Relay satellite waits for Chang’e-4 in Halo orbit
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A SATELLITE with a huge golden umbrella-shaped antenna is in an orbit more than 400,000 kilometers from Earth, waiting for Chang’e-4, which is set to be the first ever probe to land softly on the Moon’s far side.
The relay satellite for Chang’e-4 will establish a communication link between the Earth and the far side of the Moon, and might serve probes from other countries, contributing to international scientific exploration, said Ye Peijian, an academician of the Chinese Academy of Sciences and one of China’s leading space experts.
The satellite, named Queqiao, or Magpie Bridge, was launched on May 21 and has entered the Halo orbit around the second Lagrangian (L2) point of the Earth-Moon system, where it can “see” both the Earth and the Moon’s far side.
The Chang’e-4 probe, including a lander and a rover, is expected to be launched later this year. Its mission to explore the far side of the Moon was proposed by Ye, who has worked in China’s lunar exploration program since Chang’e-1 more than 10 years ago.
Chang’e-4 follows on from Chang’e-3, which was launched at the end of 2013 and became the first Chinese spacecraft to soft-land on and explore an extraterrestrial object.
After Chang’e-3 accomplished its mission, China’s space sector debated Chang’e-4’s destination. Some were in favor of landing on the near side of the Moon again, because it’s safer.
“I disagreed with that. Why should Chang’e-4 repeat what Chang’e-3 had done? We should not be afraid of failure in scientific exploration. We need innovation,” Ye said, suggesting sending the Chang’e-4 to the Moon’s far side. This would be unprecedented and innovative.
He believed the United States and Soviet Union had wanted to do that in their lunar programs, but hadn’t because of technological restrictions at the time.
Since the Moon’s revolution cycle is the same as its rotation cycle, the same side always faces the Earth, and most of the other side is never seen from Earth. Landing and roving on the far side of the Moon require a relay satellite to transmit signals.
The first ever satellite operating on the Halo orbit around the L2 point, Queqiao used relatively small amounts of fuel during its journey to the planned orbit as it was under precise control. Its designed life is three years, but Ye said it might work for seven or eight years.
A reliable long-distance data transmission link is a key technological goal for space experts. Queqiao carries an umbrella-shaped antenna with a diameter of 4.2 meters, the largest communication antenna ever used in deep space exploration.
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