Why does China want to build a kilometer-long spacecraft?

China’s space program raised eyebrows again – this time over its proposal to study how to build a large spacecraft, at least a mile long.

To put this in perspective, the International Space Station (ISS) is only 109 meters in diameter, but it cost $ 150 billion (£ 110 billion) and its construction took thirty missions over a decade. China’s proposal is for a spacecraft 10 times the size of the ISS. It might sound crazy, but don’t make the mistake of dismissing it right away.

“It’s all about ambition, long-term thinking and motivation. Such long-term thinking does not fit well with shorter-term Western thinking, which might mistakenly view this as propaganda, ”says space writer Brian Harvey, author of the book. China in space: the great leap forward.

There is no doubt that China has recently made some serious progress in space exploration. It has returned lunar rock samples to Earth for analysis, making it the third country behind the United States and Russia to do so; he landed a rover on Mars, a feat that only the United States had achieved before; and he made the world’s first landing on the far side of the moon. On top of that, China is currently building the Tiangong space station, which has been manned for 90 days this year, and is designed to compete with the ISS in the long term.

Thinking ahead, Harvey is referring to a 2009 Chinese report titled Roadmap 2050, which is the model of how China plans to become the world’s first space nation by mid-century. “The horizon of Chinese spaceflight is not years or decades but half centuries,” he said.

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In other words, this most recent announcement is the start of China’s reflection on how to build such a spacecraft in the future, rather than a statement that it intends to start construction. .

The idea was launched in a larger call for research proposals from the National Science Foundation of China – a funding agency run by the country’s Ministry of Science and Technology. It is offering 15 million yuan (£ 1.7 million) for a five-year feasibility study on new lightweight designs and materials, and construction techniques in space.

But why would China want a spacecraft ten times the size of anything built before? The answer could be artificial gravity. A space station with artificial gravity could help astronauts avoid some of the most damaging effects of weightlessness, such as muscle wasting and loss of bone density.

For long-duration space flights to Mars or beyond, artificial gravity could make a huge difference in keeping the crew healthy.

“Artificial gravity has been this ‘sci-fi’ holy grail of manned spaceflight for a century, and the main way to do it is with a large rotating structure,” says Zachary Manchester, assistant professor at the Institute of Robotics from Carnegie Mellon University, Pennsylvania. .

Inside a rotating structure, centrifugal force moves things outward. If structures rotate at the right speed, it can create a force that mimics the effects of gravity.

The problem with this is that humans are very sensitive to turnover rates. If you spin faster than a few revolutions per minute, the average person will start to suffer from motion sickness.

However, experiments have shown that these effects practically disappear at rotational speeds of one to two revolutions per minute. So, how big would a spaceship be to create Earth’s gravity by spinning at a slow speed of 1-2 RPM?

“It turns out you need a structure about a mile in diameter,” says Manchester, who received a grant from NASA in February this year so that he and his colleagues can study a construction scenario. for a kilometer-long spaceship.

While China appears to be looking to build something huge into orbit after launching many components into space, Manchester is studying whether it would be possible to build a complete structure that would fold into the front cone of a single large one. rocket, a SpaceX Falcon. Heavy for example. It would then develop enormously when deployed in space.

The key to this idea is the use of what are called mechanical meta-materials. These use scissor-shaped joints to bend back to a fraction of their deployed size. The best-known example of such a mechanical meta-material is the Hoberman sphere. This children’s toy looks like a small spiky ball when at rest, but can expand into a large sphere many times its original diameter.

“It turns out that there are some really interesting mechanisms that you can put in place that can achieve very, very high expansion rates,” Manchester explains.

The structures he studies can grow hundreds of times their original size. Science ‘fiction’ indeed! Only time will tell if either design will work, but it’s now very clear that the world’s major space powers are anxiously awaiting the creation of spaceships much larger than any we’ve created to date. .