First spacecraft for China’s Chang’e 4 lunar mission launching Sunday
China’s Queqiao communications relay satellite is undergoing final preparations before launch. It is the first spacecraft of the country’s ambitious Chang’e 4 mission, which will culminate in the first spacecraft to soft-land on the far side of the moon in late 2018.
Liftoff is scheduled to take place at around 5 p.m. EDT (21:00 GMT) Sunday, May 20, 2018. Queqiao will ride to space atop a Long March 4C rocket launched from the Xichang Satellite Launch Center in China’s Sichuan Province. Two smaller radio astronomy satellites, known as DSLWP-A1 and A2, will piggyback on the mission.
The mission was initially scheduled for June 2018. However China decided to conduct the launch one month earlier. The country did not disclose the reason behind this reschedule. Moreover, Beijing remains tight-lipped about pre-launch preparations and details of the flight that will deliver the trio of spacecraft into space.
If the mission succeeds, Queqiao will be delivered to the Earth-Moon L2 Lagrangian Point, which is located some 280,000 miles (450,000 kilometers) directly “behind” Earth as viewed from the Sun. The two DSLWP-A satellites are planned to be inserted into a lunar orbit.
“We designed an orbit at the Earth-Moon Lagrange Point L2 about 450,000 kilometers from the Earth, where a gravitational equilibrium can be maintained, and the relay satellite will be able to ‘see’ both the Earth and the far side of the Moon,” said Bao Weimin, director of the Science and Technology Commission of the China Aerospace Science and Technology Corporation.
Weighing around 937 pounds (425 kilograms) Queqiao, which means “magpie bridge” in Chinese, is based on the CAST100 satellite platform. Designed by the China Academy of Space Technology (CAST), it features two deployable solar arrays and a deployable 13.8-feet (4.2-meter) dish antenna for the relay equipment.
The relay communication equipment of Queqiao gives the spacecraft four 256-kilobit-per-second links in X-band between itself and Chang’e 4 lander and rover. Moreover it provides one link in S-band at two megabits per second between the satellite and Earth.
In order to establish a communications link with the yet-to-be-launched Chang’e 4 lunar lander and rover, China will need Queqiao. Any spacecraft on the Moon’s far side would require a relay satellite to transmit signals.
The launch of the rover and lander is currently scheduled for December 2018 and is expected to land on the lunar surface in Von Karman crater in the South Pole-Aitken Basin to investigate an unexplored region of the Moon, as well as to develop technologies required for the later stages of China’s lunar exploration program.
Besides establishing a communications link between Chang’e 4 and ground stations on Earth, Queqiao is also designed to provide radio-sky images, frequency dependence of radio in the very low frequency band and to perform low-frequency radio astronomical observations. As such, the satellite is fitted with a low-frequency radio detector.
In general, Queqiao is expected to be operational for at least five years.
“The whole mission is very complex and challenging,” Bao said. “We feel great pressure, but we are confident,”
Built by the Harbin Institute of Technology, DSLWP-A1 and DSLWP-A2, which stands for “Discovering the Sky at Longest Wavelengths Pathfinder,” are two identical micro-satellites weighing approximately 99 pounds (45 kilograms) each. Nicknamed Longjiang-1 and Longjiang-2 (meaning “dragon river”), the satellites are planned to be inserted into a lunar orbit at an altitude of 124 by 5,592 miles (200 by 9,000 kilometers).
If everything goes as planned, the twin micro-satellites should be able to conduct ultra-long-wave astronomical observations of the sky at frequencies between one megahertz and 30 megahertz. Chinese scientists hope that observations performed by DSLWP-A1 and A2 will provide insight into the nature of energetic phenomena from celestial sources. Additionally, the probes are also designed to be available for amateur radio tests.
Chang’e 4 is China’s fifth mission to the Moon. Chang’e 1 and 2 were lunar orbiters sent in 2007 and 2010 respectively while Chang’e 3 landed on the surface in December 2013 and deployed a rover that ultimately operated for about two and a half years. The most recent mission in the series—Chang’e 5-T1—launched in October 2014. It served as a technology demonstrator for Chang’e 5 lunar sample return mission, which is scheduled for 2019.
The Long March 4C booster that is being used for Sunday’s launch has an estimated liftoff mass of 250 metric tons. It is 150 feet (54.7 meters) in tall with a diameter of 11 feet (3.4 meters) and is capable of delivering payloads of up to 4.2 metric tons into a low-Earth orbit , 2.8 metric tons into a Sun-synchronous orbit, and up to 1.5 metric tons into a geostationary transfer orbit.
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