The first test of an unmanned Ares I could take place next summer. The test, however, will use a spacecraft that is very different from the Ares I to come. It will involve a solid rocket booster of the same length that the shuttle uses, and the second stage and capsule will be dummies. Four more test flights are scheduled before the rocket is used beginning in 2015.

The Ares V is a much brawnier rocket designed to send equipment to the Moon and beyond. Its first stage includes two solid rocket boosters and a liquid-fueled set of six rocket engines.

The design process has run into technical problems. Orion is far heavier than the Apollo capsule and weight issues have required redesigns of both the capsule and the rocket, further complicating technical issues. Engineers have also had to come up with ways to dampen potentially dangerous vibrations along the shaft of the rocket as the solid rocket engine empties.

Some inside the development program have complained that it is run with a my-way-or-the-highway attitude that stifles dissent and innovation. Jeffrey Finckenor, an engineer who left NASA this year, sent a goodbye letter to colleagues that expressed his frustrations with the program. “At the highest levels of the agency, there seems to be a belief that you can mandate reality,” he wrote, “followed by a refusal to accept any information that runs counter to that mandate.” The letter was posted to the independent NASA Watch Web site.

Mr. Finckenor has refused to comment further.

Leroy Chiao, a retired astronaut who flew three shuttle missions and served aboard the space station, said that the 2004 announcement by Mr. Bush of NASA’s new direction “was a time of great optimism.” Mr. Chiao is not involved with the Constellation project today, but he said it was clear from some of the leaked discussions that “the program has not panned out as I, and the vast majority of people, had hoped.”

Sunny Assessments

NASA officials say the Constellation program is actually coming along well. In an interview in November, Mr. Griffin said, “I can’t imagine somebody thinks you’re going to develop a new space transportation system and encounter no challenges.” The ones NASA is encountering, he said, are “routine in the extreme.”

Douglas R. Cooke, a leading space agency official on the Constellation program, told reporters this month that the weight and vibration issues were well on their way to being fixed. And Neil Otte, the launching chief engineer for the Constellation rockets, said that solving tough problems was what engineers did for a living. When they encounter a particularly difficult challenge, he said, their attitude is, “Hey, it’s starting to get fun now, and we’re earning our money.”