The Analysis And Design Of Swinging Fork ALT-ALT Mounting Optic-Electronic Satellite Tracker

As one kind of ground-based satellites tracking instrument, the small optic-electronic satellite tracker executes the mission of searching, capturing, measuring, numbering and monitoring satellites. These satellites fly at the altitude of about 500km and whose angular velocity is about 200 times greater than stars'. The tracker's observed data are important parameters to determine the precise orbits of those orbit-known or unknown satellites. As one of the most often used mountings, the altazimuth mounting satellite tracker has a blind area near the zenith because of the very high azimuth angular velocity, as a result, discontinuous observing data are caused. As for those fast flying satellites, this kind of blind area is very significant because it causes difficulties in precisely determining the satellites' orbits. In the meantime, mobile observation is more and more needed and it is necessary that the trackers to be compact and easy for moving.In this paper we brought forward a new type of ALT-ALT mounting satellite tracker whose fork just swings about its fixed-pointing horizontal axis. We analyzed and proved that this kind of mounting can cover all useful sky area and has much lower and smoother angular velocity and acceleration than the altazimuth one.IN THIS PAPER WE ALSO DISCUSSED THE RELATIONSHIP BETWEEN TWO MOST OFTEN USEDALT-ALT coordinate systems (SN-ALT-ALT, EW-ALT-ALT coordinate system) and the sidereal hour-angle coordinate system, the horizon coordinate system. The various coordinate system transformation formulae were derived and the tracking angular velocity and acceleration between the ALT-ALT mounting satellite tracker and the horizontal mounting one were compared. From the analysis of the maximum angular velocity and acceleration both for stars and satellites it is clear that ALT-ALT mounting has advantages on the horizontal mounting. In order to study the ALT-ALT mounting's mechanical performance, the main parts of the satellite tracker, including the main optical scheme, the axes' drive and anti-moment system, the support sets and the sizes of the two main axes were carefully designed. The pointing error of the tracker caused by the tube and the two axes' deflection under the gravity was analyzed and pointing error formula was obtained. We used Ansys(tm) to execute the FEA(Finite Element Analysis) of the main tube and the two major axes' deflection and quantitative results of the tracker's mechanical performance were obtained. In our FEA, we found out this kind of swinging fork has a very good mechanical performance thus it is a very characteristic mounting for small satellite tracker as compared to the horizontal mounting.In the last part of this paper we discussed a very simple logic control diagram of this kind of mounting satellite tracker. Our emphasis was put on the analysis of the optical flow method in order to automatically recognize and track the satellites under the complicated sky background. This kind of automatic recognition method for single moving object is especially useful to complement our existing tracking control method in which the operator's assistant is indispensable..