Poole watches a video transmission of his family and friends gathered to sing him Happy Birthday. He finds it strange, knowing that the events he is watching took place over an hour before, as it now takes longer than an hour for light beams from Earth to reach Discovery. Hal interrupts to let Poole know that the AE-35 component of the ship may malfunction within seventy- two hours and to recommend making a trip outside the ship to replace it with a spare. Poole radios to Earth to inform them of his plans. The control center confirms and asks him to prepare a brief statement to be released to the media. Poole and Bowman make a brief videotape explaining that the AE-35 keeps the ship's antenna fixed on earth to allow for radio transmissions and that replacing it should be a routine operation.
Poole carefully dons a pressure suit and boards one of the extravehicular capsules in order to step outside the ship and replace the defective part. After careful manipulation and much patience, he successfully replaces the part and returns to Discovery.
Unfortunately, not all was well. Bowman ran diagnostic tests on the AE-35 unit that Poole had replaced and reports to Poole that it is actually fully functional. Before they resolve how to handle the situation, a transmission from Earth arrives. Mission Control confirms that the AE-35 they replaced is fully functional and suggests that the problem may lie in Hal. They are to monitor Hal closely for further odd behavior. At worst, they will have to shut down Hal and hand over monitoring control of the ship to the computers at Mission Control.
Soon after, Hal reports that the newly installed AE-35 is set to fail within twenty-four hours. Bowman, who is in control of the ship at this time, asks Hal how this is possible. Hal responds that he is unsure why the unit is faulty, but certain that he is correct about the impending malfunction. Hours later, they receive a video transmission from the chief programmer at mission control. He says that Hal is incorrect about the AE-35 unit; Hal is malfunctioning and ship control must be handed over to the computers on Earth. The programmer begins outlining the steps whereby Poole and Bowman are to shut down Hal when his voice ceases to be transmitted. An alert signal sounds and Hal reports that the AE-35 unit has failed. Bowman apologizes to Hal for suspecting that he had been wrong and Hal asks if Bowman once again has complete confidence in him. Bowman assures him that he does and then sets about trying to manually fix the antenna on Earth. This fails and the two men are left wondering how to re-establish contact with Earth.
The narrator gives a lengthy description of Poole, as he is replacing the AE-35 unit. His maneuvering of Betty (the extravehicular unit), stepping outside of Betty, and carefully performing the replacement are reported to us in the minutest detail. This serves two purposes. First, this scene allows us to step into Poole's world—to gain a better understanding of what it is like to be an astronaut, nearly a billion miles from home. Second, this scene more closely introduces us to the perils of space travel and the potential for danger in the Discovery mission. An awareness of the complexities involved in even the most mundane action and the potential destructiveness of the smallest mistake lay the foundations for the reader to fully appreciate the magnitude of Hal's later malfunctioning.
In a work of science fiction, the importance of giving the reader enough detail should not be underestimated. In entering a highly fictionalized world, the reader needs more detail to feel at home and comfotable. After all, we cannot make the same assumptions about this world as we would make in reading a story set in contemporary America. Clarke makes his world seem more natural not simply by giving us details about it, but also in keeping those details not too detached from reality. First, he pays impeccable attention to the laws of physics, the same physical law that constrains us constrains the humans of 2001. Second, the central fictionalized elements of the book—Hal and Discovery—are merely improvements upon technology that existed when the book was written. It is not quite as difficult for the reader to imagine technologies that are already in the world in a more basic form.