Space Invaders
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By the end of January 2004, if all goes well, four spacecraft will be orbiting the Red Planet while three landers explore its surface. NASA's Mars Global Surveyor and Mars Odyssey spacecraft are, of course, already there. They will be joined by a Japanese orbiter named Nozomi, the Mars Express orbiter and Beagle 2 lander from Europe, and by NASA's twin Mars Exploration Rovers.
Nozomi carries a camera and numerous experiments designed to study the martian atmosphere and its interaction with the solar wind. For mission planners, Nozomi has been an exercise in patience. Launched in 1998 by Japan's Institute of Space and Aeronautical Science, it used the moon for two gravitational assists and was to swing past the Earth for another boost before heading to Mars. But the Earth assist failed to give Nozomi sufficient acceleration and maneuvers to correct its course left it short of fuel.
Mission planners opted to keep the probe in orbit for four more years so that they could use two additional gravity assists from Earth. On June 19, Nozomi passed within 6,800 miles (11,000 kilometers) of Earth, successfully completing its third and final gravity-assist maneuver.
The spacecraft's name, which means "hope" in Japanese, seems particularly apt. Last year, a solar flare damaged components of Nozomi's heating system, which warms the craft's supply of hydrazine fuel and keeps it from freezing. Although the fuel had thawed out prior to the final Earth flyby, Nozomi will need functioning heaters in December when it attempts to enter orbit around Mars. Engineers have been attempting to eliminate the crippling short in Nozomi's onboard electronics by powering the system on and off hundreds of times.
Nozomi's present course will take it to within 556 miles (894 kilometers) of the martian surface on December 14. Prodded by press reports that Nozomi was likely to impact Mars, the Japanese Aerospace Exploration Agency (JAXA) released a statement on November 20. "As you may know . . . Nozomi right now is under 'the last challenge' to repair its malfunction," the statement read. "Upon recovering from the damage, we will then work on putting the probe to orbit around Mars and resume its exploration."
JAXA stated that if Nozomi cannot be restored its engineers will try to steer the craft away from Mars. Increasing its closest approach distance would reduce the roughly one percent "theoretical possibility" that it would impact Mars.
 In December and January, three spacecraft will attempt landings
on the Red Planet: the ESA's Beagle 2, launched aboard Mars
Express, and NASA's twin Mars Exploration Rovers (Spirit and
Opportunity). The map above shows their currently assigned landing
sites. It also shows the positions of other probes that have
transmitted from the surface. (The Mars 3 lander, which made only a
20-second-long transmission, was the most successful of the Soviet
Union's numerous landing attempts.) |
Mars Express, the first planetary mission undertaken by the European Space Agency (ESA), lifted off from Baïkonur in Kazakhstan on June 2, 2003 at 17:45 GMT. About ninety minutes later, its engine fired and Mars Express began its interplantary journey. The orbiter is packed with science instruments, but the mission also includes a small lander named Beagle 2, after the ship in which Charles Darwin set sail on his voyage of discovery in 1831.
"It is exciting to think that Europe's first adventure to a planet will involve both orbiter and lander science," says Colin Pillinger, a professor of planetary science at Britain's Open University and head of the lander team. "With Beagle 2 we aim to provide ground truth for one site that will help maximize the return from the orbiter investigations."
Mars Express will release the briefcase-sized lander five days before arrival at Mars, in late December 2003. Following atmospheric entry and a parachute descent, airbags around Beagle 2 will inflate and the craft will bounce onto the surface. The target is a spot in eastern Isidis Planitia, a broad, relatively flat plain that covers the floor of an ancient impact basin. Numerous small impact craters, chains of pitted ridges, and a variety of light-toned ripples and small dunes form the local terrain. Once at rest, the airbags will deflate and the lander's circular cover will pop open, exposing solar panels and a suite of science instruments. The lander's goal is an ambitious one: to determine if life ever existed on the Red Planet.
Beagle 2 begins work at Isidis Planitia. ESA image. |
Beagle 2 will drill into promising rocks and bore beneath the surface for soil samples, thereby avoiding the effects of oxidation and ultraviolet radiation. The samples will be heated to evolve gases that can be analyzed in an onboard geochemical laboratory. Living organisms on Earth concentrate carbon-12 in their tissues, so finding organic compounds unusually rich in this isotope, scientists say, will indicate the presence of life at some point in the history of the landing site.
