by Roger Wiens
At first we didn’t know what to make of it. Was it the same effect we were seeing with oxygen? In the end, the pieces started to fall into place. The chemical characteristics of nitrogen cause it to be more strongly affected by photochemical self-shielding than oxygen, where it was first noted. The Genesis team is now investigating whether other solar-system gases—perhaps carbon or sulfur—were affected in the same way.
We were vindicated—these results were the reason we had spent years working on the mission. Even though it was not headlined in the newspapers, we were now confident that our mission was an unqualified success.
What I didn’t know, while working on Genesis, was that it was just the beginning for me. My childhood interest in the Red Planet would ultimately prove prescient—yet to come was a trip to Mars, and not just any trip, but the biggest one in history.
*Isotopes are different atomic masses of a given element. For example, oxygen has three isotopes: O-16, O-17, and O-18. Most of the oxygen atoms in the air we breathe are O-16, but a small fraction of the atoms are O-17 and O-18. The ratios of these isotopes can tell scientists important details about the history of that material.
PART II
PATH TO MARS
chapter
eight
LASERS AND ROVERS
JULY 1997. I FOLLOWED DAVE CREMERS INTO THE BACK room of an old Los Alamos lab building. The place looked like it had been constructed of cinder block in several stages in the 1950s and 1960s. Books were piled in several corners, and every flat surface was covered with instruments, lenses, or optical mounts. The filing cabinets looked like they had a bad case of acne. I found out later that they had been used for laser target practice. At one end of the room was a tiny contraption on something resembling a telescope mount. The device consisted of a laser the size of a cigar lined up with a small telescope. The laser was hooked to a small electronics box with a little 9-volt transistor battery hanging out of one end. On the other end of the room was a dusty platform with a rock on it.
I had settled in Los Alamos only a few months earlier and I had come with an idea for using lasers to investigate the surface of the Moon and other airless bodies. People in my research group thought I had a good idea, so I received funding to test the concept. In the end, my scheme did not work, but it got me in contact with Dave and a technique that held much greater promise.
As I watched, Dave connected the battery and pressed a button. “Zap!” An invisible beam shot across the room to the rock and produced a brief flash. Dave turned on a screen for a spectrometer, a small instrument that can distinguish colors with great sensitivity, and displayed the color spectrum of the flash. He explained that the spectrum consisted of unique colors from each of the elements present in the rock. Zapping a rock of another composition produced a spectrum with a different mix of colors.
My imagination was immediately captured by the simplicity of this technique, which was known as laser-induced breakdown spectroscopy, or LIBS. New technologies had recently led to the miniaturization of both lasers and spectrometers, so, as the contraption before me suggested, one could envision such an instrument small enough to fit on an extraterrestrial lander or rover. And the tool was relatively efficient. Many people had the impression that a laser powerful enough to create a spark on a rock across the room would require more power than would be available on a small spacecraft. After all, the laser provided the intensity of nearly a million lightbulbs applied to the small spot on the rock. But the pulse was brief—only billionths of a second. The tiny battery dangling from the contraption showed the doubters were wrong.
Ray guns have been a staple of science fiction since the time of Orson Welles’s War of the Worlds. The concept long preceded the invention of the laser in the early 1960s. Unfortunately for sci-fi enthusiasts, early lasers were big and bulky, and not nearly powerful enough to live up to their exalted image. The laser would turn out to have a myriad of lower-power uses, from the grocery-store bar-code reader to the stimulus in DVDs and computer drives. High-power lasers remained mostly in laboratories and military research, spurred on particularly by Ronald Reagan’s call for Star Wars missile defenses in the 1980s. By the early years of the twenty-first century, the US military had a laser powerful enough to shoot down missiles under the right conditions. The biggest laser project of all time, the National Ignition Facility at Livermore Lab, used nearly 200 lasers in a building the size of three football fields to initiate nuclear fusion, harnessing up to 500 trillion watts.
I had some experience with lasers. Five years earlier, I had worked for a time as a visiting scientist at Argonne National Laboratory near Chicago with a group using excimer* and dye lasers in resonance ionization mass spectrometry (RIMS). We were developing the technique to use on Genesis samples, but the RIMS scheme was rather complicated. The excimer lasers, which were big and bulky, provided the photons, but not at the right wavelength. To adjust the wavelength we had to shine the excimer beam into dye chambers, which converted the beam to the wavelength we needed. The dyes, which were carcinogenic, would wear out after a while, and we’d have to mix up a new batch wearing gloves and being careful not to spill. On top of all this, the excimer laser needed about 20,000 volts to make it work. When a short developed in the laser, instead of producing a powerful beam, we’d hear horrible snapping sounds inside the housing. It made me nervous when my hosts removed the housing and stuck their heads inside to try to locate where the arcs were occurring.
