The Interstellar Age (8 page)

Many other supporting facilities are also needed to design, build, and operate spacecraft and missions like
Voyager.
For example, a critical supporting facility for
Voyager
is the Mauna Kea Observatories, built high atop an extinct volcanic peak on the Big Island of Hawaii. Two large telescopes in particular, NASA’s Infrared Telescope Facility (IRTF) (with its 120-inch diameter mirror) and the University of Hawaii’s 88-inch diameter telescope (“the 88”), were used extensively to provide advance information about the giant planets and their moons in order to optimize
Voyager
’s trajectory and return of scientific data. At nearly 14,000 feet elevation out in the middle of the Pacific Ocean, telescopes there are above much of
the warmth and haze and water vapor of our atmosphere and can thus often obtain crisp images of cloud belts and storm zones on Jupiter, Saturn, Uranus, and Neptune or other detailed information on the chemistry and composition of those worlds and their moons and rings.

I did some of my graduate research up there at the IRTF and the 88 and can attest to the harsh conditions of extreme cold, high winds, and low oxygen levels often faced by observers at the summit (often, I would be the only guy on the flight to Hawaii with snow boots and a heavy parka—oh, the strange looks I would get!). Many of the scientists who worked on the
Voyager
camera team got their start as planetary astronomers, obtaining much of the advance information that they needed to plan the giant planet flybys the only way they could—by telescope.

Voyager
imaging team member Rich Terrile got his start as a graduate student at Caltech observing “hot spots” on Jupiter with the giant 200-inch diameter Hale Telescope at Mt. Palomar in Southern California. His follow-on work at the IRTF in Hawaii was interesting and relevant to the
Voyager
infrared spectrometer team, which wanted to be able to target some of these “windows” into the deeper Jupiter atmosphere during
Voyager
’s flybys in 1979. Even though Rich was directly helping out the infrared spectrometer team, secretly he was much more interested in being involved with the imaging team instead. “It was much more in line with what I was doing and what I was interested in at the time,” he recalls. A chance encounter with imaging team lead Brad Smith on an airline flight led them to strike up a conversation, and then a long-term friendship, that got Rich an invitation to be a full-fledged member of the imaging team from Saturn onward. He and Brad used the IRTF and
other telescopes around the world to make observations in support of
Voyager
’s giant-planet flybys, and they have continued their long-term collaboration beyond
Voyager.
For example, they collaborated on a telescopic observation campaign that led to the discovery of the first “circumstellar disk” of dust and gas—a nascent solar system in the making—around the nearby star Beta Pictoris.

Heidi Hammel was a graduate student at the University of Hawaii in the mid-1980s and was doing her thesis research using the 88, collecting color filter images of the atmospheres of the giant planets. With the impending
Voyager 2
flybys of Uranus and Neptune, she was focusing on telescopic observations of those two worlds, and especially on Neptune, which showed cloud features that could be monitored from Earth.

“With my Neptune work, we were trying to establish what the winds of the planet were like,” she told me. “Back in those days, we didn’t know what the wind speeds were, or even what the exact rotation rate of the planet was. But my thesis advisor, Dale Cruikshank, and I knew that the
Voyager
team would need this kind of information for planning the imaging sequences.”

Heidi’s results were different from previous studies, and she recalls Dale having her give a “dark, backroom” presentation about her results to
Voyager
imaging team leader Brad Smith and Rich Terrile. She made her case for them to use her results, rather than those from Smith and Terrile’s own observations, to plan what images
Voyager
should take.

“I laid out my data on the table, I explained what I did, and I showed how their rotation period just didn’t fit the data,” she remembers. “I was still a graduate student, and here I was—petrified—
pitching this to the head of the
Voyager
imaging team! When I was done, they just kind of looked at it, and they looked at me, and they said, ‘Well, looks like you’re right.’”

Smith was impressed enough, apparently, that after Heidi finished her PhD research, he invited her to be a member of the
Voyager
imaging team at JPL.

