Giant ‘space brolly’ to weigh down Earth’s forests

Engineers perform the “pop and catch” test to ensure the antenna mechanism will be released safely into orbit

It looks for all the world like a giant brolly, but it doesn’t rain where it goes.

This huge antenna-reflector is headed into space to “weigh” Earth’s forests.

It is a key component of the European Space Agency’s Biomass mission, now under construction in the UK by aerospace manufacturer Airbus.

When deployed, the space brolly’s 12m by 15m wire mesh membrane will be part of a very special P-band radar system.

It is special because of its long wavelength.

At 70cm, it can peer through the leaf canopy of forests to map the woody parts below – all those trunks and branches.

Wire mesh membrane

Europe has bought American know-how in large reflector antennas

Using a tomography-like approach, the 1.2-tonne satellite will scan slices through the trees in repeated passes to create a picture of how much woody material is present.

World maps must be produced every six months.

The plan is for Biomass to collect at least five years of data to be able to identify trends.

Trees are a two-way valve in the climate system. They absorb copious amounts of the greenhouse gas carbon dioxide (CO2), but also release it when they die or burn.

However, exact numbers for flows in either direction through this valve are uncertain.

“This mission is about getting a better handle on the role of forests, whether in emitting carbon dioxide through destruction or sequestering carbon dioxide through growth,” said Professor Shaun Quegan, the mission’s lead scientist from the University of Sheffield.

“Right now, the amount emitted by forests – the uncertainty on that number is 50% or a bit higher, and actually I think 50% might be optimistic,” the National Observatory researcher told BBC News of Earth (NCEO). .

Artwork: Biomass

Artwork: The 1.2-ton Biomass satellite will operate at an altitude of just over 660 kilometers

Engineers from US company L3Harris Technologies were at the Airbus in Stevenage to oversee the connection of the antenna reflector to the main body or satellite bus.

Harris are experts in these large, non-folding systems – expertise we don’t currently have in Europe.

Engineers performed a “pop and catch” test on Monday to test the performance of the mechanism that will release the 7-meter antenna and arm when the satellite reaches orbit.

“In space, the fireworks release a pin and then a motor drives the system. The goal of this test is to ensure that the antenna clears the side of the spacecraft safely,” explained Airbus chief engineer Carl Warren.

It’s been a long journey for Biomass to get to this point.

The science goes back to the late 1980s, when an experimental P-band radar flew over a forest in East Anglia to prove its credentials.

But at that stage there was no prospect of such a system ever going into space because the specific radar frequencies were reserved for military use.

The US exploits the same zone to track missiles approaching North America and Northern Europe.

A case had to be made at the International Telecommunication Union to open a small window in this sensitive part of the electromagnetic spectrum to enable a scientific application.

Even now, biomass will not be allowed to operate in western northern latitudes.

Electronic radars

Electronic radars cover a wall of the satellite structure or shuttle

However, Professor Quegan is not unduly concerned about this limitation because the forest statistics in these areas of the planet are already quite strong.

The main zones of uncertainty are in the tropics and Asia, where biomass can use its instrument without limitations.

Electronics for the radar instrument are currently located separately from the spacecraft in the clean room at Stevenage. They hang from a panel waiting to be attached to one side of the bus.

“Once this is done, Biomass will go to Airbus in Toulouse for testing,” said Vicki Lonnon, Airbus’s quality assurance manager for the project.

“The satellite will be rocked to simulate launch shocks and will also enter a thermal vacuum chamber to simulate conditions in space.”

Launch on a Vega rocket is expected in late 2023.

Biomass will map the Earth from an altitude of just over 660 kilometers.

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