Tuesday, December 11, 2007
It has been 35 years since humans last walked on the moon, but there has been much recent discussion about returning, either for exploration or to stage a mission to Mars. However, there are concerns about potential radiation danger for astronauts during long missions on the lunar surface.
A significant part of that danger results from solar storms, which can shoot particles from the sun to Earth at nearly the speed of light and can heat oxygen in the Earth's ionosphere and send it in a hazardous stream toward the moon.
Earth is largely protected by its magnetic field, or magnetosphere, but new University of Washington research shows that some parts of the moon also are protected by the magnetosphere for seven days during the 28-day orbit around Earth.
"We found that there were areas of the moon that would be completely protected by the magnetosphere and other areas that are not protected at all," said Erika Harnett, a UW assistant research professor of Earth and space sciences.
Solar energetic particles, which are generated during solar storms, carry enough energy to disrupt communications on Earth or even kill satellites in Earth orbit. During those same storms, particles from Earth's ionosphere, primarily oxygen, also can become significantly energized. Though they are not as powerful as solar energetic particles, they still pose a significant threat to astronauts working on the moon, or even en route to Mars.
Using computers to model properties of the magnetosphere, Harnett found that while solar storms can increase the danger from ionosphere particles hitting the moon they also trigger conditions in the magnetosphere that deflect many hazardous solar particles.
Particles with high enough energy can pass directly through a human without much damage, Harnett said, but particles packing slightly less oomph, though unfelt by a human, can lodge in a person. Typically it's not just one particle but many, and the accompanying radiation can damage cells, she said.
Some of the research is detailed in a poster being presented at the American Geophysical Union annual meeting in San Francisco, while other aspects are in a paper published last month in the online edition of Geophysical Research Letters. Robert Winglee, a UW Earth and space sciences professor, is co-author of the work, which was funded by the National Science Foundation and NASA.
In the longest missions of NASA's Apollo Program, astronauts spent just a few days on the moon. The last mission, Apollo 17, was launched Dec. 7, 1972, landed on the moon on Dec. 11 and arrived back on Earth on Dec. 19.
"During Apollo, people were not on the moon for very long so there wasn't the concern about the radiation hazard to humans as there is with longer missions," Harnett said.
Today there is much greater understanding of the danger posed by solar energetic particles, particularly because of the adverse effects they can have on satellite communications during periods of intense solar flare activity.
"The problem is that we can't predict when this activity is going to take place so we can't warn astronauts to take shelter, so they could be vulnerable when the moon is outside the magnetosphere," Harnett said. "The particles travel near the speed of light, so when we see them generated on the sun's surface they will arrive in a few minutes and there is little time to react."
The new research could help determine when it is safe for astronauts to work far from a lunar base, she said. But she added that models used in the work suggest that energetic oxygen from Earth's ionosphere also poses a danger, even though it is less energetic than solar particles.
"It wouldn't kill someone instantly, but it definitely could increase the radiation exposure for an astronaut on the moon," Harnett said.
However, she noted that the danger from energetic oxygen could be overstated because the models do not take into account the positive electrical charge on the daylight side of the moon that likely would significantly slow the oxygen stream
Posted by SANJIDA AFROJ at 9:55 PM
The Mars rover Spirit is racing against time to reach a resting spot for the winter after a giant dust storm drained much of its energy,
Scientists Worry About Power on Spirit.
The Mars rover Spirit is racing against time to reach a resting spot for the winter after a giant dust storm drained much of its energy, scientists said Monday. Spirit has until Christmas to drive to the sunny slope of a low plateau where it will park itself with its solar panels pointed at the sun and hunker down for the winter.
The trek is difficult because the rover needs one day to recharge after every day it moves. That means ground controllers on Earth have seven opportunities to direct the robot into position for it to have a chance to survive.
"It's scramble right now because we're losing sunlight," said rover project manager John Callas of NASA's Jet Propulsion Laboratory, which manages the mission.
Spirit's situation was detailed during an American Geophysical Union meeting in San Francisco.
Spirit and its twin rover Opportunity faced their biggest challenge yet this summer when a series of dust devils blanketed their solar panels and limited their movement. Winds managed to clean off Opportunity, but Spirit is still covered in gunk and working at 42 percent capacity.
Callas predicted further dust accumulation could cause Spirit's solar array performance to drop to 30 percent by the winter.
By contrast, the rover was operating at 70 percent capacity during its first Martian winter and 50 percent last year. That likely means Spirit will be stationary for more than seven months to conserve energy.
In October, NASA extended the rovers' mission for the fifth time since the machines landed on opposite sides of the planet in 2004.
Spirit has been exploring a plateau called Home Plate where it discovered silica-rich soil earlier this year. Meanwhile, Opportunity is analyzing exposed rock layers inside a giant crater near the equator.
The silica likely came from an ancient hot spring or fumarole and represents the best evidence yet of a past habitable environment, said principal investigator Steve Squyres of Cornell University.
Posted by SANJIDA AFROJ at 8:00 PM
Etisalat is the second-largest publicly traded Arab telecom firm with operations in 16 countries.
Etisalat buys into Indonesian telecoms sector
UAE operator Etisalat said it would buy a 16% of PT Excelcomindo Pratama for $438 million to enter Indonesia, the world's fourth most populous country.
Etisalat will buy 1.13 billion shares in Indonesia's third-largest telecoms firm from Rajawali Group in a deal that could close as early as this month, the operator said in a statement.
Excelcomindo is a 67% owned unit of Telecom Malaysia, whose third-quarter profit jumped 37.5% largely driven by growth in its home market and Indonesia.
Etisalat, the second-largest publicly traded Arab telecom firm with operations in 16 countries including Pakistan, said it wanted to gain exposure to the fast-growing telecoms market in Indonesia, home to 226 million people.
"This investment represents an important step for Etisalat's international expansion strategy into Asia," Etisalat chairman Mohammad Omran said in a statement.
Excelcomindo expected to have up to 14 million mobile phone users in Indonesia by the end of the year, up from 10.5 million at the end of July, its president said in September.
The company has 13 million subscribers and market share of 14% at the end of September, Etisalat said.
Indonesia's telecoms sector has attracted several new entrants. Telekom Malaysia said in April it had bought 7.4% of Excelcomindo, raising its stake in the Jakarta-based operator to 67%.
Khazanah Nasional Berhad, an investment arm of the government of Malaysia, owns 16.8% in Excelcomindo.
Etisalat will be able to nominate one member to Excelcom's board, it said.
Posted by SANJIDA AFROJ at 7:54 PM