by Rod Pyle
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.
In his own words, Bruce Murray was “drafted…reluctantly!” to work on Mariner 4 fresh out of grad school, but in the end, his collaboration with people like Robert Leighton resulted in not only a stellar career but also a fascinating path through deep-space exploration.1 Arriving at Caltech as a young man, he blossomed within the Mariner program and eventually headed off to spearhead Mariner 10 to Mercury—a single-spacecraft, low-cost, and high-risk mission that would be a precursor of “faster, better, cheaper” at JPL. In time he became the director of JPL, then retired to continue evaluating the massive data dumps from the Viking missions that had been stored and largely uninvestigated. Never a shy man, Murray is not one to mince words, and when he takes on a fight, his opponents had best be prepared to defend themselves…even if that opposition is NASA. Such an event occurred early in his career, as Mariners 6 and 7 were being designed.
“Mariners 6 and 7 were to be carbon copies of Mariner 4, and we had a long struggle with JPL and NASA to upgrade them with greater information capacity. This was the principal theme I played: to increase the amount of data to be returned, which was easy to do. For example, on Mariner 4…the telecommunications channel to return the data…only returned eight bits per second. That's like a teletype…It could have returned much more, and Mariners 6 and 7 would have been a similarly conservative design. But I, in particular, had a real battle with them. I had to learn about the electrical engineering, I had to learn about the communications, I had to figure out all this stuff. I realized what was happening was that the engineers were protecting themselves. They put tremendous safety margins in so that if anything went wrong they would still be able to get the signals back. But they paid for that with poorer signals. By choosing to get one-hundredth of what they could get back, they were much more certain of getting it done. It was really a sociological and psychological problem once you understood the technical principles. And that led to a long battle. Mariners 6 and 7, in fact, had sixteen thousand bits per second instead of eight bits per second. It was a factor of increase of two thousand, as a so-called engineering experiment.”
The term engineering experiment was accurate to a point but obscured a larger truth in Murray's mind: it would cover the engineer's back ends if something went wrong. He was not the type of person to tolerate that kind of game. He preferred to aim for the highest performance possible and to take your lumps if it didn't work.
“In all this, I taught myself other things. I wrote some papers…about communications to establish that I knew the subject better than they did. One of the lessons I learned from this was that in order to be successful, the scientists had to learn the engineering at least as well as the engineers; I had to learn about spacecraft stabilization, had to learn about power, had to learn about active control, had to learn about scan-platform motions. Television was the big drive, all the way through. One of the reasons I was able to become the director of JPL was that in order to do that job I had to understand the whole spacecraft.”
But it all began with Mariner 4, and the follow-on missions of 6 and 7 had to be different in some meaningful way.
“So the Mariners 6 and 7 mission: one was targeted in equatorial areas and one was to go at higher latitude over the polar ones. Mariner 7, which had a lot of technical difficulty, such as a battery explosion a week before encounter, was in fact able to confirm that indeed the seasonal caps are CO2…that was a major discovery. [The Mariners] discovered some collapsed terrain. [They] discovered some other physiographic features, but [they] didn't discover either channels or volcanism, which is, again, how Murphy's law operates in science. We have to look at the wrong places [first]. So it was not until Mariner 9 that the most significant surface features—these huge volcanic structures, and the huge water-carved channels—were discovered.”
But no probe can look anywhere if it can't talk to mission control. During the early space age, tracking of spacecraft was a rather ad hoc affair. One of JPL's crowning achievements in planetary exploration was the Deep Space Network, or DSN.
“The Deep Space Network is one of the most marvelous products of American science and technology in the world. It is also a marvelous attribute of JPL, and to a lesser extent of Caltech…. [It] consists of three principal stations for commanding—that is, communicating to and listening from spacecraft that are at some great distance from Earth. They are located at approximately 120-degree longitude differences, so as the Earth turns, the spacecraft is always in view of one of the tracking sites, which can spot occasional problems. There used to be one in South Africa, which was good, because it gave southern-hemisphere coverage and also gave additional longitude, which was about the same as Madrid. That was closed because of political pressure on US-South African ties. Among the many minor histories of JPL, there was a short period there where the official position was that we were out of there, but in fact we were still in collaboration. One can argue that sort of thing both ways. We also had to deal with Franco of Spain…. Institutionally, this has been operated, developed by JPL exclusively with relatively great independence from NASA….
“Technically the JPL group has been so superior and so outstanding, superior to anybody else in the world, that they really have been much more in charge of their own destiny than others…. The Deep Space net has gotten very, very good at introducing new technology into an ongoing, highly reliable system. It's a very, very impressive situation. They've also been able to structure the administrative and political arrangements so that they can plan ahead. The plans get changed, but they always have a long-range plan. They're always developing new technology…. It's an integrated system, sort of womb to tomb…. The result of this is they've been able to use state-of-the-art technology consistently and bring it in, and that net has been superior to anything else in the world, almost from the time it started, and it just gets better and better and better. It's absolutely incredible. It's a magnificent thing.
