The first people to step on to the surface of Mars won't arrive aboard the chemical-fueled rockets that delivered Apollo 11 to the Moon—they simply don't provide enough thrust to get to the Red Planet before exposing their crews to months of dangerous space radiation. Instead, NASA is turning to long-ignored nuclear-thermal rocket technology to deliver the first Martian explorers into history.
Gizmodo put together a nice history of nuclear rocket development. Unfortunately the headline's a little misleading. Manned nuclear rocketry is in no way guaranteed, as the details here prove.
The piece also doesn't give any consideration to legitimate competing ideas, like solar sails (sounds crazy, but they'd work - kind of - and would need to be huge) and especially futuristic sounding ion engines (slow start, but capable of huge speeds as the ship progresses).
And there's little here on timing, aside from how long it'll take to develop the plutonium. Sadly, we're in no rush to send humanoids to Mars. Building a feasible rocket is just a baby step.