I got to wondering, after the discussion last night, if a low technology (TL6) antitank rocket with simple guidance could even hit a free trader.

The gif above is depicting real time flight (1 second = 1 second, if your browser is rendering at 24 fps).

Our free trader is flying nape-of-the-earth (50 meters altitude) for who knows what reason, drive barely ticking over at 0.5% power, which results in a little less than 100 meters/second velocity. As are all high tech starships in Traveller, it is immune to gravity because it doesn't like gravity.

The local rebels, or whoever, want to take out this free trader and are equipped with a single rocket with a mass and diameter of a Javelin, and a rocket motor which produces approximately the same thrust over time that the Javelin motor does. The rebels position themselves appropriately and take the shot just as the free trader passes overhead. Impact occurs in 7.01 seconds - this is after the rocket motor burns out, so it's a good thing (for the rebels) that the free trader did not attempt to evade the shot.

My ultra simple guidance system cannot handle an incoming target, the rate of change of "position relative to the momentum of the rocket" is too much for the performance of the rocket to cope with, and it makes no estimate of where the ship will be in the future, it just aims at where it is right now. Aerodynamics other than drag aren't computed which will greatly harm the ability of the missile to maneuver, but that will take a bit of time to put together.

I had to run several times to get a situation in which the TL6 rocket was able to hit the free trader. Flying at 500 meters altitude with throttles set to 2% thrust makes the starship completely immune to this type of attack - the javelin having to climb against gravity hurts it quite a bit.

I very much doubt something unguided like an AT4 would be able to hit a starship even if the starship is in very low speed flight.