Satellite Laser Ranging (SLR) is a very precise, laser-based method for determining the distance between a satellite and Earth with an accuracy of a few millimetres. SLR is primarily used in geodesy. This is because the precise measurement of satellite orbits helps to determine changes in Earth’s structure and rotation. The SLR method also makes important contributions in the field of satellite navigation.
To date, the systems required for SLR have been large stations. Their construction is complex, costly and they require several people to operate them. The German Aerospace Center has developed a much smaller, mobile version. ‘miniSLR’ is transportable, easier to set up and maintain and can be operated automatically. This makes it considerably cheaper than the usual SLR systems. The prototype of miniSLR has already delivered measurement data under realistic operating conditions that can compete with large stationary systems.
With SLR, a ground station emits a laser beam in the form of short pulses. This beam hits the targeted satellite, is reflected back and detected by the ground station using a telescope. The distance between the object and the ground station can be calculated very precisely based on the time it takes for the laser light to travel this distance.
The satellite requires a reflector for the high-precision SLR process – similar to a reflector or cat’s eye on a road. It also helps to know the approximate orbit data, using less precise radar measurements, for example. This is because with SLR, the satellite, which is sometimes several thousand kilometres away and travelling at a speed of more than 28,000 kilometres per hour, must be targeted with the laser beam.
The compact miniSLR system developed at the DLR Institute of Technical Physics in Stuttgart is box-shaped, fully enclosed and weighs approximately 600 kilograms. It is 1.8 metres long, 1.3 metres wide and two metres high. To use it, the researchers only need a stable surface and power and internet connections. In future, miniSLR will be operated fully automatically, which will also significantly reduce the operating costs of a station. The team is currently still controlling the prototype manually.
