Destination Mars (23 page)

In late July, controllers began sending commands to Spirit in an attempt to awaken the rover. It was now deemed safe to do so, as the local environment was emerging from the Martian winter and the power drain, if communication occurred at all, would likely not be fatal. But the rover remained silent. It was hypothesized that it may have lost so much internal data that the clock in the onboard computer may not have known what day or time it was. If this had occurred, the computer should reset the clock and begin a sequence of listening for commands for twenty minutes out of every hour of daylight.

By January 2011, Spirit had been off the air for nine months. Still, controllers continued to try to awaken the rover. It was the local Martian spring, and this was the last best hope for communication. Soon solar opposition occurred, and then, once Mars emerged from the temporary blackout, efforts began again. But it was not to be.

On Wednesday, May 25, JPL sent up its last plea for Spirit to phone home. This was greeted with silence. Earth-based radio dishes had double-teamed with the orbiters around Mars in attempts to reestablish communication, but all had been for naught. Spirit, after being stuck in soft sand and enduring the coldest temperatures ever encountered on Mars, had died. After a
career of almost seven years on Mars, the rover had succumbed to the harsh elements. Still, having vastly outperformed its initial mission of ninety days, the machine had outdone itself and performed brilliantly.

Opportunity, meanwhile, has completed the drive to its next, and most exciting, target. The rover had covered about fourteen miles since it landed, almost three times as far as Spirit managed. In a fitting epitaph, JPL named Opportunity's point of arrival at Endeavor Crater “Spirit Point.” Who says engineers and scientists are not sentimental?

W
hen one hears the word
Phoenix
, one usually thinks either of a hot city sweltering in the Arizona sun, a Grammy-winning French rock band, or the mythical bird representing rebirth. The last of these is what the planners of Mars Phoenix hoped for when naming the polar lander tasked with succeeding where the Mars Polar Lander mission (MPL) failed when it crashed into the frigid wastes of the Martian north pole.

It was not a perfect analogy; for while Mars Phoenix was made largely of hardware recycled from a previous lander, it was not bits of a twin of Mars Polar Lander, but rather the later (and mothballed) Mars Surveyor 2001, canceled in a period of shock and internal review after the twin failures of the aforementioned Mars Polar Lander and the Mars Climate Orbiter. Fortunately for JPL, the Surveyor had been carefully packed away, and much of the machine was reincarnated in Phoenix.

The mission had origins unlike most interplanetary missions of discovery. After the failures of the earlier lander, various parties within the close community of planetary scientists had been talking, and out of this came a proposal to NASA from the University of Arizona. It would be inexpensive, yet would retrieve the science lost when the MPL crashed. Phoenix would also address the problems that plagued the failed MPL mission. It would be run as a tight ship. It would also be done largely off-site. It was enough to excite and terrify conservative NASA managers at the
same moment. And, amazingly, it was ultimately approved as a part of NASA's new and (relatively) inexpensive Scout program.

Of the many improvements made to Phoenix over the failed Mars Polar Lander, the method used to shut down the descent engines was perhaps most important. MPL had used a “shock sensor” that was supposed to have triggered the engine shutdown when the lander set down. Unfortunately, an unrelated shock felt during descent (probably the deployment of the landing legs), while MPL was still over one hundred feet up, shut down the rockets prematurely, and the lander crashed. Phoenix would return to a simpler method, similar to one used as far back as the Apollo lunar lander: switches on the footpads would signal
actual
touchdown. This was one of a number of improvements made in an attempt to ensure a successful mission.

The Mars Phoenix mission was unfamiliar ground for NASA. It would be the first mission in the space agency's history to be led
and operated
by an academic institution, the University of Arizona. This was worrisome to an organization used to complete control.
¹
To make things more complex, a number of foreign universities would contribute instruments and expertise to the mission, including institutions in Canada, Germany, the United Kingdom, Finland, Denmark, and Switzerland. The result was a potpourri of scientific and technical input. It is important to note that while the University of Arizona operated the spacecraft, the navigation and landing were controlled by JPL in Pasadena.

