NATIONAL BRIEFING / FLORIDA

NASA will try to launch space shuttle Discovery to the International Space Station late tonight, after back-to-back delays caused by bad weather and fuel valve trouble.

NASA is struggling to understand why a shuttle fuel valve appeared to malfunction Tuesday midway through the fueling process at Cape Canaveral. The valve was tested Wednesday night, and all indications were that it was a problem with a sensor rather than the valve itself.

Another potential issue arose Thursday when a mechanical failure canceled the test firing of a new moon rocket in Utah. The problem was a faulty valve in a power unit nearly identical to a system used in the shuttle. Shuttle managers said they’d see if there was any potential implication for Discovery.