We've already seen water ice on Mars. NASA's Phoenix lander will reach out and touch it.
- By Charles Petit
- Air & Space magazine, August 2007
THE SQUARE, EARTH-TONE industrial building on North Sixth Avenue in Tucson, Arizona, has little of the proud, high-tech gloss of NASA’s Jet Propulsion Laboratory, traditional home of U.S. Mars missions. The historic NASA center in Pasadena, California, has neatly clipped lawns and squadrons of badge-wearing engineers and scientists, who work each day surrounded by memorabilia from decades of solar system exploration. Everything about the place fairly shouts Space science is our business.
But around this building in Tucson’s commercial flatland, the ambience is quite different: There’s a car repair shop, a day care center, a small dinosaur museum, and the hum of passing traffic. The main clue that something unusual is going on is the exuberant yellow and orange mural painted along one of the building’s broad sides. The work of art students from the University of Arizona and local high schools, it depicts a fiery trail from Earth to Mars, along which travel a chariot, a bird with flames for feathers, and an interplanetary robot.
A small sign near the entrance tells visitors that this is the home of Mars Phoenix, which happens to be the only mission bound for the Red Planet this year. NASA will launch the spacecraft in August and guide it to a landing on the Martian surface in May 2008. Once it arrives, though, day-to-day operations will be run out of this building, near the university campus. It’s a new model of doing business for a new generation of smaller, leaner, more innovative Mars Scout missions.
NASA sees these missions as a way to encourage fresh thinking: Ideas for Mars missions are proposed by scientists working outside the space agency rather than by staff scientists within. The Scouts augment bigger and more expensive missions like the Spirit and Opportunity rovers, which have been exploring the planet since 2004. The cost of the Mars Phoenix, about $400 million, is roughly half that of a typical NASA mission to Mars.
The Phoenix team seems to like the low-budget arrangement just fine. “The advantage of the Scout mission concept is that the whole thing is determined by the scientists who are working on it,” says Peter Smith, the mission’s tall, plain-spoken principal investigator. “The usual NASA strategy is to have a spacecraft with some general goals, and then scientists propose instruments for it. You get committees and overlaps and competing personalities.” The Scout teams are smaller and more collegial. The 25 co-investigators under Smith (compare that to 57 on the rover team) are a disparate bunch: eight from U.S. universities, nine from NASA centers, four from private contractors, and four from institutes in Britain, Germany, and Switzerland.
Together, they hope to take the next step in understanding a world that has become a familiar destination for planetary robots. For at least a decade, the mantra for NASA’s Mars exploration program has been “Follow the water.” If Martian life ever existed, the logic goes, the evidence would most likely be found in a zone marked by the presence of water. The current rovers have therefore spent more than three years examining rocks formed under wet conditions long in the past.
The Phoenix mission comes about as close to a single-minded search for water as anything NASA has done so far. While the Spirit and Opportunity rovers have done a good job of tracing the history of water, scientists hope that Phoenix will be the first spacecraft to directly sample it. “Everybody talks about water [on Mars], water signatures, water this and water that,” says Smith. “But they’ve never seen any.” Nor will Phoenix, at least not in liquid form. Scientists would be astonished to find running water on the Martian surface today—it’s far too cold. Water ice, though, is very likely to be found where Phoenix will touch down.
The lander will head straight for the Martian arctic and the broad belt of permafrost surrounding the planet’s north polar cap. Next May, if all goes according to plan, Mars Phoenix will bore into the atmosphere near the north pole at 12,600 mph. A heat shield, then a parachute, then a set of landing jets will reduce the craft’s speed until finally the 800-pound lander thumps down on three legs at about 5 mph. As with any planetary lander, this will be a harrowing time for the Phoenix team. “Seven minutes of hell” is how NASA project manager Barry Goldstein, who’ll be at JPL during the mission, describes it.
Once Phoenix is on the ground, two circular solar panels will extend from its sides and open like Chinese fans to provide power. A column of delicate tubing will rise like a stalk, with a stereo camera on top for panoramic photography. From the lander’s flat deck will extend a robotic arm equipped with small cameras, microscopes, and, most important, a shovel and small electric grinder—the same kind used for sculpting ice. Articulated like a backhoe, the arm can in principle dig a trench about two feet deep, at least in soft ground. The whirring grinder is designed to break frozen ground into manageable bits for the shovel to scrape up. Nobody expects the grinder to penetrate more than a fraction of an inch into the permafrost, which will be deep-frozen to about –130 degrees Fahrenheit.
