Zhurong (Rover)

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Model of the rover at the IAC 2018 in Bremen

Zhurong ( Chinese 祝融 号, Pinyin Zhùróng hào ) is the rover of the Chinese Mars mission Tianwen-1, which started on July 23, 2020 . It landed in the Utopia Planitia on May 14, 2021 at 11:18 p.m. UTC .

construction

The dimensions of the rover are approx. 2 × 1.65 × 0.8 meters and the weight is 240 kg. Since the solar constant , i.e. the solar radiation averaged over many years, is less than half as large on Mars as it is near the earth, the rover not only has two solar modules , like the moon rover Jadehase 2, but four that are constantly aligned with the sun, while with the moon rover only one of the two solar modules is movable. In order to save energy for heating, the rover only works from noon, when the temperature on the surface of Mars is highest and the most favorable for the measuring instruments. Part of the energy generated by the solar modules is used to operate the rover, the rest is used to charge an accumulator, which allows the rover to continue working until after sunset. There are also two round "heat collecting windows" on the top of the rover. This includes n -undecane , which melts during the Martian day and in the evening, when it solidifies again when the ambient temperature drops - the substance has a melting point of −26 ° C - releases around 80% of the heat introduced back to the rover and the rover so protects against the night cold. For comparison: the rover's solar modules only have an efficiency of 30%.

The weather on Mars can change rapidly, with dust storms that greatly reduce solar radiation. Therefore the rover has an autonomous self-monitoring system. If it notices that its energy reserves - both in terms of electricity and heat - are only sufficient for a limited period of time, it switches itself off, goes into sleep mode and only resumes work when the weather is better . The surface of the solar modules is provided with a non-stick coating that works according to a principle similar to superhydrophobicity . As a result, little dust settles on them from the start, which reduces their efficiency. In addition, the solar modules are folded up over the rover during the night to protect against the cold. If they briefly assume a vertical position, grains of sand and dust roll away downwards.

Payloads

The rover has the following payloads:

  • Topographic camera (2048 × 2048 pixels, color images in the range 0.5 m - ∞). This stereo camera with two lenses is mounted on top of the mast. With its three-dimensional images, it should help with navigation and support geological studies.
  • Multi-spectral camera (480 nm, 525 nm, 650 nm, 700 nm, 800 nm, 900 nm, 950 nm, 1000 nm, i.e. blue to infrared ). This camera is arranged between the two “eyes” of the topographic camera. It is intended to collect information about the composition of the surface material.
  • Ground penetrating radar with two channels : a low-frequency channel for a depth of 10–100 m with a resolution of a few meters and a high-frequency channel for a depth of 3–10 m with a resolution of a few centimeters
  • Device for measuring the composition of the Martian surface material by means of laser-induced plasma spectroscopy ( Si , Al , Fe , Mg , Ca , Na , O , C , H , Mn , Ti , S etc.) and infrared spectrometer (850–2400 nm with a resolution of 12 nm). This device was developed by the Shanghai Institute for Technical Physics of the Chinese Academy of Sciences (中国科学院 上海 技术 物理 研究所) with the support of the Institut de recherche en astrophysique et planétologie in Toulouse .
  • Fluxgate magnetometer for measuring the magnetic field near the surface of Mars (measuring range: around 2000 nT, resolution: 0.01 nT, temperature-stable 0.01 nT / ° C). The device, based on the principle of the Magson Fluxgate magnetometer from Berlin, with two measuring heads at the base and at the top of the mast, interacts with the magnetometer on the Orbiter.
  • Weather station (temperature: −120 ° C to +50 ° C with a resolution of 0.1 ° C, air pressure: 1–1500  Pa with a resolution of 0.1 Pa, wind speed: 0–70 m / s with a resolution of 0.1 m / s, wind direction: 0 ° –360 ° with a resolution of 5 °, microphone: 20 Hz – 20 kHz with a sensitivity of 50 mV / Pa)

