Yutu (Jade Rabbit)

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"Yutu," (玉兔) or "Jade Rabbit," is the name of China's first-ever moon rover, which was launched into space at 1:30 a.m. on Dec. 2, 2013.

On Dec. 14, China's lunar probe Chang'e-3, with the country's first moon rover onboard, successfully landed on the moon.

On Dec. 15, the moon rover and lander took photos of each other on the moon's surface.

Yutu was awakened autonomously at 5:09 a.m. Beijing Time on Jan. 11, 2014 after a period of dormancy that lasted two weeks, or one lunar night, in a move designed to ride out harsh climactic conditions. It has finished necessary setting procedures and entered a normal working mode following orders from the Beijing Aerospace Control Center (BACC).

On Jan. 25, the State Administration of Science, Technology and Industry for National Defense announced the moon rover has experienced a mechanical control abnormality due to the complicated lunar surface environment, and scientists were organizing an overhaul.

On Feb. 13, Yutu has waken up from a troubled dormancy although experts are still trying to figure out the cause of its abnormality.

On Feb. 22, the lunar rover Yutu entered the dormancy again, with the mechanical control issues that might cripple the vehicle still unresolved.

On May 28, Li Benzheng, deputy commander-in-chief of China's lunar exploration program, said the troubled rover is still alive and functional after more than five months on the moon. But its functionality has been weakened considerably by the bitterly cold lunar nights after the rover experienced a "mechanical control abnormality" in January.

The rover can still send data back to Earth via China's Chang'e-3 lunar probe. But its wheels are no longer functioning, nor is the solar panel which should have been folded to provide thermal insulation during lunar nights.


Contents

Background

Chang'e 3's mission represents a Chinese spacecraft's first-ever soft landing on a celestial body. The probe, which incorporates many new technologies, is the embodiment of China's latest scientific and technological innovations. Chang'e-3's successful mission marks a new milestone in China's space engineering and a major contribution to the realization of the Chinese Dream.

Design features

The Yutu moon rover features a design mass of 140 kilograms. Powered by solar energy, the rover can endure the Moon's extreme environments -- such as vacuum conditions, high radiation and high temperature differences (ranging from -180 to 150 °C).

Yutu has a 20-degree gradeability and is capable of climbing over a 20 CM-high obstacle. The scientific instruments on board include a panoramic camera, an infrared imaging spectrometer, a moon radar system and an X-ray spectrometer.


Component designs

The Yutu prototype takes an oblong shape. Its dimension measures 1.5*1.0*1.1 meters. Yutu is fully covered with golden scales, used to deflect the strong sunlight on the Moon’s surface in order to lower the temperature differences occurring within the instrument. The scales also fend off the radiation from various energetic particles to protect the precision equipment -- including the infrared imaging spectrometer and laser systems inside the rover.

Yutu has two foldable solar panels installed on its shoulder to power the rover itself. A Moon-Earth communication antenna is placed on top of the rover featuring panoramic cameras for self-propellant navigation. It also has a robotic arm to drill the moon surface in order to obtain moon soil.

Yutu has a 6*6-wheeled ambulation device, following its extremely high criteria for "wheels." Researchers said they finally agreed upon installing a "6-wheel independent drive with 4-wheel independent steering" plan after debating dozens of proposals, including 4*4, 6*6, 8*8 and caterpillar tracks.

"Yutu is 100 percent completely Made-in-China," said Wu Weiren, chief designer of the Chinese Lunar Exploration Program (CLEP).

Mobility on the moon

Yutu is capable of ascending 20-degree slopes and 20 centimeter-tall obstacles. Its temperature endurance ranges from -180 to 150 °C. The Moon's gravity is one-sixth of that found on Earth. Its surface is soft and bumpy, consisting of both rocks and craters. Under these circumstances, Yutu can neither skid nor roll.

As a solution, Yutu is equipped with both panoramic cameras and navigational cameras; four in total. The cameras observe the surrounding terrain conditions and devise a cruise route for the rover. Yutu will recognize slopes tilting at more than 20 degrees, rocks higher than 20 centimeters or craters larger than two meters in diameter. It will actively make judgments and avoid any such risks.

Moon dust is another risk facing Yutu when it sets out on its tour of the Moon. Moon dust can cause many problems, including the jamming of the mechanic structure, causing the sealing mechanism to dysfunction and dimming the rover's optical system.

In a bid to prevent these issues, Yutu has been tested before flying to the moon. In an experimental lab that simulates the conditions occurring on the Moon's surface, researchers from Changbai Mountain brought along volcano ashes, which resemble the elements found on the moon. Tests showed that Yutu was capable of conducting self navigation in combination with remote control, which would ensure its maneuverability when put to the real mission on the Moon.

