ILRS Transponder Standing Committee (TSC) Charter

This charter was created June 2005.


Because transponder signal strengths fall off with range as R-2 instead of R-4 as in conventional SLR to a passive target, they offer the promise of extending precise ranging and time transfer throughout our Solar System. Over the past decade, optical transponder techniques have established themselves as a viable technology via several successful experiments such as: (1) decimeter accuracy two-way range measurements between Earth and the Messenger spacecraft enroute to Mercury at a distance of 24 million km; (2) the detection of laser pulses from Earth by the MOLA altimeter in Mars Orbit at a distance of 80 million km; and (3) optical time transfer and orbit determination support for the Lunar Reconnaissance Orbiter. There is also great technical synergy between optical transponders and laser communications systems as recently demonstrated by a 620 Mbps downlink to Earth from the LADEE spacecraft in lunar orbit.


Recognizing the existing diversity of the laser ranging technology, this working group seeks to evaluate the potential of transponder applications and to recommend basic concepts to the ILRS that provide a link between the newly emerging technology and the existing capability of the SLR network in order to promote experiments or to utilize the new technology in lunar or planetary missions. Items of particular importance are:

  • Investigate the potential of transponder applications for space geodesy, physics of the solar system, and relativity/fundamental physics
  • Evaluate the operational and technological consequences for participating ILRS stations and analysis centers, which a respective transponder application may imply. This includes hardware and operating software modifications, prediction format issues, data file structures, and formats and data reduction practices as well as laser safety.
  • Evaluate the instrumental requirements of the space segment, including the range reduction to the center of mass of the spacecraft, space transponder design and telemetry requirements.
  • Promote the use of the existing SLR satellite constellation in simulating interplanetary laser ranging, time transfer, and optical communications through the Earth’s atmosphere.
  • Act as a point of contact between interested agencies and the ILRS.

The committee organizes transponder sessions at the ILRS workshops.