NASA destroyed a shuttle on more than 1% of all shuttle flights, each time killing everyone aboard.
Meanwhile, 17 people worldwide have died in on attempted space flights, while 169 people have died on in space flight related accidents. https://en.wikipedia.org/wiki/List_of_spaceflight-related_ac... (Excluding the original V2 program which had even worse numbers.)
Just something to consider.
Those weren't "manned flights", but if anything Delta and the later SpaceX rockets show that "human rating" isn't adding any safety worth caring about.
Of course you'd want to certify the life support equipment, but that's not why these rockets have failed.
Soyuz 11 - was a life support failure (A cabin vent valve construction defect caused it to open at service module separation)
Soyuz 1 - Parachute failed so again not something the Delta II had to deal with.
STS-107 Damage to tiles resulted in failure on reentry, but again no heat shields on the Delta II.
Of the 4 only STS-51-L failed during launch.
Especially if we consider SpaceX, whose Falcon 9 should probably have gained automatic human rating based on its record, but the bureaucracy persists.
I think saying the SLS only had one launch failure amounts to creative accounting, STS-107 was also a launch failure, just a delayed one.
If the orbiter had been boosted to orbit by magic it wouldn't have broken apart on reentry, it's only because of how the launch system works that it did so (tiles damaged during launch).
So, getting back to a Delta II (or a successor system), in that case the reentry system would have been a capsule protected by a fairing, and mounted on top of the rocket, and therefore debris falling onto the reentry vehicle during launch wouldn't be a failure mode of the system.
As to man rating the Falcon 9, SpaceX CRS-7 is a great example of why you man rate things. The Dragon CRS-7 capsule “could have been recovered if the parachutes had deployed, but the software in the capsule did not include any provisions for parachute deployment in this situation.” You really don’t want that kind of oversight when human lives are at stake.
Anyway the Delta II is reasonably close to the Soyuz but again the rocket itself is only part of the story. You need to look at everything from vibration and g loads to how you get people safely onboard. In the end it was simply cheaper to use the Soyuz and it’s proven systems than independently recreate nearly identical capabilities for minimal gain.
Two is such a small number, right?
Funny now numbers can be used.
However I can see the glaringly obvious omission in my post that NASA, in its near 70 years of existence has had numerous casualties and explosions. But that's literally my gist: massive checklists, standards, and regulations are a result of that.