Apollo 8's triumphant navigation raises a question: if the state vector on board was so accurate, essentially identical with the data from the ground, why did Houston insist on overwriting it with the data tracked and computed from the ground? Hoag, and no doubt many of the IL engineers, felt that the entire mission could have been accomplished using the onboard navigation (indeed, simulations they later ran with only Lovell's onboard sightings showed that the mission would have easily hit its reentry corridor with onboard data alone). But just as the astronauts were enmeshed in a system that included power relations within and between large organizations, so were the computers and the IL. Once onboard navigation was demoted to the status of backup (as the astronauts had been years before), overwriting of its data symbolically enacted the new relationship: Houston had control. Battin was tremendously proud that, in his view, Lovell had navigated himself to the moon and back. ''Sadly,'' he lamented, ''they never did that again.''106
Apollo software, from an element of the system little understood, indeed barely envisioned, when the program began, became central to the mission, mediating much of the astronauts' critical interactions with their machine. It incorporated information from a variety of sensors around the spacecraft, tying the complex system, with its diverse equipment made by varying contractors, into a coherent whole. It unified the work of a team of programmers, all working on subsets of the problem, into a unitary ''mission.'' It tied the astronauts into the craft, recording and analyzing their navigation and control inputs into stable-state vectors. No wonder this critical, invisible component of the project proved so complex to create, unruly to manage, difficult to test, and hard to trust. In its unusual combination of virtual plan and handmade core ropes, Apollo's software embodied its missions, and embedded assumptions, fears, and social relationships. On no phase of the mission would software, and human action, prove as central, or as ambiguous, as on the lunar landing itself.
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