The race to Mars: here's how SpaceX ranks against the competition

On Tuesday, SpaceX CEO Elon Musk announced his ambitious — if crazy — plan to colonize Mars within the next 40 to 100 years. But Musk isn’t the only one with Mars dreams and ambitions. In fact, people have been drawing out missions to the Red Planet for at least the last 70 years — and we’re still waiting for one to take flight.

How do the most prominent plans stack up?

One of the early proposed missions that set the stage for today’s Mars plans was the Mars Direct proposal, which was published by aerospace engineers Robert Zubrin and David Baker in 1991. They thought it might be possible to land the first crewed mission to Mars as early as 1999. That didn’t happen of course, but some of their ideas — like sending a return vehicle to...