“The fact of the matter is they have been absolutely outstanding, and this, coupled with a group not part of them but part of the regular JPL, which does the navigation—takes this information and converts it into location and trajectories and these sorts of things—have been truly outstanding. There's just nothing anywhere close in the world.”
Planetary exploration was to suffer cuts and inconsistent funding over the next forty years, but one area would always get the money needed to continue operations.
“[The DSN] has shown remarkable resilience. Even when there are no missions, NASA keeps letting more money be put in, because NASA can never say there will never be any new missions. They can always say, ‘We won't make a new start this year.’ But for the tracking people it goes on. So that's moved marvelously well.”
Returning to the missions themselves, Murray recalls what he felt was probably the most important part of the flights past Mars, the most vital component.
“The imaging, of course, was of greatest public value. The reason is an important one: namely, that you don't need an interpreter for pictures. [For] everything else, you have to have the scientific priest interpreting the Bible for you. With pictures, however, the media are set up to transmit them—newspapers, magazines, or television—all over the world. We've developed it to a high art…. Bang! It just goes out! So I would argue that the positive aspect of the pictures was that it let peop
le participate in the exploration, and that's very good. But the result is that the NASA administrators—in general, not always, but certainly the JPL project people—were very pro-imaging, because they saw recognition coming from this. There's a lot of positive feedback, and they felt it.”
It's hard to imagine the exploration of Mars proceeding without all the wonderful images that have come back over the decades, but without people like Bruce Murray, that might have been the case. For this, and the proper utilization of the “scientific priests,” we thank him.
As the 1960s churned onward, the lion's share of NASA's budgets were devoured by the omnivorous Apollo program to land on the moon. Driven by politics as much as by science, Apollo was an insanely complex undertaking, and by the time Mariner 4 had departed Mars for the deeper solar system, Apollo had already reached the peak of its spending. Never again would NASA command so much of the national budget (at its highest, in 1965, about 5 percent). JPL and the unmanned exploration of the solar system had to make do with the leftovers.
But what a job the lab did with the money at hand. At the time of Mariner 4, JPL was also flying the Ranger series of missions to the moon. And the Rangers were traveling to the moon—in fact, they slammed smack into it, as planned. This was a simple, if inelegant, way to get ever closer images of the lunar surface. Orbital probes could do wonders from above, but even the most sophisticated of cameras had resolution limits. But by flying the probe right into the terrain, the final stream of images gave an ever-better view of the rocky, forbidding surface. It just had to be gathered quickly, very quickly.
After the Ranger program was completed, and after the flight of Mariner 4, the Surveyor program targeted the moon once again. These were landers, and infinitely more complex than the Ranger spacecraft. They had to navigate, land, and perform surface tests on the moon. And of course, with Apollo so dominating the national space agenda, they had priority over Mars missions, for the results of the Surveyor probes would help to design, and pick landing sites for, the Apollo lunar modules. Nonetheless, JPL had a knockout Mars mission planned for 1971: Mariner 9.
As a continuation of the Mariner series to Mars, it had a similar configuration as its forebears. But Mariners 8 and 9 each weighed as much as two of the previous ships, mainly due to the tremendously heavy extra fuel required to brake into Martian orbit. This fuel load made up almost half of the spacecraft's mass.
Of course, as with all the Mariners to date, a twin spacecraft had been part of the flight manifest. Mariner 8 launched in May but failed early in flight and ended its mission by splashing into the Atlantic Ocean. Some at NASA and JPL must have been wondering if they should simply skip the first launch of a Mariner mission by now.
But its twin, Mariner 9, launched successfully three weeks later. After an uneventful cruise to Mars, on November 14, 1971, Mariner 9 arrived at the Red Planet. It was the first spacecraft to enter orbit around another world. By this time, though, the mission goals had changed. With the loss of its sibling, Mariner 9 had to pick up some of the potential lost when Mariner 8 went diving into the Atlantic. Mariner 8 had been the designated mapmaker, while Mariner 9 was to study atmospheric changes over time. So, through a clever sharing of resources, Mariner 9 aimed to combine both mission profiles to the extent that it could. Some compromises were inevitable; the imaging of the polar areas, for example, was done from a high angle of inclination, and the shots were therefore somewhat degraded. Despite these compromises, the mission would be a stunner.
Mariner 9's engine fired at just the right moment to slow the craft sufficiently to allow Martian gravity to grab hold of the robot and pull it around the planet. It was now in an orbit that dipped below one thousand miles—half the previous flyby altitudes—with a vastly improved imaging capability of about 320 feet per pixel (the previous probes had managed about a half mile per pixel). This was a huge leap over previous efforts. The craft was in position to fulfill its primary mission: image and map the planet below. Its builders were elated…almost. For this time, Mars, not the spacecraft, had a problem.
