Читать книгу The Quest for Mars: NASA scientists and Their Search for Life Beyond Earth - Laurence Bergreen, Laurence Bergreen - Страница 10

The Kennedy Space Center in Florida employs sixteen thousand people and covers over a hundred thousand acres. It includes a wildlife refuge; herons, egrets, condors, crocodiles, horses, and cattle roam its expanses. From the road, you can see a six-foot-wide bald eagle’s nest suspended in the branches of a tree. If you drive in the general direction of the launch pads, away from the animals, you will see the outsized Vehicle Assembly Building, a giant hangar for rocket ships, shimmering through the haze. You can pick out the odd Shuttle transporter here and there; they resemble huge, primitive locomotives with giant cleats. Many of the transporters are rusting in the humidity. In recent years, NASA has built the center into a tourist attraction featuring life-size mockups of the Space Shuttle, a few garish exhibits, and a souvenir emporium. On the outskirts of Titusville, the nearest town, discarded rockets litter front yards like so many abandoned cars, looking nothing like the towers of power that I remember from my youth. A heavy nostalgia for the future lingers over the place like the scent of magnolia on a humid evening, and the marquee in front of the local high school always reads, “Countdown to Graduation – Six Weeks.”

This was where Pathfinder, weighing nearly a ton, arrived on a rainy day in August of 1996. There was a lot of work to do. Things were just beginning to get serious at this point. First thing, engineers wiped down the spacecraft with alcohol to prevent bacteria from Earth contaminating the surface of Mars. Then, electrical technicians wearing bunny suits to prevent dust or hair falling into the delicate machinery, took the spacecraft into a large clean room and tested every circuit. They corrected software problems and installed the rover’s heaters, which contained a tiny amount of plutonium. NASA wasn’t eager to advertise the fact, for the use of nuclear materials in space, even for purely scientific purposes, rouses environmentalists to fury. It was also a giant bureaucratic pain, because NASA had to prepare exhaustive environmental impact statements. The plutonium was deemed necessary because of Mars’ great distance from the Sun. On Mars, sunlight is only a quarter of the strength that it is on Earth, and small solar cells alone could not generate enough power to operate even a small spacecraft and rover.

After the initial preparation, Pathfinder underwent months of additional testing at Kennedy. Often, the tests were more complicated than the actual mission would be. For a test to work correctly, the ground team had to simulate the positioning of the stars and the Sun, the amount of light, and the temperature for Pathfinder, and then program Pathfinder to respond. Nothing went exactly as planned; everything required extra effort. Work became so intense that the young engineers involved with the project didn’t know what to do when they weren’t testing Pathfinder; they sought any distraction available in greater Titusville. They screamed themselves hoarse in a Karaoke bar, they played in mud volleyball tournaments, they surfed, they picnicked in the rain – anything to take their minds off the obstacles they faced to ready Pathfinder for space. At four o’clock one morning, they attended a Shuttle launch. The rocket’s glare turned night into day, and the sound of its engines was powerful enough to make observers’ clothes tremble. Pathfinder’s launch vehicle, a Delta II built by Boeing, was nowhere near as big as the Shuttle’s powerful solid state boosters, but the Shuttle simply attains low Earth orbit, about 350 miles high. It circles the Earth for a few days, and then lands on a nice smooth airstrip. If you happen to be a planetary exploration zealot, Shuttle missions, for all their sound and fury, can be a trifle dull. Pathfinder, in contrast, would travel 309 million miles to reach Mars, following the broad ellipse of its trajectory, and would arrive in a new world.

