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Government marches on! NASA’s safety panel has noticed that NASA’s SLS program either plans to spend $150 million man-rating a rocket engine it will only use once, or will fly a manned mission without man-rating that engine.
The Block 1 SLS is the “basic model”, sporting a Delta Cryogenic Second Stage (DCSS), renamed the Interim Cryogenic Propulsion System (ICPS) for SLS. The current plan calls for this [interim] stage to be used on [the unmanned] Exploration Mission -1 (EM-1) and [manned] Exploration Mission -2 (EM-2), prior to moving to the [Exploration Upper Stage] – also to be built by Boeing – that will become the workhorse for SLS.
However, using the [interim upper stage] on a crewed mission will require it to be human rated. It is likely NASA will also need to fly the [Exploration Upper Stage] on an unmanned mission to validate the new stage ahead of human missions. This has been presenting NASA with a headache for some time, although it took the recent ASAP meeting to finally confirm those concerns to the public.
Up until now, no one at NASA would admit that their SLS plans called for flying humans with an upper stage that has not been man-rated. They don’t have the funds to man-rate it, and even if they get those funds, man-rating it will likely cause SLS’s schedule to slip even more, something NASA fears because they expect the commercial manned ships to be flying sooner and with increasing capability. The contrast — a delayed and unflown and very expensive SLS vs a flying and inexpensive commercial effort — will not do SLS good politically.
However, if they are going to insist (properly I think) that SpaceX and Boeing man-rate their capsules and rockets, then NASA is going to have to man-rate its SLS systems as well. The result: more problems for SLS, contributing to what I believe will be its inevitable cancellation.