Mars Exploration Rovers Status Report

We passed another big milestone this week -- our very last vibe tests. Vibration tests are some of the scariest things you do to space flight hardware. It's a torture test: You bolt your instrument to a machine that shakes it as hard as the rocket will shake it when you launch it, or even harder. Sometimes the instrument survives the test, and sometimes it doesn't.

These were the final vibe tests for our flight APXS instruments. We should have done these tests many months ago, of course, but sometimes things don't work out the way you'd like them to. Several months ago we discovered a very bad mistake that we had made in part of the APXS that detects alpha particles. This "alpha mode", as we call it, is essential for detecting important elements like carbon, and it simply wouldn't have worked on Mars the way we originally built it. At least we found the problem in time! But it meant that we had to go out and get new and improved alpha detectors, put them in the instrument, and then do all the testing months later than we originally wanted to.

If we hadn't passed the tests this week, we would have been stuck flying our spare APXS instruments. The spares are okay in most respects, but their alpha detectors won't work right because of the design mistake we made. So it was with enormous apprehension that we shipped the APXS flight instruments, with the fixed alpha mode included, to Berlin for their final vibe tests. They both passed beautifully, and soon they'll be ready to go on the rovers. It's an enormous relief.