Destination Mars (6 page)

I
n the world of 1964, there were few go-to people when it came to exploring the solar system with robots, especially when it came to actually
seeing
the planet below. At this time, Russia and America had launched numerous satellites into Earth orbit and flown probes to the moon. But to other planets? The Soviets had attempted Mars six times, but all these missions failed, as did their three attempts to reconnoiter Venus. The United States had succeeded with a mission to Venus in 1962 with Mariner 2. But we must remember that the first Earth-orbiting satellite had been launched only in 1957, so the space age was young.

It was therefore a daring feat when NASA detailed JPL to send twin probes to Mars, Mariners 3 and 4, in 1964. One goal was to transmit TV images back to Earth, both for scientific and political reasons. The political motivations are obvious: we were in a space race with the Soviet Union, a battle of political systems and technological might. While this was paramount with the manned space programs, it had begun with Sputnik and Explorer (the first Soviet and American satellites, respectively), so unmanned exploration was also an important measure of success as well. The scientific ones were also relevant: prior to the success of Mariner 4, Mars had been seen through Earth telescopes in some detail since the mid-1800s, but viewing through the syrupy atmosphere of Earth provided little in optical detail. Mariner 4 had the potential to convert the hazy, fuzzy telescopic images of Mars into relatively
crisp, clear images of the planet most like Earth. It was time for the next step.

When JPL set out to build a team to design an onboard camera, one of the heavy hitters it sought out was a Caltech professor named Robert Leighton. Born in 1917, Leighton had attained a bachelor's degree, a master's degree, and a doctorate from Caltech and stayed on as a professor. Leighton was a garrulous fellow, plain-spoken and capable, and never hesitant to speak his mind in easily understood terms. Trained as a particle physicist under the likes of Richard Feynman, his interests ranged wide and far, and he was fascinated by this new and exciting venture. The passion he brought to the program was infectious and helped to make Mariner 4 the great success it was. He was named the principal investigator for the TV-imaging experiment.

Dr. Leighton, who died in 1997, was interviewed numerous times about his ventures into space.
¹

“In ‘61 or ‘62, I was dragooned by Bruce Murray and Gerry Neugebauer into participating in the Mariner 4 photographic experiment, [the] television experiment, and the reason for that was that there had been no reasonable proposals for a photographic component of the mission on television, for pictorial work. I think people had made studies for NASA of camera systems and stuff like that, some written stuff was available. But nobody had proposed, for that mission, putting together a particular kind of a TV camera.”

Leighton and his team would soon change this. Integral to this project was returning images of Mars; at this point, the romanticized world of Percival Lowell, while extremely unlikely, still could not be entirely ruled out, at least not in laymen's minds. But when the haunting black-and-white images from Mariner 4 did come through, everything changed.

“The reality of it just suddenly waked everybody up. Percival Lowell left us with all that business, ‘waves of darkening' and things. And unfortunately…some of the members of the scientific
team are basically romanticists. You know, they are just unbridled romantics…‘if you can't prove that there isn't life on Mars–well, then there must be life on Mars, and let's go find it.’ Well, [Mars changed]. It's got dust storms and polar caps and things.

“It's obvious…there'd be craters and everything. And yet, the fact that craters were there, and were a predominant land form, was somehow surprising. And the [imaging] limitations were so severe…that we waited a week or more, after we knew there were craters, before any kind of official announcement was made. At JPL things were protected very much, because it's one of those things where, if somebody had leaked [the term] “craters”…I think what we were trying to avoid was being drawn into a detailed discussion of things before we had had a chance to make any kind of measurements…so we took a week or two, and made measurements, and then had a press conference.”

Though a physicist by training, Dr. Leighton had become a respected astronomer over the years, specializing in planetary photography. His approach to the needs of the Mariner flights was interesting in this regard.

“Say you wanted to devote a certain amount of money, over a period of time, including mainly space experiments…as a scientific component of the space program, you want to bring back the most science within the area of coverage that you can for the amount of money [you have].

