China's two-launch Chang'e-4 mission to the far side of the Moon will include a pair of microsatellites to be placed in lunar orbit to test low frequency radio astronomy and space-based interferometry.
The pair, unofficially named DSLWP-A1 and DSLWP-A2, have a mass of about 45 kg each with dimensions of 50 x 50 x 40 cm and will launch along with a relay satellite in May or June this year.
Equipped with low frequency antennae and receivers, the astronomy objectives of DSLWP-A1 and A2 will be to observe the sky at the very low frequency part of the electromagnetic spectrum (1MHz-30MHz), corresponding to wavelengths of 300m-10m, with the aim of learning about energetic phenomena from celestial sources.
The primary aim of this first launch of the Chang'e-4 mission involves placing a relay satellite in a halo orbit at the second Earth-Moon Lagrange point beyond the Moon, from which it will facilitate communications with the Chang'e-4 lander and rover, which will be sent to the lunar far side in December.
The satellite is necessary as the far side of the Moon never faces the Earth due to 'tidal locking', and so transmitting data requires an Earth-Moon relay. This complexity is one reason the Chang'e-4 mission will be the first ever attempt at a soft-landing on the far side of the Moon.
The two microsatellites take advantage of extra space on the launch and will tag along for the journey to the Moon.
Low frequency radio astronomy
The pair of microsatellites will fly in formation at variable distances of 1-10 km in an unspecified, elliptical lunar orbit, testing space-based interferometry, which will allow for high angular resolution observations, by matching up radio waves collected by the pair from the same source at what is calculated to be the same time.
Due to the Earth's ionosphere, observations at these low frequencies is very hard, with almost nothing known about the sky in this frequency range.
This could bring unprecedented insights into the dark ages of the universe and transient astronomical events, such as supernovae and gamma ray bursts
The findings could therefore be tremendous, but the mission is only a test for potential future projects.
“As there are many limits on the preparation time, payload mass, power and communication bandwidth, the present mission is more an experiment, but what we learn from this could be very useful for the design of future missions,” says Chen Xuelei, of National Astronomical Observatory of China under the Chinese Academy of Sciences (CAS).
"Many astronomers around the world had proposed to observe at this low frequency range from space, and now we are proud that Chang'e-4 mission will give us the opportunity to make the first peek of the heaven in this frequency range," Chen says, adding that the team also look forward to collaborations with international colleagues on the low frequency radio astronomy.
Launch configuration of the Chang'e-4 DSLWP microsatellites.
DSLWP stands for 'Discovering the Sky at Longest Wavelengths Pathfinder', but the pair are likely to receive new names before launch.
A similar, larger scale mission, DSL, was proposed as a joint CAS-European Space Agency mission, but the SMILE mission was selected from the candidates.
Amateur astronomy, international payloads
DSLWP-A1 will carry an amateur radio payload developed by students at the Harbin Institute of Technology (HIT) in northeast China, allowing telecommand uplink and telemetry and digital image downlink. An open telecommand is also designed to allow amateurs to send commands to take and download an image.
DSLWP-A2 will carry a microcamera developed by the King Abdulaziz City for Science and Technology (KACST) of Saudi Arabia, one of the four international partners providing payloads for the Chang'e-4 mission.
Sweden, Germany and the Netherlands are all also involved in the mission, with a student outreach-inspired mini ecosystem, including potatoes, arabidopsis seeds and silkworm eggs, among the Chang'e-4 payloads.
The relay satellite is expected to be launched on a Long March 4C launch vehicle from the Xichang Satellite Launch Centre in Sichuan Province, southwest China in May or June.
The Chang'e-4 lander and rover, based on the Chang'e-3 mission spacecraft, will also launch from Xichang, aboard a Long March 3B, in December.
The Long March 3B launch of China's Chang'e-3 lunar landing mission in December 2013.
A soft-landing on the far side of the Moon has never been attempted, though a US Decadal Survey has highlighted the significance of such a mission.
The candidate landing sites for the lander and rover are within the South Pole–Aitken basin, a huge crater that may include lunar mantle excavated by the impact that formed it and thus offer unique insights into the interior of the Moon, what it is made of and how it formed.
