PARIS โ€” The European Space Agency (ESA) on Nov. 22 announced that its work on the propulsion module for NASAโ€™s Orion crew-transport vehicle has been slowed by a further six months as it considers design tradeoffs.

As a result, ESA said, the preliminary design review for the Orion propulsion system will not be completed until May 2014. โ€œThe overall effect on the projectโ€™s schedule is still under investigation,โ€ ESA said. The first flight with the ESA-produced propulsion module for Orion had been scheduled for 2017.

Nico Dettman, head of ESAโ€™s Automated Transfer Vehicle program โ€” the space station cargo carrier from which ESA is borrowing much Orion propulsion module technology โ€” said in a statement: โ€œWe need more time to look at options and ensure we make the right design decisions at this stage.โ€

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Peter B. de Selding was the Paris Bureau Chief for SpaceNews.