China raises the stakes with second Mars attempt
This article originally appeared in the July 13, 2020 issue of SpaceNews magazine.
China’s first attempt to reach Mars never made it out of low Earth orbit.In November 2011, China’s Yinghuo-1 orbiter — strapped beneath Fobos-Grunt, a Russian spacecraft built to retrieve samples from the larger of Mars’ two moons — lifted off from Baikonur Cosmodrome in Kazakhstan atop a Ukrainian Zenit rocket. Right around the time a series of engine burns were meant to send them on their way toward Mars, contact was lost. Two months later, after failed attempts to reestablish contact, the ill-fated pair fell back to Earth.
Nearly nine years and four Mars launch windows later, China is ready to try again. This time, however, China has the capabilities to make the attempt itself, in what will be the country’s first interplanetary mission. Success will require utilizing and combining the experience and technologies developed in lunar exploration and other areas.
The recently named Tianwen-1 mission — meaning “heavenly questions” — will combine an orbiter and a rover in a single launch. China has designated it the first in a series of deep space missions.
Officials have been cagey with launch information despite Chinese state media already preparing to cover the launch from the Wenchang Satellite Launch Center, a coastal spaceport built for the Long March 5 heavy-lift rocket that successfully returned to flight in December following a 2017 failure.
All indications are that Tianwen-1 is scheduled to lift off July 23 aboard the heavy-lift Long March 5. It will be only the rocket’s fourth mission, including the July 2017 failure, and will attempt to send the orbiter and lander/rover combo farther than any Chinese spacecraft have gone before.
China’s Yuanwang-class tracking ships will assist the launch, along with support from the European Space Agency’s ESTRACK facilities. First acquisition of the spacecraft as it separates from its Long March 5 launcher is expected to be made by the 15-meter antenna in Kourou, French Guiana. Deep space antennas in Australia and Spain will also track the Tianwen-1 spacecraft during critical activities like trajectory-change maneuvers and arrival at Mars.
Arrival and landing
Like NASA’s Perseverance rover and the United Arab Emirates’ Hope orbiter launching this summer, Tianwen-1 will arrive at Mars in early February. However, the timing of the attempt to land the roughly 240-kilogram, solar-powered Tianwen-1 is still shrouded in mystery. The lander and orbiter are expected to remain together in a parking orbit for two to three months before making the landing attempt.
The delay would allow the orbiter to survey the candidate landing sites with its cameras and provide the lander with the data required to make its landing attempt.
The early part of the lander’s entry and descent will be aided by aeroshell and parachute know-how from the Shenzhou human spaceflight missions. A blunt-body aeroshell will help slow the speed of the entry vehicle from around 4.8 kilometers per second to 460 meters per second over the course of 290 seconds. A disk-band-gap supersonic parachute will then further slow the craft to a speed of 95 meters per second over the next minute and a half.
Retropropulsion systems from China’s lunar landers will then do the rest of the work. Technologies proven on the Chang’e-3 and -4 missions China sent to the moon in 2013 and 2019, respectively, will provide altimetry and hazard avoidance.
Harmoniously combining all these capabilities for an autonomous landing attempt on a world millions of kilometers and minutes of light delay away represents a greater challenge than the Chang’e missions.
The landing site is expected to be either around Elysium Planitia, a region that includes the site of the failed Beagle 2 landing, or on the other side of the planet at Chryse Planitia, near the Viking 1 and Pathfinder sites. Areas were selected based on both science goals and engineering constraints, which include low elevation to provide more atmosphere and time to slow the lander’s descent as well as the solar power needs of the rover.
A team at the Institute of Space Sciences at Shandong University have assessed the probability of dust storms in Isidis Planitia within the first area to suggest five landing areas best suited to the rover. Papers from Chinese teams suggesting landing sites within Von Kármán crater for the Chang’e-4 lunar far side mission were likewise published ahead of time, but none revealed the final target.
When the landing attempt comes, it will have a landing ellipsis, or area within which the spacecraft is statistically expected to set down, of 100 by 20 kilometers, far larger than the 25 by 20 kilometers for Perseverance.
The mission has a range of science goals in addition to engineering objectives. The orbiter carries seven science payloads including medium- and high-resolution cameras, the latter comparable to HiRise on NASA’s 2005 Mars Reconnaissance Orbiter mission. It also carries a magnetometer, a sounding radar and instruments for atmospheric and ionosphere detections. The orbiter, which will also perform a relay function, is designed to operate for one Mars year, or 687 Earth days.
Elena Pettinelli of Roma Tre University, Italy, who was involved in the ground-penetrating radar experiments on the Chang’e-3 and -4 rovers, says the instruments on orbiter and rover could potentially provide a lot of new information.
