"Yet there are vital differences between Lewis and Clark’s expedition and a Mars mission. First, Lewis and Clark were headed to a place amenable to life; hundreds of thousands of people were already living there. Second, Lewis and Clark were certain to discover places and things of immediate value to the new nation. Third, the Lewis and Clark venture cost next to nothing by today’s standards. In 1989 NASA estimated that a people-to-Mars program would cost $400 billion, which inflates to $600 billion today."