Why is human Mars exploration so surprisingly hard? The Space Review

As space policy experts mull over alternative strategies for astronaut exploration of the solar system, possibly including human flight to Mars, the recently-concluded fortieth anniversary celebrations of the Apollo 11 moon landing inspire one specific question: what’s taken so long?
In the heady days of the Apollo triumphs, even the “pessimistic” forecasts imagined it might take as long as twenty years to get astronauts to Mars. Optimistic schedules put the first footsteps on the Red Planet—another “giant leap for mankind”—as early as 1982.
When it didn’t happen in fifteen or twenty years, or even in twice that period, or even by current plans by twice again that period, the question naturally arose: why not? Had the national will failed? Had our adventurous culture lost its nerve?