In the Freelancer data/equip.ini file
Sample missile

[Munition
nickname = missile01_mark01_rtc_ammo
explosion_arch = missile01_mark01_rtc_explosion
loot_appearance = ammo_crate
units_per_container = 10
hp_type = hp_gun
requires_ammo = true
hit_pts = 2
one_shot_sound = fire_missile_regular
detonation_dist = 4
lifetime = 6.250000
Motor = missile01_mark01_rtc_motor
force_gun_ori = false
const_effect = li_missile02_drive
HP_trail_parent = HPExhaust
seeker = LOCK
time_to_lock = 0
seeker_range = 1000 This changes how long it tracks. Change to 5000 for longer time. Can still be defeated by countermeasures.
seeker_fov_deg = 35
max_angular_velocity = 2.903330
DA_archetype = equipment\models\weapons\li_rad_missile.3db
material_library = equipment\models\li_equip.mat
ids_name = 265146
ids_info = 266146
mass = 1
volume = 0.000000

Michael "Finalday"
In Memory Of WLB

Thanx man. Just one more thing. do u or anyone else no if there is a limit u can set this value to?

Eagles May Soar. But Weasels Dont Get Sucked Into Jet Engines

I have set it as high as 10,000
If you modify the muzzle velosity too, to 5000, it can out run any ship so long range is not nessisary. The limit of range would probably be your scanner range to see the enemy.

Michael "Finalday"
In Memory Of WLB

Just trying to help here. If your trying to make your missile track for more than a few seconds. Shouldn't you also change the "lifetime=" line? I believe that's the one that determines when the missile self destructs. You should also change the "seeker_fov_deg=" to make sure that the missile can backtrack if it misses the target on it's first pass. Otherwise it will lose lock and just fly off until it blows up on its own. If you want a missile that can quickly turn and keep even evading light fighters in its sights make sure you bring up the "max_angular_velocity=" value. This makes the difference between a missile that can corner quickly or one that takes a nice big loop.