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Perturbation Theory Orbital Dynamics and Attitude Control Dr. Rafael Ramis Abril EuMAS-European Masters Course in Aeronautics and Space Technology Departamento de Física Aplicada a la Ingeniería Aeronáutica Universidad Politécnica de Madrid OCTOBER 2007 Perturbation Theory Analytical mechanics? Lagrange equations? Cyclic coordinates? Hamilton equations? Canonical transformations? Symplectic matrix? HamiltonJacobi equation? Perturbation Theory The cartensian variables are: x, y, z, x', y', and z' The classical orbital elements are: a, e, i, Ω, ω , and M The Delaunay elements are: (α, M), (h, ω ), (hz, Ω) α=µ1/2a1/2 (no specific name) h=µ1/2a1/2(1-e2)1/2 = modulus of angular momentum hz= µ 1/2a1/2(1-e2)1/2cos i = z-component of angular momentum For Keplerian motion all elements are constant in time (except M that changes linearly) For arbitrary motion one can think in the time changing orbital elements as a transformation of coordinates. Osculating orbit – the keplerian orbit associated with instantaneous elements Perturbation Theory OSCULATING ORBIT µ Frame with virtual attracting focus t e Perturbation Theory OSCULATING ORBIT µ Frame with virtual attracting focus t e Perturbation Theory OSCULATING ORBIT µ Frame with virtual attracting focus t e Perturbation Theory OSCULATING ORBIT µ Frame with virtual attracting focus t e Perturbation Theory Perturbation Theory Perturbation Theory Canonical transformations One can map a set of variables {pi,qi} into a different set {Pi,Qi} P1=P1(p1,q1,p2,q2,...), Q1=Q1(p1,q1,p2,q2,...), etc. The transformation is said to be canonical, if the Hamilton equations for variables {Pi,Qi} are derived from the transformed of the hamiltonian function. Not all transformations are canonical Perturbation Theory Example of canonical transformation: 2D cartesian to polar coordinates Perturbation Theory When is a transformation a canonical transformation ? When the jacobian matrix is “symplectic” See Goldstein book: Classical Mechanics, Chapter 9 H. Goldstein, Classical Mechanics (second edition), Addison-Wesley Publishing Company, Reading Massachussets Perturbation Theory “The transformation from cartesian variables to Delaunay variables is canonical” M, ω , and Ω are “coordinates” and α, h, and hz their “momentums” See section 4, R. Ramis, Mecánica Orbital y Dinámica de Actitud, ETSIA See chapter 8, F. T. Geyling and H. R. Westerman, Introduction to Orbital Mechanics, Chapter 8, AddisonWesley Perturbation Theory Perturbation Theory Example: constant radial force Perturbation Theory Perturbation Theory System of ODE to be solved numerically Numerical (truncation) error ~ |γ | ∆tN, instead ~∆tN Perturbation Theory Perturbation Theory Perturbation Theory Perturbation Theory Perturbation Theory Zero order (analytic solution available) First order correction (linear system) Second order correction (linear system) Perturbation Theory Perturbation Theory First order equations: can be reduced to integrals Equation for M 1 must be integrated after equation for α 1 Perturbation Theory Sometimes integrals can be evaluated analytically The parameter variations include secular and oscilatory terms Perturbation Theory r min r max e Perturbation Theory ● For ε<<1, the series converges very fast ● High order terms are difficult to be computed ● Typically only 1 or 2 orders are considered ● Non-keplerian effects are retained ● For large times the convergence can fail ● After some time, the zero order orbit can be changed ● Ussually one writes ε=1 (with G<<F) ● Correction equations are linear, but with time depending coefficients ● Equations on orbital elements are more appropriate that cartesian ones Perturbation Theory Lagrange planetary equations Perturbation Theory Lagrange planetary equations Perturbation Theory Gauss equations Página 1 Página 2 Página 3 Página 4 Página 5 Página 6 Página 7 Página 8 Página 9 Página 10 Página 11 Página 12 Página 13 Página 14 Página 15 Página 16 Página 17 Página 18 Página 19 Página 20 Página 21 Página 22 Página 23 Página 24 Página 25 Página 26 Página 27 Página 28 Página 29 Página 30
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