posted 02-21-2010 11:01 AM               

The first of these computer transitions occurred along with a communications dropout at 7:59 Central time this morning and the station flight director advised the other mission control centers of the loss the S-band communications link with the station.

Just before 9:00, station commander Jeff Williams called down, once the station had moved back into communications range and confirmed that there had been a failure of the primary and backup command and control computers, or as they are sometimes referred to, "MDMs" for multiplexer-demuliplexer.

The team in Houston was working with the crew on-orbit to get things properly reconfigured and just about 9:49 this morning, there was an indication that there was another communications outage and by 9:57 the data was showing that there had been another C&C transition, and at that point computer no. 2 was prime, no. 3 was backup.

10:36 this morning, after once again the station moved back into communications range, Jeff Williams called down, advising that the computer system was down again and once the computers were reconnected, at this point C&C no. 3 was in the primary slot, no. 1 was in the backup slot and no. 2 was in standby, though that most recent transition was not detected by the systems in the Russian segment of the space station.

All indications from the crew, as well as the telemetry received, is that all of the life support systems aboard the station are working completely normally but the teams are working through checklists and procedures to identify the cause of the command and control computer transitions.

Currently the computers are all showing they are healthy, computer no. 3 is currently in the prime position, no. 2 is the backup and 1 is in standby. That is a small change from the situation a half-hour ago, when 1 was in backup and 2 was in standby but 3 has remained in the prime position since then.

posted 02-21-2010 11:48 AM               

Space station communicator Stan Love informed commander Jeff Williams that they are going to be very selective in sending any commands to the International Space Station at this point. There is a suspicion that there may be something in the commanding itself that is causing the comptuers to transition.

Particularly, there are computers in the new Tranquility node that were showing anomalous signatures and the decision was made to send the command to try to sync them up with the other computers. To this point, that has not set off another transition.

The next step in the plan then if that command does sync up those computers is to dump the data that is in them in the hopes that it will provide some insight into the cause of the transitions.

System aboard the station are currently in a stable configuration, including voice communications.

posted 02-21-2010 02:14 PM               

The team has just informed the Expedition 22 crew that while they don't know exactly what is responsible for the transitioning of command and control computers today, they do have a clue from data in the first of those computers to fail at 7:59 this morning, which implicates a system in the Columbus module, which packages data for transmission to the Columbus control center in Germany.

While they continue the investigation, Mission Control is now is going to start working to send the backlog of commands that have been held up during the day. As the team worked through this issue, they became very selective about any commands sent to the station in order to not inadvertantly trigger another of these transitions.

While the situation today never had an impact on the life support systems onboard the station and not a direct impact to the health or safety of the crew members, they were scheduled to be off-duty today and had private family conferences scheduled. Those had to be deferred because the Ku-band communication system was down during this and along with it, the IP telephone. So the crew has been advised that the ground is going to start working now to recover the Ku-band system and IP phone.

[The crew] has been advised because they lost a good deal of their off-duty time today, their Wednesday is being cleared off so that they can have some time off-duty with everything operating back then.