Besides its wearing length, the trip was very chancy.  Only by refueling at a space station, then tacking back almost into Earth's atmosphere, could this primitive flying coffin, the Envoy, make the trip at all.  Once at Mars she might be able to return - if she did not crash in landing, if water could be found on Man to fill her reaction-mass tanks, if some sort of food could be found on Mars, if a thousand other things did not go wrong.