InFlight Repair

Hall estimated that his Block I integrated circuit computer would have a reliability of .966 (one failure in 4,000 hours), but the spec he had been given required reliability nearly ten times better. To make up the difference he proposed neither redundant machines nor exotic circuit designs. Rather, he would rely on the skills of the astronauts: they would repair the computer during flight.

In Polaris, crew members inside a submarine could remove the computers from the missiles and repair them. On long-range bombers, crews could make repairs to their guidance systems during a long mission. But on Apollo such repairs had troubling implications.

What kind of equipment would the astronauts need to isolate a fault? A meter, at least, possibly an oscilloscope. But a soldering iron?

The ''map and data viewer'' would provide the thousands of pages and manuals necessary for troubleshooting. Hall proposed that Apollo flights also carry a special machine, a ''MicroMonitor,'' a smaller version of the equipment used to check out the computer on the ground. This device was heavy and took up space, required its opera tor to ''exercise considerable thought,'' and required the operator to have a mere three to six months of training. ''This device is known to be effective,'' Hall wrote, ''in direct proportion to the training and native skill of the operator.''

The Block I computer would be made of easily removable modules, which the astronaut could replace by hand with simple tools. It would require twenty-nine types of modules, so the spacecraft would simply carry one of each type. If a failure occurred, the astronauts would diagnose the problem with the MicroMonitor, slide out one of the modules, and slide a fresh one in. To repair the computer, astronauts would require a special tool kit, complete with mundane items like gasket seals and grease (figure 6.1).

In addition, the computer would need self-check circuitry and software to detect a failure and the flexibility to allow the astronauts to do something about it. A suite of software programs would self-check and aid the astronauts' diagnoses. The IL developed a series of procedures for in flight repair, all based on the assumption that there were 100 percent spares available on board.15 Of course, making the modules

Figure 6.1

Apollo Block I computer, showing removable modules that astronauts could replace in flight to improve reliability. Such repairs required carrying extra modules, as well as specialized tools and diagnostic equipment. (Draper Laboratories photo CN-4-165-C. Reprinted in Hall, Journey to the Moon, 16.)

Figure 6.1

Apollo Block I computer, showing removable modules that astronauts could replace in flight to improve reliability. Such repairs required carrying extra modules, as well as specialized tools and diagnostic equipment. (Draper Laboratories photo CN-4-165-C. Reprinted in Hall, Journey to the Moon, 16.)

replaceable required additional electrical connectors and mechanical connections, themselves likely sources of failure. And the complete set of spares added a significant amount of weight.

Astronauts had been billed as the ultimate redundant components. Asking them to improve the reliability of their equipment seemed sensible, but it proved no simple task.

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