Engine

Setting background tech parameters

The engine is ship propulsion system that allow interplanetary travel. Engines propel the ship by burning fuel reserves. Platform without engines or Ships with damaged engines will be unable to move unless towed.

Overview

An engine is an absolute necessity for any ship that wishes to travel faster than 1km/s. Any number of engines can be mounted on a ship, although only one variety of engine may be mounted per ship. There are military and commercial engines, the difference being that an engine of size 25 HS and larger with a power rating of -50% and lower is automatically classified as commercial. Military engines flag any ship they are on as military ships, and thus subject to maintenance failures and requiring overhaul. Therefore commercial-engined ships tend to be slower than their military-engined counterparts. This is offset by a much better fuel efficiency and no maintenance failures. In effect, commercial engines are trading a high maximum speed for fuel economy.

You might get to the point where your empire operates hundreds of freighters, asteroid miners, fuel harvesters, tugs, troop transports and other non-warships. They need engines with great fuel economy or they'll eat up your reserves faster than you can build new refineries.

The total power output from a ship's engines will determine the speed of the ship. Speed is one of the most important aspects of a ship. Superior speed means higher capacity per time for cargo ships, and a battle fleet with higher speed has a significant advantage, able to dictate the range of the engagement, intercept the other force, or disengage a hostile force.

All engines use fuel to operate, limiting cruising range, with high powered engines consuming exponentially more fuel than the default value. Range and speed are generally increased at each other's expense, or by building a significantly larger and more resource-hungry ship. As you research Fuel Consumption tech, you can design engines that will use less fuel for the same power output.

Engines create a thermal signature, one that can be detected by Thermal Sensors, so having high-powered or numerous engines on a spy ship is not advisable. By dropping a ships speed or by designing engines with Thermal Reduction, a ship's thermal signature can be reduced.

There is a separate design menu for the much smaller Missile Engines. These function along the same lines, though.

Examples

Let's say you have researched Magneto-plasma Drive Tech and Fuel Consumption x 0.4.

Commercial engines

The minimum size for commercial engines is 25 HS (= 1250 tons) and the power modifier needs to be -50% (or less). It looks like this:

200 EP Commercial Magneto-plasma Drive
Engine Power: 200 Fuel Use Per Hour: 10.6 Litres
Engine Size: 25 HS
Development Cost for Project: 500RP

Compare this to an engine with maximum size (50 HS = 2500 tons) and twice the power:
400 EP Commercial Magneto-plasma Drive
Engine Power: 400 Fuel Use Per Hour: 14.16 Litres
Engine Size: 50 HS
Development Cost for Project: 1000RP

Fuel use is only 14 litres per hour, compared to 21 if you had installed two 200EP engines instead, for the same power output. Development (i.e. research) cost to design this engine is twice as high, though.

Military engines

Now you decide to design a compact but powerful standard engine for your medium-sized warships. You intend to stick two of these on a frigate, three on a destroyer and so on. 15 HS (= 750 tons) sounds like a good size and you select a power modifier of 175% because you need that extra bit of wroooom:
420 EP Magneto-plasma Drive
Engine Power: 420 Fuel Use Per Hour: 578.51 Litres
Engine Size: 15 HS
Military Engine
Development Cost for Project: 2100RP

Research costs are significant, and fuel use is fourty times higher than for the commercial engine of similar power. You can save a lot of weight with military engines, but all that engine power severely limits your range. Perhaps your destroyers would do better with a single, large engine instead? Let's see:
1260 EP Magneto-plasma Drive
Engine Power: 1260 Fuel Use Per Hour: 1123.04 Litres
Engine Size: 45 HS
Military Engine
Development Cost for Project: 6300RP
It has three times the power of the 420EP engine, but research costs, which scale with engine size, are now exorbitant. Having only one engine means being more vulnerable to lucky enemy hits, too. Fuel use compared to three smaller engines is much reduced, though.

Background Tech

Engine Technology determines the power output per HS (thrust:weight ratio, essentially) of the engine. Conventional empires start with the Conventional Engine technology, in able to represent pre-TNE engines pushing around hulls constructed from TNE materials. Conventional engines have a base output of 1 unit. One unit of engine power are the amount of power required to propel 50 tons (1 HS) against the Trans-Newtonian drag at 1000 km/s (this unit is also known as a EP (engine power)). Therefore, for a ship or missile

Speed = (Total Engine Power / Total Class Size in HS) * 1000 km/s

You are obviously going to be using the best tech, which is automatically selected.

Technology	Conventional	Nuclear Thermal	Nuclear Pulse	Ion	Magneto-Plasma	Internal Confinement Fusion	Magnetic Confinement Fusion	Inertial Confinement Fusion	Solid-core Anti-matter	Gas-core Anti-matter	Plasma-core Anti-matter	Beam Core Anti-matter	Photonic
Power per HS	0.2	5	8	12	16	20	25	32	40	50	60	80	100
RP cost	-	2,500	5,000	10,000	20,000	40,000	80,000	150,000	300,000	600,000	1,250,000	2,500,000	5,000,000

Power/Efficiency Modifiers allows for creating super-tuned or de-tuned engines, increasing output power at the cost of fuel efficiency or vice versa. Making these alterations carries with it an increased risk of engine explosion if the engine takes damage, causing a secondary explosion.

Modifier	0.1	0.15	0.2	0.25	0.3	0.4	0.5	1	1.25	1.5	1.75	2	2.5	3
Fuel per EPH	0.00	0.01	0.02	0.03	0.05	0.1	0.18	1	1.75	2.76	4.05	5.66	9.88	15.59
RP cost	30,000	15,000	8,000	4,000	2,000	1,000	-	-	1,000	2,000	4,000	8,000	15,000	30,000

Fuel Consumption determines the rate at which fuel is consumed. A ship running at its max speed consumes fuel (in litres) at a rate equal to its engine power every 10 hours, or fuel (in litres) equal to 2.4 times its engine power every day. A ship with one Conventional military engine (total power output: 1 EP) consumes 2.4 litres of fuel per day. If it had a fuel tank capable of carrying 50,000 litres (the standard fuel tank size), it could operate for 20833 days (about 58 years). If its max speed was 100 km/s, it could travel for 179 billion km before running out of fuel (about 15 round trips to Pluto).

Modifier	1	0.9	0.8	0.7	0.6	0.5	0.4	0.3	0.25	0.2	0.16	0.125	0.1
RP cost	-	1,000	2,000	4,000	8,000	15,000	30,000	60,000	120,000	250,000	500,000	1,000,000	2,000,000

Thermal Reduction applies a reduction to the thermal signature generated by the engine. This makes it harder to be detected by Thermal sensors. Great for engines meant for stealth ships, at the cost of increased cost to research and build. The thermal signature for an engine is equal to its power output * its thermal reduction modifier. A 25% reduction to a 40 EP engine would cause it to have a thermal signature of 30.

Signature (%)	100	75	50	35	25	16	12	8	6	4	3	2	1
RP cost	-	1,500	3,000	6,000	12,000	25,000	50,000	100,000	200,000	400,000	750,000	1,500,000	2,500,000

Engine Size ranges between 1-50 HS. Fuel consumption is reduced by 1% per HS, and HTK is increased per 2 HS Larger engines are therefore more efficient and sturdy at the cost of being less flexible during ship design, less redundant during combat and more expensive to maintain per-unit.