The orbiter’s radar may be able to detect clearer evidence of a subsurface water lake beneath the planet’s south pole, Pettinellli says. Observations made by the MARSIS instrument aboard ESA’s Mars Express orbit suggest the presence of a substantial body of water about 1.5 kilometers below a polar ice cap.
Werner Magnes, a scientist at the Institute for Space Research of the Austrian Academy of Sciences who heads a group which collaborated with China for the calibration and testing of the magnetometer for the mission, also has high hopes for the mission.
“There’s a big science interest in this mission and its data. We hope that the data policy on the Chinese side will be open so that we get access so that our scientists and physicists here can do science with the data.” China began its release of Chang’e-4 data one year after landing, but the policy for Mars has yet to be stated.
The rover, designed to last 90 Mars days, carries six instruments, including a laser-induced breakdown spectroscopy experiment similar to that carried by NASA’s Curiosity rover for detecting surface elements, minerals and rock types. As well as topography and multispectral imagers, the vehicle has payloads related to climate and magnetic field detections.
The rover also carries a ground-penetrating radar. Such an instrument has not been placed on Mars before, but two could arrive soon. Like the RIMFAX imager on NASA’s Perseverance rover, China’s payload will use radar waves to reveal geologic layers beneath the surface. Xu Yi from the Macau University of Science and Technology and colleagues at the China University of Geosciences, Wuhan, and the Institute of Remote Sensing and Digital Earth in Beijing, suggest in a paper that a ground-penetrating radar could, based on testing at a Mars analog site in China, detect underground deposits of water ice or brine below the Martian surface.
Such pockets could, in theory, provide habitats for halophilic microbial communities on Mars. “We suggest that [the ground-penetrating radar] on a Martian rover could be used to detect ancient brine supply channels beneath salt polygons and locate the sample position of the interior material for the detection of possible biological activity on Mars,” Xu says.
Alfred McEwen, director of the Planetary Image Research Laboratory at the University of Arizona, noted in a blog post that Utopia Planitia could lend itself to investigations into potential past subsurface habitability.
Pettinelli says having a radar on the surface could allow scientists to recognize the presence of pockets of brines or permafrost in the first few meters, but the instrument would in any case reveal precious information. “We do not have any real idea about the stratigraphic sequence of the first few meters.”
Multiple mission concepts
India’s successful insertion of the Mars Orbiter Mission into orbit around the Red Planet in 2014 made China take note. “This is the pride of India and the pride of Asia and is a landmark progress in humankind’s exploration of outer space so we congratulate India on that,” Foreign Ministry spokesperson Hua Chunying said.
What followed was China’s early 2016 approval of a more ambitious mission than India’s. But before settling on the mission that became known as Tianwen-1, China considered an even more complex concept. In addition to flying an orbit and a rover, China considered a concept from the Qian Xuesen Laboratory of Space Technology that also included three penetrators, to be released during descent, and an aerostat which would operate at an altitude of between 1 and 5 kilometers for one week. The aim would have been to obtain “three-dimensional, multi-layer and multi-source information” in one mission.
It is unclear if China has, as it’s done with its lunar missions, manufactured a backup orbiter and lander. If so, it could provide China with another shot at the Red Planet in 2022, either in the case of failure of Tianwen-1, or to follow up at a new landing site. As it stands, China’s planned second Mars mission is to be an audacious sample return around 2028- 30. Originally conceived as a one-shot mission using the in-development Long March 9 super-heavy-lift launcher, a more recent concept opts for one launch each of the active Long March 5 and Long March 3B rockets. According to the 2016 space white paper, China stated it would “conduct further studies and key technological research” into bringing back samples from Mars.
Beyond this, Tianwen-1 is designated as the first in a new series of interplanetary and deep space exploration. Next is the tentatively named ZhengHe mission, which could take on the designation Tianwen-2. The mission aims to collect samples from near-Earth asteroid 2016HO3/469219 Kamo’oalewa and return these to Earth before heading to main belt comet 133P/Elst-Pizarro. The mission profile requires launch to take place in 2022.
A mission featuring two “Interstellar Heliosphere Probes” is also being pushed. Two launches would use a Jupiter assist to follow up on the discoveries of the Voyagers. One may even include a small probe for a flyby of Neptune. In addition, concepts for missions to Jupiter are being studied for launch in 2030, which could complement the studies of the Jovian system by NASA’s Europa Clipper and ESA’s JUICE missions.
China is hoping Tianwen-1 is the first in a line of ambitious, successful deep space exploration missions.
This article originally appeared in the July 13, 2020 issue of SpaceNews magazine.