NASA's next Mars orbiter arrives at planet Thursday
Artist's conception of the Mars climate orbiter
September 20, 1999
Web posted at: 4:26 p.m. EDT (2026 GMT)
By Robin Lloyd
CNN Interactive Senior Writer
(CNN) -- A key event in NASA's first effort to look directly for water on Mars will come Thursday when a spacecraft enters the red planet's orbit to ready itself for contact with two upcoming lander missions.
Ending a 286-day journey, Mars Climate Orbiter is set to start firing its engine at 5:01 a.m. for 16 minutes, positioning itself to be captured by Mars' gravity and pulled into its orbit.
An 80-member flight and operations team has rehearsed the maneuver several times since May and feels positive that everything will work "straight up," said flight manager Sam Thurman.
But it will be a relief when the first digital data reaches NASA's Jet Propulsion Laboratory, which is managing the mission, and confirms that the spacecraft is healthy and orbiting Mars, he said.
"The big risk is that the engine won't fire," he said. "If it doesn't, the spacecraft will go sailing by and we missed."
The 629 kg (1,387 pounds) spacecraft must turn away from Earth to orient itself correctly, so engineers will only hear a "carrier tone" during the burn. They will lack definitive data that all is well until about 30 minutes later, when the spacecraft pulls out from behind Mars.
The plan is to have Mars Climate Orbiter ready to relay signals from the martian surface on December 3 when its partner spacecraft -- Mars Polar Lander -- touches down on the red planet. That mission will use a robotic arm to dig for water ice in the martian soil and conduct other science experiments.
Mars Polar Lander
Together, the missions cost $327.6 million. They're aimed at understanding Mars' history and the potential for life in its past and elsewhere in the universe. Climate Orbiter also is expected to relay signals for another Mars lander mission set for launch in 2001.
Engineers sent computer commands last week for Climate Orbiter's burn and other Thursday morning events.
"It's been marching along on its own all weekend long and we aren't going to do anything more to the spacecraft unless, in the very unlikely event that something goes wrong," Thurman said.
A short break before aerobraking
Within four days of its arrival at Mars, the spacecraft will trim its orbit to make it more circular by grazing the planet's atmosphere. This process, called aerobraking, was first tested by Mars Global Surveyor, an orbiter that started mapping the red planet last spring.
"This is a pretty aggressive mission," Thurman said. "We don't have much time to sit around and be happy about what's done."
Climate Orbiter initially will take 13 hours to circle Mars, but after 44 days of aerobraking that figure will drop to two hours. The orbiter's final path will be about 400 km (270 miles) above the surface.
Aerobraking went well for Mars Global Surveyor, although it had to be suspended and resumed at a slower pace to protect one of the craft's solar panels. A hinge connecting the panel to the spacecraft was damaged during launch and engineers saw signs that it was weakening initially during aerobraking.
With the experience gained on the Surveyor mission, mission managers decided to push Mars Climate Orbiter earlier into aerobraking. The newer craft's solar array, which extends about 18 feet, is performing fine, Thurman said.
The Mars flight team at Jet Propulsion Laboratory is busy overseeing three spacecraft -- Mars Global Surveyor's ongoing mapping operations, Mars Polar Lander's current trip to the red planet and the Climate Orbiter.
Relay and science
Throughout the Mars Polar Lander mission in December, the orbiter will dedicate itself to relaying messages from the lander to Earth.
It will serve the same purpose in two years when another lander is set to touch down to explore the martian surface with a rover. Engineers designed Climate Orbiter for longevity -- it has to last through the end of the second lander mission in December 2004.
But Climate Orbiter will do some science of its own in the interim, using a camera to track Mars' atmosphere and an infrared radiometer to measure the atmosphere's temperature, pressure and contents -- water vapor, dust, carbon dioxide.
Overall, the orbiter will study Mars' weather patterns for a martian year -- about two Earth years.
Should there be any trouble with Mars Climate Orbiter, a "fully viable" science mission is possible with the Polar Lander on its own, Thurman said.
It has its own radio communication system for "talking" with Earth, although it is less sophisticated than the relay system with the orbiter.
The '01 lander, however, will need an orbiter to function. The plan is tfor the lander to work in tandem with its own orbiter, scheduled to launch in March 2001. If that orbiter fails, the Climate Orbiter could serve as a backup.
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Mars Climate Orbiter
Mars Global Surveyor
Mars Meteorite Home Page (JPL)
Fossil Record of the Cyanobacteria
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