 A computer in the missile launcher calculates the difference between the current aim spot and the missile's location, and sends commands to the missile via radio to bring it to an impact point.The basic Javelin missile body was retained in the upgraded Javelin S15, which replaced the original's radio command guidance system with a semi-automatic laser system.This uses a laser in the launcher to "paint" the target, and a seeker in the missile nose cone sees the reflected signal and homes in on it.