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Wooden satellites: Is a project from Japan a crazy idea or an innovation?

2021-01-01T16:37:52.396Z


More than 6,000 satellites are orbiting the earth, with hundreds more this year alone. Japanese researchers now want to build some specimens out of wood - for reasons of sustainability. What is to be made of it?


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Model of a wooden satellite: "A bit strange - but not completely absurd"

Photo: Sumitomo Forestry

Much information is not yet available about what the Sumitomo Forestry company and researchers from Kyoto University are planning in detail for the former Japanese astronaut Takao Doi.

But the announcement of their plan alone has made some headlines internationally.

It is said that the experts want to work together on concepts for satellites made of wood.

These should simply burn up at the end of their lifespan - without causing danger on the ground and without releasing pollutants into the atmosphere of the earth.

"We are very concerned about the fact that all satellites that re-enter the earth's atmosphere burn up and create tiny aluminum particles that will float in the upper atmosphere for many years," Doi told the BBC.

According to the Japanese plan, if the shell of the satellite were made of wood instead of aluminum, the material could burn much more easily.

"A bit strange - but not completely absurd," is how Holger Krag called the concept in an interview with SPIEGEL.

The engineer heads the space security program at the European Space Agency (ESA) in Darmstadt.

They are also interested in technologies that make the fiery end of satellites as unproblematic as possible.

Not necessarily because of the aluminum.

From his point of view, this is not particularly dangerous, said Krag.

It is more about the question of what might still end up on the ground in the event of a crash.

Old satellites and rocket parts regularly fall on our planet.

So it was not until December 27 that the Starlink-1772 satellite from Elon Musk's SpaceX company burned up.

On New Year's Day, the stage of a Chinese "Long March 4B" rocket rushed towards Earth, which had put a satellite into orbit in September.

Satellite cemetery in the South Atlantic

Companies such as SpaceX and OneWeb are currently building huge satellite fleets for global Internet coverage.

This year alone, hundreds of new missiles should be launched in this way.

Other companies such as Amazon with its Kuiper project are also entering the market.

Although the mega-constellations are only just emerging, we must already think about the end of the satellites, says Krag.

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Launch of a SpaceX rocket with Starlink satellites on board (2020)

Photo: Joe Burbank / imago images / ZUMA Wire

If the disused devices can still be controlled, they are currently being systematically crashed over the South Pacific.

Space stations such as the Russian “Mir” also ended their careers there.

In the deserted area, it doesn't matter if debris reaches the earth.

If, on the other hand, the missiles can no longer be controlled, the matter is always a gamble.

Such as the crash of the German research satellite “Rosat” in autumn 2011 or the uncontrolled re-entry of the Chinese space station “Tiangong-1” into the earth's atmosphere almost three years ago.

There was no serious damage in either case.

Flying ghosts

Around 6,000 satellites are currently orbiting the earth.

They usually shoot along their trajectories at around 28,000 kilometers per hour.

Around half of the heavenly vehicle fleet, however, consists only of flying ghosts that no longer listen to control commands from Earth.

When such satellites collide, as happens again and again, countless pieces of junk are created.

They are not only dangerous for other missiles and also for the International Space Station.

Because of a snowball effect, they could also ensure in the long term that people can no longer fly into space at all.

According to ESA's statistical models, around 128 million objects in the size range of 1 to 10 millimeters are already racing around the earth.

The scrap cloud is regularly measured with laser and radar systems.

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Representatives of Chinese authorities with scrap waste (2014)

Photo: STR / AFP

Wooden satellites would not help against the junk in space, that much is certain.

The decisive factor here is the kinetic energy of the dangerous particles - and not the material from which they are made.

If a particle is on a collision course with the space station or a satellite, then that is a danger.

Regardless of whether it is wood or aluminum.

Incidentally, because of their sheer size, disused rocket stages, also from launches from decades ago, are particularly problematic.

A garbage disposal for space is a complicated future project.

Esa initially wants to practice with a comparatively simple goal: in 2025, with the mission "Clearspace-1", it wants to crash the payload adapter of a Vega rocket weighing around 100 kilograms.

It has been circling the earth since 2013.  

"We're thinking about how to promote the melting of the satellites."

Holger Krag, European Space Agency (ESA)

Any old missile that can be deliberately crashed at the end of its life is good news for transportation planners.

Because it can no longer cause collisions.

The space debris is slowed down so that its path leads through the higher layers of our atmosphere.

He then only needs around 10 minutes for the last 100 kilometers to the ground.

As a result of the friction with the gas molecules, a satellite is heated to such an extent that it breaks and - if everything goes well - melts completely.

"When re-entering, a shell is more of a hindrance," says Esa expert Krag.

Only when the outer walls of the satellite are gone can components made of titanium or stainless steel inside, such as tanks or battery boxes, melt due to the frictional heat.

"We are thinking about how to promote the melting of the satellites," said Krag.

However, wood has not yet been on the list.

Sumitomo Forestry and the University of Kyoto now want to find out whether the material is actually suitable.

"The next step will be the development of the technical model of the satellite, then we will manufacture the flight model," says ex-astronaut Doi.

It is not yet possible to reveal which types of wood the tests are to be carried out with.

The start date is specified in 2023.

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Source: spiegel

All tech articles on 2021-01-01

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