Three versions of SLS being developed c 2015. Modified from original to remove text and correct boosters
Hefner, Keith
Adapted from: <a rel="nofollow" class="external free" href="http://ntrs.nasa.gov/search.jsp?R=20140011078&amp;hterms=block+1b&amp;qs=Ntx%3Dmode%2520matchall%26Ntk%3DAll%26N%3D0%26Ntt%3D%2522block%25201b%2522">http://ntrs.nasa.gov/search.jsp?R=20140011078&amp;hterms=block+1b&amp;qs=Ntx%3Dmode%2520matchall%26Ntk%3DAll%26N%3D0%26Ntt%3D%2522block%25201b%2522</a>