NASA had hoped a Sunday launch was still possible, but a complicated troubleshooting process won't let that happen. Engineers still haven't been able to pinpoint why a liquid hydrogen sensor in the shuttle's external fuel tank gave a false reading just hours before Wednesday's scheduled lift-off. NASA's Kyle Herring says the space agency will err on the side of caution.
He says the orbitor has 2 million parts, so technical issues aren't all that surprising.
NASA still has until the end of July to launch Discovery. After that, the next launch window is sometime in September.