Argument: Mission to Mars will have major communications time-lag
"Going to Mars: A mission fraught with risk." Canadian Space Agency. September 3, 2008: "The 20-minute communications lag. Another difficulty is the communications lag between Earth and a spacecraft travelling to Mars. Depending on the distance between the two, it can take almost 20 minutes to send commands, and then another 20 minutes before a response is received. Scientists must react quickly when problems arise, and then wait with great patience for the response, which will arrive 40 minutes after they send the initial signal. This also means that robots and systems we send to Mars must be able to make some of their own decisions, or at least know to wait for a command if something is not right."