A huge crowd is expected at the space shuttle Endeavour's final launch today, including President Barack Obama and Rep. Gabrielle Giffords, whose husband, Mark Kelly, commands the shuttle. But it will be a bittersweet moment for many NASA officials and residents of the Florida towns that have supported them. After Endeavour, the launch of Atlantis in June will mark the end of the shuttle program, and of NASA's ability to send people into space. Giffords herself was a strong critic of Obama's plan to privatize human spaceflight when he unveiled it two years ago, and some officials now hope that the drama of her recovery and her visit to the Endeavour launch will help rekindle interest in the agency's mission, but are wary of exploiting her appearance. The launch also marks the beginning of a time of uncertainty for the residents of the Florida towns that have supported the space program, with shuttle-worker layoffs already begun and the prospect of thousands more looming.