Tianwen-1 (China's first Mars Exploration Mission)
China's first Mars exploration mission has been named Tianwen-1. CNSA (China National Space Administration) unveiled the mission name and logo in a ceremony on 24 April 2020 to mark the 50th anniversary of the launch of the country's first satellite. DFH-1 launched on a Long March 1 rocket from Jiuquan April 24, 1970, making China the fifth country to independently launch a satellite. 1) 2)
Tianwen-1, meaning ‘questions to heaven', is taken from the name of a long-form poem by Qu Yuan, a poet born in the fourth century B.C., according to CNSA chief engineer Xiaochun Ge.
The ‘Lanxingjiutian' logo includes representations of the Latin letter ‘c', referring to China, cooperation, and the cosmic velocity required to undertake planetary exploration. Further Chinese planetary missions will also carry the Tianwen name.
Figure 1: The logo for the Mars mission (l), and the general logo for Planetary exploration of China (r). The logo includes the 8 planets and 'C's, representing China, cooperation & the cosmic velocity required to carry out interplanetary exploration (image credit: CNSA, Andrew Jones)
According to the administration, the country's first Martian probe will conduct scientific investigations about the Martian soil, geological structure, environment, atmosphere as well as water.
The robotic probe will consist of three parts – the orbiter, the lander and the rover. The rover will have six wheels and four solar panels, and will carry 13 scientific instruments. The payload mass will be more than 200 kg and will work about three months on the planet, said Sun Zezhou, the probe's chief designer at the China Academy of Space Technology.
Peijian Ye, a leading scientist in deep-space exploration at the academy, said the probe will land on the Martian surface before July 2021.
China is understood to be planning a Mars sample return mission, a Jupiter orbiter and considering possible missions to icy giants and interstellar space. A joint near-Earth asteroid sample return and comet rendezvous mission has also been proposed.
"The country's first Martian probe will conduct scientific investigations about the Martian soil, geological structure, environment, atmosphere, as well as water," CNSA said in a statement.
As the Tianwen-1 spacecraft is scheduled for launch in late July or early August, the mission chief scientist and his team provide an overview focusing on the scientific objectives and instrumentation of China's first Mars mission. 3)
Background: Among the eight planets in the Solar System, Mars is the most similar to Earth and is also close by. It therefore naturally becomes a high-priority target for space exploration. Mars offers a substantial and pragmatic opportunity to answer key questions concerning the existence of extraterrestrial life, and the origin and evolution of the Solar System, and to explore the possibility of human habitation. From the first space probes to fly by the planet in the 1960s to the planetary orbiters and rovers of today, the United States, Russia, Europe, Japan and India have developed Mars exploration programs to fulfil human aspirations. So far, only NASA has successfully landed and operated spacecraft on Mars.
China announced its planetary exploration program beyond the Earth–Moon system in 2016. 4) Benefiting from the engineering heritage of China's lunar exploration program2, 5) the Chinese national strategy set Mars as the next target for planetary exploration. China's first Mars mission is named Tianwen-1, and aims to complete orbiting, landing and roving in one mission. The name means ‘questions to heaven', taken from the name of a poem by Qu Yuan (about 340–278 bc), one of the greatest poets in ancient China. Tianwen-1 is currently on track for a July or August 2020 launch, with arrival at Mars seven months later (Figure 2).
Figure 2: Artist's impression of the Tianwen-1 mission. The mission will study the Red Planet with a combination of orbiter and lander/rover (image credit: CNSA)
How Tianwen-1 will explore Mars
As China's first Mars mission, Tianwen-1 is uniquely ambitious. No nation has ever attempted to send an orbiter and rover to Mars on the first try. Getting from space to the Martian surface is a unique challenge that China will be facing for the first time. Mars landings require heat shielding, thrusters, and supersonic parachutes—a teeth-gnashing experience that NASA has dubbed the "7 minutes of terror." The landing platform and rover are expected to touch down on Utopia Planitia—the vast Martian plain where NASA's Viking 2 spacecraft landed in the 1970s, and the site of a shipbuilding yard in the Star Trek universe. 6)
Once on Mars, the Tianwen-1 landing platform will extend a ramp, allowing the rover to roll gently onto the surface—similar to the way China's Chang'e Moon rovers are deployed. The rover can communicate with Earth directly, or with the Tianwen-1 orbiter, which can relay signals. The orbiter has its own set of science instruments for studying Mars, including a high-resolution camera that should produce stunning images.