The Chang'e-3 lander on Mare Imbrium, imaged by the Yutu rover.
Chang'e-4 lander and rover undergoing thermal vacuum tests ahead of lunar far side mission
China's Chang'e-3 lander and Yutu (Jade Rabbit) rover operating on the Moon after landing in late 2013. The pair would face temperatures ranging from 120 degrees Celsius during sunshine, and -170 degrees Celsius during the lunar night. CNS
China's Chang'e-4 lunar lander and rover spacecraft are undergoing vacuum testing ahead of their pioneering December mission to touch down on the far side of the Moon.
The thermal vacuum tests are to the last of a range of space environment tests which began in January, and include vibroacoustic, electromagnetic and mechanical vibration tests, before the Chang'e-4 spacecraft can leave the Assembly, Integration and Testing (AIT) Centre.
Thermal vacuum testing simulates the extreme ranges of hot and cold temperatures to be experienced by the spacecraft on its mission.
On the Moon's surface temperatures can reach up to around 120 degrees Celsius during sunlight, and as low as -170 degrees Celsius during the lunar nights.
The assembly and environmental engineering department of the China Academy of Space Technology (CAST) have been performing the tasks, according to Zhao Xiaojin, a senior CAST official, speaking on the sidelines of China's ongoing annual parliamentary sessions.
CAST engineers working on the Chang'e-4 lunar lander and rover in 2018.
Chang'e-4 will be the first ever attempt at a soft landing on the far side of the Moon which, due to tidal locking, never faces the Earth.
The landing and roving sections of the mission will therefore be facilitated and assisted by a relay communications satellite sent into halo orbit around a Lagrange point beyond the Moon, launching in May or June.
Accompanying the relay satellite will be two microsatellites, which will carry amateur radio payloads, a micro optical camera, and instruments for pioneering astronomy at very low frequencies.
Chang'e-4 was originally manufactured at the same time as the Chang'e-3 spacecraft, which landed on the Moon in late 2013, in order to provide a backup.Testing for Chang'e-4 will also involve lunar landing and lunar surface simulation for the six-wheeled rover, as with the previous mission.
A photo of Yutu (Jade Rabbit) taken by the Chang'e-3 lander in December 2013 on the surface of the Moon.
Chang'e-4 objectives and payloads
The Chang'e-4 mission is focusing on low-frequency radio astronomy and investigation of the subsurface, topography and mineralogical composition on the lunar far side.
The landing area will be within the scientifically intriguing South Pole-Aitken Basin. While some candidates, including the Von Kármán impact crater, have been noted, the precise landing site has not been publicly released.
Five of the science payloads, including the cameras, radar and imaging spectrometer noted below, are inherited from the 2013 Chang'e-3 mission, but new and international payloads will travel to the Moon later this year.
The lander will carry a Landing Camera (LCAM), Terrain Camera (TCAM), Low Frequency Spectrometer (LFS), and Lunar Lander Neutrons and Dosimetry (LND).
The rover will be equipped with a Panoramic Camera (PCAM), a Lunar Penetrating Radar (LPR), a Visible and Near-Infrared Imaging Spectrometer (VNIS), and an Advanced Small Analyser for Neutrals (ASAN).
The relay satellite will carry the Netherlands-China Low-Frequency Explorer (NCLE).
TCAM and PCAM on Chang'e-3 returned astounding images from Mare Imbrium.
A view of Mare Imbrium from China's Chang'e-3 lander.
Flowers on the Moon? China's Chang'e-4 to launch lunar spring
China's Chang'e-4 lunar probe is expected to do many things unprecedented in space history after it launches later this year, such as touching down softly on the far side of the Moon and taking the first flowers to blossom on the lifeless lunar surface.
The probe will carry a tin containing seeds of potato and arabidopsis, a small flowering plant related to cabbage and mustard, and probably some silkworm eggs to conduct the first biological experiment on the Moon.
The "lunar mini biosphere" experiment was designed by 28 Chinese universities, led by southwest China's Chongqing University, a conference on scientific and technological innovation of Chongqing Municipality has heard.
