Star Trek Impulse Drives

## **Impulse Drive**

Starships use impulse propulsion systems (IPSs) to move slower than the speed of light, which is required for travel within a star's gravity well, through solar systems, in starship combat, and similar situations. Impulse drives use fusion reactors to generate standard thrust via a standard Newtonian reaction - the thrust "pushes" the ship forward through space. Starships usually drop to impulse when they encounter anther ship to facilitate contact (or combat).

IPSs have four components: the impulse reaction chamber (IRC), or fusion reactor, of which there are three per impulse engine; the accelerator/generator (A/G); the driver coil assembly (DCA); and the vectored exhaust director (VED). Energy released in the IRC by the fusion reaction is channeled to the A/G, which raises the velocity of the plasma and feeds it on to the DCA. Electroplasma system (EPS) taps run from the A/G to divert some energy to power other systems on the ship. The DCA creates a field effect which aids the impulse propulsion process, then passes the energy on to the VDA, which directs it to thrust the vehicle in the desired direction.

A main impulse engine (MIE) capable of propelling a starship consists of four linked impulse engines. These engines may be grouped together, or divided into two groups of two to provide balanced thrust for structures such as separated saucer sections.

An impulse engine is rated for the amount of velocity it can provide. Regardless of an engine's maximum sublight speed, Starfleet generally limits impulse travels to .25c (paradoxically referred to as "full impulse") to minimize the time-dilation problems which occur as a ship approaches speed of light travel. Only in starship combat situations do starships commonly move at impulse velocities excess of .25c.

The accompanying table lists the classes of MIEs available.

The Game Master may allow a crewmember to make a Moderate (16) Repair Test to increase the maximum output slightly +.10c (+10 Space) if the Test succeeds exactly, +.20c (+20 Space) if it succeeds by 4 points or more (a ship's impulse speed cannot exceed .95c). Any additional impulse speed obtained in this way lasts 1D+1 rounds.
Impulse engines are also equipped with impulse capacitance cells which can provide a tiny burst of power to them. By releasing the cells' power directly into the driver coils, a ship can generate a one-second burst of impulse speed when the engines are otherwise not functioning due to lack of power.

### **Velocity**

The Sustainable and Maximum velocities the engine can attain. Sustainable velocity is the highest speed it can maintain without stressing the ship or its engines (all impulse engines' Standard speed is, by definition, .25c). Maximum velocity is the highest speed it can attain. Operating at Maximum impulse speed for longer than 24 hours risks damage to the engines. The Game Master should roll 2D every 10 minutes of travel beyond 24 hours, on a result of 2, 3 or 4, the impulse drive suffers damage. Repairs take one hour to one day per point of damage as if the engine had taken 25% damage.

### **Base Speed**

This is the standard cruising speed of the engine. Keep in mind the following: One Quarter Impulse: 6.25; Half Impulse: 12.5; Three Quarters Impulse: 18.75; Full Impulse: 25. Command Authority override is required to exceed Space: 25. This feature is built into the drive itself and requires a Very Difficult or greater (25+) repair roll to bypass.

### **Max Speed**

The maximum speed a ship's impulse engines can obtain is ten times the Base Space Speed. Command Authority override is required to exceed Space: 25. This feature is built into the drive itself and requires a Very Difficult or greater (25+) repair roll to bypass.

### **Atmosphere**

This is the corresponding Atmospheric speed of the Impulse Drive. This rating is only used if the ship is atmospheric capable. This speed does NOT correspond with the actual percent of the speed of light but corresponds with the Star Wars D6 Space ratings. This was done for the ease of game play. If you wish to use the actual percent of the speed of light in km/h, please go here.

### **Base Maneuverability**

This rating is added to the vessels maneuverability rating from its Size (See Charts Below). If the ship has no sublight drive, then disregard the maneuverability ratings altogether.

### **Multiple Impulse Drives**

If the ship has multiple impulse engines, the ratings are added together as indicated on the chart below. Multiple impulse drives installed on the same ship with NOT increase the speed on a ship, only its maneuverability.

### **Total Maneuverability Rating**

To get the ship's final maneuverability rating add the base maneuverability from the impulse drive to the base maneuverability from the ship's size further modified by the number of impulse drives the ship has installed.

*ex: A size 8 ship has three class 8 impulse drives installed. Its total maneuverability rating is 1D (class 8 impulse drive) + -0D+1 (size 8) + 1D+2 (three impulse drives) = 2D+1*

## **Source**

* Stardock Starship and Construction Manual (pages 38-40)
* thedemonapostle