Starfleet Command > Technical Manuals > Starfleet > Impulse Propulsion Systems

Impulse Drive

The Impulse Drive is the main method of propulsion for sublight velocities. It also provides auxiliary power for some ship systems. The IPS consists of two sets of fusion-powered engines: the main impulse engine, and the saucer module impulse engines (in vessels capable of separated flight mode only). During normal operations, the main impulse engine is used. High impulse velocities above 0.75 c (c = speed of light) may require additional power from the Saucer Module engines. These operations, while sometimes necessary, are avoided if possible due to relativistic considerations and their time-based difficulties. Magnetohydrodynamic (MHD) and electroplasma system (EPS) taps provide energy for all ship systems in a shared load arrangement with the warp reaction core.

IPS Fuel Supply

Fuel for the IPS is stored in the primary deuterium tank in the Stardrive section and in 32 auxiliary cryo tanks in the saucer module. Redundant cross-feeds between the tanks allow for transfer of fuel. The internal volume of each auxiliary tank is 113 m3, and each is capable of storing a total of 9.3 tonnes of liquid deuterium. Emergency flight rules allow for the injection of minute amounts of antimatter into the impulse reaction chamber to give short periods of increased power generation.

Impulse Engine Configuration

The main impulse engine is a group of four individual impulse engines. Each engine consists of three basic components: reaction chamber (IRC), accelerator/generator (A/G) and driver coil assembly (DCA). The IRC is an armoured sphere six metres in diameter, designed to contain the energy released in conventional deuterium fusion reaction. It is constructed of eight layers of dispersion-strengthened hafnium excelinide with a total wall thickness of 6.74 m. A replaceable inner layer of crystalline gulium fluoride 40 cm thick protects the structure of the sphere from reaction and radiation effects. Penetrations are made into the spher for reaction exhaust, pellet injectors, standard fusion initiators and sensors.


Slush deuterium from the main cryo tank is heated and refrozen as pellets, raning in size from 0.5 cm to 5cm, depending on desired power. A pulsed fusion shock front is created by the fusion initiators, giving a total instantaneous output of 108 - 1011 MW. High-energy plasma created during engine operation is exhausted through a central operning in the sphere to the accelerator/generator, raising the velocity of the plasmas and passing it to the DCA. This part of the engine reduces the mass of the starship at its inner surface and facilitates the slippage of the continuum past the starship at its outer surface. There is also a vectored exhaust director (VED), which controls the direction of thrust, and can also direct the exhaust so as to give a nonpropulsive effect.

Impulse Engine Control

The IPS is controlled through operational sofrtware routines stored in the main computer. As with the WPS command processors, genetic algorithms learn and adapt to ongoing experiences involing impulse engine usage and make modifications in handling both voluntary external commands and purely autonomic operations.

Relativistic Considerations

Aboard a starship travelling at velocities close to that of the speed of light, time passes much more slowly aboard the starship than it does in the rest of the galaxy. Such time differences can interfere with the requirement for synchronisation with Starfleet Command as well as overall Federation timekeeping. If warp propulsion is not available, impulse flight mayu be unavoidable, but will require lengthy recalibration of the computer clock systems, even if contact is maintained with Federation Timebase Beacons (FTB). It is for this reason that normal impulse speeds are limited to 0.25 c.

Emergency Shutdown Procedures

Hardware failures and override commands can place abnormal stress on the IPS, requiring various degrees of engine shutdoiwn. System sensors, operational software and crew verification work in concert to deactivate IPS components under conditions such as excessive thermal loads, thrust imbalances and other problems. Emergency shutdown routines involve valving off the deuterium fuel flow and safing the fusion initiator power regulators, while simultaneously decoupling the accelerator by bleeding residual energy into space or into the starship's power network. If the shutdown is of an isolated engine, the power load distribution is reconfigured at the first indication of trouble.

Catastrophic Emergency Procedures

As with the WPS, the IPS may sustain various degrees of damage, requiring repair or release of the damaged hardware. Where feasable, crews will enter affected areas in standard EV (extravehicular) garments (SEWG) to assure that damaged systems are totally inert, and perform repairs on related systems as necessary. Irreparably damaged IPS components, starting with the thrust vents and moving inboard to the DCA and IRCs can be taken offline and released if their continued prescence adversely affects the integrity of the rest of the starship.


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