Thursday, May 17, 2018

First Spacecraft of China’s Chang’e 4 Lunar Mission to Be Launched on Sunday

Artist's rendering of the Queqiao satellite. Image Credit: CAST

China is in final preparations to launch the Queqiao communication relay satellite – the first spacecraft of Beijing’s ambitious Chang’e 4 mission that is planned to perform the first soft landing on the far side of the Moon in late 2018.

Liftoff is scheduled to take place at around 21:00 GMT (5:00 p.m. EDT) on Sunday, May 20. Queqiao will ride to space atop a Long March 4C rocket launched from the Xichang Satellite Launch Center (XSLC) 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, not disclosing what was behind this reschedule. Moreover, Beijing remains tight lipped about pre-launch preparations and details of the flight that will deliver the trio of spacecraft to space.

If the mission succeeds, Queqiao will be delivered to the Earth-Moon L2 Lagrangian Point - located some 280,000 miles (450,000 million kilometers) directly “behind” our planet as viewed from the Sun. The two DSLWP-A satellites are planned to be inserted into 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 lbs. (425 kilograms) Queqiao (what means "magpie bridge” in Chinese) is based on the CAST100 satellite platform. The bus, designed by China Academy of Space Technology (CAST), features two deployable solar arrays and a deployable 13.8-feet (4.2-meter) dish antenna for the relay equipment.

Relay communication equipment of Queqiao will enable it four 256 kBps links in X-band between itself and Chang’e 4 lander together with rover. Moreover it will provide one link 2 MBps in S-band between the satellite and the Earth.

China needs Queqiao in order to establish communications with its Chang’e 4 lunar lander and rover as landing on the far side of the Moon requires a relay satellite to transmit signals. The launch of the rover and lander is currently scheduled for December 2018. The mission is planned to land on the lunar surface in the Von Kármán crater in the South Pole-Aitken Basin to investigate so far unexplored region of the Moon, as well as to develop technologies required for the later stages of China’s lunar exploration program.

Besides establishing communications links between Chang’e 4 and ground stations on Earth, Queqiao is designed to also provide radio-sky images, frequency dependence of radio in the very low frequency band and to perform low-frequency radio astronomical observations. For this purposes, 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. We feel great pressure, but we are confident," Bao said about the Queqiao mission.

Built by Harbin Institute of Technology (HIT), DSLWP-A1 and DSLWP-A2 (Discovering the Sky at Longest Wavelengths Pathfinder), are two identical microsatellites weighing approximately 99 lbs. (45 kilograms) each. Nicknamed Longjiang-1 and Longjiang-2 (meaning “dragon river”), the satellites are planned to inserted in a lunar orbit at an altitude of 124 by 5,592 miles (200 by 9,000 kilometers).

If everything goes as planned, from this orbital spot the twin microsatellites should be able to conduct ultra long-wave astronomical observations of the sky at frequencies between 1 MHz and 30 MHz. Chinese scientists hope that observations performed by DSLWP-A1 and A2 will provide important insights into the nature of energetic phenomena from celestial sources. Additionaly, the probes will also 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 to the Moon in 2007 and 2010 respectively, while Chang’e 3 landed on the lunar surface in December 2013 and deployed a rover which operated there for about two and a half years. The recent mission in the series – Chang’e 5-T1 launched in October 2014 - which served as a technology demonstrator for Chang’e 5 lunar sample return mission scheduled for 2019.

The Long March 4C booster that will be used for Sunday’s launch has a liftoff mass of an estimated 250 metric tons and is 150 feet (54.7 meters) in length with a diameter of 11 feet (3.4 meters). It is capable of delivering payloads of up to 4.2 metric tons to low-Earth orbit (LEO), 2.8 metric tons to Sun-synchronous orbit (SSO), and up to 1.5 metric tons into a geostationary transfer orbit (GTO).

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