NASA says its first unmanned test flight Thursday of its spacecraft Orion is a first step toward Mars.
But Orion can't take astronauts to Mars.
Astronauts can survive within the Orion capsule for up to 21 days.
John Logsdon of the Space Policy Institute at George Washington University says NASA envisions the spacecraft as part of a broader deep space transportation system.
"It's the capsule that will take crew off the surface of the Earth and get them to a habitat, which would then be used for long-duration deep space missions."
Orion is scheduled to launch from Cape Canaveral Air Force Station on an four-and-a-half-hour mission that will test its most critical systems.
On future manned missions, astronauts will use Orion to orbit the moon, visit an asteroid and eventually Mars.
