Peak of the Hardware Effort

September 1964 saw the delivery of the first Block I guidance system, slated to fly on the unmanned missions and the early manned ones. NASA and the IL team spent that year developing and finalizing Block II with the digital autopilot, in a series of meetings with North American and Grumman. 1965 saw the peak of hardware design activity, with more than six hundred engineers at the IL (though not all worked on hard-ware).62 The Block II requirements were complete by February 1965, and soon thereafter the IL received a $15 million-dollar contract to build the Block II.63 The new design was released in July 1965, a production prototype delivered that November, and the first flight qualification model delivered to NASA in July 1966. In the fall of 1966 Block I production was terminated (Block II production would last until the summer of 1969). Block I would fly the unmanned AS-201 (August 1966) and Apollo 4 and 6 missions, while Block II computers flew on Apollo 5, 7, 8, 9, 10, and all the lunar landings.

The new computer would be sealed from moisture in the cabin, with no provision for repair. To accommodate the digital autopilot, the Block II computer's program memory was increased from 24 k words to 36 k (16-bit) and the erasable memory from 1 k to 2 k. Other aspects of the computations speeded up as well, with new machine instructions built into the architecture (where the Block I had eleven instructions, Block II had thirty-four) which allowed for more efficient code, and the clock now ran at 1,024 kHz, allowing a double-precision multiply in about 1 ms (by contrast today's desktops will do the operation in a few nanoseconds). The number of logic gates went up, although the packages for the ICs were also changed, from small metal cans to flat packs much more like modern chips. The flat packs contained two logic gates instead of one, doubling the packaging density, which halved the circuits' size and brought the AGC's weight down from eighty-seven to seventy pounds, and reduced the power from eighty-five to fifty-five watts.64

In the five years from the granting of the contract to the preparations for the first Apollo flights, the guidance and navigation system matured from a basic idea, through laboratory prototypes, to highly qualified and manufactured flight hardware. Despite its small size and modest processing capacity, the AGC was cutting-edge technology, incorporating the latest in process control, reliability, circuit design, and packaging. In what would become a familiar pattern in the computer world, memory capacity had doubled, and then doubled and doubled again. At the same time, the presence of the computer meshed with systems management methods, especially as the project became more complex and behind schedule. Hardware devices in the cockpit were gradually eliminated to save time, weight, or cost, and migrated into the flexible computer or into the astronauts' brains. But as the Block II computers began rolling off the production lines, NASA and the IL began to recognize the stress they had added to a new part of the project, one barely envisioned when Apollo began: software.

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