"It’s amazing to think that this thing I have been working on in various capacities for the last eight years is about to send four astronauts around the moon for the first time in a half-century.”

The United States is preparing to send astronauts around the Moon for the first time in more than half a century, riding a towering new rocket that is now assembled and undergoing final checks in Florida.

NASA could be sending a crew on the Orion spacecraft out past the moon in less than a month if everything falls into place. But first the agency has to get its rocket to the launch pad.

NASA is backing a radically different way to reach space, one that swaps towering rockets for a ground-based launcher that whips payloads to orbital speeds before they ever see a drop of fuel. The concept, often described as a giant space catapult, is ...