The probe landed successfully in May 2008. It was the first lander to travel to the polar regions of any planet. And Phoenix was unusual in other ways. It was small in comparison to any other Mars lander except perhaps Pathfinder, weighing in at just under eight hundred pounds. About five feet across (eighteen feet with solar panels deployed), it was almost the same size as an individual Mars Exploration Rover and would look downright puny next to Viking. And after the bouncy-ball landings of Pathfinder and the Mars Exploration Rovers, Phoenix signaled a return to the rigors of
a powered descent, where rockets must handle the final moments of a soft, pinpoint landing. It was not a mission for the faint of heart, especially with the fifteen-minute delay from Earth to Mars for communication. At times, add an hour or two for the orbiting Mars-probe relay, and you have a real issues. Planning was key.

As a largely recycled spacecraft, Phoenix was a compromise mission. It was designed to be a low-cost attempt at a Mars lander (in this case, less than $500 million). This had a number of real impacts on the mission design. And the stakes were high, as this was one of the first planetary missions since the twin losses of Mars Climate Orbiter and Mars Polar Lander; JPL could not afford another failure. Perhaps for this reason, as much as any other, the design and control of the mission followed an unusual path.

While built by Lockheed Martin, Phoenix was designed by a consortium of academic and NASA/JPL personnel. The mission proposal originated from the University of Arizona, and parts of the spacecraft (notably the camera) were actually built there. An ad hoc mission-control center was also sited at the campus, looking more like a low-end software company than a deep-space mission-control room. Many of the staffing needs were met by hiring young and inexpensive talent; some were even fulfilled via the use of grad students. Not surprisingly, many of the key players were from the Mars Pathfinder mission, itself a departure from traditional JPL methods. This was not your father's Mars mission.

Even the software intended to run it was recycled from programming originally designed to operate a Mars
orbiter.
It had to be rewritten and repurposed for a lander, resulting in some last-minute sweat and angst as the software team tested and retested the command structure to make sure it would meet the demands of short-term surface operations. Much of it was left open-ended; changes and new instructions would be regularly uploaded from the University of Arizona controllers and JPL via the Deep Space Network. This recycling of existing software created many sleepless nights for the coding team.

As with previous missions, the processing power of the flight computer was not particularly robust by consumer standards. In fact, the flash memory was only one hundred megabytes; far below off-the-shelf flash drives that were offering over four gigabytes. But given the expense of flight-rated, radiation-hardened components, it was what the budget could support. As with many of JPL's spacecraft, the CPU was the venerable RAD 6000 chip manufactured by IBM, which had been extensively proven in spaceflight, having powered the computers of the Mars Exploration Rovers, Mars Pathfinder, and Mars Odyssey, among others. This was a proven design, and there were many available engineers and programmers who knew how to squeeze the maximum performance out of the chip. It ran at a nonblistering thirty-three megahertz and cost upward of $250,000. It was a far cry from the two-gigahertz Mac G5 available down the street for under $2,000.
²

The instrumentation on the Phoenix lander was a compromise of light weight, low cost, and high reliability. Deciding what to include was, as always, a study in creative compromise.

Paramount for a lander of this type and purpose was a robotic arm. Unlike Viking's spring-steel “wind-up” arm, it utilized a more traditional and simple hinged “elbow.” Designed to extend almost eight feet from the lander, it was capable of digging about eighteen inches deep. Besides a scoop, there was a drill-like rotating rasp for shaving ice samples (a true drill would be too heavy). A small camera was affixed to the end of the arm. As powered landings were still rare at the time (as opposed to the more passive beach-ball approach) another camera, the descent imager (complete with a microphone) was installed to transmit video of the landing. Unfortunately, at the last minute an electronic flaw prevented the use of the camera or microphone. Important data and a wonderful PR opportunity were lost.

The primary camera, the surface stereo imager (SSI), was similar in design to that on the top of Pathfinder's rover, Sojourner—largely
because it was built by the same team and had worked well on that mission. It would extend vertically on a mast from the lander.

