I left my program open for 9 hours and it used up 700mb of ram, could someone review it?

[Gan via Digitalmars-d-learn]

I feel like the only way I can get better right now is if someone 
with more knowledge can give me some advice on the code I have 
written.

Here's the link: http://cl.ly/0s0Q1L1S3v0E

How can I make it use less CPU/RAM?
(Most code is in the Misc/SpaceBackground.d)