This new ocean, p.74
This New Ocean, page 74
Mariner 10’s camera sent back ultraviolet pictures of features on the top of the atmosphere that could not be seen in the visible spectrum, and which could be used to trace the atmosphere’s unique movement. The imagery showed that most of the heat from the Sun is absorbed in the upper atmosphere, making it hotter than the surface, unlike Earth and Mars. No doubt about it: old Venus was now understood to be truly unearthly. And that, for Murray, was why it was important. Certainly building knowledge for its own sake was space science’s essential driving force, and one that lent it nobility. Yet many scientists, including Murray, also saw a potentially dire necessity in scouting the solar system. Space scientists in effect lived their professional lives in the implacably hostile desolation and violence of deep space, at least where their psyches were concerned. That much became evident when they anthropomorphized their robots and flew with them in the first person plural. “We are ten million kilometers from” Mars (or Jupiter or Ganymede)…. “We have acquired Canopus.… We are twelve minutes from closest approach” is the way they would invariably describe what their machines were doing. They were in effect out there, too, like the Saltine Warrior. And being out there made them appreciate where they came from. They therefore liked to make love to their planet, which they did by hiking, skiing, mountain climbing, sailing, and camping on it, and swimming deep within its life-giving oceans.
“To avoid accidentally destroying this delicate balance in Earth’s atmosphere by mankind’s activities,” explained Murray (who flew sailplanes and biked for relaxation), “it is mandatory that we understand fully the ecosphere in which we have evolved. This understanding is difficult, if not impossible, without comparisons to other planetary atmospheres.” Venus was a warning. Mars was a potential lifeboat. Jupiter and its moons were a miniature solar system that could provide clues to how the larger system worked.
Having returned more than four thousand pictures of Venus, plus a pile of infrared, ultraviolet, charged particle, and other data, Mariner 10 set off for savagely pockmarked Mercury with a boost from Venusian gravity. A few of Aphrodite’s veils had finally been pulled off.
Encounter with Mercury
Mysterious little Mercury, named after the son of the mighty Jupiter, was the messenger of the gods, bearer of luck, patron saint of astronauts, and, more to the point, the conductor of souls to Hades’ eternal fire. Mysterious because, as the closest planet to the Sun, it is difficult to see through telescopes on Earth. So there had been a great deal of speculation that had been passed off as fact. According to one theory, the little planet did not rotate at all, so the side facing the Sun was therefore as hot as hell: 750 degrees Fahrenheit, according to RAND’s authoritative Space Handbook, published in 1958. Wrong. Radar observations in 1965 showed that Mercury does indeed rotate, though at a snail’s pace compared to Earth. Its dawn-to-dusk day is equal to almost fifty-nine Earth days, while it takes only eighty-eight days to circle the Sun. RAND was right about the temperature, though: it is hot enough to melt lead during the day. But until Mariner 10 got there, Mercury appeared as a dusky blob with no distinguishable surface features. What was known—that it is denser than the Moon and Mars, for example—had been surmised from the blotchy telescope pictures and from the radar data.
On March 24, 1974, with correspondents from around the world gathered in JPL’s von Karman Auditorium, Mariner 10 made the first close approach to this system’s innermost world. The first picture, taken that day at a distance of more than 3.75 million miles, looked about the way it would have through a telescope on Earth. Even after a computer tried to refine the details, the imagery showed a rough-textured dark globe with the complexion of a splotchy orange. But the fun of it, as it always would be with planetary encounters, was watching the new world grow and became clearer every day as its unique identity came into focus. As Mariner 10’s imagery came into JPL, so did data showing how Mercury interacts with space, and particularly with the solar wind. The heavenly breeze does not react the same way on every body it caresses. Earth’s protective magnetosphere, which is caused by the planet’s rapid rotation, holds the solar wind at bay. The charged ionospheres around Venus and Mars do the same thing. But since the Moon has neither a magnetosphere nor an atmosphere, it bears the breeze’s full brunt. Since Mariner 10’s scientists thought that Mercury also lacked protection, it was reasonable to believe that it, too, would face right into the great wind. Wrong again. Nineteen minutes before closest approach on March 29, the plasma team was astounded to see the plasma flux jump, indicating that the spacecraft had crossed a bow shock wave. They were left to ponder how a moonlike, atmosphereless planet that barely rotated and that therefore should have no magnetic field could fend off the solar wind.
The answer was not long in coming. Mariner 10’s magnetometers showed that Mercury has a magnetic field and that it’s powerful enough to deflect the wind.43 But why? One possibility was that even a slowly rotating planet can have a magnetosphere if it has the right kind of electrically conducive, fluid core.
The answers, as usual, kept raising new questions. What was sometimes difficult for the uninitiated to understand was that the new questions not only required no apology, but were what made the game fun. William K. Hartmann, who was on the Mariner 9 science team that got the first really good look at Mars, explained that the heart of the process is the endless refining of the questions. “It has become a cliché of science reporting that new questions are raised as fast as old ones are answered,” he wrote. “How, then, can a voyage of discovery be worthwhile? The answer lies in the existence of a hierarchy of questions. Ideally, the early questions are first-order questions, and as they are answered, we proceed to finer levels of detail.”
