Two groups announced plans Wednesday to send two astronauts on a 501-day trip in a spacecraft that would fly around the planet Mars in 2018. Taber MacCallum, CEO of Paragon Space Development and former NASA engineer Dennis Tito said the mission would cost under $1 billion and could use an existing rocket and capsule but must develop new life-support technology. The astronauts would likely be a married couple and because of the radiation risk, MacCallum said they'd be older and "out of the childbearing years."