CAPE CANAVERAL, Fla. (AP) — NASA's new megarocket will launch without astronauts on its test flight, now delayed until 2019 because of technical challenges, the space agency's top leaders said Friday.

In February at the request of the White House, NASA began studying the possibility of putting a crew on the first flight. After reviewing the costs and risks, the space agency decided against it. The White House took part in the decision, said NASA's Acting Administrator Robert Lightfoot.

Still in development, the super-sized Space Launch System rocket is meant to eventually send astronauts to Ma...