Whenever they could find a few minutes to spare, Pathfinder’s youthful team members posted their field journals on the Internet. These were casual, subjective reflections on their lives and work, with more questions than answers. The mere act of writing made everyone self-aware. It was weird: they were doing their jobs, and simultaneously, they were watching themselves do their jobs. They were doing their jobs on Pathfinder, and they were watching themselves at the same time. Anyone with access to the Internet could log on and check up on the team members’ psyches. As with so much else on this mission, the plan was very cool, and very un-NASA. Taken together, the team’s written observations sounded like an all-night college dormitory bull session about the meaning of God and life and truth and beauty, and that was their charm. The team members, especially the younger ones, unashamedly asked, Who am I? Where am I going? The field journals became confessional, a form of therapy. The more enthusiastic correspondents realized something unusual was going on here, something that extended beyond the boundaries of the Pathfinder mission, something that the words “faster, better, cheaper” didn’t begin to convey: a transformation of consciousness. They weren’t just devising a new way to reach Mars, although that was surely foremost in their minds. They were collaborating on a new way to solve problems, to create, to communicate, to imagine.

In late October, the engineers at KSC mated the spacecraft with the cruise stage of the Delta rocket, and loaded fuel into the spacecraft’s propulsion system. It was powered by hydrazine, nasty stuff that requires careful handling. If you touch hydrazine, it can burn your skin. If you spill it, it can start a fire. The engineers wore protective suits very much like an astronaut’s while they worked. In this instance, the fueling process proceeded safely. Soon after, technicians tested the Deep Space Network, the system for communicating with Pathfinder. The DSN consists of three ground stations – one in Goldstone, California, another in Madrid, Spain, and a third in Canberra, Australia. Exquisitely sensitive, the DSN can pick up exceptionally faint signals from spacecraft as far away as Jupiter, and possibly beyond the boundaries of the Solar System. In November, the team started holding practice countdowns. The launch was approaching rapidly; now it was days, not weeks away. Back at JPL in Pasadena, a sign read, “OBJECTS ON THE CALENDAR ARE CLOSER THAN THEY APPEAR.” It was a message that everyone on the Pathfinder team had learned to heed.

The closing of the spacecraft, supposedly a modest episode in the life of Pathfinder, inflated into a media event. Dan Goldin, the NASA Administrator, showed up at the Kennedy Space Center and gave a rousing speech. Crowds turned out to watch Pathfinder’s four petals fold shut around the rover. As everyone applauded, the engineers glimpsed a sliver of daylight between the petals. This was not a good omen: to close a spacecraft in preparation for launch, only to find that the pieces don’t fit. The event had been scheduled for television broadcast, but the engineers waved away the cameras so they could study the problem. This was the first time the spacecraft had been fully loaded, and the increased weight created structural sagging, which kept the petals from sealing as designed. During the next several days, engineers worked desperately to repair the problem, and couriers bearing modified parts flew in from JPL. “objects on the calendar are closer than they appear.” One by one the new parts were mated, and the entire assembly was stacked on to the launch vehicle, and trucked over to Launch Pad 17A at Cape Canaveral Air Station.

The launch was scheduled for December 2, and it proved to be an exercise in frustration. “The weather was so bad they decided to cancel the attempt for the day,” Donna Shirley wrote in her field journal. “On December 3, many of us went out to the launch pad to watch the gantry roll back. This was supposed to happen at 5 PM but didn’t actually occur until 7:30 PM. It got colder and colder, and there was a prelaunch party scheduled. A few diehards, including me, were all that were left to see the rocket standing free of the supporting structure. It was worth waiting for, shining in the spotlights, gleaming blue and white.” For a few hours that night, the countdown proceeded smoothly, but problems started to mount. “First, the winds aloft looked bad,” Donna recorded. “The range sent up balloon after balloon to see what the winds were like, and gradually they began to improve. By the fourth balloon they looked acceptable, and we all began to get excited. But there was another problem. One of the ground computers was having problems. After much discussion, the launch vehicle team decided to change to a backup computer. But about two minutes before launch time, that computer also had trouble, and the launch was scrubbed. Everyone sagged. We’d been running on adrenalin, not a bit sleepy, but once there was no launch everyone went home to bed.” Bridget Landry, a Pathfinder software engineer who’d been following the tortured countdown from Pasadena, also turned to her journal for consolation: “We were all so disappointed when they said we had to scrub! All that anticipation! In some ways, it’s funny, all that buildup, and then nothing happens. But it’s also scary: the Russian mission, Mars ’96, was unable to escape Earth’s gravity just a few weeks ago. Somehow, that makes us worry more about our launch. Guess scientists and engineers can be a little superstitious, just like anyone else.”

