SLR

The SLR system is a space geodesy technique used as validation and complement of the VLBI and GNSS techniques.

A basic SLR station consists of the following main subsystems:

• Building for system installation and control room, access to the building and necessary infrastructures.
• Telescope and dome subsystems. The telescope includes the mount and must and usually is suitable for the installation of the detection package.
• Optical system: pulsed solid-state laser, optic detectors, calibration system, optical bench and other devices such as filters, focusing systems, etc.
• Measurement system: range gate generator, event timer, frequency standard, test equipment.
• Control, monitoring and observation software.
• External security systems (passive radars, surveillance cameras) and internal security (personal protective equipment).
• Weather station.

A state of the art SLR system should be built with the following performance characteristics established by GGOS (GGOS Requirements for Core Sites):

• Capable of ranging to satellites from low earth orbits (LEO, 400 km) to synchronous altitudes and GNSS satellites (42000 km).
• Capable of night-time and daytime ranging.
• Normal point precision to geodetic satellites (LAGEOS) < 1mm.
• Capable of pass interleaving.
• Robust, consistent, verifiable calibration < 1 mm.
• Capable of acquiring 600 passes each on LAGEOS-1 and -2 during the course of a year.
• Capable of tracking an average of 3 pass segments with 3 normal points each segment on LAGEOS passes.
• Rapid data transmission upon completion of a session.

Besides observations to satellites equipped with retro-reflectors, currently, several SLR stations are working to improve and modify some of their capabilities to perform space debris observations. Yebes Observatory station will be designed in such a way that it could be ready in the future to carry out this kind of observations with little modifications (greater laser power, optical detectors according to wavelength, adapted software, etc.). This is an important aspect of the current policy of the European Union (EU) and the European Space Agency (ESA).

To develop a new SLR station, the first parameters that should be defined are related with the main components (location, building, dome, transmitting and receiving telescope, laser system, detection system and ToF measurement system) and the radar link equation parameters (receive and transmit optics efficiency, laser wavelength, laser pulse energy, detector quantum efficiency, far field divergence half-angle, beam pointing error, primary and secondary mirror radius). To select the values for these parameters the following aspects have to be taken into account: the satellites to be observed, the weather conditions at the station site (Yebes Observatory), the technological trends in other stations and the available economic budget.

The SLR of Yebes Observatory will have the characteristics and capacities required for its integration in the international network of SLR stations (ILRS). It will contribute to the improvement in the determination of the International Terrestrial Reference Frame (ITRF), increasing the number of observations to geodetic satellites like LAGEOS or LARES and other satellites located at high orbits such as GNSS, including Galileo or GPS satellites.