Meanwhile, Mars Express will carry on its mission far above the planet. Experiments will examine the planet's mineral composition and attempt to determine why the martian surface is so oxidizing. A radar instrument will ping the planet in an effort to locate subsurface water.
But for nonscientists, the camera system is the most exciting component. Mission planners expect to capture the most accurate and detailed images of Mars yet seen from orbit. Mars Express will map the entire planet in full color -- and in stereo -- at resolutions between thirty and ninety feet. Although cameras on other spacecraft have imaged small areas at high resolution, or large areas at low resolution, the fact that each image set was acquired separately means that scientists cannot pinpoint the location of the most detailed images to better than a few miles.
Not so for Mars Express. Even as the camera system images in its normal mode, it can simultaneously operate in a "super resolution" channel capable of detecting objects as small as six feet across. In fact, say planners, it should be able to pick out Beagle 2 on the surface. Because the most detailed pictures will be contained within a swath of lower resolution images taken at the same time, scientists will know the exact location of the most detailed pictures.
NASA returns to Mars with a pair of Mars Exploration Rovers named Spirit and Opportunity. Spirit lifted off from Cape Canaveral Air Force Station at 1:58 p.m. Eastern Daylight Time (EDT) on June 10 and, after several launch delays, Opportunity followed it with liftoff at 11:18 p.m. EDT on July 7. The mission seeks geological evidence for the planet's climate history -- and in particular the role of liquid water -- at two martian sites where conditions may once have been favorable to life.
After studying more than 150 candidate locations, NASA announced the landing site for each rover earlier this month. Spirit is targeted to land at Gusev Crater, an impact structure that appears to have once held a substantial amount of liquid water. Opportunity will explore Meridiani Planum, an area halfway around the planet from Gusev that bears deposits of an iron oxide mineral called gray hematite. Both sites lie near the planet's equator. "These two landing sites have been studied more than anywhere else on Mars," said MER program scientist Cathy Weitz.
"Meridiani and Gusev both show powerful evidence of past liquid water, but in very different ways," said Steve Squyres, one of the mission scientists and a geologist at Cornell University. "Meridiani has a chemical signature of past water. Gray hematite is usually, but not always, produced in an environment where there is liquid water. At Gusev, you've got a big hole in the ground with a dry riverbed going right into it. There had to have been a lake in Gusev Crater at some point," he said. "They are fabulous sites, and they complement each other because they're so different."
Mars Exploration Rover 1 searches for signs of water at Gusev Crater. NASA image. |
Like Beagle 2 and the 1997 Mars Pathfinder mission, each MER rover will make its final descent to the surface surrounded by inflated airbags. The spacecraft will bounce at least a dozen times and may roll up to half a mile. When it stops, the airbags will deflate, retract, and petals on the spacecraft will open to reveal the rover. Immediately after landing, the rover will make panoramic color and infrared images of the landing site. It will then drive off the petal structure to begin its exploration.
When fully deployed, the rovers measure more than seven feet across and almost five feet high. Each rover carries a set of science instruments and a rock abrasion tool, which will grind away dusty or weathered surfaces to expose fresh rock for study. A robotic arm carries the abrasion tool, a microscopic imager for close-up views of target rocks, and a trio of spectrometers for determining rock composition.
"The clues are in the rocks, but you can't go to every rock, so you split the job into two pieces," Squyres says. First, a stereo panoramic camera at human-eye height and a miniature infrared spectrometer help scientists identify the most interesting rocks. Cameras also help the rovers watch for hazards as they drive to the selected rock.
Upon arrival, the rover extends its arm. Then, a microscopic imager, like a geologist's magnifying glass, takes a close-up look at the rock's texture. Two spectrometers identify the composition of the rock. And a fourth tool substitutes for a geologist's hammer, scraping away the rock's weathered surface layer to expose its interior.
In one martian day, each rover can travel up to 40 meters (130 feet), or nearly the distance covered by Pathfinder's Sojourner rover during its entire lifetime. Each six-wheeled robot generates power through a kitchen-table-sized deck of solar panels. Engineers believe that dust collecting on those solar panels will grow thick enough in about ninety days to end surface operations.
Mars 2003:
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