On December 4, with all conditions favorable, Pathfinder finally launched from Cape Canaveral at 1:58 AM, local time. Although the blast was visible in the night sky for miles, there were no throngs along the beach. The event was the merest blip on the news radar; the public remained mostly oblivious to the fact that we were returning to Mars. Pathfinder was just another planetary mission, for the time being.

After launch, the engineers at JPL had a rough idea where Pathfinder was located in space, but now they needed to know precisely where it was. To get a better fix on the spacecraft, they planned to establish contact with it through the Deep Space Network. But before they could do that, the spacecraft was supposed to orient itself with a device called a sun sensor, a small disc covered with photoelectric cells. The event was supposed to occur about ninety minutes after the launch, with the spacecraft traveling at 17,000 miles an hour, but the sensor wasn’t working properly, and if it failed, they would soon lose the spacecraft entirely. As everyone involved with the mission knew, if Pathfinder failed, the future of the entire Mars program, including a human mission, would be in grave doubt.

After extensive searches, the Goldstone, California, antenna of the Deep Space Network finally acquired a signal from Pathfinder, which confirmed that something was seriously wrong with the spacecraft: the sun sensor wasn’t returning data. The best guess was that the sensor’s photoelectric cells had been nearly blinded by exhaust from one of the launch rockets, and Pathfinder refused to pay attention to it. The fix was simple, in theory: send three new software files to command Pathfinder to tune into the sensor. The engineers transmitted the files again and again, but each time they were only partially received, and no one could say why. The situation, already very serious, deteriorated when the spacecraft began to ignore all commands. Eventually, one of the engineers realized that Pathfinder was revolving slowly and came in position to receive commands for only five seconds at a time. Now Pathfinder had two problems – the dirty sensor and the uncontrollable spinning. The double fault was likely to be fatal to the entire mission.

Working around the clock, the Pathfinder engineers compensated for the rotation, and transmitted a complete set of commands to the spacecraft. Once they did, Pathfinder paid attention to the sun sensor, oriented itself properly, and both problems disappeared. The process of resolving them, collaborative and critical, proved to be a rite of passage for the Pathfinder team. Although they were relieved to have fixed a problem that could have killed the mission, they knew that more could appear at any time. Pathfinder was single-string all the way; if a component failed, there was no backup.

In the ensuing days, a weird sense of calm descended on JPL. There wasn’t much anyone could do for the next ten months besides monitor the spacecraft, whose instruments were powered down for the long cruise. “I’ve always known that the spirit on Pathfinder was special,” Bridget Landry noted in her journal, “but when the people who worked on Apollo 11 and 13 say this project has more sense of identity and team spirit than even those two missions, you know you’re involved with something extraordinary. But the feeling here, at least for me, is bittersweet, too. Now that we’ve launched, some people are being laid off, and even though most of us are staying, the scope of the mission means that in less than a year, all this will be over.”

In the spring of 1997, as the spacecraft approached Mars, the Pathfinder team began a new series of tests to prepare for its prime mission – the weeks Pathfinder would spend on the Red Planet, roving and returning data. “Think of it as a rehearsal,” Bridget Landry’s journal explained. “We have a computer that simulates the spacecraft, as well as a model of the lander and a duplicate rover. We put the last two in our sandbox (a room full of sand and rocks used to simulate the surface of Mars), then close the curtains so that no one can see in, and a few people go in and rearrange the rocks. Then the operations team has to take pictures with the lander camera, determine where the rocks are, and generally do all the tasks we’ll do on the first two days on Mars.”

They tried to maintain a sense of humor; any joke was better than no joke. The technician who ran the sandbox – the gremlin, they called him – planted toy Martians amid the simulated rocks, and the controllers logged the little creatures as they would in an actual mission. The tests increased in frequency until they took place nearly all the time, and Bridget, for one, felt overwhelmed by the intensity. “I refer to this as ‘a snake swallowing a gopher’: it is an enormous amount of data/work/whatever, and it can be tracked visibly as the lump makes its way through the system.”

