Research on Horizontal Limit Avoidance Strategy for Equatorial Telescope Pointing Process

Time-domain survey telescopes requires telescopes with the capability of rapid response and uninterrupted operation to observe light curves of astrophysical transients in the shortest possible time. But for equatorial telescopes, which are mainly used for meter-class telescopes, there is a certain probability that the horizontal limit stop will interrupt the observation, especially during the pointing process when the telescope slews to the next object to observe. This paper discusses the procedures to estimate whether the horizontal limit stop will occur in the pointing process. Moreover, an algorithm is proposed to prevent the occurrence it. Specifically, several factors relate to the horizontal limit stop are discussed, including the latitude of the observation site, the current axes position of the telescope, the target axes position, the degree threshold of the horizontal limit stop, and the altitude threshold of the observable sky area for astronomy, etc. Once the factors are given, a set of discrimination procedures is conducted to determine whether the horizontal limit stop will be triggered in a single pointing process. If the procedures predict it will occur, then an algorithm will be adopted by the telescope control software to prevent it by altering the pointing course. Finally, some other related factors are also discussed, for example, RA and DEC axes having different pointing speeds, observation sites in the Southern Hemisphere, etc. This study demonstrates a method to keep off the horizontal limit stop for equatorial astronomical telescopes. It is very practical and make sense to guarantee that the automatic and autonomous observation operate continuously to realize rapid response system for time-domain survey telescopes.