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
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.
China’s Mars rover ‘selfies’ suggest dust storms on red planet
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.
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 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.
China’s rover finds evidence of water on Mars more recently than thought
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.
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.
Chinese researchers are using similar materials to develop aircraft that can change shape to achieve higher efficiency in different stages of flight.