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accurate & reliable way to launch stuff at a certain speed ?

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tinkering on ballistics again, atm i have troubels getting my jet-driven projectile to accelrate nearly instantly to a certain variable speed (desired vfront between 50 and 150 ) - atm im using a pid and a counter ( maths operator&multiplexer ) to shut the jet off some 10th seconds after launch and/or as the desired speed is reached. In theory the pid shouldnt alow the projectile to get faster than its setpoint, but if the kp is to high, the initial thrust is so high that the projectile reaches speeds above the setpoint - if the kp is to low though, the projectile doesnt reach the desired speed fast enough. With some trial & error i reached a good precision when using a fixed velocity. However i want to optimise the projectiles flightpath for an relatively flat arc ( so instead of lauching almost straight up when a target is close, the projectiles launch speed should be reduced until a launch at 45° would hit the target )

I also used fast pistons  to toss grenades before, but it doesnt seem very precise / affected by framerate

any ideas ?

changed the design of my launcher a bit so it uses a larger rocket with fins. Also now using a fixed launch angle of 45° and instead just varrying the missiles speed based upon distance ( d=vē/g   if launch at 45° and startpoint and impact point at the same height ). Tends to shoot a bit too far at high distances, but hits accurate at distances around/below 500

Take a look at my AutomaticBallisticRocketTurret the rocket should be easy enough to separate from the rest of the turret. the jet just has a thrust of 2,000 and I turn it off after velocity = 2,000

mind you my speed is so fast I don't really worry too much about getting that ballistic drop until the range is REALLY far.

For small missiles it may be possible to use plasma cannons as a form of propulsion to deliver a fixed impulse.

On planets, missiles will always overshoot at long ranges due to the low gravity at high altitudes and the curved ground dropping away beneath them.

You could try not being especially accurate with the launch and always overshoot the target, then use an air brake/reverse thrust to switch to a more accurate final trajectory when close to the target.

Also thought about adding reverse thrust to that missile, set the lauch to double speed ( so the flightpath should have its highest point directly above the target ) and stop the missile midair when directly above the target, so it will fall down at the target from directly above ( maybee even accelerating as soon as pitch hits -90 )

in the meantime i tried using a hypercannon



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