The rover will have cameras, instruments for studying Mars' climate and geology, and even an instrument to zap rocks and record the resulting chemical signatures—just like NASA's Curiosity and Perseverance rovers. The rover radar works by shooting radio waves into the surface and measuring reflection times, allowing scientists on Earth to piece together a 3D map of what lies beneath.
China's Yutu-2 rover used radar on the far side of the Moon to reveal 3 distinct layers extending 40 meters beneath the surface. Scientists tested a rover-sized radar in China's Qaidim basin—a cold, desert region like Mars—and were able to detect underground water pockets of water. On Earth, these pockets can host thriving microbial communities, so detecting them on Mars would be an important step in our search for life on other worlds.
The Tianwen-1 mission (known as Huoxing 1 during development) consists of an orbiter and a lander with rover. The Tianwen-1 spacecraft is developed by the China Aerospace Science and Technology Corporation (CASC), and managed by the National Space Science Center (NSSC) in Beijing. The lander carrying the rover will use a parachute, retrorockets, and an airbag to achieve landing. If the landing is successful, the lander would then release a rover. The rover will be powered by solar panels and is expected to probe the Martian surface with radar and to perform chemical analyzes on the soil; it would also look for biomolecules and biosignatures. 7)
The Tianwen-1 probe, with a mass (including fuel) of about 5 tons, comprises an orbiter and a lander/rover composite. The orbiter will provide a relay communication link to the rover, while performing its own scientific observations for one Martian year. The orbit during the scientific observation stage is a polar elliptical orbit (265 km x 12,000 km). The lander/rover will perform a soft landing on the Martian surface some 2–3 months after arrival of the spacecraft, with a candidate landing site in Utopia Planitia. The ~240 kg solar-powered rover is nearly twice the mass of China's Yutu lunar rovers, and is expected to be in operation for about 90 Martian days.
The main task of Tianwen-1 is to perform a global and extensive survey of the entire planet using the orbiter, and to send the rover to surface locations of scientific interests to conduct detailed investigations with high accuracy and resolution. Specifically, the scientific objectives of Tianwen-1 include: (1) to map the morphology and geological structure, (2) to investigate the surface soil characteristics and water-ice distribution, (3) to analyze the surface material composition, (4) to measure the ionosphere and the characteristics of the Martian climate and environment at the surface, and (5) to perceive the physical fields (electromagnetic, gravitational) and internal structure of Mars.
Some parameters of the Tianwen-1 mission:
The total launch mass is 5000 kg. The orbiter has a mass of 3,175 kg, the rover has a mass of 240 kg.
Figure 3: This infographic shows the location of instruments aboard China's Tianwen-1 orbiter (image credit: Andrew Jones, Ref. 6)
Figure 4: This infographic shows the location of instruments aboard China's Tianwen-1 Rover (image credit: Andrew Jones, Ref. 6)
• July 23, 2020: Tianwen 1 is a Chinese-led project, but scientists and support teams from several countries have agreed to provide assistance on the mission (Ref. 12).
- Scientists from IRAP (Institut de Recherche en Astrophysique et Planétologie) in France contributed to a Laser-Induced Breakdown Spectroscopy instrument on the Tianwen 1 rover.
- French scientists, with support from the French space agency CNES, provided guidance to their Chinese counterparts on the spectroscopy technique, which uses a laser to zap a pinhead-size portion of a rock, and a spectrometer to analyze the light given off by plasma generated by the laser's interaction with the rock's surface. The technique allows an instrument to determine the chemical make-up of rocks on Mars.
