I have prepared an update to AA (1.2) which adds red line laser targeting and homing missiles.  When you pick up the rocket packs, a laser locks on to the first alien it detects and when you fire a rocket, it will follow the laser to target.  Most aliens require 2 rockets to eliminate or combination of rocket and normal bullets.

This release will not be posted until I get an iPad when they are released in the UK in April because I want to make sure the player can rotate the device in all directions and allow them to play landscape or portrait.