The magnetosphere was only one case in point. So was the possibility that Mercury had a moon of its own. On March 30, the day after closest approach, the ultraviolet team reported that analysis of spectrometer data collected a few days before seemed to show that ultraviolet sunlight was reflecting off something that was moving away from the planet at regular intervals. A search with the television camera, completed on April 1, turned up nothing. The source of the light was a distant star; a mere twinkle in Mariner 10’s ultraviolet eye. April fool!
Meanwhile, the spacecraft’s electrical power drain had begun to surge, causing an alarming rise in temperature, which was heating the instrument bay. It was the latest in a series of crises that had the potential to abruptly end the mission. Believing that Mariner 10 was having a mechanical “stroke,” its desperate experimenters reacted instinctively by arguing for one last frenzied push to collect as much precious data as possible before their spacecraft expired (along with the papers they wanted to send to journals).
The popular conception of the scientist as an unflappable individual who is always in cool control is misplaced. Good science requires an emotional as well as intellectual investment. And the fleeting nature of the early encounters—quick flybys in which the time to get the data was very limited—made the mission scientists competitive and often irritable. Mariner 10 at Mercury was no exception. James Dunne, a soft-spoken project scientist, thought that the spacecraft could be saved if it got some rest. But his science teams wanted every sensor on Mariner 10 turned on for one last shot at collecting data. It was like wanting to burn out a car’s engine in order to win a race. So Dunne became a ship captain trying to stop a mutiny. At one point he rushed into Walter E. “Gene” Giberson’s office and, pounding on the project manager’s desk, demanded that his scientists be ignored. They were. Instead, Giberson ordered that the television cameras and some other instruments be turned off. The surge subsided, and Mariner 10’s sensors began to cool down. So did Dunne.
By carefully nursing its maneuvering gas and working phenomenally difficult trajectory adjustments, Mariner 10’s unheralded navigators sent it past Mercury three times, like one horse repeatedly overtaking another as they raced around the Sun. It had its second closest approach on September 12, 1974, and the third and last on March 16, 1975, when it came within 203 miles of Mercury’s surface. There were eight trajectory corrections instead of the usual two, amounting to a fourfold increase in navigational accuracy, with Venus’s gravity playing a key role. Mariner 10 was finally shut down on March 24, 1975, when it literally ran out of gas.
The first close-up pictures of Mercury and the massive accumulation of other data from both it and Venus were obviously brilliant, with all mission objectives met. Less obviously, Mariner 10 left behind a treasure of in-flight science and engineering experience that was being applied to Pioneer’s exploration of the outer planets and to other operations as well. It was a mission, like Pioneer Jupiter Saturn, that the Russians could only envy.
Venus Is Beseiged
By December 1978, the cold war was at its height, and as a result the golden age of exploration was well under way. So intense was the competition between the United States and the Soviet Union to pry secrets out of their planet’s neighbors for prestige as well as knowledge that ten separate spacecraft were working at Venus alone that month. Meanwhile, both Viking landers were reporting to Earth from the plains of Mars and Pioneers 10 and 11 were being followed to Jupiter and Saturn by two JPL spacecraft named Voyager 1 and 2. They were the reincarnation of the demised TOPS and one of them was in fact headed for the Grand Tour.
Four of the ten spacecraft that went to Venus were Russian orbiter-landers called Venera 11 and 12. The Venera 11 orbiter arrived on December 21 in time to catch a tremendous storm and managed to spot lightning and record thunder. Its lander came down in one piece and sent data back for ninety-five minutes. Venera 12 followed four days later and ran into the same storm. Its lander transmitted for 110 minutes and reported a surface temperature of 860 degrees.
The most sophisticated of the Venus explorers were developed by Ames and were called Pioneer Venus 1 and 2, or Pioneer 12 and 13. Pioneer 12 was a radar mapper that was supposed to circle Venus and penetrate its soupy envelope. Pioneer 13, its sister ship, was a so-called Multi-Probe consisting of a main spacecraft and four babies (one of them fairly large) that went to Venus together and then parted ways for their individual missions. Those missions, as “probe” implied, were for all five to plunge into the soup and send back data on Venus’s wind, temperature, circulation, and the atmosphere’s composition and pressure before they slammed into the planet itself and were smashed to bits. (One actually survived the plunge through the thick atmosphere and continued to broadcast for sixty-seven minutes.)
Pioneer 12’s radar cut right through the shroud and sent back the first sweeping, detailed views of the surface of Venus. (Venera 9 had sent back the first pictures from the planet’s surface in October 1975.) Awestruck mission scientists looking at their television monitors at Ames saw whole continents materialize from out of the mist. One of them, named Ishtar Terra, was the size of Australia; another, Aphrodite, was as big as Africa. Out popped mountain ranges, volcanoes, valleys, impact craters, plateaus, and basins, some of which had been hinted at by Earth-based radar, but were now actually seen for the first time. Pioneer 12 made maps of 90 percent of Venus in detail, including a gravity map that indicated that there had been a lot of “adjustment” on the planet’s surface.
