Experimental assessment of laser tracking noise angle

Because of the very high antenna gains on which free space laser communication depends, beamwidths are very narrow of the order of 1 arcsecond (5 microradians), and very high pointing precision is required if the link error rates are to be maintained within the stringent levels required for a commercial communications system. Studies had been carried out at Marconi comparing the so-called `stabilised´ and `deflected´ approaches to laser transponder beam stabilisation. To avoid the danger that some important parameter had been overlooked in making the stabilised vs. deflected comparison, Marconi deemed it advisable to carry out some early hardware work to establish that the high tracking accuracies predicted by theory for some of the mechanisations studied were indeed achievable in practice. A single-axis, low budget test rig was constructed embodying the principles proposed for the later mechanisations which included: conventional wide-angle drive with rolling bearings and gearing; flexural narrow angle pivots with brushless motor actuation; and feed-forward isolation of the telescope from satellite motion