Old versions of SpaceEngine are available for free.
SPACEENGINE 0.9.8.0
SYSTEM REQUIREMENTS
MINIMUM
Dual-core 2 GHz
4 GB RAM
Nvidia or AMD/ATI 1 GB VRAM*
OpenGL 3.3
Windows XP
Note: old versions of SpaceEngine will not work with Nvidia driver version 436.02 or later.
Executable Installer (automatic install) – 1GB
Download and info:
http://spaceengine.org/download/spaceengine/