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The Tianwen spacecraft unfurled the Chinese flag on Mars in May of last year, making it the first national flag on the red planet. Photo: Harbin Institute of Technology

Researchers shed light on smart tech that made Chinese flag the first on Mars

  • Lightweight polymer allows national banner to ‘fly with the wind’ on red planet and is likely to be used in interplanetary travel and aerospace engineering
  • Patented materials could push China ahead in space race as rival Nasa relies on heavier, more expensive components
Science
Chinese researchers for the first time shared details about the technology that made China the first country to put its national flag on Mars, forcing former US president Donald Trump to eat his words.
The US placed its flag on the moon more than 50 years ago and intends to do it again on the red planet. “The United States will be the first nation to plant our beautiful American flag on planet Mars,” Trump said in 2019.
But on May 15, 2021, after an interplanetary journey of nearly 500 million km (300 million miles) lasting over 300 days, China’s Tianwen spacecraft unfurled a Chinese flag on Mars – the first national banner placed on the planet. The red flag with five yellow stars, made of a cloth-like smart material, moved gently in the Martian breeze.
In a paper published on Monday in the peer-reviewed Advances in Mechanics, Chinese researchers unveiled details of the new material, which is expected to be used in interplanetary travel, asteroid exploration and other space infrastructure projects.

A robotic device that can hold and unfold a flag typically requires several mechanical components. These metallic parts are heavy and can increase the cost and risk of a mission significantly.

Only a low-cost, lightweight and reliable technology would make it possible for the “five-star red flag to fly with the wind on Mars”, the researchers said.

The Chinese flag device weighs less than 200 grams (7 ounces), and no motors or gears were involved in its unfurling. Its key moving components are made of a smart polymer that can change shape when heated.

The device holds the rolled-up flag with a pair of clasps made from a rubber band-like material. When heated, the clasp’s “finger” straightens out and lets go of the flag, allowing the fabric to drop and unfold naturally with gravity.

Putting the US flag on an extraterrestrial body is “a symbolic gesture of national pride in achievement”, according to Nasa.

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An American flag image printed on the deck of Japan’s Hayabusa rover first made it to the surface of Mars in 2008. The stars and stripes pattern returned during the Curiosity rover mission in 2012, when it appeared on one of the Mars rover’s four moving arms.

In 2020, the American flag was printed on the bottom of a remote sensing mast and followed the Perseverance rover to Mars.

But these printed images do not meet the definition of a flag, which is typically made out of cloth or a similar material.

“The release of the flag device on the landing platform made China the first country in the world to apply intelligent structures based on shape memory polymer composites to deep space exploration,” said project lead scientist Leng Jinsong and his colleagues with the centre for composite materials and structures at Harbin Institute of Technology.

“China is leading the application of intelligent materials in space.”

The device holds a rolled-up flag with polymer clasps that release the flag when heated, allowing the fabric to unfold with gravity. Photo: Harbin Institute of Technology

The polymer can change its form freely but returns to a “memory shape” under the influence of heat, electric charge, magnetic force or a chemical solution.

This is a technology that Nasa does not possess at the moment, according to the Chinese researchers.

In the 1960s, private companies proposed a polymer to Nasa as a low-cost replacement for mechanical components in space projects. In the following decades, the space agency also funded studies that produced a few polymer prototypes.

But these projects did not get off the ground. The polymer was too soft for most applications. Its physical strength could vary significantly with temperature, and it aged quickly under the radiation of cosmic rays.

Nasa has continued to make mechanical components with alloys, which are heavier and much more expensive to produce.

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The James Webb Telescope, for instance, took over 24 years to build with a budget of US$10 billion. The complex mechanism for the storage and release of its main mirrors contributed to the delay and cost.

China could not afford this approach, the Chinese researchers said.

With continuous funding from the central government, Leng’s team spent more than two decades improving the performance of the smart polymer. They added carbon fibre to the material to bolster its strength.

They came up with a new theory to predict its behaviour, tested candidate materials in some of the most challenging environments and worked with factories to reduce the cost of mass production.

In 2016, China conducted an unprecedented experiment in space in which a spaghetti-like structure made of the smart polymer morphed into a plank, according to Leng’s team.

02:22

Inflatable Martian home designed to sustain human life on the red planet

Inflatable Martian home designed to sustain human life on the red planet

In 2020, a large Chinese satellite in geostationary orbit deployed the world’s first solar panel built without any physical joints. The soft membrane extended in less than a minute with a supporting frame made entirely of smart materials.

Unlike traditional solar panels, the deployment process did not cause any harmful vibrations or shocks.

Leng’s team said the patented materials could change the course of the space race and put China in a leading position.
“This technology is expected to be used in China’s space station, lunar exploration project, manned space flight, Mars exploration, Jupiter exploration, asteroid exploration, ice giant exploration and other major aerospace engineering projects,” they said.
China has plans for big space infrastructure projects, including a solar power station designed to send a high energy beam to Earth. These infrastructure projects were previously considered too big, costly and complex using existing technology, but the smart material could significantly reduce the budget and risk of these projects.
The same material has also found use in the development of new solid-fuel rocket engines to increase the range of hypersonic missiles, according to recent studies.

Chinese researchers are using similar materials to develop aircraft that can change shape to achieve higher efficiency in different stages of flight.

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