what type of user-space applications are you going to develop?
Take a loot at these
Leo
i am seeking ARM for startracker in space. which one of imx.6 is suitable for startracker?
If You mean space / cosmic application special protection features such as memory with ECC should be applied.
Our i.MX series is not intended for such applications. You may take a look at the Layerscape (ARM based).
Note, it is not launched yet.