WASHINGTON - NASA, still recovering from back-to-back Mars mission failures last year, plans to double up on a 2003 landing expedition by sending a pair of wheeled robots to search for evidence of water on the Red Planet.
Two spacecraft, each carrying identical roving robots, will be launched in 2003 and then bounce, 18 days apart in January 2004, to beach ball-like landings on Mar, agency officials said Thursday.
Sending two spacecraft, officials said, will double the chances of success and shed more light on fundamental questions about Mars and the possibility the planet once harbored life.
Two separate Mars exploration craft, including a lander, failed last year, forcing a reorganization of NASA's Martian program.
The National Aeronautics and Space Administration already had planned to send one robot explorer. But Edward Weiler, head of NASA's office of space science, said that ''celestial mechanics'' - an unusual alignment of Mars and the Earth in 2003 - made a second mission an attractive and economical option.
''If you have an opportunity for surface science on Mars, then maybe it is a good idea to do two landers,'' Weiler said at a news conference.
Weiler said that in the wake of last year's failures, NASA has added some new managerial positions and plans to provide more funds for testing and to solve any problems. For this reason, he said, the new Mars missions will be ''slightly more expensive'' than before the reorganization.
Even so, said Scott Hubbard, NASA's Mars program director, the two missions are a bargain in the field of planetary exploration.
While final figures are being calculated, Hubbard estimated that building, launching and operating the first rover is expected to cost $350 million to $400 million. An identical second mission, which benefits from economies in testing and development, adds about $200 million.
Jim Garvin, Mars program scientist, said that both of the sophisticated mobile robots will be able to act as mechanical geologists, examining and even breaking open rocks to search for clues to Mars' history. Instruments will analyze the rock chemistry and a microscopic camera will send close up images back to Earth.
All of this is centered on NASA's Martian exploration theme of ''follow the water,'' Garvin said.
Data from earlier Mars explorations suggest that Mars once had oceans, rivers and lakes. Recent studies of pictures from a satellite orbiting Mars even suggests there may still be water just beneath surface. Experts say that learning the water history is key to the possibility that life, in some form, once existed on Mars and could still.
''One of the engaging mysteries is what happened to the water?'' Garvin said.
Steven Squyres, a Cornell University professor and the principal scientist for the robot missions, said that the Mars 2003 rovers each will weigh about 300 pounds. They will have six wheels that will run by solar-charged electrical power. Each will communicate independently with Earth, using a pop-up dish antenna.
Pictures collected by the rovers will be relayed immediately to a Web site.
''You'll be able to see what we see,'' said Squyres. ''You'll see a rover's eyeview'' of Mars.
The robots are expected to operate for at least 90 days each. They are expected to have enough electrical power to roam about 110 yards during each of the Martian days (24 hours, 37 minutes).
Squyres said the robots will have 20/20 color vision from 10 cameras on board each vehicle. One camera will be used for navigation and will be linked to an onboard computer that will let the rovers look ahead and plot a wheeled course to specific destinations. It is so intelligent, he said, that it will avoid obstacles and try alternate paths without being told.
A single arm on the rover will contain a tool that can break open rocks and a camera that gives microscopic views of grain-sized specimens.
The rovers will be launched separately from Cape Canaveral Air Force Station in Florida by Delta 2 rockets. The first is scheduled for May 22, 2003 and the second on June 4. The launch dates are dictated by a favorable alignment with Mars that will not be repeated for six years, Weiler said.
After a trip of 7 1/2 months, the robots will reach Mars 18 days apart. They will fall through the Mars atmosphere, protected by heat shields. At seven miles above the surface, parachutes will deploy and lower the craft to 1,000 feet.
At that point, air bags surrounding the robots will inflate and the spacecraft will drop to the surface.
''It will bounce and roll for maybe a half mile,'' said Hubbard.
The air bags will deflate and the rovers will roll off on their own.
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On the Net:
Mars 2003 site: http://www.jpl.nasa.gov/facts/mars03rover.pdf