The Martian troops, moreover, had no control over where there ships were to land. Their ships were controlled by fully automatic pilot-navigators, and these electronic devices were set by technicians on Mars so as to make the ships land at particular points on Earth, regardless of who awful the military situation might be down there.
The only controls available to those on board were two push-buttons on the center post of the cabin — one labeled on and one labeled off. The on button simply started the flight from Mars. The off button was connected to nothing. It was installed at the insistence of Martian mental-health experts, who said that human beings were always happier with machinery they thought they could turn off.
— The Sirens of Titan