Robert A. Braeunig
The following is an animated graphical representation of a computer simulated hybrid lunar profile with lunar orbit insertion and transearth injection. Spacecraft position is shown relative to a fixed Earth, with Earth being located at the origin of the axes and represented by the blue disc. Location of the spacecraft is shown in four-hour increments with the path traversed since translunar injection represented by the trailing line. The yellow line is the Moon's orbit and the Moon is shown as a gray disc. The distances shown are in units of kilometers and the illustration is drawn to scale. The time scale is one second equals four hours.
A hybrid profile begins as a free return trajectory and transitions to a non-free return following a midcourse transfer maneuver (see diagram). The red line represents the free return portion of the trajectory (this is the same trajectory as modeled here). After completion of the transfer maneuver, the trajectory line changes to blue. As the spacecraft swings behind the Moon, a lunar orbit insertion (LOI) maneuver is performed. For this demonstration four lunar orbits are completed*, which are represented by the magenta line. To set the spacecraft on a trajectory that will return it to Earth, a transearth injection (TEI) maneuver is performed. The green line represents the transearth trajectory.
The following simplifying assumptions have be made:
(* Four orbits is an arbitrary selection; any other number could just as easily been used.)
Event Timeline and Propulsive Maneuvers
|Distance to Earth
|Distance to Moon
|Velocity, Earth relative||Velocity, Moon relative|
altitude = 185 km
Lunar Orbit Insertion
altitude = 111 km
altitude = 111 km
altitude = 122 km
Entry angle = -6.50o
Compare this simulation's delta-V figures to Apollo 12:
Also see the following simulation: Circumlunar Free Return Trajectory.