There is no joystick for a Mars rover. Commands crawl across the Solar System at light speed, and the replies arrive almost unimaginably faint — caught by three giant ears that keep the whole sky covered as Earth turns.
Three ears, no gaps
Every distant spacecraft humanity operates talks through the Deep Space Network: three antenna complexes — in California's Mojave Desert, near Madrid, and near Canberra — spaced roughly 120 degrees apart around the planet. The spacing is the design: as Earth rotates and one complex loses sight of a spacecraft, the next has already risen to take over. The network's largest dishes span 70 meters, and they are shared, on a schedule, by dozens of missions at once. When you read that a probe 'phoned home', one of these three sites took the call.
Whispers from the dark
The signals are almost absurdly weak. Voyager 1's transmitter broadcasts about 20 watts — a refrigerator bulb — and after crossing more than a light-day of space, the power reaching Earth is around a billionth of a billionth of a watt. Recovering data from that whisper takes the huge dishes, receivers chilled to near absolute zero, and data rates that fall as distance grows: Voyager trickles home at 160 bits per second, and New Horizons needed about 15 months to transmit its Pluto flyby home. Patience is a core technology of deep space.
The tyranny of light-time
The harder limit is time itself. Radio travels at light speed, and light is slow on Solar System scales: Mars is 3 to 22 minutes away one-way depending on the orbits; Voyager 1 is about 23 hours. That kills any dream of live control — by the time you saw a cliff in a rover's camera, the rover would have long since hit it. So nobody drives: engineers plan a day's activities, transmit the whole program, and the spacecraft executes alone. The most extreme case is landing on Mars, which takes about seven minutes — less than the one-way light-time. Every landing in Mars history was fully over, one way or the other, before mission control's first telemetry of it began.
Autonomy is the answer
That delay is why modern spacecraft are increasingly self-reliant: rovers pick their own path between waypoints, landers choose their own touchdown spot in the final seconds, probes safe themselves when something breaks and wait for instructions. The stack of tools built for talking across the dark — relay orbiters around Mars, laser links in testing, onboard judgment — is quietly one of spaceflight's great achievements: a nervous system stretched across hours of silence, still working after nearly fifty years for its farthest node.