No looking in the sky for ISS and Endeavour until at least May 2nd at 2:33 p.m. EDT. The cause of the delay was problems with the heaters to the auxiliary power units (APUs). The APUs provide power to the orbiter during key phases of the flight such as liftoff and deorbiting. The APU heaters keep the hydrazine fuel that powers them from freezing in orbit. The thermostat that controls the heater didn't kick on when it was called to do so. There are two heaters on APU#1 and they are both needed to be functioning for launch.
The First Family was on hand at the launch and they met the crew and toured the Kennedy Space Center.
There will be a launch management team meeting this weekend and further updates will be forthcoming. I will keep you informed as the details develop.
In the DC area the weather is FINALLY clear so get out and enjoy the stars tonight.
Sky Guy in VA