- Scientists from the Space Research Institute at the Austrian Academy of Sciences assisted in the development of the magnetometer on the Tianwen-1 orbiter and helped calibrate the flight instrument.
- Argentina is home to a Chinese-owned deep space tracking antenna that will be used to communicate with Tianwen-1 after launch. The European Space Agency has agreed to provide communications time for Tianwen-1 on its own worldwide network of deep space tracking stations, and help with the probe's navigation on the journey to Mars.
Figure 5: Logos for ESA (European Space Agency), the French space agency CNES, Argentina's space agency CONAE, and the Austrian Research Promotion Agency (FFG) are installed on the Long March 5's payload fairing (image credit: China National Space Administration)
Figure 6: Ground teams pose with the Tianwen-1 spacecraft in its launch configuration, with the mission's orbiter, lander and rover connected together (image credit: CASC, Ref. 12)
• April 24, 2020 was China's "Space Day," celebrated on the 50 year anniversary of their first satellite launch. On this day, China marked the occasion with the announcement of the name for their first Mars Lander: Tianwen. 8)
- According to China's National Space Administration (CNSA), Tianwen translates to "Quest for Heavenly Truth."
- China is enjoying the success of their recent Chang'e-4 mission to the Moon, which includes a lander, a rover, and also a communications satellite. Now, they're launching a mission to Mars, scheduled for this upcoming July. The Tianwen mission will also feature an orbiter, a lander, and a six-wheeled, solar-powered rover.
- The CNSA isn't as open as NASA or other space agencies, so some of the details of the mission are unclear. But it is roughly aligned with other Mars missions, which are investigating the current and past conditions on Mars, and whether they were conducive to habitability. According to the CNSA, ".... the Martian probe will conduct scientific investigations about the Martian soil, geological structure, environment, atmosphere as well as water." In 2016, the official Chinese news outlet Xinhua reported that Tianwen will "probe the ground with radar, perform chemical analyzes on the soil, and look for biomolecules and biosignatures."
- The CNSA also said, "The name represents the Chinese people's relentless pursuit of truth, the country's cultural inheritance of its understanding of nature and universe, as well as the unending explorations in science and technology." That's all well and good, but what are some of the details of the mission?
- The spacecraft, which will arrive at Mars sometime in February 2021 (if the July launch date is firm) will orbit the planet for some time. China hasn't said exactly when the lander/rover will be deployed to the surface. But when it is, it's expected that it'll use retrorockets, airbags, and a parachute to manage its descent and landing.
- It looks like the Tianwen name applies to the lander, but the rover will get its own name. The rover will be a six-wheeled, solar powered rover, and should have a mission length of at least three months. It'll carry 13 scientific instruments and will weigh more than 200 kg.
- Though important all on its own, the Tianwen mission is also a technology demonstration mission for China's next mission to Mars, which is an ambitious sample-return mission slated for the 2030s.
- None of this is a slam-dunk, of course. We're getting accustomed to successful landings on Mars, largely thanks to NASA. But many attempts at landing a spacecraft on Mars have failed abysmally. There's a lot of sophisticated technology that must be deployed effectively to work. And though China has recently had success with their Moon mission, other countries' missions to Mars have not gone well.
- The first attempt at landing on Mars dates back to 1962, when the Soviet Union tried to get a lander to Mars. That mission failed to leave Low Earth Orbit. In more modern times, March 2016 to be exact, the ESA's Schiaparelli EDM lander crashed when it tried to land on Mars. In fact, only the USA and Russia/Soviet Union have successfully landed craft on Mars, and only NASA has successfully landed rovers.
- This won't be China's first mission to Mars. They were part of the Russian Phobos-Grunt mission. That spacecraft was meant to visit the Martian moon Phobos and return a sample, but China included their Yinghuo-1 Mars orbiter on that mission. That mission was destroyed when the rocket exploded.
