Space Simulator  1.0.9
space flight simulator

Orbital Dynamics

Orbital dynamics -also refered as orbital mechanics- refers to the application of newtonian physics (forces, movements ) to bodies with mass in a gravitatorial environment. It can refer both to spacecraft or to cellestial bodies. The basic element of orbital dynamics is the concep of orbit , that is the path that -given an object with mass- will follow based purely on momentum and gravitational forces. In most (but not all !) of the cases, orbits are closed , that is : given a certain ammount of time -called orbital period- , the orbiting body will return to the same point, bearing the same velocity. Of course, this is an abstraction -every body is attracted to the mass of every single moving atom in the universe , so orbits are not perfectly periodical, not fixed. Most importanly , the "bigger" object ,either the Sun or the Earth , also is affected by the mass of the orbiting body, and indeed are following another orbit of its own.

If we can assume the orbiting body (satellite ) has a very small mass, we can consider the main object( Earth ) fixed in space .

It is important to remember that a orbiting body/satellite does not need any more energy to be orbiting .As the satellite follows its orbital path , if may trade some kinetic energy -velocity- for potential energy -altitude- , but this is later converted back to kinetic. So the total orbital energy ( being kinetic + potential ) is always the same.

Sometimes happens that the orbital energy is too large for the gravitatorial field, so the body gets too far , so far than the gravitatorial forces are so small than the object is no longer bound to a cyclical orbit. This way , the object will follow a hyperbolic ( i.e. "open" ) orbit forever , and will never come back to the starting point.

Basic concepts of orbits when applied to astronautics:

  • Without any external force, the shape and period of the orbit will not change.
  • The smaller (lower) the orbit ,the faster the satellite needs to orbit.
  • If any kind of force/thrust is applied at any point in the orbit, the rest of the orbit will change, but the satellite will return to the same point at the same velocity.
  • Positive thrust ( accelerating ) will increase the orbital altitude at the opposite end of the orbit
  • Negative thrust (reducing orbital velocity ) will decrease the altitude at the opposite end of the orbit

Orbits Orbits

Orbital Elements OrbitalElements

OrbitalManeuver Orbital Maneuver

Hohmann Transfer Orbits Hohmann Transfer Orbits

CommonOrbits Common Orbits

OrbitalPoints Special points on orbits .