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 ABORTS DURING TRANSLUNIAR INJECTION PHASE

This phase consists of the S—IVB burn which injects the spacecraft on a highly elliptical trajectory to rendezvous with the moon. The duration of this phase is approximately 3′0 seconds for a typical lunar mission. What is or interest here is to consider abort capability from orbits which would result from a premature or early burnout of the S-IVB stage

Figure 9 shows the type of preabort orbits which would result from an S-IVB underburn during this phase or the mission. Note that the family of orbits are elliptical, having very nearly coincident lines of apsides with ever increasing apogee altitude up to and beyond lunar distance. The perigee altitude, however, remains relatively fixed, very near that of the original circular earth parking orbit altitude. The periods or these orbits, as shown in figure 10, vary all the way from 1½ hours to approximately 400 hours as burn time increases. Actually, for free—return translunar profiles, the moon's gravitation perturbs the trajectory resulting from nominal burnout such that return to earth requires much less than 400 hours. Note also in figure 10 that the period remains relatively small (less than 10 hours) for more than three quarters of the way through the burn.

Table II shows the propulsion systems available which are capable of performing abort maneuvers during one portion or another of this phase as well as the subsequent phase, translunar Coasti Note that there is a large $$\Delta\mathrm{V}$$ capability with the service propulsion system even when the LM is attached. Also, there is moderate capability available with the LM propulsion systems, although use or them requires transposition and docking prior to abort. Note, however, that very little Capability is available with the Service Module RCS. Because of this, aborts using the Service Module RCS are marginal at best, as will be shown later.

Figure 11 presents a summary of the abort modes available for translunar injection. Note that redundant abort capability exists throughout the entire phase and even double redundancy for the latter part or the burn. The first and primary abort mode shown in the summary chart consists of a single burn to return the spacecraft directly to reentry, as shown sketched in Figure 12. This mode is available throughout the phase with either the SPS or DPS propulsion systems. Note also that the burn attitude is not constrained to be either coplanar or to enable horizon monitoring. A constrained attitude for aborts from the family of ellipses could result in excessive $$\Delta\mathrm{V}$$ penalties also prevent landing at a desired recovery area.