interplanetary.m

% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  function ...
  [planet1, planet2, trajectory] = interplanetary(depart, arrive)
% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
%{
  This function determines the spacecraft trajectory from the sphere
  of influence of planet 1 to that of planet 2 using Algorithm 8.2
  
  mu         - gravitational parameter of the sun (km^3/s^2)
  dum        - a dummy vector not required in this procedure

  planet_id  - planet identifier:
                1 = Mercury
                2 = Venus
                3 = Earth
                4 = Mars
                5 = Jupiter
                6 = Saturn
                7 = Uranus
                8 = Neptune
                9 = Pluto 

  year       - range: 1901 - 2099
  month      - range: 1 - 12
  day        - range: 1 - 31
  hour       - range: 0 - 23
  minute     - range: 0 - 60
  second     - range: 0 - 60 
 
  jd1, jd2   - Julian day numbers at departure and arrival
  tof        - time of flight from planet 1 to planet 2 (s)

  Rp1, Vp1   - state vector of planet 1 at departure (km, km/s)
  Rp2, Vp2   - state vector of planet 2 at arrival (km, km/s)
  R1, V1     - heliocentric state vector of spacecraft at
               departure (km, km/s)
  R2, V2     - heliocentric state vector of spacecraft at
               arrival (km, km/s)

  depart     - [planet_id, year, month, day, hour, minute, second]
               at departure
  arrive     - [planet_id, year, month, day, hour, minute, second]
               at arrival

  planet1    - [Rp1, Vp1, jd1]
  planet2    - [Rp2, Vp2, jd2]
  trajectory - [V1, V2]
 
  User M-functions required: planet_elements_and_sv, lambert
%}
% --------------------------------------------------------------------

global mu

planet_id = depart(1);
year      = depart(2);
month     = depart(3);
day       = depart(4);
hour      = depart(5);
minute    = depart(6);
second    = depart(7);

%...Use Algorithm 8.1 to obtain planet 1's state vector (don't
%...need its orbital elements ["dum"]):
[dum, Rp1, Vp1, jd1] = planet_elements_and_sv ...
              (planet_id, year, month, day, hour, minute, second);

planet_id = arrive(1);
year      = arrive(2);
month     = arrive(3);
day       = arrive(4);
hour      = arrive(5);
minute    = arrive(6);
second    = arrive(7);

%...Likewise use Algorithm 8.1 to obtain planet 2's state vector:
[dum, Rp2, Vp2, jd2] = planet_elements_and_sv ...
              (planet_id, year, month, day, hour, minute, second);

tof = (jd2 - jd1)*24*3600;

%...Patched conic assumption:
R1 = Rp1;
R2 = Rp2;

%...Use Algorithm 5.2 to find the spacecraft's velocity at
%   departure and arrival, assuming a prograde trajectory:
[V1, V2] = lambert(R1, R2, tof, 'pro');

planet1    = [Rp1, Vp1, jd1];
planet2    = [Rp2, Vp2, jd2];
trajectory = [V1, V2];

end %interplanetary
% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~