A) RS-25E is not an entirely new engine program. This design has been underway for many years now and is essentially at the point where the only big change remaining is the nozzle. Even that has already been conceptually designed and awaits only the production design and tooling to be put in place to build it (big picture).
B) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's. The ablatively cooled nozzle would not survive long enough for the vehicle to reach MECO because of the thermal environment at the base of the vehicle.
C) ...But the door has already been closed to that and the Air Force is not amicable to reopening it.
a) SSME, RS-25E, STME and RS-68 all spent years being designed. Two went through testing, production and flight. One no longer has a production line and the other is in production. By those measures, of the remaining two, the STME designed decades ago is as close/closer to flight than the RS-25E.
b) I have and do disagree with that statement. As I could design and prototype an effective, simple solution in 60 days, I find the assertion the RS-68 is "a non-viable engine choice" to be B
hand waiving. You determine the "who" and "why" for the claims.
c) Would you consider the 'door closed' for a human-rated RS-68, thus the door closed on Delta IV as well? A few links/quotes;http://www.nasaspaceflight.com/2009/09/ula-claim-gap-reducing-solution-via-eelv-exploration-master-plan/
In regards to the entire Delta IVH - " Numerous upgrades and modifications are listed, but also with cited uncertainty as to how many of the modifications would be required. ...
Of note is that quite a few of the requirements are not driven by explicit redundancy requirements, but on other anticipated safety criteria as the desire to reduce the release of burning H2 at RS-68 start, added the paper.
Also, in some cases different redundancy upgrades (RS-68 backup valves, feedline prevalves, and hydraulics redundancy) need to be traded off to find the smartest implementation path. This makes the final suite of upgrades somewhat uncertain. However, the anticipated total scope and cost of these safety upgrades is programmatically small, with engine mods the most expensive due to high intrinsic recertification cost." "http://www.floridatoday.com/content/blogs/space/EELVHumanRating.pdf
Pg 8/9 on RS-68 Human-Rating - "A representative list includes: 1) improving the reliability of the engine controller; 2) furtherevluating and mitigating any structural margin issues that do not comply with "Strength and Life Assessment Requirements for Liquid Fueled Space Propulsion System Engines," NASA-STD-5012, 13 June 2006; 3) developing redundant actuators and valves, and installing triple-redundant sensors for more robust fault detection; 4) improving quality control to meet human-rating requirements; 5) implementing a cross-strapped pressurization system; and 6) additional qualification testing to determine reliability."