Skip to main content

Satellite Laser Ranging (SLR) targets are satellites equipped with corner cubes or retroreflectors. Currently, the global SLR network tracks over forty such satellites. The observable is the round-trip laser pulse time-of-flight to the satellite.

SLR and Lunar Laser Ranging (LLR) use short-pulse lasers and state-of-the-art optical receivers and timing electronics to measure the two-way time of flight (and hence distance) from ground stations to retroreflector arrays on Earth orbiting satellites and the Moon.

The laser stations are also used to measure one-way distance from the ground stations to remote optical receivers on space and for very accurate time-transfer. Laser ranging activities are organized under the ILRS.

SLR is an accurate technique for determining the geocentric position of an Earth satellite, allowing for the precise calibration of radar altimeters and separation of long-term instrumentation drift from secular changes in ocean topography. SLR’s ability to measure the temporal variations in the Earth’s gravity field and to monitor motion of a global network of stations with respect to the geocenter, together with the capability to monitor vertical motion in an absolute system, makes it unique for modeling and evaluating long-term climate change.

SLR Overview

SLR Data and Product Archive 

NASA’s archive of SLR data and derived products primarily supports NASA programs and the International Laser Ranging Service (ILRS). This archive is managed by the Crustal Dynamics Data Information System (CDDIS).

Scientific products derived using SLR and LLR data include:

  • Precise geocentric positions and motions of ground stations
  • Satellite orbits
  • Components of Earth’s gravity field and their temporal variations
  • Earth Orientation Parameters (EOP)
  • Precise lunar ephemerides
  • Information about the internal structure of the Moon

Laser ranging data consist of a distance or range (round-trip, station to satellite and back) and time, together with data correction information such as atmospheric effects, which are to be applied to the data. Raw laser ranges are formatted at the remote station before transmission to operational data centers where the data are translated into the appropriate format.

ILRS Operations Centers interface to SLR stations, collecting, validating, and merging data from selected stations. At a minimum, laser stations forward their data to operations/data centers on a daily basis where they are merged into files by day and satellite for transmission to and archive at the global data centers such as CDDIS.

Products derived from SLR data are under development by the ILRS Analysis Working Group. These products include station positions and Earth orientation parameters (EOP) and are located on CDDIS in subdirectories by data type.

Some of the scientific results derived from SLR and LLR products include:

  • Detection and monitoring of tectonic plate motion, crustal deformation, Earth rotation, and polar motion
  • Modeling of the spatial and temporal variations of the Earth's gravitational field
  • Determination of basin-scale ocean tides
  • Monitoring of millimeter-level variations in the location of the center of mass of the total Earth system (solid Earth-atmosphere-oceans)
  • Establishment and maintenance of the International Terrestrial Reference System (ITRS)
  • Detection and monitoring of post-glacial rebound and subsidence

In addition, SLR provides precise orbit determination for spaceborne radar altimeter missions mapping the ocean surface (which are used to model global ocean circulation), for mapping volumetric changes in continental ice masses, and for land topography. It provides a means for subnanosecond global time transfer, and a basis for special tests of the Theory of General Relativity.

The current global SLR network consists of over forty systems, several of which are managed by NASA. During the past three decades, this network has evolved into a powerful source of data for studies of the solid Earth and its ocean and atmospheric systems. View a map of SLR sites.

NASA's global network of satellite laser ranging (SLR) stations has delivered a substantial share of the orbital data used to define the International Terrestrial Reference Frame (ITRF) for more than four decades. The existing legacy SLR network is nearing the end of its operational life, making it essential to deploy a new generation of systems. The growing scientific need for sub-millimeter precision, and the rapidly expanding number of tracking targets impose ambitious performance requirements on the next generation systems. NASA is developing the Space Geodesy Satellite Laser Ranging (SGSLR) system-a modern network of advanced SLR stations that will serve as key components of the Space Geodesy Project.

Read more about SGSLR.

International Laser Ranging Service
The International Laser Ranging Service (ILRS) provides global satellite and lunar laser ranging data and their derived data products to support research in geodesy, geophysics, Lunar science, and fundamental constants.
Learn more about ILRS
The acronym ILRS in bright blue text appears below a green-and-blue graphic depiction of a laser pointing toward space

QUESTIONS & SUPPORT

Have a question?

Get help with NASA Earth science data, datasets, tools, services, and metadata on the Earthdata Forum. Experienced staff in the data user community review and answer questions.

Get help on Earthdata Forum
Earthdata
Forum