In this video we introduce the keplerian orbital elements, which include semi-major axis, eccentricity, the orientation of the perifocal frame with respect to the inertial frame with the 3 angles: orbital inclination, right ascension of the ascending node, and argument of periapsis, and finishing with true anomaly.
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We start with semi-major axis and eccentricity, which correspond to the size and shape of an orbit. To begin we need to define 2 points in this orbit. The first is periapsis, which is the point closest to the center of the Earth in the orbit, and the second is apoapsis, which is the farthest point. Using just !!!next!!! These two scalar values apoapsis and periapsis, we can calculate our semi-major axis and eccentricity. Using just these two scalar values apoapsis and periapsis, we can calculate our semi-major axis and eccentricity.
Next up are the 3 orbital elements that describe the orbital plane with respect to the inertial frame. If you are unfamiliar with 3D rotations and euler angles, no worries. The most important and straightforward angle to understand is the inclination.
For those who are familiar with euler angles, the right ascension, inclination, and argument of periapsis are the angles of a 3-1-3 euler angle sequence that describes the rotation between the inertial frame and the perifocal frame, where the perifocal frame is inertial and defined as the X-axis pointing towards periapsis, z-axis pointing in the angular momentum direction (perpendicular to the orbital plane), and y-axis completes the right handed system.
Orbital inclination is the angle between the equatorial plane and the orbital plane, which can also tell us if an orbit is prograde or retrograde.
Right ascension of the ascending node (RAAN), sometimes called longitude of the ascending node, is defined as the angle between the inertial X-axis and the ascending node.
Argument of periapsis, which is defined as the angle between the ascending node and the orbit periapsis.
True anomaly is defined as the angle between periapsis and current position.
#keplerianorbitalelements #orbitalmechanics #astrodynamics
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