Mission scientists believe the lander will find ice mixed with the soil just below the dusty surface. And some researchers, like Ray Arvidson of Washington University in St. Louis, a co-investigator with the robotic arm science team, expect to see, on close inspection, patches of hard, blue ice peeking through.
All previous Mars landing missions have been dusty affairs. This could be the first one to make mud. After the arm collects the frozen samples, they’ll be placed in miniature ovens and heated for study. A suite of instruments (see “Land, Look, Dig, Cook,” p. 55) will inspect the soil and meltwater for organic molecules and other signs of biochemical activity. Ratios of hydrogen and deuterium (an isotope of hydrogen) should tell scientists whether the ice in the permafrost came from ancient groundwater or fell as rain. Meanwhile, a meteorology package provided by Canada will take weather readings; the pressure gauge comes from Finland, the wind sensor from Denmark. Phoenix’s cameras will inspect the shallow trench dug by the arm, looking for layering or variations in chemistry that would indicate whether liquid water existed at the site. The planet’s orbit and axial tilt change in cycles lasting tens of thousands to millions of years. That means there may have been epochs with warmer summers during which water persisted on or near the surface within the past 100,000 years. Phoenix will help scientists piece together that story.
The “nominal” mission—the length of time needed to achieve the major scientific goals—is three months. That’s how long the sun will stay high enough for the spacecraft to produce sufficient electrical power to run its robotic arm and shovel. Plans are to go through seven digging cycles, each lasting about eight Martian days, or sols (a Martian day is 37 minutes longer than an Earth day). By December, as the sun drops too low to keep the batteries charged, the spacecraft should begin dying. By the time the sun rises again in the Martian spring, the craft “may be buried up to its deck in carbon dioxide snow,” or perhaps frost, Smith says.
At the tucson operations center last November, things were fairly quiet. The spacecraft itself was still in a clean room at the Lockheed Martin Space Systems plant in Littleton, Colorado, where it was built. Here in Tucson a young engineer, Lori Harrison, was attaching a set of instruments called TEGA, for Thermal Evolved Gas Analyzer, to a full-size engineering test version of the lander sitting on a simulated Martian landscape. Better to discover any glitches with the instruments’ operation now instead of next year on the surface of Mars.
Smith showed me into a room equipped with computer consoles where data from the mission will be analyzed. Spread on a large table were glossy photos, blown up to the size of hall carpets, showing the Phoenix team’s first choice for a landing zone. They came courtesy of another NASA spacecraft, the Mars Reconnaissance Orbiter, whose most powerful camera, called HiRISE, was also built at the University of Arizona.
Smith is a Tucson native and has spent most of his career at this school, which has one of the best planetary science departments in the world. He led the team that built the camera for the Mars Pathfinder lander, which, with its little rover Sojourner, kicked off the modern era of Martian exploration in 1997. Since then Smith has had a hand in HiRISE and other Mars cameras developed at Arizona. He also was a co-investigator for the descent camera on the European Huygens probe, which in January 2005 returned broad panoramas of the surface of Saturn’s haze-shrouded moon Titan (see “219 Minutes on Titan,” Oct./Nov. 2005).
Not all his memories are happy. In 1999, Smith sat tensely watching monitors at JPL as the Mars Polar Lander, whose stereo lander camera his group had built, entered the atmosphere in preparation for a touchdown near the planet’s south polar icecap. It was never heard from again. “We just sat and sat, and it got quieter and quieter,” Smith recalled. Engineers later discovered a flaw in the spacecraft’s software that shut off the craft’s landing rocket, causing it to go into a free-fall high above the surface. Four years later, a British lander named Beagle also vanished on arrival—one of Smith’s devices was on that one too. “Getting to Mars is difficult,” he says slowly, leaning forward in his chair. “About 50 percent of the missions fail.”
That’s one reason the Phoenix team spent so much time scouting landing sites. The HiRISE pictures on the table show an essentially flat landscape with a pattern of cracks resembling polygons—in many places, polygons within polygons. It’s the kind of terrain seen in Earth’s polar permafrost, which is saturated with (frozen) water. Smith explained that the pattern, which repeats itself for thousands of miles at the northern latitudes where Phoenix will touch down, results from the expansion and contraction of ice.
