Page 62 - Intro to Space Sciences Spacecraft Applications

49
Orbital Principles
intermediate (transfer) orbit that intersects the initial and desired orbits
will have to be chosen and multiple Av’s performed at these intersections.
However, each of these Av’s may still be treated as separate single-
impulse maneuvers.

Hohmann Tkansfer. A commonly used orbital maneuver between nonin-
tersecting orbits is the Hohmann transfer. The classic Hohmann transfer is
characterized by an elliptical transfer orbit between two co-planar circu-
lar orbits as shown in Figure 2- 11.
The elliptical transfer orbit also lies in the same plane as the other orbits
with its perigee at the same altitude as the low orbit and its apogee at the
higher orbit altitude. At the intersections (perigee and apogee) of the transfer
orbit and the circular orbits, the orbital velocities are parallel and in the same
direction. The Av’s are simply the differences in the velocity magnitudes at
these points, with no change in direction of the velocity vectors required.

The change in velocity required to enter the transfer orbit from the low
circular orbit can be found from the relationships already discussed:

-
orbit
Figure 2-1 1. Hohmann Transfer. This is a common method for transferring
between two co-planar circular orbits.