The authors provide detailed modeling of the key elements of the Tracking and Data Relay Satellite Systems (TDRSS) S-band multiple access (MA) return service and present the beamforming and nulling operations in the Second TDRSS Ground Terminal (STGT). The performance of beamforming, nulling, and calibration processes is also analyzed. For TDRSS S-band MA return signals, a phase-array antenna with 30 elements at TDRS has its beamforming performed on the ground at STGT. There are a total of 12 advanced ground implemented phase arrays (AGIPAs) at STGT for the calibration and the beamforming processes. Ten of the AGIPAs are available to serve MA return users; one is used for calibration; and one is a hot spare. Any of the 12 AGIPAs can perform either beamforming or the calibration process when it is commanded to do so. >