There is a single tape recorder on board the spacecraft; it is a four-track digital model manufactured by Odetics Corporation that can store up to 914,489,344 bits of data (that's about 109 Megabytes, or about 300,000 pages of text; roughly as much storage as on the hard drive of the average new home computer).
Yes, the tape recorder does have an automatic shutoff at the end or beginning of tape. The problem wasn't with the automatic shutoff not working; as it turns out, the tape recorder mechanism was moving along, but the tape itself stayed put.
Okay, so why didn't engineers turn off the tape recorder as soon as they knew that there was a problem? We need to have the capability to send a command to Galileo saying "shut off the tape recorder," and, at the time of the tape recorder problem, that commanding capability wasn't present.
The problem was discovered over Goldstone, but it was too late in the tracking period to send a command to Galileo. The next station to "rise" and start tracking Galileo was Canberra (which has a 12 hour view of the spacecraft). Unfortuantely, Canberra's transmitter wasn't available--it was down for maintenance. So, it wasn't until the station at Madrid "rose" that we were able to send the "turn off the tape recorder" command, approximately 15 hours after the anomaly was detected.
Why is it now not possible to photograph Io and Europa on December 7, as planned?
Having Galileo take pictures of Io and Europa isn't the problem--the difficulty is in storing the images so that they can be sent down to Earth at some later time.
Although the tape recorder is working, the Project wants to limit use of the tape recorder until we 1) better understand the anomaly and 2) identify what are safe modes of operation for the recorder, because there is a chance that we could, unknowingly, further damage the recorder. Engineers are still analyzing exactly why there was an anomaly, as well as identifying exactly what activities the tape recorder can perform. How fast can the tape safely move? Can the tape move in both directions? Until these questions, and others like them, are answered, the project wants to use the tape recorder as little as possible.
The tape recorder will be used on December 7th-- to store probe data, the number one scientific priority of the entire mission. The spacecraft will also record over 3 hours of Io plasma torus observations, as well as recording engineering data during the Jupiter Orbit Insertion burn.
