Celestrak's NORAD Two-Line Element Sets Current Data TLE page has many pre-defined categories for quick access for groups of spacecraft that share similar characteristics.
I clicked on the
Tracking and Data Relay Satellite System (TDRSS) option, and many spacecraft named "TDRS" are listed:
TDRS 3, TDRS 5, TDRS 6, TDRS 7, TDRS 8, TDRS 9, TDRS 10, TDRS 11, TDRS 12
There are many more included as well:
AIM, AQUA, AURA, FGRST (GLAST), GPM-CORE, HST, ISS (ZARYA), JPSS-1, LANDSAT 7, MMS 1, MMS 2, MMS 3, MMS 4, SORCE, SWIFT, TERRA, THEMIS A, THEMIS D, THEMIS E, TIMED, WISE
Question: Does the user segment behave as simply TDRS "customers", or do they contribute in some way to the function? For example, is TDRS traffic ever routed through a user segment member, or buffered or stored there for later transmission? Since one of the user segments
ISS (ZARYA) is manned at all times, are there any special TDRS management functions performed there by the ISS crew?