استخراج خودكار مشاهدات اپتيكي جهت تعيين مدار اوليه ماهواره‌ها

utomatic optical observation extraction for the initial satellite orbit determination

تعيين مدار در يك جمله، كاربرد انواع تكنيك ­ها جهت برآورد مدار اجرام فضايي نظير ماه، سيارات و فضاپيماها مي­باشد. تعيين موقعيت مداري امكان شناسايي اجرام موجود در فضا را فراهم مي­آورد. به اين معني كه مي­توان جرم مورد نظر را در كاتالوگ آرشيوي تعيين مدار موجود جستجو كرد و در صورت عدم وجود در آرشيو به ‌عنوان جرم جديد، كاتالوگ كرد. به‌منظور تعيين موقعيت مداري، مشاهدات به‌ صورت اطلاعات خام در فرآيند تعيين مدار مورد استفاده قرار خواهند گرفت. مشاهدات مختلفي ممكن است جهت تعيين مدار اوليه مورد استفاده قرار گيرند، ولي از آنجا كه استخراج مشاهدات طولاني، مشكل، گران و گاهي اوقات غيرممكن است، از مشاهدات زاويه­ اي استفاده مي­شود. در اين مقاله روشي جديد براي استخراج مشاهدات زاويه­ اي از طريق سيستم تصويربرداري اپتيكي ارائه شده است. در اين روش با استفاده از يك CCD و تلسكوپ مناسب، تصويري از آسمان كه داراي اطلاعاتي مربوط به ستاره ­ها و رد پاي ماهواره است، ثبت مي‌شود. از آنجا كه براي انجام تعيين مدار اوليه بايد مقدار آزيموت و زاويه ارتفاعي حداقل دو نقطه از مدار ماهواره در يك فاصله زماني در اختيار باشد، در اين تحقيق روشي خودكار جهت استخراج مدل اثر رد ماهواره ارائه شده است تا با استفاده از مدل استخراج شده مختصات نقاط ابتدا و انتها تشخيص داده شوند. جهت ارزيابي روش پيشنهادي سمت ‌و سوي استخراج شده از رد ثبت شده ماهواره مدار ارتفاع بالا MUOS (Mobile User Objective System) با مقادير نظير آن مستخرج از مدار دقيق مقايسه شده‌اند. نتايج حاصل بيانگر اختلافي در حد ميلي‌ثانيه مي­باشد.

In recent years, the development in the space industry and the ability of building, launching and infusion of satellites in the lower orbit has put the limited number of countries with such technology. In order to complete the entire cycle of the space industry, the satellite navigation and control, which have been neglected since the beginning of the movement of space science, has to be considered specially. The orbit determination in one sentence is the application of a variety of techniques for estimating the orbits of objects such as the moon, planets, and spacecraft. In dynamic astronomy, the orbit determination is the process of determining orbital parameters with observations. In particular, orbit determination of planets of solar system is adjustment of noisy orbital observation that consist of random and systematic error for force models and estimation of model parameters by observation (In order to access a mathematical model that illustrates the path of the celestial object in the path before and after the observation time). To simplify, this process is divided into two parts. First, the initial orbit is estimated and then make corrections to the determined orbit. The purpose of initial orbit determination of object that is moving around earth, is calculation of object orbital parameters by a few observations; furthermore initial orbit determination is used for detecting missing object in space. To determine the precise orbit, it is necessary to determine the initial orbit with good accuracy, which indicates the importance of the initial orbit determination. Different type of observations is used to make an initial orbit determination in which observations can be collected by ground stations that contain angular angles, elevations, distance, and distance rate. These observations are made by the radar and the telescope, because the collection of observations without instrument and naked eye does not have enough precision and sensitivity for determination of the space object orbit, but since the extraction of distance observation is expensive and sometimes impossible, angular observation is used. In this paper, a new method has been presented for extracting angular viewing through an optical imaging system. This method is an automatic and efficient method with the ability of real-time data analysis and the base of that is astronomical imaging by CCDs (charge-coupled device). The images captured by this method have a lot of information about stars, galaxy, satellites’ streak, etc. In this paper, automatic method is presented for streak detection which consist of 5 steps: 1) image denoising, 2) extracting of star centers, 3) extracting astronomical coordinates of stars (declination and right ascension), 4) matching between astronomical and pixel coordinate of stars, 5) calculation of satellite streak model. Then, with using the extracted model, the coordinates of beginning and end points are detected. With the celestial coordinates of beginning and end point of streak Azimuth and elevation of satellite on both sides are determined. On the other hand, to evaluate the proposed method and the validity of the input parameters for initial orbit determination, the azimuth and elevation values of the beginning and end points of streak can be calculated by precise orbit file and then these results compare with results of purposed method. Comparing results indicate a difference of about milliseconds.