To search for organics (precursors to life) in the soil, a set of small, high-temperature ovens called the Thermal and Evolved Gas Analyzer (TEGA) would use a spectroscope to analyze gasses baked out of soil samples. The TEGA consisted of eight tiny, one-use oven compartments, each about the size of a pen. The instrument would look for water, carbon dioxide, and organic elements such as methane. It shared a more-than-passing resemblance to the ovens found in the Viking lander thirty years previous.
³

Phoenix was packed with other instrumentation. The Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) device would examine soil particles on a microscopic level, using a so-called wet chemistry lab or WCL. The WCL had test chambers where purified water would be added to soil samples and sensors would measure ionic activity, looking for biological compatibility of the sample (by earthly standards). This would give some idea of how able the soil would be to harbor microbial life. This was an important distinction from the Viking missions: rather than searching for life, this would search for the ability to
support
life.

Also inside the MECA was the Thermal and Electrical Conductivity Probe (TECP). This would measure soil temperature, humidity, thermal (temperature) conductivity, electrical conductivity, and other properties of the soil fed to the MECA. An optical microscope was included to take pictures of these samples at an extreme magnification, using arrays of multicolored LEDs for different results under different colors of illumination. Each color would reveal different properties in the magnified samples. The final component of MECA was an atomic force microscope (AFM) that shared space with the optical microscope. Small silicon crystal tips would brush across the sample, measuring repulsion from the sampled soil to analyze its composition at the atomic scale.

Atop Phoenix, a meteorological station would provide
ground-level measurements of the Martian day and night. The technology used ranged from a simple telltale (not unlike a wind sock used at airports) to a highly innovative and complex LIDAR (laser-powered radar) that measured dust, ice particles, and moisture in the air. Of course, temperature, humidity, and air pressure were measured as well.

As always with a lander, the decision where to set down was a long and arduous process. The vastly improved images available from the Mars Reconnaissance Orbiter and Mars Odyssey helped a lot; rocks as small as twenty inches across could be seen now. This was a far cry from even the Pathfinder mission, when the landing zones were selected by a combination of medium-resolution imagery, intuition, and luck. And, to bolster confidence further, Phoenix had fourteen inches of ground clearance, as opposed to Viking's 8.5 inches. Nevertheless, the final selection would not be made until after Phoenix had left the launch pad.

Phoenix set down in an area called Green Valley in Vastitas Borealis (“Northern Waste”), not far from the north Martian pole, on May 25, 2008. It was the first successful powered landing since Viking 2 in 1976. This region was finally selected for smoothness and other safety considerations, and it was also where the largest concentration of water ice (besides the pole itself) had been found to date.

Among its first duties were to transmit data about its orientation and status back to JPL. As it turned out, things had gone as well as they could have dreamed; the lander was just about level. Next, the giant solar panels were unfolded to give the hungry batteries the power they needed. As quickly as possible, team members needed to establish how close they had gotten to their point of aim for the landing. When the result came in, they were astonished. They were right on target. The accuracy of the landing impressed people all the way to the top of the NASA food chain, one of whom characterized the feat as making a hole in one with a golf ball launched in Washington, DC, toward a moving target
in Australia. The pinpoint arrival was confirmed by an image snapped by the Mars Reconnaissance Orbiter, which spotted not only the lander but also the parachute resting nearby.

Soon it was time for the first look at the surrounding terrain—and what a delight that turned out to be. All around the lander were fascinating polygonal shapes etched into the permafrost. The cracks in the soil appeared to be fresh—older ones would have filled in or eroded away. This indicated ongoing changes within the soil, thawing and refreezing as the ambient temperatures swung from one extreme to another. Of course, this also highlighted the urgency of getting Phoenix's work started as quickly as possible, for these polygons were a stark reminder of temperature extremes what would kill a lander. Already, the onboard thermometers were beginning to measure temperatures that would range from -22°F to -122°F. And while Phoenix was designed to operate within this range, and colder, the specter of the advancing north polar winter, about three months away, weighed heavily on everyone involved. Phoenix would most likely not survive the long Martian polar night.

Then, just as things were getting interesting, Phoenix went silent. The link between the lander and the MRO orbiting overhead failed, plunging the mission into hours of tense data darkness. A day later, the issues had been ironed out, and the Mars Odyssey orbiter, still operating after almost a decade, was also pressed into relay service. But another snag occurred almost immediately. There was an excruciating delay while issues with the robotic arm were worked out. The low-cost approach to building and operating Phoenix seemed to be manifesting gremlins. Ultimately, the arm was unable to touch Martian soil until May 31, almost a week after touchdown.