Nasa and Boeing Co. endured a possibly major setback in the deep-space ambitions when the engines for a giant new rocket shut down prematurely Saturday during a key test on the ground. The engines were meant to produce thrust for eight minutes but shut down after roughly 60 seconds while fastened to a stand at a Stennis Space Center in Mississippi. Program officials had said that the minimum time to gain confidence in the reliability of engines would be four minutes, including fuel system and surrounding structures.National Aeronautics and Space Administration officials said they couldn’t straight away determine the cause of the premature shutdown, and therefore it was too early to decide what fixes would be necessary or even if the test required to be repeated. Engineers weren’t certain whether it was hardware. Software or sensor malfunction.