Hibernation mode

The Moon circles the earth every 28 days, the same length of time for it to complete self-rotation, a phenomenon referred to as "tidal locking," or synchronous rotation. It means that one night on the moon equals 14 nights on Earth. Temperatures on the moon will fall as low as -180 °C at night, too low for any electronic devices to function.

This is why researchers have equipped Yutu with a hibernation mode, which enables the moon rover to work for 14 days and hibernate for another 14 days. This feature will greatly enhance Yutu's survivability amid the harsh lunar environment.

In designing Yutu's hibernation mode, researchers found waking up Yutu proved difficult after it had experienced extreme cold. Later on, they thus came up with a design of foldable solar panels that will collapse to cover the instruments inside. The design ensures Yutu has enough electrical power to wake itself up before unfolding the solar panel to get charged.

Additionally, a nuclear battery is installed on Yutu to power its extremely delicate equipment. A coin-sized nuclear battery is reportedly capable of lasting 5,000 days. If tested successfully on Yutu, the technology will make China the third country, after the U.S. and Russia, to power its space programs using nuclear energy.

During the Moon’s daytime, Yutu's solar panels can adjust their angle to prevent the rover from overheating in the sunshine. At noon, when the Moon temperatures rise to their maximum, the rover will need to "take a break." Its design service length extends to three months; in other words, it will endure three lunar days and three lunar nights. All its tasks have to be completed during the "mornings and afternoons" on the Moon.

Subsystems

Altogether eight subsystems ensure the Yutu moon rover to function well: movability, navigation control, power supply, heat control, structure and mechanics, comprehensive electronics, data transmission and payload.

Movability subsystem

Yutu incorporates a wheel-suspension plan which enables it to move forward and backward, perform pivot turns, turn in motion, climb slopes with an angle of up to 20 degrees and surmount obstacles as tall as 20 centimeters.

Navigation control subsystem

The cameras and various sensors featured on Yutu will determine the rover's self-attitude amid the surrounding conditions. This system provides the lunar vehicle with directions and controls its movements on the Moon’s surface.

Power supply subsystem

Yutu's power supply subsystem consists of two solar panels: a set of lithium-ion batteries, hibernation awaking modules and a power control unit. It transforms solar energy to power the instruments and equipment on the moon rover.

Heat control subsystem

A heat transfer fluid loop, heat insulating components, a heat radiator and an electric heater plus nuclear isotope heat source working coordinately keep the lunar rover's cabin temperature between -20 and 55 °C.

Structure and mechanics subsystem

This subsystem consists of the rover's structural body as well as the solar panel wings. It is mainly a working platform for all equipment and a bearer for Yutu's payload.

Comprehensive electronics subsystem

It integrates the central computer, driver module and processor module. It adopts the real-time control system to facilitate remote control, data management, navigation control and maneuverability control.

Data transmission subsystem

It ensures Yutu remains in sound connection with Chang'e 3's lunar lander and with the control center some 384,000 kilometers away on Earth.

Payload subsystem

Yutu's payload consists mostly of the scientific instruments it carries, including panoramic cameras, an infrared imaging spectrometer, a moon soil detecting radar and an X-ray spectrometer.

The name "Yutu"

"The moon rover's name has fully represented the wills from all Chinese, including those living abroad," said Li Benzheng, vice general director of CLEP, at a press conference on November 26.

He explained how in ancient Chinese mythology, the Moon goddess Chang'e flew to the moon holding her jade rabbit named Yutu. Yutu impressed people with its kindness and purity besides its agility. The name and its connotations both very much befit the Chinese lunar program. The name Yutu mirrors China's desire to peacefully explore outer space.

"Also, many online voters favored [the name] 'Qian Xuesen,' in memory of one of China's space engineering founding fathers. Their respect to him also shows the public's support of China's space program," Li added.

How Yutu differs from previous moon rovers

Five moon rovers have hitherto successfully completed their missions; two of which were unmanned -- Moon Rover 1 and Moon Rover 2, both sent up by the former Soviet Union in the 1970s. An additional three man-steered rovers were launched as part of the U.S. Apollo program (1963-1972).

China's Yutu is an unmanned autopilot moon rover. It weighs 140 kilograms, making it a "little bloke" compared with former Soviet rovers. Nevertheless, Yutu's designers have said a smaller rover will save costs. They noted how unmanned moon rovers are more difficult to develop as they carry devices and need to move around on autopilot; U.S. manned lunar rovers, however, were used more frequently as astronomers' transport tools and did not have many instruments on board.

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