A surgical system includes a preload assembly in a surgical instrument surgical instrument manipulator that is under the control of a controller. The controller can automatically cause the preload assembly to engage and disengage a preload. A surgical apparatus includes a surgical instrument manipulator assembly and a sterile adapter assembly. The sterile adapter assembly is mounted in the distal face of the surgical instrument manipulator assembly. When the preload assembly configures the surgical instrument manipulator assembly to apply a preload force on the sterile adapter assembly, the sterile adapter assembly is removable from the distal face of the surgical instrument manipulator. The sterile adapter assembly includes a mechanical sterile adapter assembly removal lockout and a mechanical surgical instrument removal lockout.