It's the next-to-last shuttle flight, as well as Endeavour's final voyage. Add to that the presence of the commander's wounded congresswoman wife, and Friday's visit by the president and his family.
Forecasters, meanwhile, were slightly more pessimistic Thursday. Still, there's a 70 percent chance of good weather for Friday's 3:47 p.m. launch.
Endeavour commander Mark Kelly is married to Gabrielle Giffords, who arrived in Cape Canaveral from Houston on Wednesday. She was shot in the head Jan. 8.
NASA officials say upwards of 700,000 people are expected to jam the area.