The only way I found to quit the game from a base is
1) take off
2) self desruction (Alt + D)
3) press "quit"
The manual says (p51) "To quit from a base, enter a base computer screen, select Options, then Quit Game". But how do I enter a base computer screen?
Alt+O does not work nor Alt+X, Strg+C, Esc or whatever. The Quine and the mission computer have no Options menu.