cold and it would freeze up if you didn't have the heaters working. and that is the fuel, the propellant that allows them to steer and to use the rudder controls, et cetera. so, they have to have those working. there are redundancies, but they do not fly without those apus. so, right now, it appears as if we are in a scrub situation here at the kennedy space center. "endeavour" will not be lifting off this afternoon. suzanne? >> so, john, what does this mean? what happens? the astronauts, they return back to their building and they take off their suits and the diplomats go home? >> reporter: correct. >> how does this all kind of unfold today? >> reporter: well, what will happen now is they have to drain the vehicle. they've got all that 500,000 gallons of liquid hydrogen and oxygen in the tank. they've got to get all that drained back out of the tank, and then they'll be able to go and start trouble-shooting whatever it is that is causing these heaters to malfunction.