Space X Mark 3 Parachute

[Brotoro]

1 hour ago, kerbiloid said:

It was not an emergency engine usage, it was an engine shutdown.

The engine shutdown was the emergency. If the other (liquid fuel) engines had not stepped in with longer/stronger burns, the shuttle would have fallen back to Earth. But the other (liquid fuel) engines did the job of saving the day and made a successful Abort to Orbit. That was the type of abort option available at that point in the flight regime (they could also have done a transatlantic abort at that point).

[kerbiloid]

14 minutes ago, Meecrob said:

Before Falcon 9, only solid boosters were refurbished. Does that make it foolish to refurbish liquid Falcon 9 boosters currently?

Only the unprotected first stage of Falcon is refurbished.
So, I guess, they find it foolish to refurbish the upper stage.

6 minutes ago, Brotoro said:

The engine shutdown was the emergency.

This was not an emergency engine engaging.