Sometimes a “wide angle camera”, in cooperation with a so- called beacon laser is used to determine the alignment data for establishing an optical communications connection between two satellites. To avoid more complex, and therefore more interference-prone, search algorithms, the camera is usually laid out in such a way that it can cover the entire uncertainty cone, which is created by the uncertainty of the position of the own and the opposite stations, as well as the uncertainty regarding tilting in the inertial systems of both stations. Because of the uncertainty cone, the camera must cover an angular area of approximately ±0.50°. However, at the same time the natural beam divergence of the communications beam being used comprises only a few micro-radians. This condition requires an extremely wide dynamic range of the ratio of visual angle/producible angular resolution. In addition, alignment errors between the optical device of the wide angle camera and the optical search device of the communications beam also have aggravating results. The transmission beam will move in a random manner within a defined solid angle area because of certain natural mechanical effects. Based on the limited resolution of the wide angle camera which can be achieved, as well as its limited electrical bandwidth, there is therefore a high degree of probability that the communications beam illuminates the opposite station only rarely. Thus, the opposite station is not provided the opportunity of becoming aligned with the received communications beam and in this way to initiate higher frequency “tracking” with a high degree of angular resolution. In the normal case, tracking of the opposite station in the communications mode takes place with the aid of the received communications light. Sensors with high spatial and/or electrical resolution are employed to obtain the spatial deviation signals (tracking signals).
For checking the optical alignment of two light sources in the course of coherent heterodyne reception, an arrangement is furthermore known from EP 0 831 604 A1, having a local laser and two detectors, each of which comprises two identical detector halves, which are respectively separated by a strip-shaped interruption, or gaps, in the photo diode electrode face between the adjoining halves, wherein the gaps of the two detectors are arranged orthogonally in respect to each other. This arrangement is used as a direction-selective optical monomode receiver. Here, an obscuration is provided in a receiving telescope of this arrangement, as well as in the beam path of the local laser. This makes it possible to generate an error signal for a spatial beam regulation of an optical heterodyne receiver, while preventing systematic losses and at the same time only minimally interfering with the data signal to be transmitted, along with a good signal-to-noise ratio.
Finally, an optical bench is known from EP 0 844 473 A1, whose bench structure is designed in such a way that, in case of a heat dilation of arms provided for connecting the receiving elements of various optical units, these receiving elements can be displaced without tilting transversely in respect to axes which assume defined angular positions in respect to each other and in relation to the bench structure. Such an optical bench can be combined with the arrangement mentioned at the outset.
Although such “tracking sensor” methods permit simultaneous communications and the determination of the spatial tracking error, the respective arrangements have been shown to be disadvantageous because of the relatively large adjustment outlay, in particular in the course of their manufacture.