Endeavour blasted off on the next-to-last shuttle flight Monday morning under the command of Mark Kelly, the husband of Rep. Gabrielle Giffords. The wounded congresswoman watched the launch in private from Kennedy Space Center. As many as 45,000 guests jammed NASA's launch site. The crowd outside the gates was estimated to be in the tens of thousands, if not more. It was the second launch attempt. Late last month, an electrical problem halted the countdown. Endeavour and its six astronauts will arrive at the International Space Station on Wednesday. They are delivering a $2 billion particle physics experiment. The mission will last 16 days. Only one other shuttle trip remains.