NASA's new moon rocket passed a key design milestone late Wednesday: Senior NASA management unanimously approved the preliminary design review of the planned Ares I rocket that would launch astronauts into space by 2015 and back to the moon by 2020.

But next year there will be another narrowly focused "delta" preliminary design review for one pending engineering issue — too much shaking after launch.

This artist rendering shows NASA's next-generation of moon rockets being developed. Ares I, left, will carry astronauts into space. Ares V is the cargo launch vehicle that will carry the lunar lander and other large hardware. (NASA, Marshall Space Flight Center/ Associated Press)This is the first preliminary design review approval for a rocket that carries astronauts since 1973, when the space shuttle passed the same stage, said Steve Cook, NASA's Ares projects manager.

These reviews are to make sure that the broad design, plans and software mesh properly and pass early safety questions. A more detailed test — a critical design review — is scheduled for March 2011.

Most of the rocket is not built yet.

"This is where we wrap the entire vehicle together to say we have a sound design from stem to stern," Cook said in a Wednesday evening teleconference. "It's really a big step in our journey to launch."

NASA engineers last month said they had figured out how to fix the remaining shaking issue with giant shock absorbers, but still more work is needed before that can pass review.

About 10 per cent of the problems that engineers brought up are still to be resolved but do not require a separate review, including noise problems and questions if the rocket could fly through rough weather, especially lightning, Cook said. NASA is also looking at potential problems that could come when the lower part of the rocket separates.

The Orion crew capsule, which will sit on top of the Ares I, will have its preliminary design review in late 2009.

One issue raised was that engineers would have to make sure they shrunk the launch platform design by 20 cm to match an equivalent reduction in the size of the the bottom part of the rocket.

It's mostly a matter of paperwork, Cook said.

NASA is spending about $3 billion US a year on the return-to-the moon program.