Most light sources produce a range of colors. The unique feature of lasers is that they produce light at a single wavelength—and they do this coherently—that is, every photon looks exactly identical—with the result that they can be focused into a tight beam. In fact, the term laser is short for light amplification by stimulated emission of radiation, because the light is produced using electronic properties of crystals. When electrons are exited to a certain level above the ground state in these crystals, a trigger causes the crystal to “relax.” The energy released by each electron results in a photon with the properties already mentioned. Various kinds of lasers use different chemicals or crystals to produce different wavelengths. The excimer lasers I had seen at Argonne Laboratory used fluorine gas, which was nasty stuff. The military’s biggest laser used iodine, only a little better.
In spite of the challenges of laser systems, at least one type of instrument was successfully doing research from space. The laser altimeter accurately measures distances using the speed of light. Modern electronics can time signals with an accuracy of better than a billionth of a second, which is the time it takes light to travel about 1 foot. An accurately timed laser pulse can be bounced off of a surface to determine the distance between the origin and the surface. The Apollo 11 astronauts had placed a reflector on the Moon, allowing Earth-based laser systems to study the Moon’s precise orbit by accurately timing the reflected light. Later Apollo missions had been equipped with laser altimeters on board the spacecraft, permitting them to map the topography of parts of the Moon. In the 1990s this concept was carried to Mars in the form of the Mars Orbiting Laser Altimeter (MOLA). These instruments were relatively simple in their operation, but were still bulky, as they needed to sense the laser light reflected back from rocks or soil up to several hundred miles below. A rover instrument would have to be smaller, given the mass constraints on these vehicles.
As I learned more about the LIBS technique Dave had introduced me to, I became more convinced that it was simple enough to fly to the surface of another planet. For LIBS the laser didn’t have to output any particular wavelength—it merely had to project enough energy to flash-heat the surface atoms on the target. The little laser Dave had used looked impressively simple. It was no bigger than a cigar and it looked like it was practically made of cardboard. It was actually some brown plastic material with a little window on the end. Inside was a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, which used a solid-state crystal to produce an invisible infrared beam without any pois
onous chemicals. This was the same kind of laser that MOLA had used, only in miniature. I was not yet familiar with Nd:YAG lasers, but the small size and simplicity of the one Dave had just demonstrated really intrigued me.
Dave had started working on LIBS in the early 1980s with another colleague at Los Alamos. The instrumentation was quite large at the time, but by the late 1980s Dave had discovered that LIBS could work on samples some distance away—making it useful for new applications. And the components were becoming more compact. Besides the laser, the other main part was the spectrometer used to sense the light emitted by the plasma. As an undergraduate I had used a spectrometer big enough to cover a whole desktop. Light went in through a slit at one end and was bounced off a diffraction grating to some other optical elements several feet away, through another slit, and onto a detector. The device could only detect one wavelength at a time, and one had to turn a knob to change the wavelength it was sensing. By contrast, Dave had shown me a spectrometer that fit into the palm of my hand. These compact spectrometers had gone into production in the 1990s. They could accurately sense a large range of wavelengths simultaneously, and there were no knobs to turn.
Dave and his colleagues had started dreaming of putting the device on a rover, possibly for use on Mars.
In the months leading up to my meeting with Dave, the motivation to explore Mars had received a huge push from a purported discovery of microscopic fossils, supposedly of early primitive life on Mars, in a meteorite from the Red Planet. Although there were a couple dozen meteorites in existence that appeared to be from Mars, such as the one I had studied as a graduate student, this curious specimen was the only one that dated from the earliest epoch in Mars’ history. It contained small, carbon-rich shapes that researchers identified as possible microfossils of bacteria-like organisms. The alleged discovery came out in 1996 and immediately caused a storm of controversy. As I was still at Caltech at the time, a number of us were called into its vice president’s office to be queried about whether these were truly microfossils and how Caltech could use its resources to study the objects. Everyone became focused on whether these objects were real fossils of ancient life on Mars.
This was exciting for Mars enthusiasts and mesmerizing to the public, but the issue turned out to be highly polarizing within the scientific community and turned Mars exploration in an unexpected direction. Professional discussions became heated. In short order, scientists began to divide into two camps—those who were quite sure these objects were not fossils, even if they believed life might have existed on Mars, and those who believed these really were microfossils. It was the most impassioned controversy in many years for the Mars science community.
Only one meteorite contained the purported microfossils, and as with most scientific issues, the need for more data to confirm or deny the theory became of utmost importance. This caused a huge push for further Mars exploration. The program clearly needed new missions and new instruments to address this fascinating controversy.
Within a year of my arrival at Los Alamos, NASA issued a call for instrument concepts appropriate for new Mars missions. The selected teams would start a three-year program to build and test their instruments. Winning a contract would not guarantee a flight into space, but the prototypes were to be installed on a NASA rover for field testing in the desert. This was just the opportunity we were looking for. It could be the start of a new career in Mars exploration, perhaps leading to a spot on a new mission. Dave looked to me to provide the necessary experience working with NASA.
In the few spare hours afforded to me during my work on Genesis, which was now in full swing, I met with Dave to assemble a small team and write a proposal. I phoned some of the people working on the rovers that were being built for tests in the desert to understand what we would need to do to fit an instrument on their vehicle. Although I had been around JPL a lot in the past few years, I had not yet interacted with the team designing and building rovers. Rovers were a relatively new development for JPL, with flight work on such a vehicle having started just four years earlier. The rover jocks were intrigued by our “laser gun” and encouraged us to submit our proposal. We sent it in and waited.
Late in the summer of 1998, NASA sent word that our proposal was one of the most highly rated and had been chosen for three years of funding. We were elated!
Even before the funding arrived, while I was at JPL for Genesis work, I decided to visit the Rover Technology Group to discuss how to integrate our planned LIBS instrument with the test rovers. JPL consists of a few small city blocks of high-tech buildings nestled up against the San Gabriel Mountains at the north end of the Los Angeles Basin. It traces its origins back to the late 1930s when a few Caltech aeronautical engineers started working with rocket engines. They were kicked off campus because they were working with explosives, and so they set up shop in an arroyo, a flat, dry river bottom, next to the mountains. Twenty years later, JPL scientists were the first to send an American satellite into orbit.
By the time of my visit, JPL was heavily into the new rovers and robotics, having sent a successful small rover, Pathfinder, to Mars just a year earlier and gearing up for additional such missions. Our LIBS team sought information from the rover developers on how to build our device so it would fit inside their vehicle, how the rover would aim our laser at various targets, what voltage our instrument would be provided with, how much current it could draw, and how to send commands to and receive data from our prototype. I was looking forward to learning all about rovers, which seemed like the wave of the future for planetary exploration.
Eric Baumgartner, the leader of the Rover Development Team, ushered me into a building the size of a large garage. In the middle of the room, the guts of a rover were scattered across several workbenches. Wheels, chassis, mast, arm, cameras, and cables were everywhere. It was my first glimpse of a real rover—or what was to become one. As we stood among the array of parts, my host described all the different components and his team’s plans for construction. The vehicle was to be completed within the year, and the group was starting to plan its first excursion into the desert. After viewing the construction site, Eric took me into a conference room and offered me a seat. Then he broke the news that we would not get to test our instrument with their vehicle. Their plans, as well as their funding, called only for testing instruments already on approved missions, not those being developed for missions in the indefinite future. I was reminded that our instrument was still in the dream phase—we were a long way from having flight reservations.
I went home disappointed. Although the NASA program description had said we would test our instruments on JPL’s rover, it had failed to fund the rover developers for their role in our projects. Back at my office, I phoned our program administrator at NASA Headquarters to find out what we were to do in place of the rover tests. The director was upset to hear my story and vowed that we would be able to test our instruments on the rover before the end of our three-year program.
Dave and I waited seven months and heard nothing. In the spring of 1999, we met with the rover managers at JPL, and it became clear that they still had no plans for accommodating our instruments as NASA Headquarters had promised. We were caught in the middle of a power struggle. Headquarters had promised us that we would get to use the JPL rovers to test our instruments. However, the program had simply not provided the money to JPL to accommodate the work. Apparently there was no money available. NASA was in the middle of the era of bare-bone missions, and JPL was getting squeezed too hard financially. They simply could not handle another unfunded mandate.
Dave and I were frustrated by the stalemate between NASA Headquarters and JPL. There was a whole range of things we had hoped to gain from a test on one of NASA’s rovers. What size instrument could we realistically build? How much power could it use? What kind of operational scenarios should we plan for—that is to say, what distances would be useful to reach with our device? How many analyses would be needed to characterize a give
n rock or soil sample? What element abundances would tell us the most about various rocks? Along with settling these questions, there was the inside information and PR that we would get from a rover demo. We figured that bragging rights were worth a lot in convincing a future review board that our instrument should be chosen to fly to another planet. And getting to know the people most involved in the rover program would help us politically. After all, they might be involved in a flight payload decision. In the meantime, Dave was completing analyses in the lab showing which elements we could detect, with what accuracy, and at what distance. We were also looking for the smallest commercially available components that could be used in our system.
Finally we got a call from Washington telling us to phone the Ames Research Center, a NASA facility in the San Francisco Bay area. Ames had just received a clone of the original rover that JPL had built, and the team at the research center was excited about the opportunity to test it. We visited Ames right away and came away with the information we needed. We were now ready to build an instrument that could be integrated with the rover at Ames. This rover test, we hoped, would bring us one step closer to a real Mars mission.
*“Exited dimer” refers to a di-atomic molecule that only exists in an excited state for a few nanoseconds.
chapter
nine