“I think time and again, the atmospheric pressure on Mars, the water vapor on Mars, the temperature of Venus—and there's other things—the rings of Uranus and so on, have come first, or at least equally from ground-based work. And [while] the space work [was] a unique contribution…the prior knowledge of those properties, if we'd known them a few years earlier, could have greatly enhanced the scientific return from the missions that were flown. And so I've always felt that one of the first things NASA should have done was to build four more 200-inch telescopes…as it was, one mission—one damned spacecraft mission
would cost as much as five 200-inch telescopes, plus the mountains to go with them.”

He felt that more could be done, once in space, by furthering the knowledge that could be gained from Earth via telescopic observation. However, at this point, imaging from Mars was becoming critical to Mariner 4. But to date, the approach seemed to him to have been somewhat ad hoc:

“We were sort of approached by JPL. The people there had done a lot of thinking about [imaging], but they didn't have any scientists. They had the technical know-how, and had the tubes and everything else, and they'd even sent the Rangers [to the moon]…they had good cameras. And [JPL] had a lot of experience with television cameras and so forth, and to the extent that they thought they were just going to the moon again, they were well up the curve. And so by the time they latched onto a few of the scientists, and we got together and made a group that would do it, it just was a leaderless, headless thing, where there was knowledge…but it was not in places where the people…could propose as a team. So it was a sort of a fluke, in a way.”

So, in the end, was it all worth it? On this point, he seemed assured.

“Oh yes, absolutely. And that's one of the best parts of it all. Some of the letters that came in, from the milkmen, the dairy farmers in Oregon—they'd been watching TV at, I don't know, 5 a.m. or whenever the thing went over [the airwaves]…they said, ‘I'm not very close to your world, but I really appreciate it, keep it going.’ I thought that was kind of nice.”

It was indeed. And it was the beginning of a whole new understanding of Mars.

I
n 1969, Mariners 6 and 7 continued the quest by performing two more flybys of Mars, this time at a range of only two thousand miles from the planet instead of five thousand as with Mariner 4. And both spacecraft made the trip successfully.

While these probes were bigger and heavier than Mariner 4, they were assigned a similar mission: fly past the planet and perform as much science and imaging as possible. By following divergent paths past the planet, the twins would cover as much of Mars as possible while whizzing past. It was, like Mariner 4, a bit like firing the spacecraft out of a cannon, at a point where Mars would be when they reached its orbit after a 200-million-mile voyage, and snapping photos as they passed it. It was a carefully controlled train wreck, with one train snapping pictures of the other as they crossed paths.

Complex as it was, there was more drama behind the scenes. While this Mariner mission was one of the few in this era in which both twins would complete the voyage together, Mariner 7 nearly didn't make it. A week prior to encountering Mars, the craft dropped out of Earth contact. JPL mobilized its Deep Space Network and began an intensive effort to make contact with the missing probe. After numerous efforts, contact was regained via the low-gain antenna, and the craft was able to reorient itself and resume the mission with only minor delays. While at the time it was suspected that Mariner might have been impacted by a meteorite, it
was later decided, based on the best sleuthing JPL could manage, that an onboard battery had exploded, temporarily disorienting the craft. In the final analysis, Mariner 7 actually outperformed its twin during the high-speed flyby.

The mission of each craft, while similar, had slightly differing objectives. Since Mariner 6 launched before Mariner 7, and the Mars encounters were separated by almost a week, the data gleaned from 6 allowed mission planners to implement last-minute changes to the data-gathering efforts of 7. Each had new and improved camera systems, one for wide-angle imaging and one for telescopic imaging. This was a vast improvement over Mariner 4, with its single low-res camera.

In addition, each craft sported an infrared spectroscope, an infrared radiometer, and an ultraviolet spectroscope. These instruments were improvements over the Mariner 4 package, and a reaction to the discoveries made by that pathfinding mission. By today's standards, this was a very basic package, but for the time it was quite sophisticated and incorporated a lot of lessons from Mariner 4.

Unlike that first flight, these two Mariners were not tasked with performing scientific investigations during their cruise to Mars. Their specific goal was to begin—and end—their primary operations at Mars encounter. The space age was maturing. They were to fly over the equator and southern hemisphere of Mars, respectively.