- As for landing sites, initially the CNSA was looking at two possibilities. Those were the Chryse Planitia region, and the Elysium Mons region. However, in 2019 China announced that they had identified two preliminary landing ellipses, both in the Utopia Planitia region. Each of the ellipses is about 100 by 40 km.
• March 25, 2020: China aims to become only the second country to land and operate a spacecraft on the surface of Mars (NASA was first with a pair of Viking landers in 1976 if you don't count the former Soviet Union's 1971 Mars 3 mission). With just a few months before launch, China is still keeping key mission details quiet. But we can discern a few points about where and how it will attempt a landing on the Red Planet from recent presentations and interviews. 9)
- The launch: Celestial mechanics dictate that China, along with NASA's Perseverance rover and the Hope orbiter from the United Arab Emirates, will launch around late July during a Hohmann transfer window, which comes around only once every 26 months and allows a trip to Mars using as little propellant as possible.
- A huge Long March 5 rocket will send the Chinese spacecraft on a journey for about seven months, after which it will fire rockets in order to enter orbit around Mars in February 2021.
- The 5-metric-ton spacecraft consists of an orbiter and the landing segment for the rover. It's expected that the spacecraft will remain coupled in orbit until April. The orbiter will employ a pair of cameras to image the preselected landing sites, before attempting to set down the 240-kilogram rover (which has yet to be publicly named) on the surface.
- The landing: Landing on Mars presents unique challenges. There's a thin atmosphere that dangerously heats spacecraft but does little to slow them and a different gravitational field than is found on Earth. But China has experience from earlier space exploits to guide the way.
- Earth and Mars will be around 150 million kilometers apart when the orbiter arrives, so it will take eight minutes for communications signals to travel each way. Therefore the spacecraft's guidance, navigation, and control, or GNC, for the landing process will be fully autonomous. This system will be based on the GNC of Chang'e-4, which autonomously achieved the first landing on the far side of the moon in 2019.
- The blunt body aerodynamics of the entry capsule's heating shield, which is shaped like a spherical cone whose tip forms a 70-degree angle, will provide the first deceleration as it hits the atmosphere traveling at a rate of kilometers per second. Next, while traveling at supersonic speeds, a disk-gap-band parachute will deploy to further slow the spacecraft, and then be discarded. China has drawn on technology and experience from its Shenzhou crewed spacecraft, which has allowed astronauts to re-enter Earth's atmosphere and safely land, for these phases.
- Retropropulsion will be responsible for slowing the spacecraft during its final descent. Most of this will be provided by a 7,500-Newton variable thrust engine, like the main engine used by China's Chang'e-3 and -4 lunar landers. The lander will employ a laser range ﬁnder and a microwave ranging velocity sensor to gain navigation data—technology that was also developed initially for China's moon missions.
- The lander will separate from the main body of the spacecraft at an altitude of 70 meters, according to Zhang Rongqiao, mission chief designer, and enter a hover phase to search for a safe landing spot. 3D laser scanning, or lidar, will provide terrain data such as elevation. Obstacle-avoiding mode, facilitated by optical cameras, will begin at 20 meters above the surface.
- Some of these processes are apparent in this mesmeric footage of the Chang'e-4 landing. An obstacle avoidance phase is apparent as the spacecraft makes its descent to the crater-covered lunar surface which appears fractal in nature.
• In late 2019, the Xi'an Aerospace Propulsion Institute, a subsidiary of CASC, 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 7500 newtons of thrust. The spacecraft's supersonic parachute system had also been successfully tested previously. 10)
- CNSA initially focused on the Chryse Planitia and on the Elysium Mons regions of Mars in its search for possible landing sites for the lander and its associated rover. However, in September 2019, during a joint meeting in Geneva 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 km.
