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 Figure 4 shows how the suborbital mode with SPS landing control differs from the free-fall mode. Note that the procedure is identical except for an additional retrograde SPS burn.

This burn is a variable length depending on the time of abort and causes landing to be at the end of the continuous Atlantic recovery area, approximately 3,200 nautical miles downrange. The next mode of interest, as shown in figure 1, is the S-IVB contingency orbit insertion followed by an SPS de-orbit to reentry. This mode, as shown, is available and prime for approximately the second half of the S-II burn. The reason that this mode is considered prime over the suborbital free-fall mode is that it allows landing to be pinpointed precisely to a given recovery force and would allow additional "thinking" time to consider alternate missions.

The next mode is similar in nature to the S-IVB contingency orbit insertion, except the SPS is used for both the COI and the deorb it burn.

This mode, as shown in figure 1, is only possible during approximately the latter half of the S-IVB burn, but it is the prime mode for this time period.

Figure 5 shows the basic features of these latter two abort modes.

As shown, insertion into earth parking orbit is com­pleted by e ither the S-IVB or the SPS. After a certain coast time in earth parking orbit, during which CSM S-IVB separation occurs (if it has not already), an SPS coplanar deorbit burn is performed to return the spacecraft to reentry. The time of deorbit is chosen so as to result in landing at a discrete recovery area, as done in Projects Mercury and Gemini. The SPS deorbit burn is targeted so as to place the earth's horizon at a specified point in the spacecraft window for monitoring purposes.

In summary, then, as regards launch aborts, the main things to remember are: (1) abort capability in one mode or another is available throughout the entire launch phase on a continu­ous basis; (2) contingency orbit insertion followed by de­orbit is always prime when it is available.

ABORTS FROM EARTH PARKING ORBIT COAST

This mission phase consists of coasting in a circular earth parking orbit from earth orbit insertion to the initiation of translunar injection, a duration which is usally one orbit or longer. As might be expected for this phase the abort procedures being planned are very similar to those used in Projects Mercury and Gemini.