The third step is to actually run the test. This is the most exciting part because the spacecraft never seems to behave exactly as expected. When you find something unexpected, you have to respond quickly--is it a problem you can work around or is it something dangerous enough to call off the test. We are dealing with equipment that costs millions of dollars so we have to be very careful in what we are doing. On the other hand, launch is scheduled for December so we don't have as much time as we'd like to get all the testing done. If we don't make the December launch, we will have to wait over a year and a half before Mars and Earth line up again to allow us to launch (and there isn't enough money to pay people to wait around that long!).

The last step is go back to the design engineers to tell them what we learned from the test and what they have to fix in order to make everything work. Finally, we run the test again and again until everything works as expected.

All of the testing has been completed at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., where Mars Pathfinder was built. It is now at Kennedy Space Center in Florida being prepared for launch. We had to disassemble the spacecraft in order to install fresh batteries, pyrotechnic devices, and radioactive curium in one of the science instruments. We are now rebuilding the spacecraft and my job is to test it at every step along the way to make sure that every component is still working.

Pathfinder will be mounted on a Delta II rocket in November. We will then watch data from the spacecraft during the launch countdown. One of the best parts about my job is that I get to be the one to tell the launch director that the spacecraft is "Go for Launch!"