[lamontcg]

NASA was also considering reusable two stage to orbit for the shuttle back in the 1960s. By 1998 NASA was proposing Liquid Flyback Boosters:

https://ntrs.nasa.gov/api/citations/19980237254/downloads/19...

Those were still winged boosters, but were not helicopter-caught and did RTLS.

Musk didn't invent the concept.

[inemesitaffia]

You can write papers all you want.

I know only one company landing orbital boosters.