mission

Positioning of the rover

The rover should first photograph the surroundings from the landing platform with the stereo camera on the mast on its front. On the 8th day of Mars after landing, it should roll off the loading area and begin the actual Mars exploration. The nominal maximum speed of the rover is 200 meters per hour, and in the laboratory it was able to cope with gradients of up to 30 °. The rover can drive over smaller stones on the way; the six wheels have tough, abrasion-resistant treads and elastic spokes for vibration and shock absorption. He can raise his ground clearance a little by means of the arms to which the wheels are attached, but in principle tends to avoid larger obstacles, for which he can move sideways by turning the wheels by 90 °. As a result, the distance actually covered will be relatively short. Before the start of the mission, the developers assumed an effective cruising speed of 40 meters per hour.

The rover is navigated according to a principle similar to the orbiter's orbital maneuvers. During the Martian day, when the rover is on the side of the planet facing the sun and thus also the earth, its position is determined by the Chinese deep space network using long-base interferometry , taking into account the position of the orbiter known from the orbital data. Since Mars is relatively close to Earth, all stations of the Chinese VLBI network are suitable for this, even the small 25 m antenna of the Shanghai Astronomical Observatory in Sheshan . The scientists of the National Astronomical Observatories decide on the basis of the knowledge obtained up to this point in time which point the rover should approach next. The technicians at the Beijing Space Control Center use the images from the topographic camera and the maps created during the parking orbit to decide whether this is possible and then give the rover the destination. The rover approaches this destination autonomously.

Zhurong has two obstacle avoidance cameras with fisheye lenses on the front and two on the back of the housing , which not only have a very large angle of view , but also a considerable depth of field and provide the on-board computer with terrain data over a large area, on the basis of which it can make decisions about the course to be taken can meet.

Avoiding contamination

The landing site of the rover

At the Zhurong landing site in the Utopia Planitia there is no water ice near the surface, which means that it does not fall into category IVc (special zone) of the COSPAR rules for the protection of planets . Since the rover does pure geology and astrophysics and does not carry any equipment for the detection of life forms on Mars, the mission falls instead into category IVa, for which the Committee on Space Research recommended in 1994 that there should be no more than 300 on the spacecraft in question Spores per square meter and a total of no more than 300,000 spores should be located in order to avoid contamination of Mars with terrestrial microorganisms. The Chinese Academy for Space Technology (CAST), as the manufacturer of the probe, is responsible for compliance with this standard . For this purpose, one has been in contact with international experts since 2016, when the Mars program of the People's Republic of China was launched. The actual disinfection of the Lander and Rover was carried out by Beijing Shenzhou Astrobiologie GmbH (航天 神舟 生物 科技 集团 有限公司), a subsidiary of CAST, with the support of the Research Center for Astrobiological Projects of the China Aerospace Science and Technology Corporation (中国 航天 科技 集团公司空间 生物 工程 研究 中心) and the Technical Research Center for Astrobiological Projects of the City of Beijing (北京市 空间 生物 工程 技术 研究 中心).

Surname

Zhurong

When the spacecraft launched, the rover was initially nameless. On July 24, 2020, the center for lunar exploration and space projects of the National Space Agency launched an international competition in which all those interested in space could submit proposals for the name of the rover by August 12, 2020. A commission then pre-selected the ten best proposals, from which three names could be selected in an online vote from January 20 to February 28, 2021. From these three names, Zhurong , Nezha and Hongyi ("determination"), a commission selected the final name, which was officially announced on April 24, 2021, Chinese Space Day . Zhurong is a late Neolithic kitchen god who lived around 500 BC. BC, at the beginning of the Warring States Period , rose to become the god of fire. However, due to Confucian atheism, its importance declined again and it became one of many minor deities in Chinese popular belief , especially in Hunan Province . Chancellor Zhang Yue (张 说, 667–730) describes him in his essay “Praise of the Pujin Bridge” (蒲 津桥 赞) again only as a stove god. As part of the Chinese planetary exploration, Zhurong is now supposed to kindle the fire and lead all of humanity to a further exploration of the unknown expanses of the universe.

Web links

Commons : Zhurong  - collection of images

Individual evidence

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