It's a start. It would probably feel more interesting if you made it a bit quicker (using the speed slider).
Regarding adding asteroids: Have a look in your Space class. There is code where the rocket gets added. You need very similar code to create and add the asteroids.
For example:
Asteroid asteroid1 = new Asteroid();
and then you add it in a similar way to adding the rocket.
A new version of this scenario was uploaded on Sun Nov 23 14:37:13 UTC 2008
A new version of this scenario was uploaded on Sun Nov 23 15:28:07 UTC 2008
2008/11/22