Tianwen-1 is now headed for the red planet. The probe’s mission is to study the chemical composition of the Martian surface.
Never have interplanetary flights to Mars been on such a busy schedule, with three international probes to the planet leaving within days of each other.
The United Arab Emirates’ Hope orbiter blasted off aboard a rocket on Monday in Japan, becoming the first of three probes headed to Mars this summer. On Thursday, China launched its Tianwen-1 probe, aiming to complete orbiting, landing and roving in one mission. The US will launch its Mars 2020 probe in tow with the liftoff of the Perseverance rover.
The probes are launched in quick succession due to the occurrence of a biennial launch window, the optimal period for spacecraft to fly to Mars.
At their furthest, Earth and Mars can be about 400 million kilometers apart, nearly 1,000 times the distance between Earth and the moon. At their closest, they are still 55 million kilometers apart.
Roughly every 26 months the two planets get closer, which creates a launch window, usually lasting for a few weeks.
Even when the two planets are closest, it still takes about seven months to get to Mars, compared with about 10 days to the moon.
This year’s launch window opened in mid-July and is expected to end in mid-August. Within this period, China launched the first-ever Mars probe as expected, about four years after the country’s Mars exploration program was approved.
It’s a long way to Mars, and the Shanghai Astronomical Observatory of the Chinese Academy of Sciences is offering navigational aid.
Researchers will use the most advanced version of Very Long Baseline Interferometry (VLBI) to precisely track and position Tianwen-1 all the way from Earth to Mars.
“By the time we discover deflection from trajectory, the probe may have veered some 1,000 kilometers off course, and it would require a lot of fuel to bring it back. But with the help of VLBI, we can correct it when it deviates from orbit by only about 10 kilometers,” said Liu Qinghui, a researcher at the observatory.
China’s VLBI system is made up of a VLBI center and four stations in Shanghai, Beijing, Kunming in southwest Yunnan Province and Urumqi in northwest Xinjiang Uygur Autonomous Region.
For the Mars probe, they have upgraded the system.
“We have developed more than 40 pieces of equipment, such as a new data analysis system and new positioning system, as well as atomic clock and vapor radiometer,” Liu said.
Humans are particularly interested in Mars, believing that it could be our second home. The two planets, indeed, share some similarities.
Mars has an atmosphere and two natural satellites. It experiences a day-and-night cycle in a period of 24 hours and 40 minutes, and four seasons in one Mars year, equaling approximately two years on Earth.
Much smaller than the Earth, Mars, however, has roughly the same land surface area. But it’s a desert world with glaciers, mountains and dust storms. Also, temperatures on Mars vary from minus 130 degrees Celsius near the poles to 30 degrees near its equator.
Uninhabitable today, however, Mars might have been much like the Earth more than 4 billion years ago when it was surrounded by an oxygen-rich atmosphere and filled with water. The warm and wet conditions might have once hosted life.
“Basically, Perseverance will scour Mars in search of signs of life,” said Shu Rong, deputy director of the Shanghai Institute of Technical Physics of the CAS.
Perseverance is equipped with SHERLOC, a life-detection instrument which can uncover organic material. Tianwen-1 lacks such equipment, but advanced laser technology is onboard to analyze the elements on Mars, Shu said.
“What Chinese scientists want to detect most is hydrogen and oxygen, essential elements of water,” he said.
“Our main mission is to detect the mineral composition on the surface of Mars,” said He Zhiping, a researcher at the institute. “Based on detection results, we can further study how Mars has evolved to a barren land, providing reference for the study of Earth.”
The institute has designed two state-of-the-art payloads for Tianwen-1.
The spectrometer onboard the orbiter works based on sunlight reflected on Mars. It can reveal the mineral composition of rocks, whether silicate or titanic iron ore, according to He.
Meanwhile, a detector on the rover can determine the composition of rocks, according to Shu.
It can emit laser pulses to vaporize rocks, as strong as the energy of millions of bulbs released onto a pinhead, turning its molecules into plasma and producing its ion spectrum. This will reveal chemical elements in the rocks, Shu said.
“Technically, the two payloads are up to an international advanced level,” Shu said.
The extremely tough environment on Mars is a big challenge to the detector, installed just in the front of the rover, according to Xu Weiming, a researcher at the institute.
Historically, more than half of Mars probes have ended in failure. This hasn’t discouraged scientists, and instead more countries are sending spacecraft to Mars.
“It’s a venture into the unknown,” Shu said. “What we detect also depends on where the rover lands, and we are expecting to land in a place with hidden treasures.”
When more countries get involved in Mars probes, it requires more international collaboration, Shu said.
China started international cooperation in deep space exploration with the Chang’e-4 lunar probe, which used imported equipment. The cooperation moves deeper with Tianwen-1, as China will be able to provide and share data with others, rather than just receiving unilateral help, he said.
“Other countries have realized China’s rapid progress in deep space exploration. And there will sure be more international cooperation,” he said.
Li Qian / SHINE