2/20/2024 0 Comments Orbital shiftA satellite in a direct orbit with an orbital period greater than one day will tend to move from east to west along its ground track, in what is called "apparent retrograde" motion. ![]() (Direct orbits are by far the most common for artificial satellites, as the initial velocity imparted by the Earth's rotation at launch reduces the delta-v needed to achieve orbit.)Ī satellite in a direct orbit with an orbital period less than one day will tend to move from west to east along its ground track. A satellite with an orbital inclination between 90° and 180° (or, equivalently, between 0° and −90°) is said to be in a retrograde orbit. A satellite with an orbital inclination between zero and ninety degrees is said to be in what is called a direct or prograde orbit, meaning that it orbits in the same direction as the planet's rotation. Typically, satellites have a roughly sinusoidal ground track. (This article discusses closed orbits, or orbits with eccentricity less than one, and thus excludes parabolic and hyperbolic trajectories.) The ground track of a satellite can take a number of different forms, depending on the values of the orbital elements, parameters that define the size, shape, and orientation of the satellite's orbit. Aircraft routes are planned to avoid restricted airspace and dangerous areas, and to pass near navigation beacons. In order to follow a specified ground track, a pilot must adjust their heading in order to compensate for the effect of wind. In air navigation, ground tracks typically approximate an arc of a great circle, this being the shortest distance between two points on the Earth's surface. In other words, the ground track is the set of points at which the satellite will pass directly overhead, or cross the zenith, in the frame of reference of a ground observer. Ī satellite ground track may be thought of as a path along the Earth's surface that traces the movement of an imaginary line between the satellite and the center of the Earth. In the case of satellites, it is also known as a suborbital track or subsatellite track, and is the vertical projection of the satellite's orbit onto the surface of the Earth (or whatever body the satellite is orbiting). ![]() The light and dark regions represent the regions of the Earth in daylight and in the night, respectively.Ī ground track or ground trace is the path on the surface of a planet directly below an aircraft's or satellite's trajectory. Additionally, we find these materials are also fragile topological insulators with hourglass like surface states.Path on the surface of the Earth or another body directly below an aircraft or satellite Ground track of the International Space Station for approximately two periods. Metallic surface states, hinge states, or corner states cover the large bulk energy gap (for example, more than 1 eV in TlGaTe$_2$) at related boundary, which are ready for experimental detection. To demonstrate such orbital-shift-induced boundary obstructed topological insulators, we predict eight material candidates, all of which were overlooked in present topological databases. On the open boundary, Wannier charge centers can shift to different atoms from those in bulk, leading to in-gap surface states, higher-order hinge states or corner states. Download a PDF of the paper titled Orbital shift-induced boundary obstructed topological materials with a large energy gap, by Ning Mao and 5 other authors Download PDF Abstract:We propose boundary obstructed topological phases caused by Wannier orbital shift between ordinary atomic sites, which, however, cannot be indicated by symmetry eigenvalues at high symmetry momenta (symmetry indicators) in bulk.
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