Chinas Long March 5 rocket prepares for rollout from an assembly building to its launch pad July 17 at the Wenchang Space Launch Center on Hainan Island. Credit: Xinhua

Chinas heaviest rocket has rolled to its launch pad for liftoff Thursday with the countrys first Mars landing mission, an ambitious attempt to place an orbiter around the Red Planet and a robotic rover on the Martian surface in early 2021.

The Chinese mission, named Tianwen 1, is the second of three probes taking aim on the Red Planet this month, when Mars is properly positioned in its orbit around the sun to allow a direct journey from Earth. Such launch opportunities only come about once every 26 months.

A Mars orbiter named Hope developed by the United Arab Emirates in partnership with U.S. scientists successfully launched Sunday aboard a Japanese H-2A rocket. NASAs Perseverance rover is scheduled for liftoff from Cape Canaveral on an Atlas 5 rocket July 30.

The UAE, Chinese and U.S. missions are all due to arrive at Mars in February 2021.

A Long March 5 rocket is set for liftoff with Chinas Tianwen 1 mission some time between 12 a.m. and 3 a.m. EDT (0400-0700 GMT) Thursday, according to public notices warning ships to steer clear of downrange drop zones along the launchers flight path.

Chinese officials have not officially publicized the launch date. Chinese state media outlets have only reported the launch is scheduled for late July or early August, and officials have not confirmed whether the launch will be broadcast live on state television.

The launch will be the first operational flight of Chinas Long March 5 rocket, the most powerful launch vehicle in the countrys inventory. Ground crews at the Wenchang Space Launch Center on Hainan Island Chinas newest launch site transferred the Long March 5 rocket to its launching stand Friday for final pre-flight checkouts.

China has launched four Long March 5 rockets since the heavy-lift launcher debuted in 2016. Three of the four missions have been successful, including the last two test flights.

The Long March 5 will aim to send the Tianwen 1 spacecraft away from Earth on a seven-month trip to Mars. The ambitious mission is Chinas first probe to another planet, following a series of progressively complex robotic expeditions to the moon.

Most recently, China has landed two rovers on the moon, including the first to explore the surface of the lunar far side. The next Chinese lunar mission, named Change 5, is scheduled for launch late this year on a mission to return samples from the moon.

China kicked off development of the Mars mission in 2016.

It will be the countrys second attempt to reach Mars with a robotic probe, following the Yinghuo 1 orbiter, which was stranded in Earth orbit after launch as a piggyback payload on Russias failed Phobos-Grunt mission.

Benefiting from the engineering heritage of Chinas lunar exploration program,the Chinese national strategy set Mars as the next target for planetary exploration, wrote Wan Weixing, chief scientist of Chinas Mars exploration program, in a paper published this month by the science journal Nature Astronomy. Chinas first Mars mission is named Tianwen 1, and aims to complete orbiting, landing and roving in one mission.

Wan died in May after a long illness.

Chinese officials announced the Tianwen name for the countrys planetary missions in April. The name Tianwen comes from the work of ancient Chinese poet Qu Yuan, meaning quest for heavenly truth, according to the China National Space Administration, or CNSA, the countrys space agency.

The countrys first Martian probe will conduct scientific investigations about the Martian soil, geological structure, environment, atmosphere, as well as water, CNSA said in a statement.

The entire Tianwen 1 spacecraft weighs about 11,000 pounds, or 5 metric tons, fully fueled for launch, according to the mission summary in Nature Astronomy.

Assuming a successful launch this month, the spacecraft will enter orbit around Mars in February 2021, eventually settling in a loop around the Red Planet ranging between 165 miles (265 kilometers) and nearly 7,500 miles (12,000 kilometers) 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. The prime candidate for the Tianwen 1 missions landing site is in Utopia Planitia, a broad plain in the northern hemisphere of Mars where 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.

The Tianwen 1 rover weighs about 529 pounds, or 240 kilograms, nearly twice the mass of Chinas Yutu rovers on the moon.

The orbiter is designed to operate for at least one Martian year, or about two years on Earth. The solar-powered rover, fitted with six wheels for mobility, has a life expectancy of at least 90 days, Chinese officials said.

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 Marss internal structure.

The orbiters seven instruments include a:

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 Planets 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 Chinas 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 rovers six science payloads include a:

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 theInstitut de Recherche en Astrophysique et Plantologie in France helped develop a Laser-Induced Breakdown Spectroscopy instrument on the Tianwen 1 rover. Scientists from the Space Research Institute at the Austrian Academy of Sciences contributed to 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.

When it takes off, ten liquid-fueled engines will power the Long March 5 rocket and Tianwen 1 off the launch pad with nearly 2.4 million pounds of thrust.

The Long March 5s flight path will take the rocket east from Hainan Island over the South China Sea, where it will drop its four-strap on boosters each powered by two kerosene-fueled YF-100 engines around three minutes after liftoff. Unlike launches from Chinas inland spaceports, missions originating from Wenchang follow trajectories over the sea, allowing rockets to jettison stages over water rather than over land.

Two YF-77 engines on the Long March 5s core stage will burn super-cold liquid hydrogen and liquid oxygen propellants for nearly eight minutes. During the first stage burn, the Long March 5 will jettison its clamshell-like payload fairing once the launcher climbs above the thick, lower layers of the atmosphere.

Two restartable hydrogen-fueled YF-75D engines drive the Long March 5s second stage. The second stage engines are expected to perform two firings before deploying Tianwen 1 on its trajectory toward Mars.

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China moves massive rocket into place for ambitious Mars shot - Spaceflight Now