Relay satellite waits for Chang鈥檈-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鈥檈-4, which is set to be the first ever probe to land softly on the Moon鈥檚 far side.
The relay satellite for Chang鈥檈-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鈥檚 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 鈥渟ee鈥 both the Earth and the Moon鈥檚 far side.
The Chang鈥檈-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鈥檚 lunar exploration program since Chang鈥檈-1 more than 10 years ago.
Chang鈥檈-4 follows on from Chang鈥檈-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鈥檈-3 accomplished its mission, China鈥檚 space sector debated Chang鈥檈-4鈥檚 destination. Some were in favor of landing on the near side of the Moon again, because it鈥檚 safer.
鈥淚 disagreed with that. Why should Chang鈥檈-4 repeat what Chang鈥檈-3 had done? We should not be afraid of failure in scientific exploration. We need innovation,鈥 Ye said, suggesting sending the Chang鈥檈-4 to the Moon鈥檚 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鈥檛 because of technological restrictions at the time.
Since the Moon鈥檚 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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