Perhaps the most important practical finding would be that Venus’s landscape was a lot like Earth’s and that its hellish surface temperature almost undoubtedly came not from heat pouring out of its clouds but from a massive greenhouse effect in which carbon dioxide and a tiny amount of water vapor prevent surface heat from being radiated back to space.
Technically, the major part of its observation mission was supposed to be completed by the following August, but the orbiter would actually keep sending data back until Venus’s gravity pulled it to a fiery finale in October 1992. Eleven of its twelve science experiments functioned to the end.
The Reincarnation of Voyager
The bitter memories of its first Mars lander project notwithstanding (or maybe because of them), JPL changed Mariner Jupiter Saturn’s name to Voyager in 1977, the year two of the spacecraft finally took off for what was still on the books as a two-planet mission. Voyager, unlike Mariner Jupiter Saturn, was an unrestrictive name, a name that would be valid no matter where it went. No one would be able to hold NASA to the two-planet mission on a technicality should a decision be made to extend the trip to Uranus and Neptune.
The two Voyager spacecraft were built in-house and showed their Mariner bloodline. Yet they were designed to be bigger, tougher, and more sophisticated than either their predecessors or Pioneers 10 and 11. These arrows were crafted to reach the outermost planets and return a great deal of data. Their inherent design, in fact, gave the clearest indication that the possibility of making it at least as far as Neptune was under serious consideration at JPL. It does not take an ocean liner to cross a lake, even a Great Lake.
Unlike the Pioneers, for example, Voyagers 1 and 2 were autonomous. Each was fitted with three different computers (each of which in turn had a backup) that steered the spacecraft, processed scientific and engineering data, and coordinated onboard systems. While all three combined did not have the capacity of one of today’s laptops, they were the state of the art at the time, and were not used frivolously. With instructions loaded at JPL or transmitted from there and then updated, they could run the science experiments and operate Voyager’s own flight systems. And they were even programmed to automatically react to problems or simply changing conditions. The computers could therefore keep the two spacecraft functioning semiautomatically for months if necessary, making them the smartest robots ever to head for deep space.
The heart of each Voyager was a rugged ten-sided bus that was made of ten bays holding science instruments, electrical and communication equipment, and tape recorders. A sphere in the center of the aluminum doughnut held hydrazine for the steering thrusters. Attached to the bus were a twelve-foot-wide high-gain antenna (three feet wider than Pioneer’s), three RTG nuclear power plants stacked on one boom like drums (one more than Pioneer had); a pair of magnetometers attached to another, longer boom; a pair of rabbit-ear radio astronomy and plasma-wave antennas; and a movable scan, or science, platform. If, as Oran Nicks said, exploring machines resemble living creatures, then Voyager’s movable scan platform amounted to a head that could be turned and that contained its eyes. The eyes themselves were narrow- and wide-angle television cameras, ultraviolet and infrared spectrometers, a photopolarimeter, and cosmic-ray and plasma detectors. Three-axis stabilization would keep the Voyagers steady for the clearest possible imagery. Stabilizing spacecraft on three axes had by then become so finely engineered that the infinitesimal squirts of hydrazine could adjust the machine’s attitude at a rate one tenth to one hundredth the speed of a clock’s hour hand.
At a takeoff weight of 1,819 pounds, the Voyagers would be the heftiest planetary explorers except for the Viking Orbiters, which were two and a half times as heavy. But then the Vikings only had to get to Mars.
The spacecraft would also carry messages for extragalactic intellectuals and would be virtual encyclopedias compared to the relatively simple discs fastened to the Pioneers. The new records, twelve-inch gold-plated copper plates, were developed by a Voyager Record Committee whose chairman and executive producer was Carl Sagan and whose members included Drake and Timothy Ferris, an observer who wrote eloquently about cosmology and who believed implicitly that scientists are as obsessed, intuitive, and driven as artists. Ever mindful of the storm of criticism that had been provoked by the Pioneer plaque, the committee spread the widest possible cultural net. The record’s greeting, for example, was given in 55 languages including Mandarin, Bengali, Urdu, Farsi, Latin, Welsh, Nguni (Zulu), English, French, Vietnamese, and Japanese. There were 38 sounds, including rain, a barking dog, a Saturn 5 liftoff, Morse code, crickets chirping, heartbeats, laughter, and a kiss, plus 115 images, some of which showed a fertilized ovum, a snowflake, Bushman hunters, rush-hour traffic in India, DNA, and a supermarket. A proposal to send a photograph of a naked man and a pregnant woman looking at each other and holding hands was rejected by NASA, which had been burned by the Pioneer plaque, but Sagan and the others managed to include silhouettes anyway so as not to break the continuity of the human reproductive sequence, as they put it. There were also ninety minutes of eclectic music, including Bach’s Prelude and Fugue in C from The Well-Tempered Clavier, an initiation song for pygmy girls in the Zaire rain forest, a bamboo flute rendition of the Japanese “Cranes in Their Nest,” Chuck Berry’s classic “Johnny B. Goode,” and a Navajo night chant.
The record also contained greetings from President Jimmy Carter, who opened by noting that the bearer of the message was made in America but then grew cosmically expansive:
