Destination Mars

by Rod Pyle

  Technology had come a long way since then, and even off-the-shelf components (which was what composed most of Pathfinder's data capabilities, another budget-conscious choice) were a quantum leap over what had gone before. So with this added assurance, and the reasonably good images from the Viking orbiters, the Pathfinder team had made its choice of where to land.

  Ares Vallis was a flood plain, adjacent to a wide channel, that appeared to have been cut by flowing water—lots of it. The exact landing area was a spot where this channel approached a delta, and eventually opened into Chryse Planitia, the area where Viking 1 had landed (though still over 525 miles distant). If this was what it appeared to be (and it was), lots of different kinds of rocks and minerals should have been washed out of the channel and into the delta. The hope was that Pathfinder would have lots of interesting samples to choose from.

  Once the sun rose over Ares Vallis, temperatures shot up to a comparatively balmy 10°F. It was now light enough, and warm enough, to begin operations on the lander. The first images were obtained and sent back to Earth, a twenty-minute trip. The meteorology package was also activated, and weather reports began streaming in. A quick analysis of the images showed that one of the airbags was not fully retracted and might impede the rover in its operations. This was quickly remedied, and Pathfinder prepared to take more pictures and spend its first full night on a frigid Mars.

  There was a heart-stopper at 10:30 that night when the computer onboard the lander stopped sending information. Then, at about 3:20 a.m. the next day, signals received seemed to indicate that for some reason the computer had reset, or rebooted, itself. The reason was not immediately apparent, but it was working again. Everyone breathed a sigh of relief. It was the first, but would not be the last, technical cliff-hanger of the mission.

  On sol 2, Sojourner was ready to roll. The command was given: the tiny rover, only about twenty-three pounds in operational trim, “stood up” and rolled down its ramp. Ever so slowly it began to move. Sojourner's optimum speed was about one half inch per second, but it would navigate the ramp down to the surface much more slowly than that. By the end of the day, it had worked its way to the bottom of the ramp and waited patiently for orders. They came at dusk: sniff the soil right where you are. Sojourner spent the night doing just that.

  The next day, at 3:45 a.m., JPL controllers “woke” Pathfinder with the song “Final Frontier” from the TV show Mad about You. It seemed fitting. Instructions were uplinked to Sojourner to prepare it for an experiment in “soil mechanics,” a fancy way of asking, “How does Martian dirt work?” So the rover was instructed to lock five of its six wheels and turn the sixth one, first one direction, then the other, grinding away at the dirt. By observing the reactions of the surface to this abrasion from the tiny stainless-steel wheel, the geology team on Earth would be able to divine much about the real estate close by the Pathfinder lander.

  At the conclusion of this Martian version of smoking tires, Sojourner would begin its historic traverse to Barnacle Bill, the first of many rocks to be visited in the immediate area. Now, the word traverse might be misleading…it conjures thoughts of a long overland voyage. In this case, the total trip from Sojourner's position at the base of the ramp and Barnacle Bill was a slim fifteen inches! Still, this was a new technology on a new mission on a distant planet, so everything had to be planned with care.

  Sojourner started her short journey. While this was under way, the lander began work on a so-called monster-pan, a complete 360-degree sweep of the landing area. The results were spectacular. After years of studying the Viking lander images from the 1970s, these new, highly saturated high-resolution pictures were simply breathtaking. They showed a whole new Mars. Not only was the topography and weathering different from that shown in the Viking landing zones, but the details of rock surfaces, types, and general weathering were far more evident.

  The images in general were so superior that when combined with orbital photos from the various probes that had been investigating Mars from high above, assumptions could be rapidly made about the surrounding terrain.

  One thing became clear right away: their interpretation of the landing area as resulting from water flows was spot-on. As one scientist put it, the flooding was so catastrophic that it could have filled Earth's Mediterranean basin. That's a lot of water for a desert planet. Water-transported deposits were seen nearby. Rocks such as Barnacle Bill had small “moats,” or eroded depressions, around them. Areas of bright and dark soil were seen, indicating wear. And the rocks nearby appeared to be of differing origins, if not differing types altogether. It was, as one scientist phrased it, a geological grab bag. And this offered opportunities to have Sojourner “sniff” a variety of nearby rocks, presumably washed down from different regions in Mars's wet and wild past, to build a better picture of the planet's history.

  As if to underscore this, the next rock visited, Yogi, was markedly different from Barnacle Bill. It was more primitive, not having experienced the heating, cooling, and general geological nightmares that the previous rock had.

  These were exciting times. The first machine to land on Mars in twenty years was operating perfectly, and gathering reams of new and detailed data. And as usual, it was exceeding expectations.

  By the time Pathfinder had been on Mars for six weeks, the mission was still proceeding well, but some glitches had popped up. On August 16, the flight computer on the lander had reset itself. It had not asked “DO YOU MIND IF I REBOOT?” or sent any other indication; it simply restarted of its own accord. Why this happened was not known, but at the time it was suspected that the temperature extremes experienced on the planet this time of year were severe enough to cause issues with the computer's circuitry. In any case, JPL worked the problem, sent a command to the lander to ensure proper aim of its high-gain antenna, and through this process reestablished contact at about 10 p.m. on the seventeenth. The sense of relief was palpable. However, this was neither the first nor last time this problem would rear its ugly little silicon head, and each time it did, the concern increased.

  Soon controllers were receiving images from the lander again, and immediately another problem became apparent: Sojourner, still not far from the lander, was stopped on a rock called Wedge, and for obvious reasons. It had been heading toward another rock named Shark, and the onboard sensors, ever vigilant against hazards, had sensed a tilt that was more than it was willing to accept. The small computer shut down the rover and waited patiently for advice from Earth. After an intense conference, the team worked out a new course and sent the commands skyward. Sojourner headed off to Shark and the area called Rock Garden beyond.

  Sojourner was traveling moderate distances unassisted now, as had been planned. Much of the Pathfinder mission was a test bed for future missions, so it was important to learn as much as possible while the rover was operational and within view of the lander's cameras. There were glitches of course—false stops, occasional digital confusion, and misaimed trajectories. But overall, Sojourner was proving to be a tough, smart, and plucky little rover.1

  By the end of August, ice clouds were seen in the surrounding skies, and the sunsets were picking up color. Blue sky was observed around the sun at some of these times; this is due to the Martian dust scattering the blue wavelengths. Temperatures were consistent—the low was -103°F, the high 14°F. Pathfinder recorded this, but cared not. The mission was always rocks, rocks, and more rocks. Sojourner, after spending the better part of a week getting there, explored the area called Rock Garden, which was replete with interesting samples. Things went well until the rover got stuck on a rock, Half Dome, and again shut off automatically. It was too steep. But each time Sojourner did this in automatic mode, and had to be driven off of the obstacle, the teams back on Earth were learning. What this would mean for future missions was not yet quite clear, but gaining experience was the key, and it would bode well for future rovers.

  Scientists continued to observe the smallest of details from the images r
eturned: ongoing looks at the dirt under Sojourner's wheels—the soil-mechanics experiments—saw many layers of material, almost certainly deposited by water, and created an ever-expanding database of soil types. Farther out, the ground was covered by a layer of fine sand and drift, bright in color, indicating some differentiation of local soil conditions. This was in keeping with the idea of landing in a river-delta area.

  In early October, communications problems returned. While signals returned from the errant lander computer indicated that the spacecraft was still functional, getting a meaningful conversation going was tough. Pathfinder was in trouble. The onboard battery seemed to be the culprit. It was losing capacity and was not only allowing the transmitter to get entirely too cold in the long Martian nights, but also failing to track time and date measurements. Low voltage and continuing resets of the computer were bedeviling JPL's plans.

  If communications disappeared for more than five days, the rover was programmed to go into a contingency mode and, like a loyal dog, return to the base station (lander) and begin to circle it. This was designed to keep it from wandering too far afield or getting irretrievably hung up on a rock.

  By mid-October it was becoming clear that the mission's days were numbered. On Earth, JPL engineers were testing identical hardware at a range of increasingly low temperatures in an effort to try to predict behaviors for the radio, but the results were not as useful as hoped. Still, the Pathfinder lander had outlived its planned primary mission of thirty days, and the rover had outlived its mission design of just seven days, but the ongoing sporadic failure of the radio was still a disappointment.

  In three months of operations, Mars Pathfinder continued to refine the image of Mars as a planet awash in water during ancient times 3-4.5 billion years previous. However, the area surrounding Pathfinder appeared to have been dry and untouched by flooding for at least two billion years.

  Sojourner's “nose,” the Alpha Proton X-Ray Spectrometer, found some of the rocks confusing. There was far more silica in them than expected from studying Martian meteorites that had fallen to Earth. They appeared to be volcanic in origin, which argued for a highly active geological period in Mars's past. This rock type, called andesite, is typical of rocks formed by magma cooling in subterranean pockets, as opposed to the types of rocks found on some parts of Earth and on the moon. This latter type, called basalts, results from lava flowing onto the surface and cooling there in large sheets. But andesites are also indicative of active plate tectonics, which Mars did not appear to have, and are usually found at plate boundaries. Later observations from Mars Global Surveyor and other spacecraft indicated that Mars may indeed have experienced plate tectonics early on, with that activity ending far long ago (Earth's are still active).

  By the end of its three months, Pathfinder had returned 2.3 gigabytes of data (by far the most accomplished in such a short period), over seventeen thousand images from the lander and the rover, performed sixteen detailed examinations of rocks, and sent back almost nine million bits of weather information. The team on Earth had gained valuable experience landing in an unorthodox fashion and driving a rover on Mars, which would prove invaluable for the next surface foray, the Mars Exploration Rovers. The understanding of the landing area had increased manifold, and modern electronics had been tested on the harsh and unforgiving surface of Mars.

  Not a bad haul for a faster, better, and cheaper experiment called Pathfinder.

