NASA’s Perseverance rover made its spectacular landing on Mars in February, but there’s another spacecraft still awaiting its chance at setting down on the Red Planet.
Tianwen-1, China’s first interplanetary expedition, successfully and spectacularly entered Mars orbit February 10. Consisting of both an orbiter and rover, the spacecraft has been circling Mars, preparing for its own landing attempt.
The China National Space Administration (CNSA)—the public face of a generally lowkey, taciturn space program—has said the Tianwen-1 rover will land sometime in May or June. Wang Chi, director general of China’s National Space Science Center, said during the National Academies’ Space Science Week Plenary Session on March 23 that the attempt would take place in mid-May.
While this is still vague, we know a lot about where and how the rover will land, and what it aims to do if the rover successfully sticks the landing—something only NASA has so far achieved.
A model of the Tianwen-1 Mars rover is displayed during an exhibition at the National Museum of China in Beijing on March 4, 2021.Photo: Wang Zhao/AFP/Getty Images
The 1.85 meters tall rover is solar-powered and has a mass of around 240 kg, making it far smaller than the huge, 1,025-kg radioisotope-powered Perseverance but larger than NASA’s earlier Spirit and Opportunity rovers. It is notably roughly twice as massive as China’s own Yutu lunar rovers.
The six-wheeled rover has a top speed of 200 meters-per-hour and was tested out at a site built by the China Academy of Space Technology. It carries six payloads for science.
China has operated rovers on the moon and has drawn from these missions in developing their Mars rover program. But the far greater distance and communication time challenges mean the vehicle needs to be more autonomous. Additionally, its four solar panels are designed in the shape of foldable butterfly wings. Solar power collection needs to be greater, with Mars receiving around 44% of the levels of sunlight that reach Earth.
The rover’s design lifetime is 90 Sols, or 92.5 Earth days. However, Yutu-2, China’s lunar far side rover had a similar design lifetime, but is still going after more than 800 days.
The CNSA is in the process of deciding a name, with a shortlist of candidate names drawing on Chinese mythology, history, and terms.
Tianwen-1 Rover Science
The rover carries six science payloads to study the topography, geology, soil structure, minerals and rock types and atmosphere in the area.
NaTeCam: A pair of 2048 × 2048 pixel navigation and terrain cameras mounted on the mast of the rover to provide 3D panoramic imaging, assist navigation and study Mars topography and geology.
MSCam: A multispectral camera installed on the mast between the NaTeCams to provide information on surface materials and their distribution across nine spectral bands. It covers eight spectral bands as well as visible light.
MarSCoDe: The Mars Surface Composition Detector includes a laser-induced breakdown spectroscopy (LIBS) spectrometer, which vaporizes rocks to analyze their composition.
RoPeR: A penetrating radar picking up echo data to study the soil and potential water ice below the surface. Two frequency channels will probe subsurface layers down to 10 meters with centimeter-level vertical resolution and to 100m with 1m resolution, respectively.
RoMAG: A mast-mounted magnetometer for measuring the magnetic field. It will work together with another magnetometer aboard the orbiter.
MCS: The Mars Climate Station combines a number of sensors to collect data on temperature, pressure, wind speed and direction.
The rover also carries calibration targets and samples for some instruments, as with Perseverance. It also carries a pair of hazard avoidance cameras on the front of the chassis.
Where will the Tianwen-1 rover land?
Tianwen-1 shot this image of the expected landing siteImage: CNSA/TPG/AP
The primary landing area is in Utopia Planitia, a large plain and impact basin, selected by balancing engineering constraints—including low altitude to provide more atmospheric slowing of the spacecraft, low latitude for solar power, and relatively smooth surface—with science goals, including those offered by the topography and geology of the area.
Alfred McEwen, director of the Planetary Image Research Laboratory (PIRL) at the University of Arizona, noted last year that “Utopia Planitia may have been extensively resurfaced by mud flows, so it is an interesting place to investigate potential past subsurface habitability.”
The orbiter has already entered an orbit optimized for repeated passes over the target area, collecting imagery to assess the terrain. The target site has been precisely noted as 110.318 degrees east longitude and 24.748 degrees north latitude by official Chinese outlet China Space News.
CNSA recently released two images taken by the high-resolution camera on Tianwen-1 which match the given coordinates, according to Phil Stooke, an associate professor at the Department of Geography and the Centre for Planetary Science and Exploration at the University of Western Ontario in Canada.
Stooke, a planetary cartographer, says the small white lines in both images are sand dunes. “They will probably have to be avoided by the rover, but they are not continuous enough to be serious obstacles,” he says. “There are small craters, but not enough to really get in the way. The surface should be easy to navigate and it would be really nice to be able to visit one of the little volcanic cones if they are in range.”
Another, earlier candidate landing area is Chryse Planitia, close to the landing sites of Viking 1 and Pathfinder.
How will the rover land?
Landing on Mars presents unique challenges, above and beyond China’s own impressive lunar landings. The great distance from Earth and ensuing light-time delay demands spacecraft automation, while a thin atmosphere dangerously heats spacecraft but does little to slow them.
The attempt itself is known as entry, descent and landing (EDL), a sequence of automated maneuvers that NASA engineers have dubbed the “seven minutes of terror”—because teams can only watch and wait for signals of success from the surface.
After separating from the orbiter, the rover will enter the atmosphere traveling at a rate of four kilometers per second. It will be protected by an aeroshell, shaped like a spherical cone whose tip forms a 70-degree angle, providing the first deceleration as it hits the atmosphere and protection from the intense heat generated by contact with the Martian air.
Next, while traveling at supersonic speeds, a disk-gap-band parachute will deploy to further slow the spacecraft during descent, before being 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 two phases.
Retropropulsion will be responsible for slowing the spacecraft during its final descent, aiming to softly put a lander platform on the service. Most of the thrust 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. 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.
The rover will then need to descend from the platform onto the surface, a painstaking process that may take more than a week.
How to follow?
China did not provide live streams of its Chang’e-4 lunar far side landing nor the recent Chang’e-5 moon sample-return mission, so it is unlikely we’ll get to witness the scenes at mission control as with NASA’s Perseverance and other missions. If coverage is provided, it would likely be through Chinese social media, through Chinese TV, or in English via CGTN.
Regular updates through Chinese media and space authorities such as CNSA will follow swiftly however in the event of a successful landing.
Andrew Jones is a freelance journalist based near Helsinki. He writes about the space industry and technology with a particular focus on China's activities.