3) Satellite Subsystems — Bus and Payload

I. The Bus
• Structure — mechanical support, thermal path.
• Power — solar arrays, batteries, PCU.
• Attitude & Orbit Control (AOCS).
• Propulsion — chemical or electric.
• Thermal control — radiators, heaters, MLI.

II. Telemetry, Tracking & Command (TT&C)
• Downlink — housekeeping telemetry.
• Uplink — commands to the satellite.
• Ranging — measures distance.
• Beacon — continuous ID signal.

III. The Payload
• Antennas — reflectors, horns, phased arrays.
• Receivers — LNA, downconverter.
• Transponders — amplify, convert, retransmit.
• High Power Amplifiers (HPA) — TWTA or SSPA.

IV. Transponder Types
• Bent-pipe — no demodulation, simple.
• Regenerative — demodulates, decodes, remodulates.

V. High-Throughput Satellites (HTS)
• Multiple spot beams — 20–100+ beams.
• Ka and Ku bands.
• Digital transparent processors.
• Throughput in hundreds of Gbps per satellite.

VI. On-Board Processing
• Channelisation — split bandwidth.
• Beamforming — direct power to beams.
• Regeneration — clean signal.
• Inter-satellite links — route traffic.