By this point, the team members had left terrestrial time behind; they lived on Martian time. A Martian day, or sol, is forty minutes longer than an Earth day; every twenty-four hours, the team migrated forty minutes around the clock to remain in synchronization with the Red Planet. The time shift was very disorienting; after a while, they began to feel as though they were living on Mars. “I had no clue as to what time it was on Earth, although I could tell you what sol it was,” Bridget recorded. “I even tried to date a check with the sol number during this time, and I dated leftover food in the refrigerator with the sol. I totally lost track of time. I couldn’t tell you what planet I was on, never mind what day it was. I was often surprised to walk out of JPL and find the sun up.” While she worked the graveyard shift, she found it “strange to be driving home under rosy skies, pulling the pillow over my head to shut out the morning light. Stranger still to hear meetings called for midnight or 2 AM, and having to ask whether an event scheduled for 6 means AM or PM.” One night, while driving home on the freeway, Bridget fell asleep at the wheel. There was no accident, no one was hurt, fortunately, but the mishap terrified her. After that, she kept a sleeping bag and pillow in her office so she could sleep there, if she needed.

Bridget’s role on Pathfinder changed along with her schedule, and throughout the project, she never knew what to expect. Her first job was straightforward: adapting sequencing software to Pathfinder’s commands and instruments, but then she worked with the imaging team in a job so idiosyncratic there wasn’t even a name for it. For official purposes, she called herself an Uplink System Engineer, but the title didn’t begin to describe the nuances of the position. After a while, she came to see the benefits of this elastic, improvisational approach; it was liberating, as long as she could keep up with it. “I think this is the main reason we succeeded – there was so little redundancy in staff and hardware that you had to understand not only your little piece of the puzzle, but how it all fit together. There was no one else to do it. If people couldn’t think this way, they left.” She managed to hang on, but found her new job staggeringly intricate and pressured. If just one system on which she worked malfunctioned, the entire mission could go haywire. “I always mean to go back and clean up the code I write, but there is only so much time and money and energy – you do the things that matter most, until it’s good enough. Striving for perfection is a good and worthwhile effort. Expecting actually to attain perfection can kill you.”

What started out as a cool new job – but still, just a job – became much more than that to Bridget and to the other team members. Most were young, this was their first big mission, in some cases their first job at NASA, and while they were confident of their technical skills, which was the reason they were hired in the first place, they were less certain they could manage the emotional strain. That was something they didn’t teach you back at Caltech or MIT: how to deal with failure and uncertainty. “This is a nerve-wracking experience,” Rob Manning confided in his journal. “It is really tough to go to another planet.” Normally a jovial soul, Rob endured nightmares. In one, “I launched my dog Scooter up in the spacecraft, and it landed on Mars. I realized, too late, how was I going to get him home? I was really upset for letting him go!”

On Monday, June 23, David Mittman, the new Pathfinder flight controller, awoke at three o’clock in the morning and showered in the dark so as not to disturb his sleeping family. He had managed a few minutes extra sleep by shaving the night before. He dressed, and drove to work at JPL. The place was already alive; June 23 was going to be a crucial day in the life of Pathfinder, which would land on Mars on July 4. “All the flight engineers have been developing ‘sequences’ – collections of commands executed in order by the spacecraft – in preparation for landing,” he wrote. “These sequences have gone through many reviews and revisions. Some sequences have been changed as many as twenty times as we’ve learned more about how to operate Mars Pathfinder.” Mittman and his team were about to send nearly 300 sequences to Pathfinder via the Deep Space Network’s transmitter in Madrid. The task was time consuming, because each sequence, traveling at the speed of light, as fast as anything can go in the universe, required nine minutes and forty seconds to reach Pathfinder as it sped toward Mars. The transmission proceeded smoothly for nearly twelve hours, until glitches in terrestrial equipment halted the proceedings.