  Rob Manning is a congenial and soft-spoken, if unintentional, folk hero. If you were a fan of the Mars Pathfinder website during that heady mission, you saw his bearded likeness all over the webcasts—calling out the numbers during the descent, announcing a successful touchdown, and throwing his head back with a fist pump when Pathfinder bounced to a stop. He was what might be termed the “principal cheerleader” as well as the chief engineer for the project, and has since taken these talents on to the Mars Exploration Rovers and the upcoming Mars Science Laboratory. When not busy with his projects at JPL, he pursues his varied hobbies, including jazz trumpet, in his Southern California home (just minutes from JPL) with his wife and daughter.

  His introduction to the Pathfinder mission was a bit of institutional serendipity: “We have a paper here at JPL called the Universe, and it had an artist's rendering of this funny little mission, a rover, a very odd painting. I thought, ‘JPL has no skill in this, it's been so many years since we've actually had to do something where we had to land on the planet.’…We hadn't really done a lander at JPL for many years. And while Viking was done at JPL, the lander was built at NASA Langley Research Center, who [sic] had since gotten out of the business of planetary exploration.”1

  Rob was puzzled that the lab would take on a Mars landing after all these years, yet at the same time, it was intriguing: “So I thought about this for some time. Soon I got a phone call from one of the people involved with this mission [spacecraft manager Brian Muirhead] who said ‘I need an electronic whiz to work for me, someone who knows about computers and software.’ I was an electronics- and software-systems engineer, so then we spent time in the JPL cafeteria and we hit it off, so he hired me as the chief engineer. I think he liked the fact that I wasn't super aggressive or controlling, and also that we really understood each other. That was around 1993. He taught me how to stuff a lot of electronics and complexity into a small little vehicle, and that was my charter: to work with the electronics team and the software team and the systems team. Over time it all grew together.”

  Mars Pathfinder and the Sojourner rover were built at JPL, giving folks like Rob a chance to have a very hands-on involvement with the project from planning to nuts-and-bolts to execution. This was a great way to have a personal stake in the mission, as well as save a lot of development money.

  “You see, Galileo and Voyager, in fact nearly all of the flagship missions were built right here [at the lab], so JPL had a long history of hands-on work. I guess they just hadn't done one where they went through the atmosphere and actually landed, so that was going to be unique. The Sojourner rover was part of the Mars Pathfinder project, and that team was within JPL. So at the time I was actually responsible for Pathfinder. Now I didn't design Sojourner, but I was very involved with the design of Mars Pathfinder. Later I was also put in charge of the entry and landing [for the mission], as the main guy behind that. It was actually a trio of us, and we were the three legs that held the entry-and-landing part of it together.

  “Now, for a long time Tony Spear, who was the project manager, was very concerned that we didn't have an entity to pull all those complicated systems together, and so he was looking to outsource it to another company. But it's a very complicated thing to outsource, and we didn't have much time before we launched. Launch was in late 1996 and [by this time it was] 1993, and I couldn't imagine writing a [specification] to tell people how to interface all those complicated things. How do you interface an airbag [landing system], for instance? So we finally talked Tony into letting us continue the process and building it here. Of course, we had lots of contractors working with us, so, for example, we designed the airbag architecture, but we didn't fabricate the airbag itself.”

  Outside contractors were brought in for key components—the airbags, the aeroshell, and the rocket motor. But the overall design and assembly of these components were to be in-house, and the people working on it worked hard—and enjoyed it.

  “There was a lot of concern at NASA headquarters that connections for all those things that you need to build a vehicle like that might not exist here. JPL had the chops to build spacecraft, but nobody had all the chops to put the whole system together. So [in a leap of faith], Wesley Huntress, NASA's associate administrator for space science, called Tony Spear and said ‘Tony, we would actually like you to implement this,’ and so we did.

  “So we started our own testing once the job came to us, [we] tried out different airbag concepts. We had to [figure out how] to [deflate] these airbags upon landing. On Mars the atmosphere is so thin th
at the air coming out of the holes vents supersonically, really fast. It doesn't do that on Earth, so the ability to test it on Earth, at least outdoors, was really lousy. Nonetheless we continued to try and get the venting to work.

  “Now earlier on, JPL had proposed working with other vendors to do a nonairbag system, thinking that would be perceived as a more reliable and safer way to land. But the price tag for that was much higher. Viking had landed with throttleable engines, and the throttle is the coolest part. But coming up with a throttle that actually has the precision that you want, the dynamic range, was a very difficult and expensive proposition back in early seventies when it was developed for Viking.”

  One might think that this would be child's play by now, in the twenty-first century. But not so. As with the Apollo program, much of the brain trust and technical expertise of the 1960s and 1970s have been lost, as has the manufacturing capability. It was a problem for the Pathfinder team.

  “The trouble is, there isn't a big call for these kinds of [rocket motors] in the space industry, and that throttling mechanism simply no longer existed by the time the 1990s rolled around. To make matters worse, all the people [who worked on it] were gone, and there was the sense that it would be very expensive to restore that technology. So [NASA] headquarters said, ‘Keep it simple.’ Remember that we're talking about a $150,000,000 spacecraft, all together, including the launch vehicle. That's actually really cheap, cheaper than a big movie at the time.”

  Amazing, but true. The motion picture Titanic cost $200 million to produce. Pathfinder was in line with the largest movie budgets of the time, and a bargain at that.