In the novels of
Arthur C. Clarke, a control unit
component of the Spacecraft
Discovery. This unit was installed in the spacecraft's main
antenna complex and relayed control signals to the antenna motors to keep the main
dish pointed at
Earth. Due to the location of the unit, replacing it required an
EVA.
Discovery's
spare parts store carried two backup AE-35 Units.
During the Jupiter mission in 2001, the HAL 9000 onboard computer reported an impending fault in the AE-35 Unit. Astronaut Frank Poole took a space pod out to the antenna complex to replace the unit, but, during later troubleshooting, no failure was indicated or predicted in the unit. HAL suggested that the initial unit be reinstalled and allowed to fail so the problem could be traced. Poole did so, but was killed by HAL during the EVA. (There was no fault in the AE-35 Unit; the reported failure was a manifestation of HAL's developing psychosis.)
Source: Arthur C. Clarke, 2001: a space odyssey; the film 2001: A Space Odyssey