I am using the video tutorials posted on this teachers / students website: http://www.teach-ict.com/programming/greenfoot/greenfoot_video_advanced.htm The Making Explosions video 2 refers to Vector.java and SmouthMover.java classes, but the webpages are all but missing.

I just uploaded a new scenario, Asteroids w/improved QActor SuperClass. The QActor class is a support class I created that provides smooth movement and turning for your actors. It is quite easy to use and the project has three different type actors that use it, 'Rocket', 'Rock' and 'Rocket.Shot'. If you decide to use it and come across any issues, I will be happy to help resolve them.

The videos are a bit old and the classes mentioned aren't available directly from the website anymore. However, I believe they can both be found in this scenario. Alternatively, you can import a newer version of the SmoothMover class via the "Import class" option in the edit menu.

Smoothe Mover: import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)