In an op-ed on AOLNews.com, Buzz Aldrin, the famous Apollo 11 astronaut, lays out a rather simple plan for sending humans to Mars by 2019: extend the shuttles by three or four missions then use commercial firms to carry crew and cargo to the space station while NASA builds a prototype spacecraft called the Exploration Module, or XM.

The prototype of this craft, which would operate only in space, could be built using excess modules and parts left over from constructing the station itself. Brought up as cargo aboard the space shuttle–which I also propose we keep flying for several additional missions and not retire it as NASA is planning to do–the XM would be docked to the station and outfitted by astronauts.

Once a rocket engine is attached to the prototype XM, we could take it out for a spin, cycling between the station and the moon. The XM wouldn’t land on the moon but conduct a flyby, like the Apollo 13 mission did back in 1970.

Aldrin has been a proponent of scraping plans for returning to the moon, and instead focusing on Mars. He even called the new plan for NASA proposed by the Obama administration the president’s “JFK moment.”

Aldrin also says in his op-ed that his plan, which he calls a “unified space vision”, would keep NASA in the human spaceflight business. Many congressional members, for example, have voiced strong concerns that the administration’s new plan would threaten America’s leadership, and the very existence of the U.S. human spaceflight program.

By building a deep-space craft, NASA can use much of their engineering know-how and put a form to Charlie Bolden’s Mars mission dream. It allows the commercial folks their unfettered access to the station, as President Obama proposes. And it recommits America to leadership in space by aiming at Mars, using parts and equipment already paid for by the taxpayers.