NASA’s chief reminded employees Thursday that “the consequences of us not getting it right are catastrophic,” as the space agency paused to remember the dead crew members of Columbia, Challenger and Apollo. Administrator Sean O’Keefe said in a televised address that space exploration is risky but never should result in fatalities because of “complacency, indifference, failure to attend to detail.” That should be a solemn pledge for anyone who works in the space program, he said.