Laser ranging is one of the most accurate techniques for observing orbits of artificial satellites. The state-of-the-art Satellite Laser Ranging System (SLR) at RGO Herstmonceux began operations in October 1983 and is considered one of the best installations of its kind worldwide. As part of the International Laser Ranging Service (ILRS), the data obtained with the RGO’s SLR system is made available to researchers worldwide within 1-2 hours. On average during the year the SLR system observes some 45% of the available satellite passes both by day and at night.

The RGO’s SLR is a high-precision SLR system, with two Global Navigation Satellite Systems (GPS and GLONASS) receivers and associated environmental monitoring systems. Laser ranging is used only for satellites carrying retro-reflectors. The technique uses time-of-flight measurements with short pulses of light to determine the range to a satellite as it moves in orbit around the Earth. The satellites routinely tracked form two broad classes.

First, geodynamic satellites (inert massive spheres designed solely to reflect laser light back to the ranging systems). These objects include: Starlette and Stella, lower altitude satellites which are important for studies of the Earth’s gravitational field and of indirect tidal effects; Ajisai, Etalon-I and Etalon-II which are used for similar purposes; and Lageos and Lageos-I satellites which are observed primarily to obtain information about the rotation of the Earth and the geometry and deformation of its surface.

Second, satellites carrying radar altimeters such as ERS-1 and ERS-2 (launched by ESA in 1991 and 1995) and TOPEX/POSEIDON (launched by NASA in 1992). Data from these satellite types allow for the study of variations of the height of the surface of the sea or of the snow and ice in polar regions, and thus to obtain information about ocean currents and eddies and the profile and structure of the ocean floor.

The UK Satellite Laser Ranging facility at Herstmonceux was developed by the RGO in collaboration with the University of Hull, with financial support from SERC. In 1974 Desmond King-Hele and others developed a proposal for a UK SLR project in which the RGO would participate. It was not approved by the SRC but a new meeting to discuss a revised proposal was arranged for 5 July 1977. The revised proposal was approved in autumn 1978 on the basis that the RGO would be responsible for the project but would give a contract to the University of Hull (UoH) for the laser, the detector package and the timing system.

The Time Department was given responsibility for the installation and running of the SLR system, with John Pope initially as Project Manager (until June 1980). The SLR team included John Pilkington, Andrew Sinclair, Graham Appleby, Phil Cottrell (who was in charge of the Engineering Workshop), Bill Matthews (an electronic engineer) and Geoff Harvey who developed the control software and maintained and documented it. Sinclair played a major role in developing the computer software and Dr Paul Sharman was recruited in February 1981 to work on the hardware, in collaboration with staff at the University of Hull (including Dennis Hall and Bob Hyde).

The Solar Dome at Herstmonceux was modified for use for the SLR telescope, with a new ‘eyelid done’ installed in February 1981, the room below converted for use for the laser, timing and computer systems, and adjacent office used for the control desk. The telescope was installed on its pier on 3 July 1981 and the laser was installed in April 1982 by staff of the Physics Department of the University of Hull who designed and built it. The first laser returns from Lageos and Starlette were detected at night on 31 March 1983 and the system was fully operational by October 1983.

The RGO’s SLR at Herstmonceux is now run by the Space Geodesy Facility (SGF) which supports geodetic and geophysical research though satellite tracking data and related produces. It is a research facility of the Natural Environmental Research Council (NERC), which funds the facility in collaboration with the Ministry of Defence.

Series RGO 93/1, RGO Satellite Laser Ranger Project Papers and Photographs, includes three administrative files for the project, covering 1976-1983. These include project proposals and revisions, planning documents, correspondence, and documentation from meetings. The series also includes a set of sample SLR data sheets for the first and second SLR returns of 1983, various sets of photographs of SLR systems at Herstmonceux and elsewhere, and two SLR publications.

Also catalogued here are a set of reports for a separate, later RGO project for observing satellites, the PIMS Project (1995-1998), series RGO 93/2. PIMS was 'A wide-angle optical space surveillance sensor', one of the uses of which was to detect space debris.