Each craft was just under one thousand pounds in mass (or about double the mass of Mariner 4), and measured ten feet tall and about nineteen feet wide when in cruise mode. As before, there was an analog tape recorder for image storage and retransmission. There was also a digital recorder for science data storage. And, like Mariner 4, internal temperature control of the spacecraft, critical to successful operation, was governed by an ingenious system of slatted louvers, like Venetian blinds, on the sides of the boxy main body.

One stunning difference was the amount of data that could be sent back to Earth. The designers of Mariner 4 had been very conservative, so concerned were they that things be kept simple to ensure mission success. With these new spacecraft, there was an intense effort to maximize the data return and speed with new techniques; but this was not implemented without conflict. Conservative engineers sparred with the more aggressive science team in a running battle over data rates. Ultimately, the newer system was couched as an “engineering experiment,” which would have provided political cover in case of a failure. But the net result was that its data transmission was about two thousand times that of its predecessor. While a stunning success, this would not be the last time unmanned space exploration would suffer internal squabbles over political concerns.

Launched a month apart, the twin spacecraft arrived at Mars separated by only five days. Mariner 6 entered the vicinity of Mars on July 29, 1969. The probe was flying via inertial guidance as opposed to relying on the problematic Canopus sensor. This had caused much drama on Mariner 4. And on this flight, when the explosive retainers of Mariner 6's scan platform were ignited to release the cameras and instruments into their postlaunch science-gathering configuration, they blew a small cloud of detritus into the craft's immediate vicinity. Of course, being in midflight, the particles kept right on traveling with the spacecraft, and the Canopus star sensor began trying to lock on these small, brightly lit particles instead of the proper guide star. So rather than track bits of paint and ash as they flew past Mars (and possibly end up imaging the black of space instead of the planet), they relied on the internal guidance system to orient the craft.

Fifty hours prior to flyby, the instruments were activated. Two hours later, the “bomb run” began, and for the next forty-one hours, forty-nine images were snapped of the approach to Mars via the narrow-angle (or close-up) camera. On July 31, the close encounter began, and another twenty-six close-ups were captured.
The craft sped past Mars at a distance of about two thousand miles, or less than half that of Mariner 4. As it left Martian space, it sent home the data and images it had acquired, then began a limited set of observations of the outer solar system and the Milky Way's galactic edge.

The only equipment failure on Mariner 6 was insufficient cooling of the infrared spectrometer at Mars encounter, limiting its usefulness. Overall, though, the mission was a crowning success. Shortly it would be Mariner 7's turn to barrel its way past Mars.

Despite the early navigation and communication problems, Mariner 7 behaved very politely as it neared its target. Reaching Martian space on August 2, 1969, the craft captured ninety-three images of Mars as it closed on the planet. After fifty-seven hours of approach, the close flyby began. The craft was taking a more southerly trajectory than originally planned, due to early analysis of Mariner 6 images. There was some awfully interesting scenery showing up in the southern hemisphere, and this was a chance to see it close-up. By August 5, the craft had snapped an additional thirty-three close-encounter images and left Mars. As it sped away, it followed a similar program to Mariner 6's, adding observations of a small comet to its dance card.

After the first tantalizing twenty-plus low-res images from Mariner 4, Mariners 6 and 7 were a smash. A total of 201 images were sent home, with fifty-nine of these being close-encounter images. These images covered about 20 percent of the Martian surface. Ultraviolet and infrared data were acquired from the planet, and the atmospheric pressure was further refined to about 7 millibars. The south polar cap revealed itself to be composed primarily of carbon dioxide after all (a thick layer of water ice would be identified below this over thirty years later).

The missions sent back enough information to allow for future planning of missions like Mariners 8 and 9, as well as early thinking about the Viking mission. Surface composition, atmospheric density, and ambient temperatures were tracked and
studied. The mass of Mars was refined and lots more experience was gained in deep-space flight and control. Atmospheric data showed large amounts of dust present, as well as water and carbon dioxide clouds, and finally, the atmospheric pressure measurements of Mariner 4 were confirmed.

All in all, these Mariners accomplished about all that could be done in a fast flyby. It was time to try something much more challenging: send a craft into orbit around Mars.