The Interstellar Age

Free The Interstellar Age by Jim Bell

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Authors: Jim Bell
25,000 miles per hour to escape Earth’s gravity and head toward its first encounter, with Jupiter. The spacecraft were launched in late summer 1977 on the Martin Marietta (now Lockheed Martin) Corporation’s Titan III-Centaur rockets, the same kind of rockets that had launched the twin Viking orbiters and landers to Mars almost exactly two years earlier. The powerful Centaur upper-stage rocket, a variant of the Atlas Intercontinental Ballistic Missile design of the early 1960s (beating swords into plowshares!), was mounted atop the Titan III rocket and would give the Voyagers the big push needed to get them on their interplanetary trajectories.
    By a strange quirk of celestial mechanics, Voyager 2 was launched on August 20, 1977, almost three weeks before Voyager 1 , which launched on September 5 . Voyager 1 was initially targeted for a Jupiter flyby, followed by a Saturn flyby that included a very close pass by Saturn’s large moon Titan, whereas Voyager 2’s trajectory did not include a Titan flyby. It worked out, then, that Voyager 1 would travel on a slightly shorter path to Jupiter and Saturn on the trajectory designed by the navigation team. So even though it launched three weeks later, Voyager 1 passed Voyager 2 by the time both spacecraft were passing through the Main Asteroid Belt between Mars and Jupiter.
    Building and launching a spaceship is just the beginning of the work of the human team back on Earth. There has to be a way totrack them to make sure they’re heading in the right direction, to steer them if they need course corrections, and of course to communicate with them—sending them commands needed to perform their mission and getting back the photos and other data that they were sent to collect. That critical communications job is the work of the men and women of NASA’s Deep Space Network (DSN), a trio of giant radio telescope facilities in California, Australia, and Spain that is managed by JPL. The DSN’s sensitive antennas are spread roughly equally around the Earth so that at least one of them can always be in contact with any of the thirty or so active space missions being run by NASA and other space agencies. These radio antennas and their diligent operators are booked solid twenty-four hours a day, seven days a week, keeping tabs on the trajectories of all these spacecraft, sending them routine commands or responding to “spacecraft emergencies” that they sometimes have, and receiving and relating the billions of bits of digital data that are relayed back to the Earth every day to operations centers around the world, like JPL.
    I visited the DSN station in Canberra, Australia, a few years ago and stood in awe under the superstructure of the 70-meter-wide (more than 200 feet) antenna used to communicate with Voyager and other missions. The DSN’s radio telescopes need to be so big because the signals from Voyager are so small. By the time the spacecraft got out to Jupiter, for example, Voyager ’s 23-watt radio transmitter produced a signal that was only about a hundred-millionth as powerful as a cell phone battery by the time it reached Earth. These days, with both spacecraft now well beyond the orbit of Neptune, the power levels received at Earth of Voyager ’s radios are more than five hundred times fainter than they were at Jupiter.
    While the DSN sends command sequences to the spacecraft, the people making those commands, people called sequencers , work at operations centers like JPL or at other government labs or universities around the world. Sequencers are like the accountants of the space business. All they do is figure out how to get complex machines to do intricate things with small, simple sets of instructions, often written in arcane languages. For a spacecraft, a sequence is like a time-stamped to-do list of individual commands. Fly to a certain place, turn on the camera, point it in that direction, take twelve photos, turn off the camera, turn on the magnetic-field

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