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

AE-35 Unit

An X-ray scan of the unit, showing the internal structures.

—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 DiscoveryEdit

"Sorry you hit this little snag, fellas."

—Mission Control


Commander Bowman replacing the "faulty" unit.

A month into the flight of Discovery, the on-board AI unit, HAL 9000, was having a seemingly casual conversation with commander David Bowman. However, the conversation was cut short, when Hal reported that, "I've just picked up a fault in the AE-35 unit. It is going to go 100 percent failure within 72 hours." Of course, the mission could not run smoothly without communication with Earth, so Dave immediately notified Frank Poole, his partner on Discovery, as well as mission control. As soon as they were given the go-ahead to go EVA and replace the unit, Bowman suited up and left in one of Discovery's three EVA Pods. He maneuvered the pod around to the antenna complex, where he egressed the pod and drifted over to the back of the dish, where the AE-35 unit was installed. He replaced the malfunctioning unit, and returned to the Pod bay, where he and Poole carried out extensive diagnostics. Despite this, they could not find anything wrong with the supposedly faulty unit. Hal, however, stated that this was because of human error. He suggested 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.

At this point, both Poole and Bowman were growing suspicious. They notified Mission control of Hal's dubious behavior. Even they, based on their studies with their twin 9000 computer (possibly SAL 9000), stated that HAL was in error predicting the fault. Still, the astronauts couldn't think of any reason not to put the unit back in operation. This time, Frank went EVA.

Hal immediately became worried. If they put the unit back, they would realize that it was all a complete fabrication. Hal panicked, and rammed the pod into Frank, tearing his life support system and allowing the air to leak out and send his body drifting out into space. By the time Dave could get out in an attempt to rescue him, Frank was already dead. HAL did not allow Dave's pod to reenter Discovery. Infuriated with the mischievous computer, Bowman jettisoned himself from the pod into an open airlock, then forced his way into HAL's memory and logic center, and disconnected the higher brain functions, so that Hal was essentially "dead".