The deviation from your initial trajectory is 1/2at^2 where "t" is time of flight, and "a" is net unexpected accelerations. A 30 minute flight time is 1800s, me

The deviation from your initial trajectory is 1/2at^2 where "t" is time of flight, and "a" is net unexpected accelerations. A 30 minute flight time is 1800s, meaning that if you have a target with 20m of give, you can only tolerate an error in your predicted net acceleration of 0.000001g. This is not even close to achievable at launch time. Long story short: make sure you have corrective gliding maneuvers as part of your imaginary system;)