real-time communication and diagnosis of problems, so they had to devise ways for the spacecraft to recognize problems on their own and to protect themselves from further damage or harm. The engineers who design software fault-protection routines are the kind of paranoid (in a good way) people you’d want with you while you are preparing for a camping trip. Did you pack the tent? How about rain gear? What if the tent starts to leak? And then it freezes? And then the wind picks up? And you run out of water? And there’s a bear—no, two! Problem after imagined problem has to be anticipated and a solution thought through. Practitioners of this art talk about exploring every possible branch of the “fault tree”—every conceivable, even unlikely, bad thing that could happen—and having a solution for each situation that saves the day. Having a backup system is one risk-reducingstep, but figuring out how to have it switch on by itself when needed was another. Voyager 2 ’s automatic switch to its backup receiver was one example of fault protection in action.
A variety of additional subsystems and instruments were attached to Voyager ’s bus. These included seven sets of “booms,” or appendages of various lengths, extending away from the bus. The longest is a boom made of fiberglass, known as the magnetometer boom; at forty-three feet in length it keeps the magnetic sensor at its tip as far away as possible from magnetic “contamination” by the spacecraft’s other metallic and electronic components. The next longest appendages are a pair of thirty-three-foot-long antennas used by the plasma wave and radio astronomy experiments, extending down and away from the rest of the spacecraft. Opposite the magnetometer boom, an eight-foot-long “science boom” holds the Plasma Wave, Cosmic Ray, and Low-Energy Charged Particle instruments along its length, and a steerable scan platform on its end that carries the imaging and spectroscopy remote sensing instruments. By turning the scan platform in different directions, the Voyager team could point the cameras and other instruments at targets of interest without having to slew the whole spacecraft. This was a substantial time-saving feature, but it introduced the risks of yet another set of moving parts that would have to continue to work well over more than a decade in deep space. Indeed, a problem with the scan platform on Voyager 2 would cause some tense and dramatic moments for the team during the spacecraft’s passage through the ring plane of Saturn.
The shortest boom holds the spacecraft’s radioisotope thermoelectric generators (RTGs), small nuclear reactors that convert energy from the heat given off by the radioactive decay of a few dozengolf-ball-sized spheres of plutonium-238 into electricity to run the spacecraft and instruments. Mounted on top of the bus is a parabolic radio telescope twelve feet in diameter called the high-gain antenna, used for communicating with Earth. And finally, dangling from the bottom of the bus are some triangular struts that look like odd, spindly legs because they’re not attached to anything. During launch, however, those struts were attached to an upper-stage propulsion module that helped the Voyagers reach their final departure velocity and were then jettisoned.
Before any spacecraft is sent into space, it has to be put through a bunch of tests that simulate the conditions and environments that it will face. These include vibration tables, where the individual instruments and the spacecraft as a whole are violently shaken in the same ways that they will be during launch—and, for good measure, they are shaken much more than they will be during launch. For the engineers involved, seeing their creations treated like this can be a painful experience.
The Voyagers were assembled from about 65,000 separate parts in JPL’s Building 179—the famous “High Bay” Spacecraft Assembly Facility where spacecraft like the Rangers ,
A variety of additional subsystems and instruments were attached to Voyager ’s bus. These included seven sets of “booms,” or appendages of various lengths, extending away from the bus. The longest is a boom made of fiberglass, known as the magnetometer boom; at forty-three feet in length it keeps the magnetic sensor at its tip as far away as possible from magnetic “contamination” by the spacecraft’s other metallic and electronic components. The next longest appendages are a pair of thirty-three-foot-long antennas used by the plasma wave and radio astronomy experiments, extending down and away from the rest of the spacecraft. Opposite the magnetometer boom, an eight-foot-long “science boom” holds the Plasma Wave, Cosmic Ray, and Low-Energy Charged Particle instruments along its length, and a steerable scan platform on its end that carries the imaging and spectroscopy remote sensing instruments. By turning the scan platform in different directions, the Voyager team could point the cameras and other instruments at targets of interest without having to slew the whole spacecraft. This was a substantial time-saving feature, but it introduced the risks of yet another set of moving parts that would have to continue to work well over more than a decade in deep space. Indeed, a problem with the scan platform on Voyager 2 would cause some tense and dramatic moments for the team during the spacecraft’s passage through the ring plane of Saturn.
The shortest boom holds the spacecraft’s radioisotope thermoelectric generators (RTGs), small nuclear reactors that convert energy from the heat given off by the radioactive decay of a few dozengolf-ball-sized spheres of plutonium-238 into electricity to run the spacecraft and instruments. Mounted on top of the bus is a parabolic radio telescope twelve feet in diameter called the high-gain antenna, used for communicating with Earth. And finally, dangling from the bottom of the bus are some triangular struts that look like odd, spindly legs because they’re not attached to anything. During launch, however, those struts were attached to an upper-stage propulsion module that helped the Voyagers reach their final departure velocity and were then jettisoned.
Before any spacecraft is sent into space, it has to be put through a bunch of tests that simulate the conditions and environments that it will face. These include vibration tables, where the individual instruments and the spacecraft as a whole are violently shaken in the same ways that they will be during launch—and, for good measure, they are shaken much more than they will be during launch. For the engineers involved, seeing their creations treated like this can be a painful experience.
The Voyagers were assembled from about 65,000 separate parts in JPL’s Building 179—the famous “High Bay” Spacecraft Assembly Facility where spacecraft like the Rangers ,
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