Mars traffic needs specialized transport legs

A Mars voyage divides into distinct transport jobs instead of asking one vehicle to do everything. One craft lifts passengers and cargo from Earth, another performs the long transit, and a third handles descent to Mars. Meeting those vehicles demands careful timing, but specialization prevents every expensive transport from carrying the equipment needed for every environment. A conveyor of outbound and inbound ships also gives the colony a regular supply link and some prospect of assistance between departures.