Artificial city

China builds the world’s first artificial moon

Chinese scientists have built an “artificial moon” with moon-like gravity to help them prepare astronauts for future exploration missions. The structure uses a powerful magnetic field to produce the skyscape – an approach inspired by experiments once used to levitate a frog.

The key component is a vacuum chamber that houses an artificial moon measuring 60cm (about 2ft) in diameter. Image credits: Li Ruilin, China University of Mining and Technology

Preparing to colonize the moon

Simulating low gravity on Earth is a complex process. Current techniques require either piloting an aircraft that goes into freefall and then climbing back up, or jumping from a drop tower – but the latter two only last a few minutes. With the new invention, the magnetic field can be turned on or off as needed, instantly producing no gravity, lunar gravity, or earth gravity. It is also powerful enough to magnetize and levitate other objects against gravitational force for as long as needed.

All of this means scientists will be able to test the equipment in the extreme simulated environment to avoid costly mistakes. This is beneficial as problems can arise in missions due to the lack of atmosphere on the moon, which means the temperature changes rapidly and dramatically. And in low gravity, rocks and dust can behave in a completely different way than they do on Earth – because they’re more loosely bound together.

Engineers from the China University of Mining and Technology built the facility (which they plan to launch in the coming months) in the eastern city of Xuzhou in Jiangsu province. A vacuum chamber, containing no air, houses a mini “moon” measuring 60 cm (about 2 feet) in diameter at its core. The man-made landscape consists of rocks and dust as light as those found on the lunar surface – where gravity is about a sixth stronger than that on Earth – due to powerful magnets levitating the piece above the ground. They plan to test a host of technologies whose primary purpose is to perform tasks and build structures on the surface of Earth’s only natural satellite.

Group leader Li Ruilin of China University of Mining and Technology said it was the “first of its kind in the world” that would take lunar simulation to a whole new level. Adding that their artificial moon makes gravity “disappear”. For “as long as you want”, he adds.

In an interview with the South China Morning Post, the team explains that some experiments only take a few seconds, such as an impact test. Meanwhile, others like creep test (where the amount of deformation of a material under stress is measured) can take several days.

Li said astronauts could also use it to determine if it’s possible to 3D print structures on the surface rather than deploying heavy equipment they can’t use during the mission. He keeps on:

“Certain experiments conducted in the simulated environment can also give us important clues, such as where to look for trapped water below the surface.”

It could also help assess whether a permanent human settlement could be built there, including questions such as the surface’s ability to trap heat.

From amphibians to artificial stars

The group say the idea stems from the experiments of Russian-born British physicist Andre Geim which saw him levitate a frog with a magnet – which won him a satirical Ig Nobel Prize in 2000, which celebrates the science that ” makes people laugh first, then think Geim also won the Nobel Prize in Physics in 2010 for his work on graphene.

The basis of his work involves a phenomenon known as diamagnetic levitation, where scientists apply an external magnetic force to any material. In turn, this field induces a weak repulsion between the object and the magnets, causing it to move away from them and “float” in the air.

For this to happen, the magnetic force must be strong enough to “magnetize” the atoms that make up a material. Essentially, the atoms inside the object (or frog) act like tiny magnets, subject to the magnetic force existing around them. If the magnet is strong enough, it will change the direction of the electrons spinning around the nuclei of the atom, allowing them to produce a magnetic field to repel the magnets.

Diamagnetic levitation of a small horse. Image credits: Pieter Kuiper / Wiki Commons.

Different substances on Earth have varying degrees of diamagnetism which affects their ability to levitate under a magnetic field; adding a vacuum, as done here, allowed the researchers to produce an isolated chamber that mimics a microgravity environment.

However, simulating the harsh lunar environment was no easy task as the magnetic force required is so strong that it could tear components such as superconducting wires. It also affected the many metal parts needed for the vacuum chamber, which don’t work well near a strong magnet.

To counter this, the team came up with several technical innovations, including simulating lunar dust that could float much more easily in the magnetic field, and replacing steel with aluminum in many critical components.

The new space race

The breakthrough signals China’s intention to take first place in the international space race. This includes its lunar exploration program (named after the mythical moon goddess Chang’e), whose recent missions include landing a rover on the dark side of the moon in 2019 and 2020 that saw rock samples brought back to Earth for the first time in over 40 years.

Next, China wants to establish a joint lunar research base with Russia, which could start as early as 2027.

The new simulator will help China better prepare for future space missions. For example, the Chang’e 5 mission returned with significantly fewer rock samples than expected in December 2020, as the drill encountered unexpected resistance. Previous missions led by Russia and the United States have also had related problems.

According to a study by the Xuzhou team published in the Journal of China University of Mining and Technology. The authors hope that this article will enable space engineers around the world (and in the future, the Moon) to modify their equipment before launching multi-billion dollar missions.

The team is confident that the facility will be open to researchers around the world, including Geim. “We definitely invite Professor Geim to come and share other good ideas with us,” Li said.