A little empty
This piece seems empty even if there are four ships in view, this is mainly because of your background and viewpoint. At first glance it's hard to make out that there's a planet that has rings behind those ships, all that's noticeable is the sharp white crescent and this green orb with yellow rays coming out There should also be more stars in the background and maybe a few more planets too, to give it the feeling that there's a real solar system around them. I like the design you chose for the ships, but maybe alter their individual colors or details a little.
It's a good piece, it could just be a little better.