NASA engineers are still working to figure out exactly what caused a brief, one-time irregular power drop to one of the main engine controllers on the shuttle Discovery. But even if they fix the glitch the thrice-delayed mission faces an 80 percent chance of being delayed by weather tomorrow, Kathy Winters – NASA’s appropriately named shuttle weather officer – says.

If Discovery doesn’t fly by Sunday it will have to wait until December 1 to try again.