It was initially attached to the nadir (bottom, or Earth-facing) hatch of Unity. About six weeks later, when STS-97 delivered the P6 solar array truss structure, Endeavour docked at PMA-3.
Initially, the device was attached to the bottom hatch of Unity. Later, around six weeks after STS-97's delivery of the P6 solar array truss, Endeavour moored itself at PMA-3.