There was something else in the pictures. Speckled on the polygons were irregular blobs. They looked pretty, like pebbles with a bluish sheen. Those, Smith explained, were boulders. How big? He compared them to the size of SUVs, like the ones in the parking lot outside. The boulders weren’t packed in; the density was more like a stadium parking lot an hour after the game ends. But there were still enough to pose a danger. “You land on one of those, it’s over,” Smith says.
That’s why, after much discussion, the Phoenix team abandoned their first-choice landing site and looked in other places, including a region north of a collapsed volcano called Alba Patera, the broadest mountain on the planet. One promising site—the current top pick for a landing zone—was dubbed Green Valley because the computerized maps were coded by boulder density, and green has the fewest boulders. By comparing the detailed HiRISE images to wider-angle infrared images taken from another orbiter, the scientists found that rocky terrain appeared warmer in infrared images taken in the morning (a boulder’s surface holds heat longer than sandy soil does). That helped speed up the process of scouting landing sites, since the infrared images cover larger areas of ground. The target landing zone is about 100 by 30 miles—the smallest footprint for which the scientists can accurately predict the spacecraft’s aim.
The name Phoenix comes from the mythical bird that periodically dies in fire, then arises reborn from the ashes. It’s an appropriate metaphor for this mission, some of whose parts originated with another spacecraft that died before reaching its goal. Phoenix’s Surface Stereoscopic Imager and the ovens for soil analysis are close copies of gadgets on the Mars Polar Lander, the spacecraft that crashed in 1999. The loss of that lander, which came during a nightmarish stretch of Mars program failures, led NASA to cancel another mission, the 2001 Mars Surveyor Lander, and stash its hardware, which had already been built, in a cold-storage clean room in Colorado. The basic structure of Phoenix, including its robotic arm, the camera on the arm, and the chemistry lab on the main deck, was recycled from the 2001 lander. That spacecraft was to have touched down near the equator in dusty soil. To accommodate the switch to hard permafrost, the Phoenix team put stronger bearings in the robotic arm joints, added the ice-cutting rasp, and beefed up the drive motors.
Thinking back to the failed 1999 mission, Smith is amazed at how close to the wire that project was run. “We literally did not have enough time in those days to track down the reason for every anomaly we might have found during testing,” he says. Those were the days of “faster, better, cheaper,” a speed-it-up, keep-it-cheap philosophy espoused by NASA’s then-administrator Dan Goldin. The 1990s saw a dramatic increase in the rate of space science missions, but even Goldin admitted later that he pushed the agency’s workers and contractors too hard. When the low-cost Scout program was proposed, NASA agreed that the scope of the missions would also be scaled back; scientists and engineers wouldn’t be forced to do more with less.
Phoenix originated with a phone call in early 2002. Chris McKay, a planetary scientist at NASA’s Ames Research Center in California, called Smith to say, “Hey, let’s do something with the Surveyor lander.” NASA was inviting ideas for the first Scout, due to fly in 2007, and McKay and some of his colleagues at Ames had already been studying, with NASA money, ways to take the hardware from the canceled mission out of storage. “The word on the street was that headquarters would never let the 2001 lander fly,” McKay recalls. “Not just ‘No’ but ‘Hell no.’ ”
So, as a way to keep costs down, the scientists adapted the unused lander for their Scout proposal, with the idea that they’d use the equipment to do a detailed analysis of some patch of Martian soil. There was one small problem. “We didn’t know where to go,” Smith says. “We’d have a shovel, a bunch of instruments, and a pretty good general-purpose lab. We just didn’t know where to land it.”
Like an answer to a prayer, another NASA mission provided a solution. The Mars Odyssey entered orbit around Mars just as the space agency was getting ready to decide which Scout mission proposals to fund for further study. Measurements of hydrogen by Odyssey’s gamma-ray spectrometer strongly suggested that at both polar regions, shallow ice exists at or near the surface. Planners would select a launch window for the 2007 mission that would enable the craft to land on Mars during northern spring and summer, when the days would be longest. And because it included instruments from the 2001 spacecraft, Phoenix would have more capabilities than the 1999 lander, and be more economical. Smith, in essence, was asking for a second chance at the mission that broke his heart.
