[MBCook]

Oh, perhaps I have the name wrong. I meant the part connected to the payload with the Merlin engine designed for vacuum, above the three main rockets (the center of which must be the core).

[pikchurn]

That's the 2nd stage. It's still attached to the payload I believe, so that they can test mid-course corrections to the transfer orbit.

[skykooler]

It will relight its engine again in about five and a half hours to depart Earth orbit for interplanetary space.

[MBCook]

Thanks.