Two weeks later, after the second launch, everyone headed home. The show was over — both spacecraft were performing flawlessly — but behind the scenes, the mission, on a tight budget, lagged in hiring the more than 200 computer engineers needed to shepherd the spacecraft through a planetary encounter. Many of those on the flight team were fresh out of college, running the most sophisticated electronics systems in the world. They had barely had a chance to jell, when, in April 1978, not yet halfway to Jupiter, Voyager 1 experienced a problem. Its scan platform, where the cameras and instruments are mounted, got stuck.
As the engineers scrambled to figure out what they could do from more than 100 million miles away, someone forgot to send a weekly command to reset a timer on the other spacecraft. When it ran down without hearing from Earth, it triggered so-called fault-protection software, 600 lines of code that respond to malfunctions automatically. In this instance, fault protection assumed the radio receiver was broken and switched to the backup. On the mission-control monitors in a situation like this, the crawl of numbers reporting the status of the receivers would have turned crimson: a ‘‘red alarm.’’
Realizing their mistake, the engineers tried to stop the fault-protection routine, but the newly awakened backup receiver would not register their command. Helpless, they waited for the spacecraft to reason its way back to the original receiver; when it did, and the command went through normally, they were giddy with relief. They were still high-fiving when the working receiver shorted out like a blown fuse. Now it really was dead.
Fortunately, the malfunctioning backup receiver was still drawing current. They guessed that its oscillator, which allows it to accept a wide range of frequencies, had quit, essentially shrinking the target for transmissions from Earth. Assuming a much narrower bandwidth, and manually subtracting the Doppler effect, they recalibrated their signal. It worked — but to this day, the same calculation must precede every command. The original receiver remains useless: one engineer’s simple oversight nearly doomed humankind’s lone visit to Uranus and…