Designing a Landing

We are banking our whole program on a fellow not making a mistake on his first landing. —Pete Conrad

This book began with a detailed description of the Apollo 11 landing, focusing on the human-machine interaction. We now revisit the landings as the culmination of the debates over pilots' roles, computer engineering, software, and human abilities. This focus necessarily excludes a great deal of the Apollo flights, but the landings represented critical moments of each mission. Neil Armstrong described them as ''the hardest for the system and hardest for the crews.'' On a scale of one to ten, Armstrong rated walking around on the moon a one, whereas ''the lunar descent on a ten scale was probably a thirteen'' (he noted the speed, range, and altitude covered by the LM during its descent was similar to that of an X-15 flight).1 Such trepidation, he would find, was well justified.

An Apollo flight encompassed hundreds of complex operations, but none were as demanding, time-critical, and plagued with uncertainties as the landing, executed in extreme conditions of darkness and cold, far from home. The landing trajectory had to accommodate a wide range of factors, from constraints on the systems' performance to the abilities of the crew and the idiosyncrasies of communications. Even the very calendar of the mission, the ''launch window'' of a few days per month, derived from the requirement for appropriate lighting conditions on the moon so the pilots could see while they were touching down.

The lunar landings played a microcosm of the entire Apollo program in dramatic ten-minute phases. Here the tensions between human and machine, between manual and automated, between pilots as controllers and pilots as systems managers manifested themselves in a string of life- and mission-critical operations, some smooth and some surprising. Engineers with computers and slide rules analyzed and scheduled every minute, and virtually every foot, of the final descent to the lunar surface. Constant testing and negotiation defined the human role and how it would trade off with the computer. Astronauts repeatedly practiced the intense moments prior to landing and constantly updated their procedures. Designing the landing was a task of systems engineering, trading off quantities like fuel for the pilot's visibility. Like the software itself, the design of the landings embodied the dreams and uncertainties instilled in each mission.

Telescopes Mastery

Telescopes Mastery

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