The Ground-based Experiment of the Prototype of Planetary (& Lunar) Rotation Monitor Telescope

The scientific objective of the Planetary (& Lunar) Rotation Monitor (PRM) telescope is to study the planet's (the Moon's) rotation and their inner structure and physics by in-situ observation. In this work, the prototype of the telescope is designed and manufactured. The prototype's optical system is a commercial astronomical telescope. A trihedron mirror set is placed at the beginning of its light path to realize observing three fields of view (FOVs) simultaneously. The ground-based validating observation began in 2017. Images containing stars from three FOVs were achieved. Star images from different FOVs initially mix together, and can be categorized into three FOVs respectively, in which motion behavior of star images on CCD plate between adjacent exposures differs with FOVs. The principle, hardware design and image process are demonstrated here. From the observational images, the direction change of three FOVs in space due to the Earth's rotation are shown, and the mean direction of the rotation axis of the Earth in celestial sphere can be calculated. The deviation of the determined celestial coordinate of the rotation axis from the theoretical values is shown around 1'. The main errors in observation are discussed, including atmospheric reflection, thermal deformation of the commercial telescope, low optical resolution caused by short focal length, optical aberration in multiple FOVs' observation, etc. All these experience and knowledge will be adopted in the next-generation design of PRM, and help to realize the goal of the final PRM which will be launched to the Moon in future.