. In the Reaction Chamber, the Fuel undergoes fusion. The expanding shock-waves of fusing plasma escape the Reaction Chamber via the Thrust Guides, and vent into space to the rear through the thrust chamber.

Slush deuterium from the main cryo-tank is heated and fed to interim supply tanks on Deck 7, 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 108 to 1011 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 ships 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).

Speeds attained via Impulse Drive range from .03 c (Orbital Maneuvering) to .98 c (Inter-Solar-System Velocity). The Emergency Impulse Speed of .995 c can only be achieved using the auxiliary reactors as a engine powerplant.

Auxiliary Operation

If the Main Reactor is non-functional, the auxiliary reactor is capable of heating up the Reaction Chamber. The auxiliary is a Tokamat-Moscow - VII Helium-Beryllium Fusion Reactor, mounted to the rear of the auxiliary deuterium tanks between the Thrust Chambers. It can feed energy to the Impulse Deflection Crystal via a Secondary Energy Conduit connected to the Impulse Energy Conduit. While on Auxiliary Power, the Impulse Drive is capable of one-half Impulse Speed.

IMPULSE ENGINE CONTROL

The Impulse propulsion system is commanded through operational software routines stored within the spacecraft main computers. As with the warp propulsion system commend processors genetic algorithms learn and adapt to ongoing experiences involving Impulse engine usage and make appropriate modifications in handling both voluntary external commands and purely autonomic operations. Voice commands and keyboard inputs are confirmed and reconciled by the current active main computer, and then handed off to the IPS command coordinator for routing to the engines for execution. The IPS command coordinator is cross-linked with its counterpart in the WPS for flight transitions involving warp entry and exit. Specific software routines react to prevent field energy fratricide (unwanted conflicts between warp fields and impulse engine fields). The command coordinator is also in the cross linked with the reaction control system (RCS) for attitude and translational control at all speeds.

Bibliography:

Star Trek The Next Generation Technical Manual by Rick Sternbach and Michael Okuda
Starfleet Dynamics by David Schmidt
Jackill's Star Fleet Reference Manuals Vols 1, 2 and 3 by Eric Kristiansen
The Star Trek Encyclopedia by Michael Okuda and Denise Okuda
Star Trek The Next Generation Officer's Manual by FASA Corporation

Author - Lt. Wayne N Snyder
Date - 07 - 06 - 98
Next Week's Article – Dilithium Crystals.