laying out orbital

Exercises/ClassicalMechanics/Orbital/Python/orbital.py

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+############################################################
+# Martian Invasion
+############################################################
+
+# Import 'numpy' for numerical calculations, vectors, etc.
+import numpy as np
+from numpy.linalg import norm as norm
+
+# Import our parameter file, the '*' says take everything in that
+# file, and make it available for use in this file
+from params import *
+
+def force_gravity(r1, r2, m1, m2):
+    r = r2 - r1
+    F = - G*m1*m2*norm(r)**(-3.)*r
+    return F
+
+
+# Calculate the forces on the current system
+def calculate_forces(positions):
+    print "force"
+
+# Update the positions using verlet integration
+def update_pos(positions, velocities):
+    print "verlet"
+
+
+def main():
+    print "Starting calculation."
+
+    # positions is an array of vectors in a 2D plane specifying the
+    # positions of [sun, earth, mars, rocket]
+    positions = np.array([
+            [0, 0], 
+            [RADIUS_E, 0],
+            [RADIUS_M, 0],
+            [RADIUS_M + RADIUS_R, 0],
+            ])
+
+    masses = np.array([MASS_S, MASS_E, MASS_M, MASS_R])
+
+    print force_gravity(positions[0], positions[1], 
+                        masses[0], masses[1])
+
+# This is Python syntax which tells Python to call the function we
+# made called 'main()' only if this file was run directly rather than
+# with 'import orbital'
+if __name__ == "__main__":
+    main()
+

Exercises/ClassicalMechanics/Orbital/Python/params.py

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+############################################################
+# Constants and initial parameters for Martian invasion
+############################################################
+
+dt       = 1
+G        = 6.67e-11 # Gravitational constant [N m^2/kg^2]
+
+RADIUS_E = 1.521e11 # Earth to sun           [meters]
+RADIUS_M = 2.296e11 # mars to sun            [meters]
+RADIUS_R = 4.256e5  # Mars to rocket orbit   [meters]
+
+MASS_S   = 1.989e30 # Mass of the Sun        [kg]
+MASS_E   = 5.972e24 # Mass of Earth          [kg]
+MASS_M   = 6.417e23 # Mass of Mars           [kg]
+MASS_R   = 4.500e5  # Mass of rocket         [kg]
+
+VEL_E    = 2.98e4   # Velocity of Earth      [m/s]
+VEL_M    = 2.41e4   # Velocity of Mars       [m/s]