The White House has approved NASA's plan to replace the nation's aging fleet of winged spaceships with a new generation of vehicles meant to carry human explorers back to the Moon and onward to Mars and beyond, aerospace experts said yesterday. The new rockets and spaceships are a radical departure for the space program, rearranging the components of the space shuttle into a new design expected to be more powerful that the shuttle but also safer. The shuttle has had two fatal accidents in 114 missions. "It's a thumbs-up for NASA to pursue the shuttle-derived vehicle," said John M. Logsdon,...