China’s Long March 5B rocket rolls out with new space station module – Spaceflight Now

China’s Long March 5B rocket rolls out with new space station module – Spaceflight Now

The Long March 5B rocket slated to launch the Wentian module to China’s space station rolls out of its assembly building at Wenchang Launch Base on Hainan Island on Monday. Credit: CMSE

China moved a Long March 5B heavy rocket to its launch pad on Monday in preparation for liftoff this weekend along with a 22-tonne module for the country’s Tiangong space station, a mission that could end in another uncontrolled reentry of the Long March 5B. large central stage.

The mighty launch vehicle moved from its assembly building to the launch pad at Wenchang Launch Center on southern China’s Hainan Island on Monday. The Chinese space station’s Wentian module is encapsulated in the rocket’s payload fairing.

The Long March 5B rocket is expected to launch around 2:20 a.m. EDT (0620 GMT) on Sunday, July 24, according to airspace warning advisories associated with the mission. This is also the approximate time when the Tiangong space station’s orbital plane passes over the Wenchang launch center.

The Wentian module, with a launch weight close to 44,000 pounds (20 metric tons), will dock with the Tianhe core module on China’s Tiangong station in low Earth orbit. Chinese astronauts Chen Dong, Liu Yang and Cai Xuzhe living on the Tiangong complex will watch for Wentian’s arrival and then become the first crew members to float in the station’s new module.

This weekend’s launch will add the second of three large pressurized modules needed to complete the initial construction of the Tiangong space station. The Tianhe main module was launched on a Long March 5B rocket in April 2021, and Chinese ground teams are preparing the Mengtian module for launch on a Long March 5B rocket in October.

The Wentian module carries a small robotic arm designed for more precise movements than the larger arm positioned outside the central Tianhe module. The Wentian module will mainly host experiments in life sciences and biology, Chinese officials said.

A Long March 5B rocket with the module from China’s Wentian space station rolls toward its launch pad Monday at the Wenchang Space Center on Hainan Island. Credit: CMSE

The Wentian module will initially dock with an axial port on the Tianhe module, a docking mechanism that was recently obliterated by the departure of a Tianzhou freighter that is no longer needed. Tianhe’s mechanical arm will move the module to its final position on the side of the central section of the space station.

The Mengtian module slated for launch later this year will arrive at the Tiangong space station in the same way. Once Wentian and Mengtian are in their final positions, the Chinese station will have a distinctive “T” shape with its three main pressurized elements.

With the Long March 5B on the launch pad to send the Wentian module into orbit, Chinese Wenchang teams will perform final pre-flight checks and tests before loading kerosene, liquid hydrogen and liquid oxygen propellants into the rocket in the final hours before launch. Sunday.

Ten engines will fire to blast the 176-foot-tall (53.7-meter) Long March 5B rocket into the sky with 2.4 million pounds of thrust.

The Long March 5B rocket is a variant of the Long March 5, China’s most powerful launch vehicle, which flies without the upper stage needed to place payloads into high-altitude orbits or send spacecraft to the Moon. or on Mars. On Long March 5B, the upper stage is replaced by an enlarged payload volume to accommodate large modules for the Chinese space station.

This means the Long March 5B rocket can achieve low-altitude orbit using four kerosene-fueled belt boosters and a hydrogen-fueled core stage. On the previous two Long March 5B flights, including the Tianhe core module launch last year, the core stage remained in low orbit after its payloads were deployed.

The mission patch for the Wentian module launch shows the lab item docked to an axial port of the Tianhe core module, before it was repositioned to a side port with the robot arm. Credit: CMSE

The main stages of previous Long March 5B missions returned to the atmosphere about one to two weeks after launch. The center stage of Long March 5B is about 100 feet (30 meters) long and has an empty mass of about 23.8 tons (21.6 metric tons), making it one of the most man-made objects largest and most massive to ever re-enter the atmosphere. in an uncontrolled way.

After the last launch and reentry of Long March 5B last year, NASA Administrator Bill Nelson said China “failed to meet responsible standards for its space debris”.

“Space nations should minimize the risks to people and property on Earth from space object reentries and maximize transparency regarding these operations,” Nelson said in a statement last year.

Wang Wenbin, a spokesperson for China’s foreign ministry, told a news conference last year that it was “standard practice” for the upper stages of rockets to burn up on re-entering the atmosphere. He incorrectly referred to the body of the Long March 5B rocket as an upper stage and said “most of its parts will burn out on reentry, making the likelihood of damage to air or ground facilities and activities extremely low.” “.

But no other launcher in the world leaves such a massive component in orbit to fall back to Earth. Dead satellites and old rocket stages regularly re-enter the atmosphere, but re-entering objects with masses of more than a few tons are rare.

Artist’s rendering of China’s Tiangong space station as it will appear when construction is complete. Credit: CCTV

Larger booster and base stages used on other rockets typically fall back to Earth without reaching orbit, usually in areas downwind of the launch site that are away from people.

Like most space junk that reenters the atmosphere, much of the Long March 5B rocket burns up when temperatures reach thousands of degrees during reentry. But some debris could reach the Earth’s surface intact.

The risk of any of the rocket debris injuring anyone or damaging property is low, with items most likely to fall into the ocean or unpopulated areas. But the uncontrolled re-entry of the central first stage of Long March 5B in 2020 has spread debris across Côte d’Ivoire. The reentry of Long March 5B last year occurred over the Indian Ocean.

Without any design changes, the Long March 5B rockets used for the Wentian Module launches on Sunday and the Mengtian Module launches in October will meet a similar fate with unguided reentry. Airspace warning messages broadcast to pilots for Wentian’s launch this weekend show no reentry zone for the center stage, suggesting it will remain in orbit for an uncontrolled descent within days or years. weeks after launch.

The Chinese space station orbits about 236 miles (380 kilometers) above Earth, at an inclination of 41.5 degrees from the equator. The orbit means that the core stage of Long March 5B could descend anywhere between 41.5 degrees north and south latitude.

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Follow Stephen Clark on Twitter: @StephenClark1.

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