Vol.:(0123456789) 1 3 Journal of Geodesy https://doi.org/10.1007/s00190-019-01241-1 ORIGINAL ARTICLE The ILRS: approaching 20 years and planning for the future Michael R. Pearlman 1  · Carey E. Noll 2  · Erricos C. Pavlis 3  · Frank G. Lemoine 2  · Ludwig Combrink 4  · John J. Degnan 5  · Georg Kirchner 6  · Ulrich Schreiber 7 Received: 3 July 2018 / Accepted: 13 February 2019 © This is a U.S. government work and its text is not subject to copyright protection in the United States; however, its text may be subject to foreign copyright protection 2019 Abstract The International Laser Ranging Service (ILRS) was established by the International Association of Geodesy (IAG) in 1998 to support programs in geodesy, geophysics, fundamental constants and lunar research, and to provide the International Earth Rotation Service with data products that are essential to the maintenance and improvement in the International Terrestrial Reference Frame (ITRF), the basis for metric measurements of changes in the Earth and Earth–Moon system. Other scientifc products derived from laser ranging include precise geocentric positions and motions of ground stations, satellite orbits, components of Earth’s gravity feld and their temporal variations, Earth Orientation Parameters, precise lunar ephemerides and information about the internal structure of the Moon. Laser ranging systems are already measuring the one-way distance to remote optical receivers in space and are performing very accurate time transfer between remote sites in the Earth and in Space. The ILRS works closely with the IAG’s Global Geodetic Observing System. The ILRS develops (1) the standards and specifcations necessary for product consistency, and (2) the priorities and tracking strategies required to maximize network efciency. The service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientifc, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost efectiveness of its data products. The ILRS works with (1) new satellite missions in the design and building of retrorefector targets to maximize data quality and quantity, and (2) science programs to optimize scientifc data yield. Since its inception, the ILRS has grown to include forty laser ranging stations distributed around the world. The ILRS stations track more than ninety satellites from low Earth orbit (LEO) to the geosynchronous orbit altitude as well as retrorefector arrays on the surface of the Moon. Applications have been expanded to include time transfer, asynchronous ranging for targets at extended ranges, free space quantum telecommunications, and the tracking of space debris. Laser ranging technology is moving to lower energy, higher repetition rates (kHz), single-photon-sensitive detectors, shorter pulse widths, shorter normal point intervals for faster data acquisition, and increased pass interleaving, automated to autonomous operation with remote access, and embedded software for real-time updates and decision making. An example of pass inter- leaving is presented for the Yarragadee station (see Fig. 4); tracking of LEO satellites is often accommodated during break in LEO and GNSS passes. New satellites arrays provide more compact targets and work continues on the development of lighter less expensive arrays for satellites and the moon. The service now provides operational ITRF products including daily/ weekly station positions and daily resolution Earth orientation products; the fow of weekly combination of satellite orbit fles for LAGEOS/Etalon-1 and -2 has recently been established. New products are under testing through a pilot project on systematic error monitoring currently underway. The article will give an overview of activities underway within the service, paths forward presently envisioned, and current issues and challenges. Keywords ILRS · Laser ranging · Satellite laser ranging · Space geodesy · Laser retrorefectors · Lunar ranging · Laser tracking of space debris 1 Introduction Satellite laser ranging (SLR) and lunar laser ranging (LLR) are basic space tools for making accurate measurements for applications in geodesy, geophysics, lunar science, and * Michael R. Pearlman mpearlman@cfa.harvard.edu Extended author information available on the last page of the article