For the second month in a row, the aerospace upstart SpaceX landed a rocket on an ocean platform early Friday, this time following the successful launch of a Japanese communications satellite.A live webcast showed the first-stage booster touching down vertically in the pre-dawn darkness atop a barge in the Atlantic, just off the Florida coast. The same thing occurred April 8 during a space station supply run for NASA. That was the first successful landing at sea for SpaceX, which expects to start reusing its unmanned Falcon rockets as early as this summer to save money and lower costs.Because of the high altitude needed for this mission, SpaceX did not expect a successful landing. But it was wrong. As the launch commentator happily declared, "The Falcon has landed.