I did not have success using the solution proposed above.
KSP is prevented from running on macOS Sierra by a new security feature in called "app translocation."
The good news is that there is an easy fix:
Install KSP normally by dragging the "KSP_osx" folder into your "Applications" folder
Move "KSP.app" from your Applications folder to your desktop by holding down the "command" key and dragging it (If you don't hold down "command" you'll make a shortcut. We want to actually copy the file.)
Move "KSP.app" from your desktop back to the "KSP_osx" folder within the "Applications" folder
