The planned 13 April launch of the space shuttle Atlantis will be delayed for several days while one of the engines is replaced. There are thought to be defective seals in a fuel pump, which could cause serious problems. Replacement of the engine will take several days. NASA originally sold the space shuttle to Congress based on the theory that the engines would be good for several flights. Critics who charged that the main engines would require complete rebuilding after every trip were proven correct several years ago.--Stephen V Cole