The problem is you just can't plug an SSME, ground ignited into a 2nd stage configuration as-is! While everyone touted that in the original concept, it was always with the idea of, "Well, we'll make a simpler version that will cost less to build." <br /><br />"All" they had to do was change the turbopump design, enlarge the bell for more efficient use at higher altitude, add an igniter, use a different style construction, etc. But that amounts to changing out every part except the manufacturer's name plate. And then you have to change the plate! And then you have to do a LOT of testing to man-rate the "old, but improved SSME"! Apparently there are J-2 drawings and even tooling left over from Saturn V. Still have to re-certify the new units, but you are starting from a design that was INTENDED to be at-altitude ignited in the first place. Lower thrust, and larger propellant tanks (I think), so the weight goes up and you need a higher-thrust 1st stage. That's where the 5-segment SRM comes in. I'm NOT enthusiastic about ANY SRB/SRM/firecracker, but ATK-Thiokol has already static tested one, and apart from a decision on whether to recover the 1st stage (would require a larger parachute subsystem), and installing the retros on the aft skirt, plus some sort of roll control, it should be ready to go.<br /><br />No, I don't like the idea of the smaller diameter command module. But I like the idea of NO manned vehicle after the orbiters are grounded A LOT LESS! In other words, I'll take what I can get, and hope for more later!<br /><br />What's REALLY a pain is that I now have to modify my 1/144 scale model of the "Stick" that I use in my talks to "future" engineers, scientists, astronauts (K-12th grade kids)! <img src="/images/icons/frown.gif" /><br /><br />Ad Luna! Ad Aries! Ad Astra!