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A MATLAB Script for Propagating Interplanetary Trajectories from Earth to Mars

A MATLAB Script for Propagating Interplanetary Trajectories from Earth to Mars

by

David Eagle (view profile)

 

Numerically integrate the orbital equations of motion of an Earth to Mars interplanetary trajectory.

eqxra (tjd, k)
function raeq = eqxra (tjd, k)

% this function computes the intermediate right ascension
% of the equinox at julian date tjd, using an analytical expression
% for the accumulated precession in right ascension.  for the
% true equinox the result is the equation of the origins.

% input

%  tjd = tdb julian date

%  k = equinox selection code

%      set k = 0 for mean equinox
%      set k = 1 for true equinox (equation of the origins)

% output

%  raeq = intermediate right ascension of the equinox, in hours (+ or -)

% ported from NOVAS 3.0

%%%%%%%%%%%%%%%%%%%%%%%

% t0 = tdb julian date of epoch j2000.0 (tt)

t0 = 2451545.0d0;

t = (tjd - t0) / 36525.0d0;

% for the true equinox, obtain the equation of the equinoxes in time seconds

if (k == 1)
    
    [a, a, ee, a, a] = etilt1 (tjd);
    
    eqeq = ee;
    
else
    
    eqeq = 0.0d0;
    
end

% precession in ra in arcseconds taken from capitaine et al. (2003),
% astronomy and astrophysics 412, 567-586, eq. (42)

precra = 0.014506d0 + ...
    (((( -0.0000000368d0 * t ...
    - 0.000029956d0) * t ...
    - 0.00000044d0) * t ...
    + 1.3915817d0) * t ...
    + 4612.156534d0) * t;

raeq = -(precra / 15.0d0 + eqeq) / 3600.0d0;


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