KEYWORDS: Sun, Space operations, Process control, Solar sails, Solar radiation, Remote sensing, Spherical lenses, Telecommunications, Systems modeling, Solar radiation models
Heliotropic orbits and frozen orbits possess unique advantages in Earth observation missions and communication service. However, few scholars have found an orbit that possesses heliotropic and frozen characteristics at the same time. Heliotropic frozen orbits are obtained through a proposed control strategy, which is accomplished by adjusting the area-to-mass ratio and the attitude angles. First, we construct the dynamical model of high area-to-mass ratio spacecraft under the effect of J2 perturbation and solar radiation pressure. Then, nominal heliotropic frozen orbits are solved by assuming that the obliquity angle of the ecliptic with respect to the equator is zero. Finally, a control strategy is proposed to maintain heliotropic frozen orbits when the obliquity angle of the ecliptic with respect to the equator is considered. In addition, practical examples are provided to verify the heliotropic and frozen characteristics and the robustness of the controlled orbits. Orbit design for Earth observation and communication service is also studied.
We design a distributed situational observer using formation flying in a displaced orbit. The main focus of our investigation is the relative dynamics and control of displaced orbits obtained by low-thrust propulsion. The spatial dynamics in Newtonian form are used to derive the numerical relative motions, and their natural frequencies discovered by eigenvalue decomposition separate from each other at a critical height that differentiates the structural stability, bifurcation, and instability. Using the Jordan decomposition, six fundamental motions are achieved, including the stationary multiequilibria, the periodic oscillations that correspond to the natural frequencies, and the maximum leaving or approaching velocity caused by the different geometric and algebraic multiplicities. Off-axis equilibrium is obtained by a proposed open-loop control, and the motions nearby are proven to be equivalent to the numerical relative motions. The reduced dynamics in Hamiltonian form are used to derive the analytical solutions for linearized relative motions. Bounded relative trajectories with arbitrary initial values are achieved by two extraclosed-loop controls. Using the off-axis equilibrium and resonance of natural frequencies, the applications of a fixed relative baseline vector for interferometric SAR or Fresnel zone lens missions and repeating relative ground tracks for a phased array antenna mission are addressed in terms of the trajectory design.
Super low altitude remote sensing satellite maintains lower flight altitude by means of ion propulsion to improve
resolution and positioning accuracy of imaging images. The design of engineering data for achieving image positioning
accuracy is discussed in this paper based on principles of photogrammetry theory. The line-of-sight exact rebuilding of
each detection element and this direction intersects with the earth's elliptical precisely are ensured by the joint design of
key parameters when the camera on satellite is imaging. These parameters include orbit determination accuracy, attitude
determination accuracy, exposure time of camera, synchronizing time of getting ephemeris and attitude data accuracy,
geometric calibration and checking precise on orbit. Simulation calculation of precision proves that image positioning
accuracy of super low altitude remote sensing satellites is not improved obviously. Attitude determination error of
satellite still restricts positioning accuracy.
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