The cylindrical tin, made from special aluminum alloy materials, is 18 cm tall, with a diameter of 16 cm, a net volume of 0.8 liters and a weight of 3 kilograms. The tin will also contain water, a nutrient solution, air and equipment such as a small camera and data transmission system.
Researchers hope the seeds will grow to blossom on the Moon, with the process captured on camera and transmitted to Earth.
Although astronauts have cultivated plants on the International Space Station, and rice and arabidopsis were grown on China's Tiangong-2 space lab, those experiments were conducted in low-Earth orbit, at an altitude of about 400 kilometers. The environment on the Moon, 380,000 kilometers from the Earth, is more complicated.
Liu Hanlong, chief director of the experiment and vice president of Chongqing University, said since the Moon has no atmosphere, its temperature ranges from lower than minus 100 degrees centigrade to higher than 100 degrees centigrade.
"We have to keep the temperature in the 'mini biosphere' within a range from 1 degree to 30 degrees, and properly control the humidity and nutrition. We will use a tube to direct the natural light on the surface of Moon into the tin to make the plants grow," said Xie Gengxin, chief designer of the experiment.
"We want to study the respiration of the seeds and the photosynthesis on the Moon," said Liu.
"Why potato and arabidopsis? Because the growth period of arabidopsis is short and convenient to observe. And potato could become a major source of food for future space travelers," said Liu. "Our experiment might help accumulate knowledge for building a lunar base and long-term residence on the Moon."
The public, especially young people, are being encouraged to participate in the Chang'e-4 mission. The China National Space Administration (CNSA) launched a contest among students across China in 2016, collecting ideas on the design of the payloads.
The "lunar mini biosphere" experiment was selected from more than 200 submissions, according to the CNSA.
Tidal forces of the Earth have slowed the Moon's rotation to the point where the same side always faces the Earth, a phenomenon called tidal locking. The other face, most of which is never visible from the Earth, is the far side of the Moon.
With its special environment and complex geological history, the far side is a hot spot for scientific and space exploration. However, landing and roving there requires a relay satellite to transmit signals.
It has been reported that China plans to send a relay satellite for Chang'e-4 to the halo orbit of the Earth-Moon Lagrange Point L2 in late May or early June 2018, and then launch the Chang'e-4 lunar lander and rover to the Aitken Basin of the south pole region of the Moon about half a year later.
The Von Karman Crater, named after a Hungarian-American mathematician, aerospace engineer and physicist, in the Aitken Basin, was chosen as the landing site for Chang'e-4. The region is believed to have great scientific research potential.
The transmission channel is limited, and the landscape rugged, so the mission will be more complicated than Chang'e-3, China's first soft landing on the Moon in 2013, said Liu Tongjie, deputy director of the Lunar Exploration and Space Program Center of CNSA.
As the relay satellite will be sent to the Earth-Moon Lagrange Point L2 about 450,000 kilometers from the Earth, where a gravitational equilibrium can be maintained, it could stay in stable orbit and operate for a long time.
"We will make efforts to enable the relay satellite to work as long as possible to serve other probes, including those from other countries," said Ye Peijian, a leading Chinese aerospace expert and consultant to China's lunar exploration program.
The Lunar Exploration and Space Program Center of the CNSA has invited the public to write down their hopes for lunar and space exploration, and those hopes and the names of participants will be carried by the relay satellite into deep space. More than 100,000 people have taken part, according to the center.
Quelle: Xinhua
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Chang'e-4 relay satellite to be named through contest held by space science centre
The Earth and Moon seen from Earth-Moon L2 by the C5-T1 service module. Chang'e-4 will use a relay satellite deployed in at L2 to provide communication with the far side lunar lander and rover. SASTIND
A competition has been opened to name the communications relay satellite that will soon launch to facilitate the pioneering Chang'e-4 lunar far side landing mission in late 2018.
The Chang'e-4 relay satellite is a necessary part of a lunar far side landing mission, as that area of the Moon never faces the Earth. The satellite will be be placed at a Lagrange Point beyond the Moon to provide a communications link between the lunar lander and rover and Earth.
