Terra Invicta – Missile Acceleration Mechanics

Explanation of Missile Acceleration Mechanics

How missiles decide when/how much to accelerate and how that differs between missiles is not explained at all in the game, so I decided to find the code that governs it to see how it works.

I made this so I can evaluate which missiles to use in what situations, but I’ve seen this question come up a lot so I’m posting it here as well. The numbers I calculate and formulas I give will be in the simplest case of a missile going directly at a stationary target, but this is fine for looking at the relative performance of different missiles.

All missiles follow the same basic flight plan with 3 phases:

1) After being fired, the missile accelerates until it reaches what I’m calling its “cruising speed”. This depends on the missile and your velocity when shooting. If your ship velocity is at or exceeding the highest cruise speed or the target is close enough when firing, your missiles don’t do the initial burn.

  • Formula: Accelerates until missileVelocity <= currentDV * 1/tan(pi/180 * ManeuverAngle). This is the cruising speed. This means missiles with higher dV and lower ManeuverAngles have higher cruising velocities.

2) Once at the cruising speed the missiles don’t accelerate until they get close enough to the target. How close depends on the missiles remaining dV, so depends on how much fuel was burned in the initial acceleration and trajectory adjustments.

3) When close enough, the missile accelerates until it runs out of fuel or hits the target.

  • Formula: Accelerates when distanceToTarget <= currentDV * missileVelocity / maxAcceleration. This means it will start burning as soon as it is close enough that it can burn constantly without running out. Higher dV and lower max acceleration increase this distance.

Google Doc Link.

In the linked doc, I took the relevant stats from the missile template file and calculated max cruise velocity and what it would be if shot from a stationary ship or a ship going 0.65kps, the fastest starting speed. For each of these cases I calculated the distance at which the missile will stop cruising and accelerate at the target. I also put the initial speed needed for a missile to start phase 3 acceleration immediately. Any trajectory adjustments will decrease these cruise velocities and increase the distances, so these aren’t quite accurate for moving targets.

Additional Information:

  • In terms of “cruise speed” what matters is your ship and your target relative velocity. Which may not be obvious for less phyisics-savvy folks.
  • In cruise mode missile still tracks its target.
  • While maneuver angle is a separate stat, right now it tightly corellates with warhead type.
  • Missile tracking is zero-order. Meaning, it always flies towards target without accounting for its velocity or acceleration.
  • Those three phases are a lie. Missile runs decision-making algorithm at each tick and there is nothing preventing it to e.g. fall back from p.3 to p.2 if target tries to dodge and suddenly is further away than terminal phase criteria allows.
Volodymyr Azimoff
About Volodymyr Azimoff 494 Articles
Being a big gaming fan, I believe that I have a lot to share with other gamers. I got my first official job in the game industry in 2005 and continue to develop there. It's a true blessing when your passion, hobby, and job combine into something one. My favorite console is the Nintendo Switch. I think you can all guess why. Because I just bought a Steam Deck. I love playing on PC, but my main love for me will always be Xbox. Anyway, it's complicated and simple at the same time. After all, I'm back in the days of the ZX Spectrum (1994)…

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