# Quasi-Newtonian Propulsion (SEIV)

Quasi-Newtonian Propulsion (QNP) is a movement scheme for SE4 that tries to mimic real-world Newtonian movement as closely as possible. A hull's total movement is represented as a function of a hull's mass. In other words, in a QNP system, the bigger ship's hull, the more engines it takes to move at a given speed.

Newtonian physics would have that the acceleration of a ship be dependent on the thrust of its engines divided by its mass (F=ma). Unmodded SE4 uses a system where Speed is equal to the thrust of the engines, no matter what the mass of the ship.

Since SE4 does not model acceleration in its movement system, the QNP compromise is that speed should be dependent on thrust divided by mass (F=mv).

In most QNP implementations, the max number of engines per hull restriction is either eliminated or much more relaxed, allowing the user more choice in how fast they make their ships.

## Contents

## SE4 limitations

There are a few limitations in SE4 that you must be aware of when implementing a QNP scheme.

- Acceleration is not modeled, so F=mv is the closest to Newtonian physics that can be achieved in SE4.
- There is a maximum of 255 "standard movement" points allowed on a design (before factoring in the hull's engines per move requirement). This restricts the scale of your QNP scheme, and may limit the maximum speed of larger ships. Any more than 255 and the ship's total movement will reset to zero.
- Only integer values for "standard movement" points are allowed.
- Ship speeds above 30 movement points will not be useful in simultaneous-turn games. Ships of over 30 speed will only move once per "day", and will cover at most 30 sectors, so any total movement beyond that is irrelevant. Ships in sequential games have no movement limit.

## Calculating Speeds in SE4

To calculate the final speed of a ship in SE4, the following method is used:

- Add up all "Standard Movement" points on a ship.
- Divide by the "Engines Per Move" setting on the vehicle, rounding DOWN.
- If the speed of the vessel is at least one, add any "Bonus Movement" points, add any "Extra Movement" points, and add 1 speed if the race has the "Propulsion experts" trait chosen.

## Designing a QNP scale

Any QNP model requires a scale. This only fixes the numbers that will be used internally by the mod, and does not determine how much space is required on a ship to move at a specific speed.

*NOTE: Since ships, fighters and drones use completely separate engine components, the mod can and should have a separate scale for each type of vehicle.*

If the scale is very large, then bigger ships will be able to be packed with engines without exceeding 255 base movement points and having their total movement reset to zero. Unfortunately, a large scale may cause inaccuracies due to rounding errors. Given the default ship sizes in SE4, a value of 1 "standard move" per 50kt of ship providing 1 Speed is the best choice. If the escort were changed to a size of 100kt or removed entirely, then 1 "standard move" per 100kt of ship providing 1 speed would be an option. For fighters, a value of 1 "standard move" per 5kt of fighter providing 1 speed would likely be the best choice. In any case, the value you choose should divide evenly into all hull sizes (or as many as possible).

## Implementing the QNP system

Once you have chosen a scale for your QNP system, you can start editing the mod files. Open VehicleSize.txt (SEIV), and for each ship:

- Find the Hull size in kT.
- Divide the hull size by your scale, determined above.
- Set the "Engines per Move" setting to the value calculated in step 2
- Set the "Requirement Max Engines" to 255.

Go back through the file, and repeat the process for all fighters, using the fighter scale chosen above.

## Balancing the QNP system

If you were to start a game you should quickly find that larger ships do indeed require many more engines to reach a particular speed than smaller ships. However, you will also notice that it takes an incredibly large number of unmodded engines to achieve even speed 1.

It is time to mod the engine components. What you will have to do is increase the number of "Standard movement" points each engine component provides. Too much, and your ships will zoom through the galaxy at 30+ sectors per turn. Too few, and your ships will be giant clusters of engines that can barely crawl through space.

A good choice for a scale of 50 is 3 Standard movement on an Ion engine. The bonus movement points provided by the higher-tech engines are clearly not Q-N. Instead of providing a bonus movement, simply have the engine provide more standard movement! If an Ion engine provides 3 standard movement, you could have a Contraterrene drive provide 4, a Jacketed Photon drive 5, and Quantum engines 6. Thus an escort (3 engines per move) would need 4 Ion engines to move at speed 4, but only 3 CT drives to move the same speed, and only 2 Quantum drives to move speed 4. Alternatively, you could reduce the size of the higher-tech engines, while they provide the same amount of thrust. There are many ways to balance the speed of the engines at this point, just be creative.

Once you have modded the engines, be sure to check that the maximum speeds are all reasonable throughout the range of hull sizes. Be sure that escorts cannot travel beyond a speed of 30, and that the largest ships can actually move.

*Note: the fastest possible hull size is not actually the escort! While the escort must spend almost 20% of its hull space on bridge/life support/crew quarters, a Light Cruiser spends only 8%. Under a QNP system, and given equal technology, a larger ship can go faster if all of its free space is devoted to engines.*

Some other components that you will have to alter will be:

- Solar sails
- Afterburners
- Higher-tech fighter engines.

## QNP side-effects

When implementing a QNP system some common side effects will show up.

- Larger ships will burn vast amounts of supplies moving from one sector to another. Since they require more engines, they use up proportionally more supplies. This means that it will take exactly the same amount of supplies to move Two 400kt ships from point A to point B as it will to move One 800kt ship from A to B at the same speed.
- Smaller ships remain useful late in the game. The fact that large ships must spend about the same fraction of their space on engines as the little ships means that given fleets of equal mass, the fleet of small ships will carry roughly the same tonnage of ordnance as the fleet of large ships. The large ships will have mounts and be harder to kill individually, but the smaller ships will have a defense bonus due to size.
- The final speed of a ship will be totally dependent on the designer. Ship designs will be more diverse, with very fast scout ships composed only of engines and supply tanks, and slower warships that carry extra firepower or shields. Each race may have a different opinion of the optimum balance between engines, shields and weapons.