Build:Impulse Propulsion System
6.2 Impulse Propulsion Systems
(Required)
Cost: Varies
Power Generation: Varies
Power Requirement: Varies
Starships use impulse propulsion systems (IPS) 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 another ship to facilitate contact (or combat).
6.2.1 Chemical Propulsion Systems
Cost: 10 x Size
Power Requirement: None (see text)
The earliest space vessels, such as the DY-100 class, used chemical propulsion systems which generated thrust by burning liquid oxygen and hydrogen as fuel. Ships with these engines can achieve velocities of up to 40,000 kilometers per hour, or 11 kilometers per second (approximately .00004% of the speed of light, or .00004 impulse). Compared to more advanced vessels, they are extraordinarily slow, clumsy, and primitive. A ship with chemical propulsion carries enough fuel for a number of seconds of burn equal to Size x 100.
A vessel with a chemical propulsion system has small internal batteries to provide sufficient power to run its minimal systems, such as life support and crude sensors (it can also have solar power generation, if desired). The crew makes do with stored food, gravity generated by rotating the ship, and so forth. The Narrator must evaluate and approve all equipment installed on a ship with chemical propulsion; most systems listed here or in Spacedock are not appropriate for these ships (in particular, ships with chemical propulsion cannot mount weapons, except perhaps for a single chemical or nuclear rocket launcher).
6.2.2 Fission Propulsion Systems
Cost: 10 x Size
Power Generation: 4
Power Requirement: 3 Power per 0.1 c used per round
Available: 1991
With the unveiling of the DY-B2 interplanetary drive in 1991, Humans were catapulted into the solar system in vessels far more capable than in the previous decade, equipped with the relatively limitless fuel of fission-powered nuclear thermal propulsion. By replacing the previous chemical propulsion systems, range was no longer limited to onboard fuel, but by the crew's capacity to generate its own oxygen and subsist on available food sources.
Note: this was an addition for game-canon, as the 2nd generation of interplanetary drive modules clearly did not make use of chemical propulsion. Velocities are established by the technology of the individual vessel classes and are not handled with that degree of granularity in these rules.
6.2.3 Fusion Propulsion Systems/Atomic Piles
Cost: varies
Available: 2036
Power Generation: Varies (see table)
Power Requirement: 2 Power per 0.1 c used per round
Ref: Omega1967's Spacedock Notes, p 121 (modified by me to match DD-published materials)
Primitive impulse engines arrived before warp technology was discovered and, due to their reliance on the new shipboard fusion reactors, were often referred to as "atomic piles". The first vessels to use other than chemical propulsion were those of the TAU extrasolar sublight explorer series, and these early fusion-powered engines were notorious for their quirky and dangerous nature. Being older and less-developed than their later full impulse cousins, they are much larger and less powerful.
Table
| Engine | SU | Sustainable / Maximum Impulse Speed |
Power Generation |
Year |
|---|---|---|---|---|
| Type I | 5 | .1c / .2c | 6 | 2036 |
| Type II | 10 | .11c / .23c | 8 | 2040 |
| Type III | 15 | .13c / .26c | 10 | 2045 |
| Type IV | 20 | .14c / .29c | 12 | 2049 |
| Type V | 25 | .16c / .32 | 16 | 2054 |
| Type VI | 30 | .17c / .35c | 20 | 2058 |
6.2.4 Main Impulse Engines
(Required)
Cost: Varies
Power Generation: See table
Power Requirement: 1 Power per 0.1 c used per round
Available: 2063
Impulse propulsion systems (IPS) 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, expressed as a percentage of c (the speed of light). Thus, an impulse engine might be said to provide .5c thrust, meaning it can propel a vehicle at half the speed of light. Regardless of an engine’s maximum sublight speed, Star Fleet 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. An impulse engine’s Standard speed is .25c or its listed Sustainable speed, whichever is less. Only in starship combat situations do starships commonly move at impulse velocities in excess of .25c.
Impulse travel costs 1 Power per .1c used per round (round fractions of .05 or lower down) (if the ship has multiple impulse engines, it only pays this cost once; additional engines only generate Power, they don’t propel the ship). Thus, a ship traveling at .75c must spend 7 Power per round to use its impulse engine. The Narrator may allow a crewmember to make a Challenging (8) Propulsion Engineering (Impulse) Test to increase the output of the impulse engines slightly (+.10c if the Test succeeds exactly, +.20c if it succeeds by 2 points or more; a ship’s impulse speed cannot exceed .95c). Any additional impulse speed obtained in this way costs 4 Power per 0.1c per round and lasts 1 + 1d6 rounds. For example, if a ship with a Class 3A impulse drive was made to move at .95c, it would cost 15 Power (7+4+4) per round to do so.
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.
A typical Type-series impulse engine can maintain Maximum impulse speed for a number of hours equal to Type + 1 before exhausting its fuel. (For example, a Type 6, 6A, or 6B engine could maintain maximum speed for seven hours.) If a ship runs out of impulse engine fuel, it cannot fly at impulse speeds or supply power from the impulse engines to other systems. Since impulse engines use deuterium for fuel, a warp-capable starship can drain deuterium from the matter tanks supplying the matter/antimatter reactor to power the impulse engines if necessary, but then risks running out of fuel for the warp propulsion system. Production developments allowed for a more efficient and proficient impulse engine starting in 2303, resulting in a new series name. Type-series engines that saw enhancement became Class-series engines and also enjoyed the increase in fuel range.
