嫦娥二号的火星新使命：Chang'e 2 To Lay Groundwork For Mars Missions

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Chang'e 2 To Lay Groundwork For Mars Missions

Jun 10, 2011

By Bradley Perrett
Beijing

Smashed to smithereens, a return to Earth orbit for retirement, or a voyage into deep space—those are the alternative fates that have awaited the Chinese lunar probe Chang’e 2 since its launch last October.

Now the decision has been made: Chang’e 2 will go to the second Sun-Earth Lagrangian point this month, laying the groundwork for Martian missions.

The opportunity to send Chang’e 2 far from Earth has resulted from the good condition of the spacecraft as it approaches the end of its lunar observation mission, says the China Academy of Sciences.

“We made this choice because the instruments aboard Chang’e 2 are normal, the spacecraft’s remaining life is still long and its remaining fuel is fairly plentiful, enough to support a future mission,” says an official of the academy.

Lagrangian points are positions that remain constant relative to two other bodies in an orbital system. The second Lagrangian point (L2) of the Sun and the Earth is in line with the two but 1.5 million km (932,000 mi.) farther out. “The second Lagrangian point is relatively ideal, because interference from solar radiation there is relatively low,” says the official, quoted in a People’s Daily report that can be taken as a government announcement.

Program managers considered three options for Chang’e 2 after its lunar mission: crashing it into the Moon, as they did with its predecessor, Chang’e 1; bringing it back to an orbit around the Earth; or sending it into the Solar System beyond the Moon’s orbit.

They have chosen the third but limited themselves to L2 as a destination because, they say, their deep-space tracking capability is not good enough to send the spacecraft farther. Even so, the additional mission will help prepare for missions to Mars, says the People’s Daily.

In fact, going farther into the Solar System has always been a function of Chang’e 2. The chief designer of the lunar program, Wu Weiren, said after the Oct. 1, 2010, launch of Chang’e 2 that the mission would demonstrate telemetry, tracking and control technology that could be used for missions to study Mars and Venus. For those more distant missions, only larger antennas would be needed, because other facilities were already being built, he said.

Chang’e 2 will conduct unspecified observations and experiments at L2. To get there, it might have to miss a total eclipse of the Moon on June 15 (GMT), the academy says. The trip will take 2-3 months.

It will not be the first spacecraft to go to L2. NASA’s Wilkinson Microwave Anisotropy Probe, among others, is already there.

Chang’e 2, based on the CAST DFH-3 satellite bus, has operated for more than 200 days. Program officials are wrapping up the lunar observation phase, which should be completed by mid-June. Imagery data has all been transmitted back to Earth, where scientists and technicians are assembling it and making three-dimensional images. The academy says that with this data it will be able to publish the most precise complete set of images of the Moon by the end of the year. Resolution will be 7 meters (23 ft.).

The probe is named after a legendary goddess who traveled to the Moon. “Chang” is pronounced as “chahng” and “e” as in “her.”

Meanwhile, China has renewed its polar-orbiting weather satellite group with the in-orbit delivery of Fengyun 3B alongside Fengyun 3A, halving the country’s global observation interval to 6 hr.

Fengyun 3B was subject to half a year of in-orbit checkouts after its Nov. 5 launch. With all systems functioning properly, it was handed over to the national weather bureau on May 26, says national space contractor China Aerospace Science and Technology Corp.(CASC). Tests showed the satellite exceeding the performance of Fengyun 3A, CASC says, without giving details.

The Fengyun 3 program was the largest civil space project of China’s 10th five-year plan, for 2001-05, says the manufacturer. The designed image resolution has been stated as 250 meters and the altitude variously as 870 or 890 km.

This is China’s second series of polar-orbiting weather satellites. The first, the Fengyun 1 series, comprised four spacecraft launched in 1988-2002. The third unit in that series, Fengyun 1C, was destroyed in an anti-satellite missile test in 2007.
http://www.aviationweek.com/aw/g ... &headline=Chang

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