The Small Deep Space Transponder is a transponder

Transponder

In telecommunication, the term transponder has the following meanings:...

 designed by JPL specifically for deep space probes. 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

X band

The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...

 uplink and both X band

X band

The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz . In radar engineering, the frequency range is specified...

 and Ka band

Ka band

The Ka band covers the frequencies of 26.5–40 GHz. The Ka band is part of the K band of the microwave band of the electromagnetic spectrum. This symbol refers to "K-above" — in other words, the band directly above the K-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.

Functions

The capabilities of the SDST include:

• X-band receiver/downconverter capable of carrier tracking at or below −156 dBm
  DBm
  dBm is an abbreviation for the power ratio in decibels of the measured power referenced to one milliwatt . It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form...
  
  .
• 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
  MIL-STD-1553
  MIL-STD-1553 is a military standard published by the United States Department of Defense that defines the mechanical, electrical, and functional characteristics of a serial data bus. It was originally designed for use with military avionics, but has also become commonly used in spacecraft on-board...
  
  .
• Data interface via EIA-422
  EIA-422
  RS-422 is a technical standard that specifies electrical characteristics of a digital signalling circuit. Differential-mode signals can be sent at rates as high as 10 million bits per second, or may be sent on cables as long as 1200 metres. Some systems directly interconnect using RS 422 signals,...
  
   (also known as RS-422).
• External ports for temperature sensors.
• External port for an analog signal.

Missions

SDST has been used in the following missions:

• Deep Space 1
  Deep Space 1
  Deep Space 1 is a spacecraft of the NASA New Millennium Program dedicated to testing a payload of advanced, high risk technologies....
  
  . This was a developmental mission that used the transponder for the first time, as part of an effort to qualify new technologies for flight.
• Deep Impact
• Dawn used a pair of SDSTs
• Mars Exploration Rover
  Mars Exploration Rover
  NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars...
  
  s
• Mars Reconnaissance Orbiter
  Mars Reconnaissance Orbiter
  Mars Reconnaissance Orbiter is a NASA multipurpose spacecraft designed to conduct reconnaissance and Exploration of Mars from orbit...
  
  
• MESSENGER
  MESSENGER
  The MErcury Surface, Space ENvironment, GEochemistry and Ranging space probe is a robotic NASA spacecraft in orbit around the planet Mercury. The spacecraft was launched aboard a Delta II rocket in August 2004 to study the chemical composition, geology, and magnetic field of Mercury...
  
  
• STEREO
  STEREO
  STEREO is a solar observation mission. Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth...
  
  
• Spitzer Space Telescope
  Spitzer Space Telescope
  The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
  
  
• A pair of SDSTs were used in the cruise stage of Phoenix (spacecraft)
  Phoenix (spacecraft)
  Phoenix was a robotic spacecraft on a space exploration mission on Mars under the Mars Scout Program. The Phoenix lander descended on Mars on May 25, 2008...
  
  . The lander used only UHF communication.
• The yet to be launched Mars Science Laboratory
  Mars Science Laboratory
  The Mars Science Laboratory is a National Aeronautics and Space Administration mission with the aim to land and operate a rover named Curiosity on the surface of Mars. The MSL was launched November 26, 2011, at 10:02 EST and is scheduled to land on Mars at Gale Crater between August 6 and 20, 2012...
  
  . This includes 2 SDSTs, one on the descent stage and one on the lander itself. The SDST on the descent state is the main transponder for the cruise and landing portions of the flight, with the SDST on the rover as a backup. During the landing, the descent stage will crash after lowering the rover, and the SDST on the lander becomes the active transponder.

As do many tightly constrained, high performance systems, the SDST has an number of idiosyncrasies in operation. 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.