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About orbit or ode

  1. Oct 15, 2008 #1
    MY problom is easy,but i can't get the reasonable answer.problom dipicted:
    In the Cartesian coordinates,A satellite'higth is 200KM,and just in two dimensions.the initial position is (-6571KM,0),and initial velocity is (0,-7.8KM/S).I need the final running solution of program.I want to solve the problom in ode45.The result figure just is a circle
    program as following:
    ============================================
    function Yd=orbit(t,y)
    global u
    rx=y(1);
    ry=y(2);
    vx=y(3);
    vy=y(4);
    rr=sqrt(rx^2+ry^2);
    vxy=[vx;vy];
    xy=[rx;ry];
    Yd=[vxy;-u*xy/rr^3];
    ===================================

    function wlow3
    global u
    u=3.986e14;
    t0=0;tf=24*60*60;
    tspan=[t0,tf]; %
    y0=[-6.571e6;0;0;-7.8e3];%
    [t,YY]=ode45('orbit',tspan,y0);
    X=YY(:,1);
    Y=YY(:,2);
    plot(X,Y);
    xlabel('x')
    ylabel('y')
    hold on
    axis('image')

    ==========================================================
    I hope anyone who researches orbit or others can communicates with me.
    thans a lot.
     
  2. jcsd
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