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PI Update - November 2003

Spacecraft Computer
The team is currently working very hard to solve a host of problems associated with the spacecraft computer, including both hardware and software issues. This has been the most problematic system in the spacecraft. In early November, however, we appear to have crested the hill. More problems are now being solved than are being discovered in the testing so we are confident that we are on the right track. The team working on the problems includes key people from all of the institutions involved - JPL, Ball, and Southwest Research Institute.

We achieved another major milestone in the testing program in early November. The encounter sequence, which controls all the attitude adjustments and data taking from before impact until after closest approach, was successfully run all the way through on our testbed (ground support equipment that simulates the spacecraft) and at least in the simulation the attitude control system held the spacecraft on target all the way through the sequence. It still remains to run the sequence on the flight system (with the actual thruster commands disabled), but having run successfully on the simulation testbed gives us confidence that we will be able to run on the flight system.

For some time now the team has been concerned that our gyroscopes, which were vibration tested to much higher loads than are needed for our launch, might have developed micro-cracks in the welds that mount the gyroscopes to their mounting flanges. Some test gyros, that were tested to even higher loads, did have cracks but there is no way to tell non-destructively whether the flight gyros have cracks. The Ball engineers, with consultants from JPL, have now come up with a new mounting plate for the gyros that will damp out the vibrations at launch so that, even if there are microcracks in the welds, they will not be vibrated enough to grow into macroscopic cracks.

Mike A'Hearn, University of Maryland

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