China aims to launch a rover to Mars on Thursday on a journey coinciding with a similar US mission as the powers take their rivalry into deep space.
The two countries are taking advantage of a period when Earth and Mars are closest to send their probes, with China's mission due to lift off by Saturday and the US spacecraft on July 30.
But the race to watch is between the United States and China, which has worked furiously to try and match Washington's supremacy in space.
The Chinese mission has been named Tianwen-1 ("Questions to Heaven") in a nod to a classical poem that has verses about the cosmos.
It is expected to launch on a Long March 5 -- China's biggest space rocket -- from the southern island of Hainan on Thursday, depending on the weather.
Tianwen-1 is expected to arrive in February 2021 after a seven-month, 55-million-kilometre (34-million-mile) voyage.
The mission includes a Mars orbiter, a lander and a rover that will study the planet's soil.
"As a first try for China, I don't expect it to do anything significant beyond what the US has already done," said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics.
The next one, Perseverance, is an SUV-sized vehicle that will look for signs of ancient microbial life, and gather rock and soil samples with the goal of bringing them back to Earth on another mission in 2031.
The Chinese mission is similar to NASA's Viking missions in 1975-1976, in that it has both an orbiter and a lander, McDowell said.
Tianwen-1 is "broadly comparable to Viking in its scope and ambition," he added.
After watching the United States and the Soviet Union lead the way during the Cold War, China has poured billions of dollars into its military-led space programme.
"China joining (the Mars race) will change the situation dominated by the US for half a century," said Chen Lan, an independent analyst at GoTaikonauts.com, which specialises in China's space programme.
China has made huge strides in the past decade, sending a human into space in 2003.
The Asian powerhouse has laid the groundwork to assemble a space station by 2022 and gain a permanent foothold in Earth orbit.
China has already sent two rovers to the Moon. With the second, China became the first country to make a successful soft landing on the far side.
The Moon missions gave China experience in operating spacecraft beyond Earth orbit, but Mars is another story.
The much greater distance means "a bigger light travel time, so you have to do things more slowly as the radio signal round trip time is large," said McDowell.
It also means "you need a more sensitive ground station on Earth because the signals will be much fainter," he added, noting that there is a greater risk of failure.
China has upgraded its monitoring stations in the far-western Xinjiang region and northeastern Heilongjiang province to meet the Mars mission requirements, state news agency Xinhua reported last week.
The majority of the dozens of missions sent by the US, Russia, Europe, Japan and India to Mars since 1960 ended in failure.
Now, Beijing is trying on its own.
"As long as (Tianwen) safely lands on the Martian surface and sends back the first image, the mission will... be a big success," Chen said.
Factfile on China's aim to reach Mars with an orbiter, a lander and a rover. The mission is expected to launch between July 20 and 25.
