Short-Arc Association and Orbit Determination for New GEO Objects with Space-Based Optical Surveillance

For Geosynchronous Earth Orbit (GEO) objects, space-based optical surveillance has advantages over regional ground surveillance in terms of both the timeliness and space coverage. However, space-based optical surveillance may only collect sparse and short orbit arcs, and thus make the autonomous arc association and orbit determination a challenge for new GEO objects without a priori orbit information. In this paper, a three-step approach tackling these two critical problems is proposed. First, under the near-circular orbit assumption, a multi-point optimal initial orbit determination (IOD) method is developed to improve the IOD convergence rate and the accuracy of the IOD solution with angles-only observations over a short arc. Second, the Lambert equation is applied to associate two independent short arcs in an attempt to improve accuracy of the single-arc IOD semi-major axis (SMA) with the use of virtual ranges between the optical sensor and GEO object. The key idea in the second step is to generate accurate ranges at observation epochs, which, along with the real angle data, are then used to achieve much improved SMA accuracy. The third step is basically the repeated application of the second step to three or more arcs. The high success rate of arc associations and accurate orbit determination using the proposed approach are demonstrated with simulated space-based angle data over short arcs, each being only 3 min. The results show that the proposed approach is able to determine the orbit of a new GEO at a three-dimensional accuracy of about 15 km from about 10 arcs, each having a length of about 3 min, thus achieving reliable cataloguing of uncatalogued GEO objects. The IOD and two-arc association methods are also tested with the real ground-based observations for both GEO and LEO objects of near-circular orbits, further validating the effectiveness of the proposed methods.

CubeSat formation architecture for small space debris surveillance and orbit determination

Introduction: Satellites which face space debris cannot track it throughout the whole orbit due to natural limitations of their optical sensors, sush as field of view, Earth occultation, or solar illumination. Besides, the time of continuous observations is usually very short. Therefore, we are trying to offer the most effective configuration of optical sensors in order to provide short-arc tracking of a target piece of debris, using a scalable Extended Information Filter. Purpose: The best scenario for short-arc tracking of a space debris orbit using multipoint optical sensors. Results: We have found optimal configurations for groups of satellites with optical sensors which move along a sun-synchronous orbit. Debris orbit determination using an Extended Information Filter and measurements from multipoint sensors was simulated, and mean squared errors of the target's position were calculated. Based on the simulation results for variouos configurations, inter-satellite distances and measurement time, the most reliable scenario (four satellites in tetrahedral configuration) was found and recommended for practical use in short-arc debris tracking.

Sustainable and Efficient Processing of Gh4169 Superalloy With Rotating Short Arc Milling Method

High processing efficiency and low environmental pollution have been recognized as important goals of sustainable electrical discharge machining (EDM). This paper proposed a sustainable and efficient EDM method called rotating short arc milling. In order to improve the processing efficiency and reduce pollutant emissions, the principles of this method to achieve high material removal rate (MRR), low tool electrode wear rate (TEWR) and environmentally friendly dielectric are described separately. The rotating short arcs generated by the compound field can improve the machining efficiency. The action of the magnetic field and the internal high-pressure dielectric can quickly remove the debris avoiding irregular discharge, thereby improving the machining quality. Due to the attraction effect of the magnetic field on the debris, several debris adhere to the processing end of the tool electrode to form a protective layer and participates in the processing as a part of the tool electrode, which can reduce the tool electrode wear. Tap water is used as the working fluid to reduce pollutants generated during processing. Then, a series of experiments are conducted to study the influence of process parameters on the processing of GH4169 superalloy. The results show that the machining voltage, machining depth and magnetic field strength are the three most important factors that affect the efficiency and sustainability of rotating short arc milling. Furthermore, the optimal process parameters are obtained by using gray relational analysis method to optimize the machining process in terms of high efficiency and environmental protection.

Investigation of nonlinearity in inverse problems of satellite dynamics

The report presents the results of a study of the total and intrinsic nonlinearities as applied to the outer satellites of Jupiter observed on a short arc. The relationship between the nonlinearities and the conditions of satellite observations is revealed. In particular, it is shown that the total nonlinearity is very strong when the observation period is less than 0.1 of the orbital period, while the intrinsic nonlinearity is weak enough for all satellites, which indicates the possibility of using nonlinear methods for adequate modeling of their orbital uncertainty.