 The Space Shuttle 's a very complex machine . It 's got a lot of moving parts that move and operate at pretty much the limit of what we 've been able to engineer . Spaceflight is risky . I think with regards to the tank , we 've reduced some of the risk there . We 've changed the design a little bit and we 've made some pretty big strides in trying to get foam not to shed from the tank anymore . So there is some risk reduction there and I guess overall the risk is probably a little less . But this is a risky business , but it 's got a big reward . Everybody on board Discovery and the space station here thinks it 's worthwhile . 
