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 disappear and then reappear in ever-widening bands as the landing site again rotated into the favorable position with respect to the inertial pre abort orbit plane. This effect of course, is very mission dependent and the exact opposite could have occurred. In other words, the band could have become wider and wider with delay time instead of more narrow if the landing site chosen for consideration had been rotating into the plane rather than away from the plane. Another noticeable trend on this data plot which is also true for the general case is that the ΔV requirements decrease with increasing translunar injection burn time. Also for late premature shut downs, abort solutions are available continuously with delay times and no gaps or voids occur.

Figure 18 shows typical return times to the same primary recovery site as considered on the previous plot. As for the previous plot, the data is shown plotted as a function of trans lunar injection burn time and abort delay time. These data assume that the entire SPS capacity available for use. Note that although a few regions are available where return is in a few hours are possible, in general, returns are forced to at least one day in return time.

Summarizing the trans lunar injection phase, then, one can state that: (1) redundant abort capability exist continuously throughout the translunar injection phase; (2) spacecraft performance margin is great enough to allow considerable flexibility in selection of return times and choice of a landing area; (3) the only critical or marginal abort mode is when the Service Module RCS system must be relied upon to perform the abort maneuver. This mode would only be required in the event of an SPS failure as well as failure to perform transposition and docking to obtain the LM propulsion systems. Thus, the use of this mode would seem very improbable.

ABORTS DURING TRANSLUNAR COAST PHASE

This mission phase consists of the coast period from translunar injection burnout to the initiation of lunar orbit insertion, a period of approximately 62 to 74 hours for free-return trajectories. Since the nominal translunar coast trajectory is a free return to earth, the minimum ΔV to abort is essentially zero. Thus, as will be shown later, large ΔV capability margins exist which can be used in an abort situation to speed up the return to earth and/or control the point of landing.

Figure 19 presents a summary of the abort modes for the translunar coast phase. Note that redundant abort capability exists throughout the entire phase due to the presence of three independent propulsion systems.