AE-35 unit

"Roger your plan to go EVA and replace Alpha-Echo three-five unit prior to failure."

- Mission Control

The AE-35 unit was a small, gyroscopic device used on the American spacecraft Discovery One. The unit was used to maintain a communications link between the spacecraft and mission control by holding the large antenna pointed directly at Earth.

The AE-35 was installed into the back of the antenna mount, and could easily be removed and replaced in a relatively short amount of time; a ten to fifteen minute EVA was all that was required to replace it.

Trouble on Discovery
HAL is discussing the Mission with Bowman when HAL interrupts to announce that a fault has been detected in the AE-35 unit, a device critical for maintaining radio contact with Earth, and that it is expected to fail within the ensuing 72 hours.

"I've just picked up a fault in the AE-35 unit. It is going to go 100 percent failure within 72 hours."

- HAL 9000

Upon report of the communication unit error, Bowman immediately notifies Mission Control, as the mission cannot run smoothly without communication with Earth.

"Sorry you hit this little snag, fellas."

- Mission Control

As soon as they are given the go-ahead to go EVA and replace the unit, a pod is taken out to investigate the antenna complex, where the AE-35 unit is installed. The “malfunctioned” unit is replaced, and the Pod returns to bay, following Bowman and Poole carrying out extensive diagnostics. Bowman conducts tests on the AE-35 unit that has just been replaced, but discovers that nothing is wrong with it. Hal, however, states that this was because of human error. He suggests that the malfunctioning unit be put back in operation and allow it to fail. It should then be a simple matter to track down the cause. Later, Hal claims that the second AE-35 unit is set to fail. Suspicious, Poole and Bowman radio back to Earth; they are told that something is wrong with Hal and are given instructions to shut him off. These instructions are interrupted as the signal fades—the AE-35 unit has malfunctioned. Poole and Bowman begin to wonder how they will re-establish communication with Earth.

The astronauts cannot think of any reason not to put the unit back in operation. So Poole goes EVA. Hal then trips: If they put the unit back, they will realize that it was all a complete fabrication. Hal rams an EVA pod into Poole, tearing his life support system. Air leaks out and his body drifts out into space.

Meanwhile, HAL does not allow Bowman’s pod to reenter Discovery. Infuriated with the mischievous computer, Bowman jettisoned himself from the pod into an open airlock. He then forces his way into HAL's memory and logic center, and disconnects the higher brain functions, so that Hal goes offline.