During the past decade, several heliostat development projects have been implemented in various parts of the world (MBB, ASINEL, MARTIN MARIETTA, ARCO SOLAR, etc.). These projects have concen­ trated on the segmented glass mirror design, as used in the solar tower facilities of SSPS (Spain), BARSTOW (USA), THEMIS (France) [1] as well as in other test and prototype facilities. The main emphasis in these projects has been on the individually curved glass facets, on dimensioning, mounting and adjusting them, as well as on th~ structural rigidity of the system as a whole. Particular attention has had to be paid to developing drive units with minimum play: the tracking concept generally employed, where the points of rotation of azimuth and elevation almost coincide, places great demands on the drive as regards play and tracking accuracy, and has resulted in some extremely compact, but also some very heavy and expensive units.