Estimate arrival mission feature

I need help coding a mission system where enemies near your planet, but its show their estimate arrival. You the have an option to attack them or wait and attack near by enemies.

e.g The game Super Kasier Earth has this feature. (Here is a link<font color="brown">of the video, its in the beginning of the video</font>)

video link

I would like someone to help me by either telling how I can make this feature, or provide a sample capx.

Also would I need to learn arrays to make this type of game?

Thanks in advance

You can also download the demo at desura, click install game and then direct download.