http://blogs.nasa.gov/Rocketology/2015/09/17/four-lessons-in-four-years/?linkId=17162176"Way back in 2011, when the world’s attention was on the end of the space shuttle program, a small group of engineers was tasked with planning what would come next. NASA revealed the answer on Sept. 14 of that year in the form of Space Launch System (SLS) – which would be the most powerful rocket in history and would allow astronauts to travel beyond Earth orbit for the first time since Apollo.In the four years since, we’ve made substantial progress, going from an early concept into manufacturing, testing, and even flying our first hardware on Orion’s Exploration Flight Test-1 in December 2014.In honor of the fourth anniversary of that announcement, here are four things we’ve learned in four years. (With a big thanks to former SLS Program Manager and now Marshall Space Flight Center Deputy Director Todd May, who helped with this list.)"