Useful comment posted by George and copied from the forums

(sysVectorRandom) is designed to find a spot that is not near anything. The “10” in your call is the minimum distance from any “t”; it is not the maximum distance. If you want to pick a random spot near a planet, you can use something like:

(sysVectorRandom
     (random (sysFindObject Nil "t"))
     50
     10
     )

This will pick a random spot 50 light-seconds away from a random planet and not less than 10 light-seconds from any other object.