TTC Modem for AIT (Modulator / Demodulator) - Celestia STS

About TT&C Modem for AIT


The TTC-IMBU (Integrated Modem and Baseband Unit) is a TT&C Modem for AIT (Modulator/Demodulator) allowing direct control and monitoring of the spacecraft in EGSE environments, such as RF SCOE’s and for use in operational ground stations.

The system provides Telemetry, Tracking and Command (TT&C) in an Integrated Modem and Baseband Unit (IMBU).

The TTC-IMBU is typically integrated into an RF SCOE such that it is used to test and communicate with a spacecraft via the RF link.

The system can be configured such that it operates as a stand-alone combined TT&C/Baseband system or as a pure modem that connects to an external TMTC Front-End.

RS422/LDVS IO allows closed-loop RF subsystem testing or connection to external EGSE such as the TM/TC Front-End.

In addition to the modulation, demodulation and baseband processing, the modem also includes radiometric processing for Doppler simulation, Doppler measurement, Ranging uplink signal generation, Ranging downlink extraction and processing.

FPGA-based signal processing provides real-time modulation, demodulation and radiometric processing in association with software, allowing the system to be used locally via the system GUI or remotely via LAN.

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Key Features


  • 2 IF inputs (typically 70MHz)
  • 2 IF outputs (typically 70MHz)
  • Ranging and Doppler measurements
  • Data rates from 10Mbps down to 7.8125bps
  • ESA Standard, ESA Tone and PN Ranging (T2B, T4B)
  • Suppressed carrier schemes—BPSK, QPSK, OQPSK, GMSK
  • Remnant carrier schemes— SPL/PM, BPSK/PM (sine/square)
  • DSSS modulation and demodulation (configuration dependent)
  • Uplink and downlink generation and acquisition
  • Doppler Simulation and Uplink sweeping
  • Data interfaces via RS422, LVDS or LAN
  • Gigabit LAN for Control and Monitoring via TCP/IP (using RJ45)
  • External Time/Reference inputs, such as 10MHz, PPS and IRIG
  • Optional baseband processing including Viterbi and R-S
  • Remote interfaces such as SLE, EDEN and C&C available
  • Built-In Bit Error Rate Transmitter / Receiver
  • TC Plop mode support

Additional Baseband Processing Information

  • Telemetry and Telecommand processing system (ESA, ECSS, CCSDS)
    • TM Acquisition and Simulation
    • TC Generation and Acquisition
    • Bit Error Rate Tester
  • 24x RS422/LVDS pairs for baseband interfacing
  • Selectable error correction, line encoding/decoding
  • Telemetry Frame and Packet processing to/from bit level
  • Telecommand Packet and CLTU processing to/from bit level
  • Flexible source and destination routing for unit and spacecraft AIT
  • Galvanically isolated FMEA compliant for direct connection to the flight equipment
  • Includes closed-loop testing, TC Echo, Transponder/RF SCOE end-to-end testing
  • Local data generators allow performance testing including error injection
  • Sophisticated error catching, statistics, logging and data archiving
  • Can be used stand-alone or remotely via CCS

Key Features


  • 2 IF inputs (typically 70MHz)
  • 2 IF outputs (typically 70MHz)
  • Ranging and Doppler measurements
  • Data rates from 10Mbps down to 7.8125bps
  • ESA Standard, ESA Tone and PN Ranging (T2B, T4B)
  • Suppressed carrier schemes—BPSK, QPSK, OQPSK, GMSK
  • Remnant carrier schemes— SPL/PM, BPSK/PM (sine/square)
  • DSSS modulation and demodulation (configuration dependent)
  • Uplink and downlink generation and acquisition
  • Doppler Simulation and Uplink sweeping
  • Data interfaces via RS422, LVDS or LAN
  • Gigabit LAN for Control and Monitoring via TCP/IP (using RJ45)
  • External Time/Reference inputs, such as 10MHz, PPS and IRIG
  • Optional baseband processing including Viterbi and R-S
  • Remote interfaces such as SLE, EDEN and C&C available
  • Built-In Bit Error Rate Transmitter / Receiver
  • TC Plop mode support

Additional Baseband Processing Information

  • Telemetry and Telecommand processing system (ESA, ECSS, CCSDS)
    • TM Acquisition and Simulation
    • TC Generation and Acquisition
    • Bit Error Rate Tester
  • 24x RS422/LVDS pairs for baseband interfacing
  • Selectable error correction, line encoding/decoding
  • Telemetry Frame and Packet processing to/from bit level
  • Telecommand Packet and CLTU processing to/from bit level
  • Flexible source and destination routing for unit and spacecraft AIT
  • Galvanically isolated FMEA compliant for direct connection to the flight equipment
  • Includes closed-loop testing, TC Echo, Transponder/RF SCOE end-to-end testing
  • Local data generators allow performance testing including error injection
  • Sophisticated error catching, statistics, logging and data archiving
  • Can be used stand-alone or remotely via CCS

The system consists of a 19” 3U hardware platform that is connected to the C-STS Control and Monitoring Software (CMS). The system can be used as a desktop connected with a standard PC or integrated into a 19″ rack with a dedicated server platform.

The TTC Modem for AIT provides Spacecraft Compatible, FMEA proven, galvanically isolated interfaces to the spacecraft with up to 24 differential IO pairs allowing connection to OBC (bypass) interfaces, TM/TC Front Ends, Transponders and other equipment. Additional interfaces can be used for Network Data Interface Unit (NDIU), Closed Loop connections as well as RF Suitcase applications.

The system uses a highly configurable platform that allows C-STS to readily adapt to specific customer needs.

The optional baseband processing within the IMBU performs real-time Frame/CADU and CLTU processing as well including selectable error correction coding and time stamping plus additional test functions such as Bit Error Rate Testers.

The system is available with both classic TT&C modem functions to CLTU/Frame layer or as a “hybrid modem” where full TMTC packet processing layers are added.

The software offers archiving, logging, local GUI and statistics regarding the modulation, demodulation, TM and TC incoming and outgoing data with counters for both good and bad information e.g. received frames, frames with RS corrections, MCFC errors, VFCF errors, SPSC errors, etc.

The TM Frame viewer allows identification of bit errors and corrections in RS decoded data. The monitors allow TM Frames, TM Packets, TC CLTUs, and TC Segments/Packets to be viewed at a raw hexadecimal level with header decoders.

Support for more advanced functions, such as Service A TC and TC Authentication, is available. Support for Space Link Extension (SLE) is also available.

The TTC Modem for AIT is used directly through the local GUI or via the remote (LAN) interface.

The remote interface of the system is configurable by C-STS to meet the needs of the customer RF SCOE, Central Checkout System or Ground station. Many interfaces are available off-the-shelf such as EDEN, C&C and SLE.

The system includes hardware time stamping support through optional interfaces such as PPS, IRIG-B, and IRIG-G.

The systems are highly customizable to fulfill specific spacecraft needs.

Celestia-STS have delivered TT&C modems systems for major European prime contractors such as AIRBUS, THALES, OHB to support ESA and non-ESA spacecraft missions including Bepi Colombo, JUICE, Euclid, PROBA-V, Galileo, ExoMars, Solar Orbiter, etc.