Figure 7: The China Aerospace Technology Corporation (CASC) unveiled the first picture of the country's Mars explorer, a spacecraft set to be launched for Planet Mars in 2020 (image credit: CASC)
• November 21, 2018: China has selected two preliminary areas on Mars for what will be the country's first landing attempt at landing on another planet, to take place in early 2021. 11)
- The mission ambitiously involves a combined orbiter and rover and is set to launch in summer 2020 with a fleet of vehicles from other nations that includes NASA's Mars 2020 rover, the United Arab Emirates' Hope Mars Mission and ExoMars 2020.
- The colorized topographic map showing two candidate areas is based on data from the Mars Orbiter Laser Altimeter (MOLA), an instrument on NASA's Mars Global Surveyor (MGS) spacecraft launched in 1996.
- The first area targets Chryse Planitia, close to the landing sites of Viking 1 and Pathfinder, while the second covers Isidis Planitia and stretches to the western edge of the Elysium Mons region. The final landing site has yet to be selected, with several teams likely involved in providing candidate sites—a process similar to China's lunar missions.
Figure 8: China Mars 2020 rover landing sites Map indicating two preliminary landing areas for China's 2020 Mars rover presented at the sessions of COPUOS in Vienna, Austria in June 2018 (image credit: CNSA)
- The map recently appeared in a presentation at the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) in June, and again in a presentation by mission engineers at the International Astronautical Congress (IAC) in Germany last month.
- As this is China's first independent interplanetary mission, teams will need to succeed on a range of technological challenges including orbital insertion and landing. The country recently made progress on that front with successful supersonic parachute tests and tests of a subsurface detection radar from a hot air balloon in October (link in Chinese).
Launch: On July 23, 2020 (04:41 UTC) a heavy-lift Long March 5 rocket propelled China's first Mars landing mission toward the Red Planet from the Wenchang spaceport on Hainan Island in southern China. CNSA confirmed the Long March 5 rocket placed Tianwen-1 on the proper course toward Mars about 36 minutes after launch. The China Aerospace Science and Technology Corp. (CASC), the government-owned prime contractor for China's space program, declared the launch a success in a statement. 12)
Figure 9: A Long March 5 rocket takes off from the Wenchang Space Launch Center on Hainan Island with the Tianwen-1 Mars mission (image credit: Xinhua)
Tianwen-1 is scheduled to arrive at Mars next February after a seven-month voyage. If successful, the mission will be China's first probe to enter orbit around another planet.
Two-to-three months later, the Tianwen-1 orbiter will release a lander to enter the Martian atmosphere and aim for a controlled touchdown in Utopia Planitia, a broad plain in Mars's northern hemisphere. Once on the surface, the lander will lower a ramp and a 240 kg rover will drive onto the surface.
If China pulls off those feats according to plan, they will make China the third country to perform a soft landing on Mars — after the Soviet Union and the United States — and the second country to drive a robotic rover on the Red Planet.
Mars orbit: After reaching Mars in February, the Tianwen-1 spacecraft will initially enter a long-period capture orbit around the Red Planet. The orbiter will eventually settle in a loop around Mars ranging between 265 km and nearly 12,000 km over the Martian poles.
As soon as next April, the lander and rover modules will detach from the orbiter to begin a descent through the Martian atmosphere. Radar soundings from orbit have indicated the presence of a reservoir of ice containing as much water as Lake Superior, the largest of the Great Lakes, in the Utopia Planitia region targeted by Tianwen-1's lander.
Figure 10: Planned orbital trajectory at Mars. A scheme of the different orbits that the Chinese probe Tianwen-1 will use around Mars, with informations on the orbital parameters of each of them 13)
• January 5, 2021: China's Mars probe Tianwen-1 has traveled more than 400 million km by Sunday (Jan. 3) morning and is expected to enter Mars orbit next month, according to the China National Space Administration (CNSA). 14)
- As of 6 a.m. on Sunday (Beijing Time), the Mars probe had flown in space for 163 days. It was about 130 million km from Earth and about 8.3 million km from Mars.
