Probably Radar based tracking with the possible add-on of multiple visual angles being able to communicate with each other. If you are interested in some further reading, here are some interesting articles/videos:

Shuttle launch imagery from land, air and water - http://www.nasa.gov/pdf/167722main_LaunchImagery06.pdf

Software to control a telescope (with sample videos) - http://www.optictracker.com/Home.html

Description of NASA's setup - http://photo.net/casual-conversations-forum/00cv5p

PDF of L3's system which provides a great overview - http://www2.l-3com.com/ios/pdf/L-3%20Brashear%20Capabilities...