How the Mars Exploration Rovers Work

We aren't really at the point yet where we can send human beings to Mars. The first and most important reason for that hesitation is our track record -- different nations have sent more than 30 probes toward Mars, but fewer than one-third of those probes have survived the trip. It's not a very good track record, and certainly not one that would encourage us to replace those robotic probes with human beings, at least until we've improved the odds of success.