Satellite Standards¶

Overview¶

The satellite protocol stack implements CCSDS (Consultative Committee for Space Data Systems) standards the internationally agreed protocols used by virtually all spacefaring nations for space-ground communication. These protocols handle everything from packaging telemetry data on a Mars rover to commanding the Hubble Space Telescope.

CCSDS Protocol Stack¶

┌─────────────────────────────────────────────────────────────────┐
│                    Application Layer                              │
│              (Instrument data, commands, housekeeping)            │
├─────────────────────────────────────────────────────────────────┤
│                  Space Packet Protocol                            │
│               (CCSDS 133.0-B-2 / Blue Book)                     │
│         Packetization: segmentation, APID routing                │
├─────────────────────────────────────────────────────────────────┤
│          TM Transfer Frame    │     TC Transfer Frame            │
│       (CCSDS 132.0-B-3)      │    (CCSDS 232.0-B-4)            │
│     Downlink framing + sync   │  Uplink framing + CLTU          │
├───────────────────────────────┼──────────────────────────────────┤
│           TM Physical          │      TC Physical                │
│      (Convolutional/LDPC      │   (BCH encoding, CLTU           │
│       coding, modulation)      │    start/tail sequences)        │
├───────────────────────────────┴──────────────────────────────────┤
│                    RF / Physical Layer                            │
│            (S-band, X-band, Ka-band, Optical)                    │
└─────────────────────────────────────────────────────────────────┘

Layer Responsibilities¶

TM Downlink vs TC Uplink¶

The space link is fundamentally asymmetric downlink and uplink face different challenges:

graph LR
    subgraph Spacecraft
        A[Instruments] --> B[Space Packets]
        B --> C[TM Frames]
        C --> D[Convolutional<br>+ RS Coding]
        D --> E[Modulator<br>TX]
    end

    subgraph "Space Link"
        E -->|"Downlink (high rate)<br>10 Mbps - 1 Gbps"| F[Ground Station<br>RX]
        G[Ground Station<br>TX] -->|"Uplink (low rate)<br>1 kbps - 1 Mbps"| H[Receiver<br>RX]
    end

    subgraph Ground
        F --> I[Frame Sync]
        I --> J[Decode + CRC]
        J --> K[Packet Extract]
    end

Standards Covered¶

Real Missions Using CCSDS¶

Link Budget Basics¶

Understanding why the protocol stack exists requires understanding the link budget the calculation of signal strength from transmitter to receiver across the space link:

Link Budget Equation¶

Received Power (dBm) = P_tx + G_tx - L_path + G_rx - L_system

Where:
  P_tx    = Transmitter power (dBm)
  G_tx    = Transmit antenna gain (dBi)  
  L_path  = Free-space path loss = 20·log₁₀(4πd/λ) (dB)
  G_rx    = Receive antenna gain (dBi)
  L_system = Implementation losses (dB)

Example: Mars Link Budget¶

Protocol Design Implications¶

The harsh link environment drives protocol design choices:

Architecture¶

graph TD
    subgraph "Our Implementation"
        A[Application Data] --> B[ccsds_spp<br>Space Packet Protocol]
        B --> C[ccsds_tm<br>TM Transfer Frame]
        B --> D[ccsds_tc<br>TC Transfer Frame]
        C --> E[ASM + CRC<br>+ FEC coding]
        D --> F[CLTU encoding<br>BCH + start/tail]
        E --> G[Bitstream output<br>for modulator]
        F --> G
    end

    style B fill:#4a4,stroke:#333,color:#fff
    style C fill:#28a,stroke:#333,color:#fff
    style D fill:#a82,stroke:#333,color:#fff

Build¶

# Build all satellite modules
make -C src/satellite/ccsds_spp
make -C src/satellite/ccsds_tm
make -C src/satellite/ccsds_tc

# Run demos
./build/ccsds_spp_demo
./build/ccsds_tm_demo
./build/ccsds_tc_demo

References¶

• CCSDS 130.0-G-4: Overview of Space Communications Protocols (Green Book)
• CCSDS 133.0-B-2: Space Packet Protocol (Blue Book)
• CCSDS 132.0-B-3: TM Space Data Link Protocol (Blue Book)
• CCSDS 232.0-B-4: TC Space Data Link Protocol (Blue Book)
• CCSDS 131.0-B-4: TM Synchronization and Channel Coding (Blue Book)
• CCSDS.org All Blue Books freely available