The National Space Science Centre (NSSC) under the Chinese Academy of Sciences (CAS) last month launched (Chinese) the naming contest for the satellite, running from March 27 to April 15.
The winning entry will be announced on China's third annual Space Day, on April 24.
Image demonstrating a halo orbit around the second Earth-Moon Lagrange point, from which the Chang'e-4 communications relay satellite will operate.
Unlike a recent, prior contest for sending messages aboard the relay satellite, the naming competition is only open to a select number of institutes and universities close to the mission.
In March, China's General Office of Lunar and Deep-space Exploration selected nearly 8,000 names and messages to travel along with the relay satellite, from over 120,000 submitted. Three lucky winners were also chosen(Chinese) to travel to see the launch.
The relay satellite is expected to launch in May or June from the Xichang Satellite Launch Centre in the southwestern province of Sichuan, carried by a Long March 4C rocket.
Preparations for the November 2017 launch of the Beidou-3 M1 and M2 satellites via Long March 3B from Xichang, Sichuan Province.
China has been increasingly using such contests to boost public awareness of and participation in space missions, including the naming of the 2013 Chang'e-3 rover, 'Yutu', or Jade Rabbit, and the 2020 Mars mission.
Another Chang'e-4 competition, launched in 2016, saw students across China submit ideas for a science payload, with a lunar mini biosphere experiment, containing silkworm eggs and potato seeds, being selected.
The far side of the Moon and the distant Earth, imaged by the Chang'e-5T1 mission in 2014.
Lunar microsatellite companions
The upcoming launch will also be carrying a pair of microsatellites, unofficially named DSLWP-A1 and DSLWP-A2, which will be placed in lunar orbit to test low frequency radio astronomy and space-based interferometry.
They will be equipped with low frequency antennae to observe the sky at the very low frequency part of the electromagnetic spectrum with the aim of learning about energetic phenomena from celestial sources.
DSLWP-A2 will carry a microcamera developed by the King Abdulaziz City for Science and Technology (KACST) of Saudi Arabia, one of the four international partners providing payloads for the Chang'e-4 mission.
Testing on the Chang'e-4 DSLWP-A1 and DSLWP-A2 microsatellites in early 2018.
Sweden, Germany and the Netherlands are all also involved in the mission, providing Chang'e-4 payloads.
The Chang'e-4 lander and rover, using the backup spacecraft from Chang'e-3, have meanwhile been undergoing thermal vacuum and other space environment tests in preparation for launch around November or December this year.
For latest news and developments on the mission, see our feature on China's Chang'e-4 mission to the far side of the Moon
The Chang'e-3 lander on Mare Imbrium, imaged by the Yutu rover.
China to name relay satellite for Chang'e-4 lunar probe
China will give a name to the relay satellite for the Chang'e-4 lunar probe, which is expected to land softly on the far side of the Moon in late 2018.
The name will be announced on China's Space Day on April 24, marking the day the country's first satellite was sent into space in 1970, according to the China National Space Administration (CNSA).
Together with the relay satellite, two microsatellites, developed by the Harbin Institute of Technology, will also be sent into orbit to conduct scientific research. The names of the two microsatellites will also be announced on April 24.
The development of the Chang'e-4 lunar probe is progressing well, said Li Guoping, a spokesman of CNSA.
The Chang'e-4 probe will also carry scientific payloads developed by the Netherlands, Sweden, Germany and Saudi Arabia.
Tidal forces of the Earth have slowed the Moon's rotation to the point where the same side always faces Earth. The other face, most of which is never visible from Earth, is the far side of the Moon.
With its special environment and complex geological history, the far side is a hot spot for scientific and space exploration. However, landing and roving there require a relay satellite to transmit signals.
According to previous reports, China plans to send the relay satellite to the halo orbit of the Earth-Moon Lagrange Point L2 in late May or early June 2018, and then launch the Chang'e-4 lunar lander and rover to the Aitken Basin of the south pole region of the Moon about half a year later.
