What does TS stand for?

The thermal subsystem uses mainly and as often as possible, passive control solutions.

In addition to managing solar array output, battery charging, and power distribution to the IMAGE spacecraft and science payload, the PDU: 1) receives commands from the System Controller Unit (SCU) over a MIL-STD-1553 serial data bus, 2) reports Health and Status Telemetry to the SCU over the 1553 bus, 3) controls the Torque Rod current for the Attitude Control System (ACS), 4) controls power to the Thermal Subsystem heaters, including payload survival heaters, and 5) turns the MagLatch relay drivers on and off.

And because the high-power payloads also generate more heat, Hughes upgraded the HS 601's thermal subsystem by adding heat pipes, using direct-radiating traveling-wave tubes and enlarging the thermal radiator panels.