After four months in orbit, NASA’s Gravity Probe B is finally ready to begin its scientific mission – to find out if two predictions by Einstein about relativity are correct. It wasn’t easy, though. Controllers expected to get the spacecraft orienting on its target star within a few days, but it took weeks because sunlight reflecting off of dust particles confused its tracking system. Engineers also had to tweak the spacecraft’s software to compensate for cosmic rays that flashed into its telescope. Everything’s working fine now, and in a year or so, we should have some answers.