Quelle: Xinhua
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Update: 2.06.2018
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Queqiao update: Chang'e-4 lunar relay satellite establishing halo orbit after approaching Lagrange point
It has been a week since the Queqiao Chang'e-4 lunar relay satellite made its lunar swing-by, sending it on a transfer trajectory towards the second Earth-Moon Lagrange Point (EML2). There have been no official updates from China, so where is the spacecraft now?
Having launched late on May 20 UTC, Queqiao made its lunar swing-by on May 25, performing a braking burn at 13:32 UTC to send the communications satellite towards EML2, some 60-80,000 km beyond the Moon.
EML2 is one of five libration points in the Earth-Moon system that allow a much smaller third body to orbit while maintaining its position relative to the larger two, making it a perfect place for Queqiao to perform its main objective.
Queqiao should have approached the EML2 point by May 29 after two orbital corrections, but no updates have come from China. This has brought confusion, but making the distinction between reaching EML2 and establishing the desired orbit around it helps bring clarity.
On approaching EML2, assuming all is well, Queqiao will have begun manoeuvres required to obtain a halo orbit (or more accurately a Lissajous orbit shown below) around EML2 with a radius sufficient to allow it constant line of sight with both tracking stations on the Earth and the lunar far side, on which a lander and rover are planned to set down in late 2018.
A demonstration of the Lissajous/halo orbit to be used by the Queqiao Chang'e-4 relay satellite mission.
According to the illustration below - showing the planned trajectory, manoeuvres and orbit for Queqiao - the spacecraft will have made a gravitational capture manoeuvre around May 29 to begin a 15-day segment of its journey to obtain a halo orbit around EML2, which is its mission orbit.
This fits with the preliminary flight profile design outlined in an article published in Science China - Technological Sciences in 2017 titled An Overview of the Mission and Technical Characteristics of Change’4 Lunar Probeauthored by senior figures from the China Academy of Space Technology (CAST) and the Institute of Spacecraft System Engineering in Beijing.
A chart laying out the trajectories for the Queqiao Chang'e-4 lunar relay satellite to obtain a halo orbit around the second Earth-Moon Lagrange point.
The paper outlined three transfer options for arriving at EML2, with the lunar swing-by chosen over direct and low-energy transfers. The flight profile outlines that the spacecraft will make three orbital corrections after the EML2 capture phase to establish the halo orbit.
According to the outlined schedule, the halo orbit may not be obtained until mid-June, which may also be the next time we get an official Queqiao mission update. Hopefully this will include images from the onboard cameras.
We are also awaiting an update on the status of the one of two microsatellites (Longjiang-1/-2 or DSLWP-A/B) launched along with Queqiao. While Longjiang-2 successfully entered an elliptical lunar orbit, there has been silence from Longjiang-1.
The Longjiang-1 and -2 (aka DSLWP-A/B) microsatellites launched to the Moon with the Queqiao Chang'e-4 lunar relay satellite on May 20 UTC, 2018.
Landing, astronomy and...sample return?
Queqiao is expected to be able to operate in this orbit for at least three years, with the fuel requirement for station keeping at EML2 being relatively low. It will use a 4.2 m diameter parabolic antenna and s- and x-band frequencies to facilitate data relay between the Earth and far side of the Moon.
The lander and rover for the mission, to be launched on a Long March 3B from Xichang in November or December, in March underwent thermal vacuum testing, which are the last of a range of space environment tests which began in January before the Chang'e-4 spacecraft can leave the Assembly, Integration and Testing (AIT) Centre.
After the initial landing and roving section of the mission, with the rover designed to operate for at least three months, a low-frequency radio astronomy antenna, NCLE, will be deployed to determine the activity in the solar system at frequencies between 1-30 MHz, and eventually attempt to detect a signal from the cosmic 'Dark Ages'.
The relay satellite could facilitate future international missions, or a lunar far side sample return with Chang'e-6, should the 2019 near side Chang'e-5 sample return mission be successful.
China's Chang'e-3 lander and Yutu (Jade Rabbit) rover operating on the Moon after landing in late 2013.
Quelle: gbtimes