The JMissions

Just prior to PDI on Apollo 15, LMP Jim Irwin commented: ''I'm going to write me a joke—Astronauts come back from the Moon;said it's great, but no atmosphere.''48 The moment of lightheartedness reflected a relaxation typical of the later landings as successful flights built confidence and refined techniques. First of the so-called ''J-missions,'' Apollo 15 incorporated a number of changes in design and operations that allowed a heavier LM to descend to the surface, stocked with consumables for a longer surface stay.

Apollo flights PDI to landing

Apollo flights PDI to landing

Figure 10.2

Comparison of radar altitudes for PDI to landing for Apollos 11, 12, and 16. Note the steeper descent for the later, J-mission (16). (Drawn by the author from Apollo mission transcripts.)

Figure 10.2

Comparison of radar altitudes for PDI to landing for Apollos 11, 12, and 16. Note the steeper descent for the later, J-mission (16). (Drawn by the author from Apollo mission transcripts.)

The J-missions also carried the lunar roving vehicle, the small buggy the crews used to cover significantly greater distances on the moon. The rover had implications for landings, because the ability to drive around extended the radius of operations from a few hundred feet to several miles. This extended range in turn relaxed the requirements for precision landing. If the LM ended up far away from a landing spot, the astronauts could just drive there in the rover. At least one commander mentioned that the presence of the rover eased his concern for accuracy at touchdown.49 For the J-missions the angle of descent also increased from fourteen degrees to twenty-five degrees, and the vertical descent phase began at 200 rather than 100 feet. The steeper, longer, descent would provide improved accuracy, better visibility at pitch over, and better control of the LPD redesignations.50 Figure 10.2 illustrates the different trajectories for three of the six landings. Note the higher angles for the J-mission, Apollo 16.

By Apollo 15, the landings themselves were considered proven, although hardly routine. In training the astronauts began to focus more on new techniques and scientific work on the lunar surface.51 For them, the simulators were more regularly available than for the earlier flights, allowing their training to become more reliable and routine. Now the astronauts spent as much as 40 percent of their time training for lunar surface science work, whereas the earlier missions concentrated on systems and procedures.52 ''Everybody else had done it,'' Charlie Duke said of the Apollo 16 landing, ''and so we felt real confident, when we were there, that we were going to have plenty of gas.''53

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