[dwndrgn]

The main reason that HAL (as an AI computer instead of just a 'regular' computer) was on the ship was to be the last resort crewmember - should anything happen to the biological crew, mr. mechanical crew would take over so that no matter what, images and information regarding the portion of the solar system the ship was travelling through and to would get back to earth. The ship itself was never expected to go back to Earth so the images and info had to continue to be collected and sent back.