You see, the probe had arrived at a costume party uninvited. Mars was wearing a planet-wide robe of dust, the largest storm ever observed. Virtually the entire planet was enveloped in a solid cloud of dust. This was a fact of life…but the question now was: how long would the storm last? Days? Weeks? In fact, it was mid-January 1972 before productive imaging of the surface could begin, two months after the robot's arrival.
But the waiting period was not wasted. After a time, a trio of specks were spotted in the clouds below, poking up from the northern hemisphere. It was soon realized that these were the tops of mountains, and the mountains were volcanoes. They were identified as the three major features of the area known as the Tharsis Bulge. A fourth peak was also spotted, that being the massive top of Olympus Mons.
It is worth mentioning that since this was the height of the space race, the Soviet Union had dispatched its own set of twin spacecraft to Mars, dubbed Mars 2 and Mars 3. Both reached Mars shortly after Mariner 9. Unfortunately, these Soviet ships were not reprogrammable, as was the case with Mariner 9, and rather than wait out the dust storm, they proceeded to follow their programming right on schedule. Landers were dispatched from each, the first crashing and the second apparently reaching the surface intact but losing radio contact immediately. The orbiters fared little better; following their simple logic, both used up their available resources snapping images of the featureless dust clouds below. Another Mars loss for the Soviet program and another blow to Soviet prestige in the space race.
Once the dust storm abated, Mariner 9's real work began. In just under a year of operation, Mariner 9 mapped the surface of the planet in 7,329 dazzling images.1 Previous Mars flybys had returned less than one thousand images, so the increase in coverage was nothing short of astounding.
But the real gems lay in the unexpected bonanza of surface features below, specifically the weathered terrain. The previous Mariners had sent back data from what appeared to be a mostly dead planet. Not so for Mariner 9. Gullies, streambeds, canyons, even clouds and fogbanks were seen. And of course, the incredible gash across Mars, Valles Marineris (which was named in honor of the mission), was discovered. The complex terrain patterns that crisscrossed the planet were charted. The massive volcanoes, seen in tantalizing glimpses through the dust storms of just a few months before, were extensively photographed. The unusual gravitational field, lumpy and surprising, was first measured by Mariner 9. Even the tiny, elusive moons of Mars were imaged. It was a hands-down winner of a mission.
Of these finds, the most arresting was the profound evidence of weathering. At the imaging resolution available, it was difficult to define exactly what they were seeing, but it was clear that the surface below had been heavily influenced by wind, water, or both. The extensive aeolian (wind-sculpted) features made sense; the dust storm that greeted the probe indicated as much. But what about the more robust areas of surface change? How had the channels been dug? Why were there areas that looked like river deltas? It was hard to ignore the fact that some of the weathered regions looked just like water-worn features on Mariner's home planet. But to jump to this conclusion meant that sometime, somewhere, Mars had enjoyed ample amounts of water. When? Where was it now? The general understanding of Mars, just a few years old at this point, stated that liquid water could not exist on the surface. So these enormous aqueous floods, which scoured areas the size of some US states, must have occurred well in the past. But what mechanisms were at work? As with every encounter with Mars, more questions were raised than answers supplied. But space scientists would not have it any other way. These were exciting times.
By October 1972, the attitude-control gas onboard had been depleted, and the mission was terminated with the spacecraft being shut down. Its mission was complete. Mariner 9 continues to orbit Mars to this day, sailing around the planet deaf and dumb in the cold darkness.
The legacy of Mariner 9 was to prepare the way for futur
e missions, especially the Viking landers. The treasure trove of images was unparalleled for the time. The mission longevity was likewise impressive, and the flexibility of the flight, both in the recovering of the primary mission objectives once Mariner 8 was lost and the long stand-down upon the probe's arrival at a dust-enshrouded Mars, is legendary. It is a testament to the mission planners, those who executed it, and of course the spacecraft itself. This next-to-last Mariner (Mariner 10 flew past Mercury) was a demonstration of what a bargain these early missions were. For a total cost of $554 million, the inner solar system had been opened, and brilliantly.
Up next: Mars, prepare yourself to be invaded…by a Viking.
Laurence Soderblom got his first taste of planetary science working on the Mariners 6 and 7 mission. This was a time when many people were getting their first taste of planetary exploration…the field was only a few years past the age of the telescope. But Soderblom was bitten by the planetary bug early in life.
“As a kid I was interested in astronomy, and I actually built a spectrograph. I was in high school then, and my mother in particular was an avid rock collector and we used to go out to look for rocks and minerals a lot of the time. My dad's background was physical science, so when I went to college, I went into geology, and then into physics, and by the time I got done, I ended up with two complete bachelor's degrees in physics and geology. I went to Caltech, and planetary exploration seemed like a natural blend of physics, math, and geology.”1
As a graduate student at Caltech in the early 1960s, Soderblom had the good fortune of landing Dr. Bruce Murray as his graduate advisor. While Dr. Murray may not have been the gentlest soul to ever grace that august campus, he was a forthright, hard-charging explorer of the cosmos. Soderblom felt fortunate to know him.