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June 15 2021
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Previous story China says Martian rover takes first drive on surface of Red Planet Next story
Published on May 22, 2021 6:12 AM

by Ryan WooYilei Sun | reuters.com

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A remote-controlled Chinese motorised rover drove down the ramp of its landing capsule on Saturday and onto the surface of Mars, making China the first nation to orbit, land and deploy a land vehicle on its inaugural mission to the Red Planet.

Zhurong, named after a mythical Chinese god of fire, drove down to the surface of Mars at 10:40 a.m. Beijing time , according to the rover's official Chinese social media account.

China this month joined the United States as the only nations to deploy land vehicles on Mars. The former Soviet Union landed a craft in 1971, but it lost communication seconds later.

The 240-kg Zhurong, which has six scientific instruments including a high-resolution topography camera, will study the planet's surface soil and atmosphere.

Powered by solar energy, Zhurong will also look for signs of ancient life, including any subsurface water and ice, using a ground-penetrating radar during its 90-day exploration of the Martian surface.

Zhurong will move and stop in slow intervals, with each interval estimated to be just 10 metres over three days, according to the official China Space News.

"The slow progress of the rover was due to the limited understanding of the Martian environment, so a relatively conservative working mode was specially designed," Jia Yang, an engineer involved in the mission, told China Space News.

Jia said he would not rule out a faster pace in the later stage of the rover's mission, depending on its operational state at the time.

Jia said the rover was designed to be highly autonomous because the distance to Mars, at 320 million km , means a signal takes 40 minutes to travel both ways, posing a hurdle for real-time control of the rover...


Background

Tianwen-1 is an interplanetary mission by the China National Space Administration to send a robotic spacecraft to Mars, consisting of an orbiter, deployable camera, lander and the Zhurong rover. The spacecraft, with a total mass of nearly five tons, is one of the heaviest probes launched to Mars and carries 13 scientific instruments.

The mission's scientific objectives include: investigation of Martian surface geology and internal structure, search for indications of current and past presence of water, and characterization of the space environment and the atmosphere of Mars.

The mission was launched from the Wenchang Spacecraft Launch Site on 23 July 2020 on a Long March 5 heavy-lift launch vehicle. After seven months of transit through the inner solar system, the spacecraft entered Martian orbit on 10 February 2021. For the next three months the probe studied the target landing sites from a reconnaissance orbit. On 14 May 2021, the lander/rover portion of the mission successfully touched down on Mars, making China the third nation to both land softly on and establish communication from the Martian surface, after the Soviet Union and the United States. On 22 May 2021, the successful deployment of the rover made China become only the second nation to accomplish this feat, after the United States, as well as the first nation to orbit, land and release a rover during its first mission to Mars.

The Tianwen-1 mission was the second of three Martian exploration missions launched during the July 2020 window, after the United Arab Emirates Space Agency's Hope orbiter, and before NASA's Mars 2020 mission, which landed the Perseverance rover with the attached Ingenuity helicopter drone.

Mission overview Launch of Tianwen-1 from Wenchang on Hainan, 23 July 2020 A schematic of the Tianwen-1 spacecraft stack

The new Chinese Mars spacecraft, consisting of an orbiter and a lander with an attached rover, was developed by the China Aerospace Science and Technology Corporation and is managed by the National Space Science Centre in Beijing. The mission was formally approved by Chinese authorities in 2016, and became a reality five years later. It was launched from Wenchang Spacecraft Launch Site on the Chinese island of Hainan atop a Long March 5 heavy-lift launch vehicle on 23 July 2020.

In September 2020, the Tianwen-1 orbiter deployed the Tianwen-1 Deployable Camera , a small satellite with two cameras that took photos of and tested a radio connection with Tianwen-1. Its mission was to photograph the Tianwen-1 orbiter and the lander's heat shield.

During its cruise to Mars, the spacecraft completed four trajectory correction maneuvers plus an additional maneuver to alter its heliocentric orbital inclination; it also performed self diagnostics on multiple payloads. After payload checkouts, the spacecraft began scientific operations with the Mars Energetic Particle Analyzer, mounted on the orbiter, which transmitted initial data back to ground control. The lander/rover portion of the mission began its Martian landing attempt on 14 May, 2021. About 9 minutes after the aeroshell housing the lander/rover combination entered the Martian atmosphere, the lander safely touched down in the Utopia Planitia region on Mars. After a period spent conducting system checkouts and other planning activities , the lander will deploy the Zhurong rover for independent surface operations. This rover is powered by solar panels and will probe the Martian surface with radar and conduct chemical analyses on the soil; it will also look for biomolecules and biosignatures. Mission objectives

This is the CNSA's first interplanetary mission, as well as its first independent probe to Mars. The primary goal is therefore to validate China's deep space communications and control technologies, as well as the Administration's ability to successfully orbit and land spacecraft.

