OFJ Field Journal from Randy Herrera - 11/10/95
PROBLEMS WITH TIME TAG DATAIt's 8 am on Friday morning and I've been here since 10 pm last night. Our team conducted an Operational Readiness Test (ORT, for short). That went well but a much larger problem looms on the horizon. The equipment at the station that records our data is apparently not working correctly. The data file on the magnetic tape has "headers" (something that tells us what data is coming up next) which time-tag the information. The scientists working on the experiment *must* have the time tags in order to analyze the data. The time tags are being duplicated or they are being skipped - we don't know why.
This is a VERY big problem. We are only four weeks from our experiment (on December 8). We think right now that the problem is with a piece of equipment which was replaced in July of this year, so the solution is to go back to using the old piece of equipment. But, the Project has placed a configuration freeze on the Deep Space Network, or DSN (the network of tracking stations around the world thru which the Project receives all of its data), meaning that nothing is supposed to be changed around at the DSN. The configuration freeze is meant to insure that we are ready for arrival at Jupiter; we want to be sure that no one changes *anything* that could possibly affect the Project's ability to receive telemetry or tracking information or to command the spacecraft. Basically, "if it ain't broke, don't fix it." We will have to appeal our case to the Project management and request an exception to the freeze. Since the Radio Science system is independent from the command, telemetry, and tracking systems (the most critical systems), we think we have a good chance for having our request granted.
A common question I've been getting is "How did we come this far and get this close to the experiment without previously detecting this problem?" Well, one factor is that we're switching our work between two different computers. That meant that some of the software that we'd normally use to check for problems couldn't be used, so we were relying on the investigators (the scientists working on the Radio Science experiment) to help us check that the data tapes were okay. We checked areas that we thought might cause problems (by performing what's known as a spectral analysis of the data) but we didn't check on the header information, because we didn't think there'd be any problems there. This portion of the tape was NOT supposed to have changed.
Our investigators pointed out some discrepancies back on October 23 but we figured it was a problem in reading the data off the tape - not a real problem with the data on the tape. It was last week (11/3) that the investigators sent us an e-mail detailing the problems they were seeing. That's when we knew that there was a real problem.
Once we've received an OK from the Project to change back to the old system, we'll still have a lot of work ahead of us. Our experiment takes place over the ground station in Madrid, Spain, so there will be different people actually running the experiment. To make sure that everything goes as planned, the Operations Engineer must put together a detailed script telling the station personnel in Spain what to do, step by step.
Then, we must test the old system to insure that it is still working and that we don't see the same problems. If we get the approval weeks before our experiment. I believe that everything MUST be ready at least one week before the experiment. That leaves us with two weeks to implement and test the old system. That is cutting it VERY close.
Boy, considering that a week ago, I thought that we would easily slide into home plate, whew!! The next few weeks are going to be very busy. Luckily, I'm sailing to Catalina Island this weekend with four other friends. Sort of the calm before the storm......ciao!