Is there a next generation SLR-technology?

Space geodetic techniques have established a remarkable measurement resolution. The relative error of satellite laser ranging (SLR) range measurements for example is as low as 10(-9). Since this corresponds to a precision of a few millimeter and reflects the current state of the art of electronic devices, no substantial technical improvement can be expected for the coming years. For the sake of completeness it should be mentioned that there are also some limitations in the modelling of the atmosphere, which also contributes to the error budget. However this is beyond the scope of this paper. So it will need a dramatic conceptual change to develop this technology further. A drawback of all space geodetic tools is the fact that they only produce a partial estimate of the topocentric line-of-sight- or velocity-vector. A next generation laser ranging system for example could be characterised by the fact that it generates the full topocentric vector by simultaneously measuring a precise range and a precise direction towards the satellite. This paper looks at the basic requirements to obtain this information. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.