From our Expert Voices conversation on travel to Mars.

For four months in 2013, I lived and worked as if I were an astronaut on Mars, thanks to the NASA-funded HI-SEAS project. My crewmates and I produced data on the social challenges inherent in long-duration space exploration, because a breakdown in human systems can be just as catastrophic as a rocket failure.

While Elon Musk's Mars plan highlights reusable rockets and in-orbit fueling schemes, it appears thin on details of the people who would fly. We do know he intends his first crews to be wealthy: recent estimates put a ticket for a would-be Mars colonizer at $500,000.

How will these crews of high rollers divvy up the work necessary to build a city on Mars? Which of the paying customers will clean the toilets, collect the trash, or restock the food supply? Or, will a service crew be sent along, perhaps on a free ride? And if so, what might be their path into a society that presumptively belongs to those who bought their way in?

The bottom line: As we know from history, colonization isn't simply about building better ships to take bold adventurers to new and exotic shores.

Other voices in the conversation:

• Bobby Braun, aerospace engineer, University of Colorado, Boulder: Mars is within reach
• Francis Cucinotta, radiation researcher, University of Nevada, Las Vegas: There are too many unknown health risks to go to Mars soon