- According to the CNSA, the probe is functioning stably and is scheduled to slow down before entering Mars orbit in more than a month and preparing itself to land on the red planet. Since its launch on July 23, 2020, the Mars probe has captured an image showing both Earth and the moon, as well as taking several selfies. It has carried out three orbital corrections, a deep-space maneuver and self-checks on multiple payloads.
- The Tianwen-1 probe, with a mass of about five tons, consists of an orbiter, a lander and a rover. It is designed to complete orbiting, landing and roving in one mission.
- After entering the Mars orbit, it will spend two to three months surveying potential landing sites, using a high-resolution camera to prepare for the landing in May.
- The most challenging part of the mission will be the soft landing, an autonomous process of the probe lasting seven to eight minutes. The probe will use its aerodynamic shape, parachute and retrorocket to decelerate and buffer legs to touch down.
- After the landing, the rover will be released to conduct scientific exploration with an expected lifespan of at least 90 Martian days (about three months on Earth), and the orbiter, with a design life of one Martian year (about 687 days on Earth), will relay communications for the rover while conducting its own scientific detection.
- Tianwen-1 means Questions to Heaven and comes from a poem written by Qu Yuan (about 340-278 BC), one of the greatest poets of ancient China. The name signifies the Chinese nation's perseverance in pursuing truth and science and exploring nature and the universe, according to the CNSA.
• November 2, 2020: China's Mars probe Tianwen-1 conducted its third orbital correction Wednesday night (28 October), according to the China National Space Administration (CNSA). 15)
- The probe carried out the orbital correction at around 10 pm (Beijing time) with its eight 25N engines working simultaneously. The performance of the 25 N engines was also tested during the operation.
- The orbital correction aims to fine-tune the transfer orbit after the deep-space maneuver, ensuring that the probe achieves a sound planned rendezvous with Mars.
- Launched on July 23, the probe carried out its first orbital correction on Aug 2 and the second one on Sept 20.
- The probe has traveled about 97 days in orbit, flown about 256 million km and is currently 44 million km from the Earth. All probe systems are in good condition, CNSA said.
- Tianwen-1 is designed to complete orbiting, landing and roving in one mission, taking the first step in its planetary exploration of the solar system.
- It is expected to reach the red planet around February 2021. After entering orbit, it will spend another two to three months surveying the candidate landing sites before it touches down.
• October 11, 2020: China's Mars probe Tianwen-1 successfully conducted a deep-space maneuver on Friday night (Beijing time), according to the China National Space Administration. 16)
- The probe completed the maneuver at 11 p.m. after its main engine worked for over 480 seconds.
- The maneuver took place 29.4 million km from Earth, aiming to help the probe achieve a sound rendezvous with Mars.
- Going forward, the probe will travel along the Earth-Mars transfer orbit for about four months and complete two or three mid-course orbital corrections.
• September 14, 2020: China's Mars probe Tianwen-1 has traveled 137 million km, said sources with the Lunar Exploration and Space Program Center of the CNSA (China National Space Administration). 17)
- As of 9 am Friday (11. Sept.), the probe was in stable condition at a distance of more than 15.3 million km away from Earth, according to a center statement.
- The probe captured a photo of Earth and the moon in late July, and completed its first mid-course orbital correction in early August.
- When arriving at Mars in February 2021, the probe will be about 195 million km from Earth with an actual flight distance of 470 million km, said the center.
• August 31, 2020: China's Tianwen-1 Mars probe had traveled 100 million kilometers as of Friday morning (28 August), according to the China National Space Administration (CNSA). 18)
- The administration said in a statement that the spacecraft was in good condition and several of its mission payloads had completed self-examination and sent scientific data back to ground control.
- By Friday morning, the robotic probe had flown about 36 days in an Earth-Mars transfer trajectory toward the red planet, around 10.75 million km from Earth, it added.
- China launched Tianwen 1, the country's first independent Mars mission, on July 23 from Wenchang Space Launch Center in Hainan province, thus beginning the nation's planetary exploration program.
