"A year ago, I said that return to flight was going to be difficult," said Bill Readdy, NASA associate administrator for space operations.

"I'm happy to report that a year later, we have been making steady progress on that path to return to flight next spring," he said in a telephone briefing.

"I am extremely proud of the team, their morale is very high," said Readdy, adding that NASA was aiming to launch a shuttle destined to dock at the orbiting International Space Station between March 16 and April 18.

"It has been a hard year," said space shuttle program manager Bill Parsons. "We are in familiar territory now, getting the vehicle ready. That work is going well, on schedule."

Bill Gestenmaier, ISS program manager, said the space station, which relies on shuttle flights to ferry up equipment needed for its own construction, "is in very good shape to begin assembly when the shuttle returns to flight.

"It has not been easy to keep the station flying," he said. "The crews have been doing a phenomenal job. When the shuttle gets back to flight, lots of supply will go up and down. Then we will be ready for assembly."

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