Inside NASA's Next Space Project

March 24, 2009— -- For 27 years, the space shuttle has been the center of the U.S. space program and the only means to send crews up to space. But, in a year and a half, the shuttle -- now on its 125th mission -- will be retired by presidential mandate. With only nine or 10 flights left to go, the program is on the brink of a major transition.

So, what's next for NASA when the space shuttle quits flying? In effect, it will be back to the future. NASA will launch two rockets -- not one as they did in the Apollo days, when man first landed on the moon.

The Ares V rocket will take a lunar landing vehicle into Earth orbit, and another will carry a crew of four astronauts into a similar orbit to rendevous with the cargo rocket.

"The Ares V will be the largest launch vehicle that anyone has ever built," said Jeff Hanley, manager of NASA's Constellation Program, charged with paving the way for America's re-entry into space exploration. "[Ares V] will be assembled down at the Kennedy Space Center in the same building that the Saturn V was assembled in. But it will be able to lift substantially more than what Saturn was able to do.

"One of the things we wanted to do was separate the crew from the major cargo of the flight, which would be the lunar lander, all of the experiments and gear that the crew would take with them to the lunar surface," Hanley said.

The astronauts in their capsule will link with the spacecraft carrying their lander, then will reignite the engine from the larger rocket and head for a three-day trip to the moon. All four of the astronauts will get into the lander to go to the moon's surface.

Hanley told ABC News' Charles Gibson that it will be very demanding to achieve the goals of going back to the moon, and eventually, getting to Mars.

"We will go to the moon -- anywhere on the moon. We will stay twice as long as Apollo did with twice as many people, and be able to bring that crew home any time," he said.

The plan is for astronauts to live there for weeks at a time and perfect the systems that will later take man even deeper into space.

"The plan that we've laid out will actually lead humans to Mars some time in the next two or three decades," Hanley said.