• August 20, 2020: China's Mars probe Tianwen-1 has traveled more than 8 million km away from Earth and is functioning normally, according to the Lunar Exploration and Space Program Center of the China National Space Administration Thursday. 19)
- As of 11:20 pm Wednesday (19 August), the Mars probe has traveled 8.23 million km away from Earth. Starting from 10:20 pm Wednesday, multiple payloads on the Mars probe, including Mars Magnetometer, Mars Mineralogy Spectrometer and High-resolution Camera, have completed self-check to confirm that they are in normal condition.
- Medium and high-resolution cameras will be used for imaging the Mars surface and conducting research on the topography and geological structure of the planet's surface. The Magnetometer will detect the magnetic environment on Mars, and the Mineralogy Spectrometer will be used to analyze the composition and distribution of minerals on Mars.
- The Mars probe is expected to reach the red planet around February 2021. After entering the orbit, it will spend another two to three months surveying the candidate landing sites before landing.
• On July 27 2020, the Tianwen-1 probe captured an image of the Earth and the Moon with its optical navigation instruments from some 1.2 million kilometers away from Earth. 20)
- China has made a lot of preparations for the mission. The Beijing Aerospace Flight Control Center has carried out repeated drills for various systems to support the launch, while the Xi'an Satellite Control Center in northwest China's Shaanxi province has improved the adaptability of the space-ground communication system for the mission.
- Deep-space ground control stations in Kashgar, northwest China's Xinjiang Uygur Autonomous Region, and Jiamusi, northeast China's Heilongjiang province, had been well-prepared to provide support in measurement and control before the launch.
- Meanwhile, two Tianlian satellites, China's tracking and data relay satellite series, had constantly sent telemetry data back to the ground from the geosynchronous orbit.
- The reason why China chose to launch its Tianwen-1 probe to Mars at this time of the year is to take advantage of the Hohmann transfer orbit, which is considered the best route from Earth to Mars. — Proposed in the 1920s by German engineer Walter Hohmann, the Hohmann transfer orbit forms every 26 months and falls in the summer this year.
What's the most difficult part of the Mars mission?
- To escape Earth's gravitational field and fly to Mars, an object has to reach the "second cosmic velocity" of about 11.2 km/s. The greater the mass of the object is, the more difficult it is for the object to attain the speed.
- The Tianwen-1 probe, however, weighs about five tons, making it the heaviest deep-space probe ever launched by China.
- This mission marks the first time that Long March-5 carrier rocket exceeds the second cosmic velocity, the fastest China's carrier rockets have gone to date.
- Another problem for the mission lay in the information transmission. The fastest speed at which human beings can transmit information is the speed of light, which is 300,000 km/s.
- However, the distance between Mars and the Earth exceeds 50 million kilometers at the closest and reaches 400 million kilometers at the farthest, which results in an information transfer delay ranging from several minutes to dozens of minutes.
- The delay in information transmission means the Tianwen-1 probe can't be directly controlled by the control center on Earth and needs to deal with the unknown environment in the deep space by itself and make judgments and choices on its own.
What's the purpose of the Mars mission?
- The purpose of the Mars mission is not just reaching Mars, as the real goal is to collect as much effective scientific data as possible, according to Liu Tongjie, spokesperson for China's Mars probe mission as well as deputy head of the Lunar Exploration and Space Engineering Center under the China National Space Administration (CNSA).
- The orbiter is equipped with seven instruments and the rover set up with six payloads, Liu added.
- After it landed on Mars, the Tianwen-1 probe will send back images of Mars, investigate the surface and geological structure of the planet, measure and record the climate and magnetic fields, and collect a large amount of scientific data.
- Mars has similar natural environment with Earth and has always been a priority target for manned deep-space exploration outside the Earth-Moon system, Liu pointed out.
- In previous explorations, human beings have found evidence that suggests the existence of water on Mars.
