CNN19980425.1600.0054 NEWS CAPTION Repair efforts are taking priority over neurological research experiments on board the space shuttle "Columbia." A life support system that removes carbon dioxide from the shuttle failed late last night. Nasa says the astronauts aren't in any immediate danger because a backup system is working. Ground control is instructing the crew how to fix the primary system. If nothing works, "Columbia" will have to return home early. Some of the crew members are continuing to conduct experiments, in spite of the problems.