Small Deep Space Transponder

The Small Deep Space Transponder is a transponder designed by JPL specifically for deep space probes.[1] It unifies a number of communication functions - receiver, command detector, telemetry modulator, exciters, beacon tone generator, and control functions - into one 3-kg package. The SDST is designed to handle X band uplink and both X band and Ka band downlink. JPL estimates that performing the same functions with separate units (as was done previously) requires over twice the mass and 4 or 5 individual subassemblies.[2]


The capabilities of the SDST include:[3]

  • X-band receiver/downconverter capable of carrier tracking at or below −156 dBm.
  • Command detector unit function.
  • Telemetry modulation function.
  • X- and Ka-band exciters.
  • Beacon mode operation.
  • Coherent and noncoherent operation choice.
  • X- and Ka-band ranging.
  • Differential one-way ranging (DOR) for both X-band and Ka-band.
  • Command and Data Handling (C&DH) communication via MIL-STD-1553.
  • Data interface via EIA-422 (also known as RS-422).
  • External ports for temperature sensors.
  • External port for an analog signal.


SDST has been used in the following missions:[4]

As many tightly constrained, high-performance systems, the SDST has a number of idiosyncrasies in operation.[5] However, as the Dawn telecom 'lessons learned' section points out, the use of common hardware such as the SDST allows knowledge of these characteristics from previous projects.[5]


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