Figure 11: China's first Mars exploration mission, Tianwen-1, takes a photo of the Earth and Moon at about 1.2 million kilometers from Earth, July 27 (image credit: (China National Space Administration)
- Since then, whether Mars is hospitable to life and whether it has connections with Earth have become major scientific issues of the research on Mars. The study of Mars is believed to be significant for understanding the evolution of the Earth.
- Representing a starting point of the planetary exploration program in China's aerospace cause, the Mars mission symbolizes China's pursuit of and progress in exploring the deeper space.
- So far, China has established space stations hundreds of kilometers away from the ground, sent spacecrafts to the Moon that is 300,000 kilometers away from the Earth, and started to explore Mars in the deeper space.
- Step by step, China is marching toward farther places in the universe with the exploration spirit and persistent efforts of Chinese astronauts.
Chinese scientists say the Tianwen-1 mission will perform a global survey of Mars, measuring soil and rock composition, searching for signs of buried water ice, and studying the Martian magnetosphere and atmosphere. The orbiter and rover will also observe Martian weather and probe Mars's internal structure (Ref. 12).
The orbiter's seven instruments include:
• Medium-Resolution Camera
• High-Resolution Camera
• Mars-Orbiting Subsurface Exploration Radar. After landing on Mars, China's Tianwen-1 probe will detect the surface and internal structure of the red planet by using its onboard radar equipment. 21)
- A ground-penetrating radar, a key probe instrument, was developed by the Aerospace Information Research Institute under the Chinese Academy of Sciences. It is expected to survey the Martian soil and ice, and to collect data about the structure beneath the planet's surface at depths of between 10 and 100 meters.
• Mars Mineralogy Spectrometer
• Mars Magnetometer
• Mars Ion and Neutral Particle Analyzer
• Mars Energetic Particle Analyzer
The Tianwen-1 rover is cocooned inside a heat shield for a fiery descent to the Martian surface. After releasing from the orbiter mothership, the lander will enter the Red Planet's atmosphere, deploy a parachute, then fire a braking rocket to slow down for landing.
"Tianwen-1 is going to orbit, land and release a rover all on the very first try, and coordinate observations with an orbiter," Wan, the late chief scientist for China's Mars program, wrote in Nature Astronomy. "No planetary missions have ever been implemented in this way. If successful, it would signify a major technical breakthrough.
"Scientifically, Tianwen-1 is the most comprehensive mission to investigate the Martian morphology, geology, mineralogy, space environment, and soil and water-ice distribution."
The rover's six science payloads include:
• Multispectral Camera
• Terrain Camera
• Mars-Rover Subsurface Exploration Radar
• Mars Surface Composition Detector
• Mars Magnetic Field Detector
• Mars Meteorology Monitor
The rover's ground-penetrating radar would be one of the first science instruments of its kind to reach the surface of Mars. NASA's Perseverance rover carries a comparable instrument to scan subsurface layers of the Martian crust in search of water ice deposits.
Tianwen-1 is a Chinese-led project, but scientists and support teams from several countries have agreed to provide assistance on the mission.
Scientists from IRAP (Institut de Recherche en Astrophysique et Planétologie), in France contributed to a Laser-Induced Breakdown Spectroscopy instrument on the Tianwen-1 rover.
French scientists, with support from the French space agency CNES, provided guidance to their Chinese counterparts on the spectroscopy technique, which uses a laser to zap a pinhead-size portion of a rock, and a spectrometer to analyze the light given off by plasma generated by the laser's interaction with the rock's surface. The technique allows an instrument to determine the chemical make-up of rocks on Mars.
Argentina is home to a Chinese-owned deep space tracking antenna that will be used to communicate with Tianwen 1 after launch. The European Space Agency has agreed to provide communications time for Tianwen 1 on its own worldwide network of deep space tracking stations, and help with the probe's navigation on the journey to Mars.
China is using a combination of its own tracking antennas and ESA's global network of ground stations.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).