/u/JeffHoffman on I am Jeff Hoffman, MIT Professor of Aerospace Engineering and former NASA Astronaut. Ask Me Anything!19 Feb 2015, 19:10 UTC
My biggest concern with SLS is not technical. The people who are designing and building it know what they are doing, and I have confidence that it will work. What I am most concerned about is that there is serious doubt about how often we will be able to fly it because of the cost. A critical factor for a system that can support real deep space exploration is that we have to be able to fly it with sufficient frequency. Once every two or three years is not enough.