The accompanying table lists the classes of MIEs available.
Table
| Engine | SU | Sustainable / Maximum Impulse Speed |
Power Generation |
Year |
|---|---|---|---|---|
| Type 1 | 2 | .1c / .2c | 3 | 2063 |
| Type 2 | 5 | .25c / .5c | 8 | 2092 |
| Type 3 | 8 | .4c / .5c | 10 | 2103 |
| Type 3A | 10 | .5c / .5c | 12 | 2109 |
| Type 4 | 12 | .4c / .6c | 15 | 2125 |
| Type 4A | 13 | .4c / .65c or .66c | 18 | 2162 |
| Type 5 | 15 | .5c / .7c | 20 | 2188 |
| Type 5A | 18 | .5c / .75c | 23 | 2215 |
| Type 5B | 20 | .5c / .8c | 25 | 2250 |
| Type 5C | 22 | .55c / .8c | 28 | 2252 |
| Type 6 | 23 | .6c / .8c | 30 | 2284 |
| Type 6A | 25 | .6c / .85c | 32 | 2293 |
| Type 6B | 28 | .65c / .85c | 33 | 2297 |
| Class 1 | 5 | .25c / .5c | 8 | 2303 |
| Class 2 | 10 | .5c / .5c | 16 | 2303 |
| Class 3 | 15 | .5c / .7c | 24 | 2303 |
| Class 3A | 18 | .5c / .75c | 28 | 2303 |
| Class 4 | 20 | .6c / .8c | 32 | 2303 |
| Class 4A | 22 | .6c / .85c | 35 | 2303 |
| Class 4B | 23 | .65c / .85c | 38 | 2303 |
| Class 5 | 25 | .7c / .9c | 40 | 2317 |
| Class 5A | 28 | .72c / .9c | 44 | 2324 |
| Class 6 | 30 | .75c / .9c | 48 | 2341 |
| Class 7 | 35 | .75c / .92c | 56 | 2349 |
| Class 8 | 40 | .75c / .95c | 64 | 2357 |
6.2.5 Acceleration Upratings
Cost: Varies
Power Requirement: Varies (see table)
Available: 2063
Standard impulse engines accelerate at half their maximum impulse speed per round. Some vessels are equipped with uprated impulse systems which can accelerate more quickly than this. The accompanying table lists packages and SU costs.
The SU cost for the uprating includes modifications to the SIF and IDF so that the ship can handle the increased stress on the hull. If a ship has multiple impulse engines, it must buy an acceleration package for each one, and the packages must all be the same one. TOS-era ships may only take the Class Alpha acceleration uprating package.
Table
| Package | SU | Power | Rate of Acceleration | Year |
|---|---|---|---|---|
| Class Alpha | 2 | 1 | 66% of max impulse/round | 2063 |
| Class Beta | 4 | 2 | 75% of max impulse/round | 2307 |
| Class Gamma | 8 | 4 | 100% of max impulse/round | 2328 |
6.2.6 Reaction Control System
(Required)
Cost: 1 x Size (Primary), 0.5 x Size (Auxiliary)
Power Requirement: 2 Power per round (Primary)1 Power per round (Auxiliary)
Ref: Spacedock, pp 39-40
The Reaction Control System (RCS), colloquially known as “thrusters”, is used to move the ship while entering or leaving spacedock, or in other situations where precise control of the ship’s motion is necessary. RCS engines are located at appropriate points on the body of a ship. They consist of a gas-fusion reaction chamber, magnetohydrodynamic (MHD) energy field trap, and vectored-thrust exhaust nozzles. Some ships also have an auxiliary RCS system which functions at half strength; this costs 0.5 x Size in SUs. An auxiliary RCS improves a ship’s maneuverability.
When using the RCS system, which requires a Routine Crew Skill Test for most delicate operations, a ship moves at a top speed of .025c (one-quarter of a Movement Unit per round, in game terms). An RCS occupies 1 x Size in SUs and costs 2 Power per round of use. A ship can double its thruster speed to up to .05c for an additional 3 Power per round.
If a ship has no RCS, or its RCS is malfunctioning, it can try to use impulse engines as thrusters.
6.2.7 Impulse Thrusters
Cost: 2 x Size
Power Requirement: 2 Power per round
Available: 2326
Ref: Spacedock, p 40
Ships of Size 5 and smaller can also install impulse thrusters, a special type of thruster which improves a ship’s speed and maneuverability. They add +.1c to the ship’s impulse speed (maximum of .95c) and provide +1 die to roll when the pilot makes Shipboard Systems (Flight Control) Tests to maneuver the ship at speeds of .6c and above. Impulse Thruster technology was not available prior to 2326.
SFC Technology Index
- Chemical Propulsion Systems: Index
- Fission Propulsion Systems: Index
- Fusion Propulsion Systems: Index
- Reaction Control System: Index