From a scientific point of view, the mission must meet five objectives:

Study the geological structure of Mars and that structure's historical evolution. To do this, the probe will analyze topographical data from characteristic regions such as dry riverbeds, the reliefs of volcanoes, glaciers at the poles, areas affected by wind erosion, etc. The two cameras present on the orbiter are dedicated to this objective.

Study the characteristics of both the surface and underground layers of Martian soil, as well as the distribution of water ice. This is the role of the radars present on the orbiter and the rover.

Study the composition and type of rocks on the Martian surface, carbonate minerals present in ancient lakes, rivers, and other landscapes resulting from the past presence of water on the planet, and weathering mineral such as hematites, lamellar silicates, sulphate hydrates and perchlorate. The spectrometers on board the orbiter and the rover as well as the multispectral camera are dedicated to this objective.

Study the ionosphere, the climate, the seasons, and more generally the atmosphere of Mars, both in its near-space environment and on its surface. This is the role of the two particle detectors present on the orbiter as well as of the rover's weather station. Study the internal structure of Mars, its magnetic field, the history of its geological evolution, the internal distribution of its mass, and its gravitational field. The magnetometers as well as the radars present on the orbiter and the rover are dedicated to this objective.

The aims of the mission include searching for evidence of current and past life, producing surface maps, characterizing soil composition and water ice distribution, and examining the Martian atmosphere, particularly its ionosphere.

The mission also serves as a technology demonstration that will be needed for an anticipated Chinese Mars sample-return mission proposed for the 2030s. Zhurong will also cache rock and soil samples for retrieval by the later sample-return mission, and the orbiter will make it possible to locate a caching site.

The orbiter's transfer orbit and trajectory correction maneuvers

Map of Mars with the targeted landing site of the Tianwen-1 lander and Zhurong, and the locations of previous Mars landings

In late 2019, the Xi'an Aerospace Propulsion Institute, a subsidiary of China Aerospace Science and Technology Corporation , stated that the performance and control of the future spacecraft's propulsion system has been verified and had passed all requisite pre-flight tests, including tests for hovering, hazard avoidance, deceleration and landing. The main component of the lander's propulsion system consists of a single engine that provides 7,500 N of thrust. The spacecraft's supersonic parachute system had also been successfully tested.

CNSA initially focused on the Chryse Planitia and Elysium Mons regions of Mars in its search for possible landing sites. However, in September 2019 during a joint meeting in Geneva, in Switzerland, of the European Planetary Science Congress-Division for Planetary Sciences, Chinese presenters announced that two preliminary sites in the Utopia Planitia region of Mars have instead been chosen for the anticipated landing attempt, with each site having a landing ellipse of approximately 100 by 40 kilometres.

In July 2020, CNSA provided landing coordinates of 110.318° East longitude and 24.748° North latitude, within the southern portion of Utopia Planitia, as the specific primary landing site. The area appears to provide a relatively safe place for a landing attempt but is also of great scientific interest, according to Alfred McEwen, director of the Planetary Image Research Laboratory at the University of Arizona. Simulated landings have been performed as part of mission preparations by the Beijing Institute of Space Mechanics and Electricity.

By 23 January 2020, the Long March 5 Y4 rocket's hydrogen-oxygen engine had completed a 100-seconds test, which was the last engine test prior to the final assembly of the launch vehicle. It successfully launched on 23 July 2020. Entering Mars orbit

The three Tianwen-1 spacecraft were launched by Long March 5 Heavy-lift launch vehicle on 23 July 2020. Having traveled for about seven months, it entered Mars orbit on 10 February 2021 by performing a burn of its engines to slow down just enough to be captured by Mars' gravitational pull. The orbiter spent several months scanning and imaging the surface of Mars to refine the target landing zone for the lander/rover. It approached at about 265 km to Mars' surface, allowing a high-resolution camera to return images to Earth and to map the landing site in Utopia Planitia, and to prepare for landing. The values of the orbital elements characterizing the final orbit are given in the table hereafter. Values of final orbital parameters Parameter Value

At 23:18 UTC, on 14 May 2021, the Tianwen-1 lander successfully landed in the preselected landing area in the southern part of the Mars Utopia Planitia. The landing phase began with the release of the protective capsule containing the lander/rover. The capsule made an atmospheric entry followed by a descent phase under parachute, after which the lander used retro-propulsion to soft-land on Mars.

On May 19, 2021, the China National Space Administration released for the first time images showing the preparation of the final transfer of the Zhurong rover from the platform of the lander to the Martian soil. The photographies show the solar panels of Zhurong already deployed while Zhurong is still perched on the lander. The long delay for the publication of the first images is explained by the short periods of time when the rover Zhurong and the orbiter are in radio contact and can effectively communicate and transfer data.

The rover Zhurong was successfully deployed on 22 May 2021, 02:40 UTC. The rover is designed to explore the surface for 90 sols; its height is about 1.85 m and it has a mass of about 240 kg . After the planned rover deployment, the orbiter would serve as a telecommunications relay for the rover while continuing to conduct its own orbital observations of Mars.