LEAVING EARTH

Just before they were launched in 1977, what would have been
Mariner 11
and
Mariner 12
if the earlier naming series had continued, the spacecraft were officially renamed
Voyager 1
and
Voyager 2
, partly in recognition of their radically different outer-solar-system missions, and partly because between 1972 and 1977 the spacecraft design had
significantly changed from the original
Mariner
configuration.

Once the spacecraft is built and has been tested and proven to be ready for the harsh environment of space, and once its mission and trajectory are defined, someone then has to figure out how to strap it onto a rocket and launch it off the planet. Whenever I’d tried as a kid to launch a small automated film camera “spaceship” on the top of my model rockets, the extra weight proved too much for the engines to lift, and they would either fizzle out or tip over and skip across the lawn (even my monster “Saturn V” model, with five Estes “D” engines, couldn’t get more than two feet off the ground!). The lesson I learned, that I now know professional rocket designers have to live by, is that for any given kind of rocket, there is a limit to
how much mass can be lifted and accelerated to the required speed, and that mass limit can be only a very small fraction of the rocket’s total mass.

In the case of the
Voyagers,
each spacecraft weighed in at around 1,600 pounds (with about 15 percent of that making up the science instruments) and had to be accelerated to more than 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 to
track 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 sensor and collect those measurements for twenty hours, restart the camera, point it at another location, and so on and so forth. Sequences are not written in English, though, but in computer code that ultimately has to be broken down into the binary strings of ones and zeros that can be transmitted to the spacecraft by the DSN.

This is hairy, intricate work, with catastrophic (for the mission) consequences for making mistakes, and so sequencing often attracts certain kinds of fastidious, patient, perhaps even borderline OCD kinds of people. Perhaps you know people who can quickly spot a typo on a newspaper page, who are masters of details that others might consider trivial, who can easily visualize and describe the three-dimensional positions of objects in their heads, or who can easily see patterns in large groups of numbers—these are the kinds of highly sought-after traits in sequencers. Even though fault protection against fatal mistakes is often built in to the software that spacecraft run, scientists and engineers learn to
trust
sequencers with the very life of the mission. This is especially true of flyby missions like
Voyager
, where all the action can happen only once, as it zips past each of the planets at high speed.

My planetary science colleague Candice (“Candy”) Hansen started her career at JPL as one of these sequencers, working with the
Voyager
imaging team. Her job title was “experiment representative,” which meant that she was a liaison between the rank-and-file scientists on the team—many of whom didn’t know much about how the cameras or the spacecraft were operated—and the rank-and-file instrument and sequence engineers on the team—many of whom, such as a fresh-out-of-college engineer named Suzy Dodd, didn’t know much about the kinds of science that
Voyager
was being asked to do. Candy spent most of her time designing the detailed plans for pointing
Voyager
’s cameras at specific targets of interest (especially icy moons), devising the best ways of stringing individual photos into larger mosaics. Another of Candy’s jobs was to try to estimate the exposure times for
Voyager
’s photos of planets and moons. In some cases, the team would be photographing places that had never been seen before, and so they had no idea if the surface would be bright like snow or dark like coal (or, like some places turned out to be, both). If she commanded exposure times that were too long, the photos would come out all white (“saturated”) or super blurry because of
Voyager
’s high speed relative to the targets of interest. If she commanded exposure times that were too short, everything would come out all black or at least way too dark to be able to be scientifically useful. The stakes were high, given that each spacecraft had only one shot to photograph these places as it sped past.

Someone on the team like Candy would be tasked with making the initial estimates of the exposure times and other parameters for each of
Voyager
’s planned images. They’d use whatever information they could, from ground-based telescope observations, laboratory studies, theoretical calculations,
Pioneer
data, or previous
Voyager
images (especially for
Voyager 2
, given that it passed through the Jupiter and Saturn systems after
Voyager 1
had gone through first). Then they would present their estimates to the full team for review and critique. They’d make changes, rerun calculations, redo the imaging sequences, and present it again. And sometimes again, and again. Each time, they’d have to run their plan by one of the sequence engineers, like Suzy Dodd.

“They would design the science observations for each of their instruments,” Suzy recalls, “and then we would lay them out and see if they would fit within the resources on the spacecraft.”