In August 2003, NASA selected Phoenix as its inaugural Scout mission. Smith’s proposal beat two dozen others, including one that would have returned samples of the Martian atmosphere to Earth. Mike Meyer, the senior scientist for NASA’s Mars exploration program, is all in favor of resurrecting the goals of an approved but never-realized mission: “Mars Polar Lander was built for a very good reason, and Phoenix recaptures many of its advantages,” he says. “It should give us a very good idea what that ice is made of, and also what the seasonality of Mars is and how that fits into long-term orbital cycles and climate change.” That information, combined with remote sensing data from other spacecraft, could help scientists plan future Mars missions by suggesting regions where water is likely to have flowed in the past.
It hasn’t been all smooth sailing since the NASA selection. The space agency has become more cost-conscious than ever, and if a Scout spacecraft can’t be built properly within the approved budget, says Smith, it either gets scrapped or is scaled back to match the available funds. Despite the team’s best efforts, it ran its budget dry. Into the discard heap went a radio transmitter, called the X-band antenna, which would have enabled Phoenix to transmit data directly to Earth. Now the only means of communication will be through the two spacecraft already circling the planet, the Mars Odyssey and the Mars Reconnaissance Orbiter, which will act as relays. The 1999 failures taught NASA one important lesson, however. Phoenix will continue transmitting data and reports on its condition all the way from atmospheric entry to touchdown. If something goes wrong during descent, mission managers will at least know what happened. Losing a spacecraft is bad enough, says Smith; never finding out why “is just horrible.”
Late last year the project team let NASA know it was having money trouble. The biggest headache had been the landing radar, or altimeter. The original unit was inherited from the stored 2001 lander. Adapted from an altimeter used on F-16 fighters, “it was old when they put it in,” Smith says. “The Air Force doesn’t use this one anymore. We couldn’t even get parts, and the guys who knew it best had retired.” Tests revealed its performance was erratic, making data dropouts at critical times possible. The engineers spent months, with Lockheed doing much of the work, making a reliable altimeter.
The project’s budget had included a reserve fund for just these kinds of unexpected problems. Even so, the extra altimeter work, combined with fixes for other glitches and the late scramble to find a safe landing zone, put Phoenix tens of millions of dollars over the $386 million cap NASA had set for the mission. The team had been warned that a cost overrun would set off a formal NASA termination review. One was held in late January. After Phoenix passed, Smith said it had been unlikely all along that NASA would actually cancel a mission so close to launch. But he did tell a Rocky Mountain News reporter that watching the bills run up had kept him in agony for months.
Even with the overrun, if Phoenix continues the Mars program’s current string of successes, NASA will likely consider its money well spent. Since the 1999 loss of the Mars Polar Lander, the news has been all good: Mars Odyssey (launched in 2001 to further the study of Martian geology and weather), the twin rovers, and the Mars Reconnaissance Orbiter (launched in 2005) all arrived safe and sound, and all four are still working. The orbiters are busily mapping the composition of the atmosphere and the surface, as well as using ground-penetrating radar to explore the subsurface. The Mars Express, a European orbiter with a suite of powerful cameras and other sensors, has performed flawlessly. The Spirit and Opportunity rovers have delighted their operators by running well into their third year and traveling a combined total of more than 11 miles.
If Phoenix does find traces of organic materials and conditions suitable for life, or if it just helps scientists understand how water cycles between the ground and the atmosphere, it will shape the scientific questions to be answered by subsequent Mars missions. Favorable launch windows (meaning those that require the least amount of rocket fuel to reach the planet) come around every 26 months, and NASA tries to hit every window. Next up after Phoenix is a long-range rover called the Mars Science Laboratory, which in 2009 will carry an even more advanced organic chemistry lab to extend the search for life. Another Scout mission, still to be selected, is slated for the following opportunity, in 2011. Beyond that, things become uncertain. NASA’s Mars program has gotten leaner in recent years as the agency has shifted money from space science into preparations to send astronauts back to the moon. A Mars sample-return mission, once the program’s highest priority, has been pushed off into an indefinite future.
Most scientists believe such a mission will eventually be necessary, not only to answer questions about the possibility of Martian life but to help engineers prepare for an astronaut landing. There is some evidence that the soil may be toxic or corrosive, and NASA would want to carefully analyze it before designing spacesuits and other equipment for human explorers.
Until then, look for more Scouts like Phoenix to fill the gaps between the big, expensive missions and to pioneer a new approach to the continuing exploration of the second most visited planet in the solar system.
Click here to read about the novel landing systems designed for this Mars mission and others to come.