Seven sub-modes exist which would be available from the ground for short in this one basic mode. In other words, there exists seven different classes or abort trajectories which will be possible with a single unconstrained atttude burn, There was really no requirement for this kind of flexibility in the previous phase—in otherword, during the earth parking orbit phase—because the spacecraft was always in the close proximity of the earth, and there was really no significantly different ways to return to reentry, Beginning, with this phase, however, the spacecraft could be in a preabort orbit which extends a consderable distance from the earth, This fact, combined with the large spacecraft performance capability, means that abort trajectories having significantly different characteristics as regards 
, return time, and landing point are possible, Therefore, plans are being made to take advantage of this situation to provide greater flexibility in real time planning.
Returns to primary recovery sites - This class of abort trajectory returns the spacecraft to a specfic primary recovery site within the major constraints mentioned previously, For premature S-IVB shutodwn during all but the very last few seconds of the nominal burn, this class of abort trajectroy requires that the short initiation time must be selected very carefully to cause landing at a discrete site, i. e., there will exist only small regions of abort initiation time which will allow returns to a discrete site, For late premature S-IVB shutdowns, however, reasonably placed recovery sites can be reached for any abort initiation time, This sub-mode also required, in general, that a plane change be made in order to reach a primary recovery site, unless there exists sufficient time for the spacecraft to remain in the pre-abort orbit until the primary recovery site rotate; into the proper position for a colplanar abort maneuver. The delay time to abort, however, is usually limited if the apogee of the spacecraft preabort orbit extends into the radiation belts.
Time critical returns to a contingency area. This class of abort returns the spacecraft to a contingency recovery area in the quickest possible retrun time consistent with the constraints of the situation. A contingency recovery area is a continuous line (illegible text)
