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Unstrange Phenomena

30 November 2009

Slamming Low-Ride Satellite Maps Earths Magnetic Field

Photo of Ion-propelled Gradiometer, the GOCE satellite

From Denny: The European Space Agency have been busy boys and girls, James Bond style. These guys are serious about mapping the Earth's magnetic field. The whole point of this exercise is to better understand the planet's natural processes.

They threw up a satellite about six months ago and it is just now fully calibrated and sending back data. Earth's magnetic field has the tiniest of variations so it is necessary to carefully calibrate this satellite to record accurately. Even the Russians did their satellite version back in March called the Gravity field and steady state Ocean Circulation Explorer.

OK, so we all know about gravity. But did you know that even though gravity exists everywhere on the planet it varies and is not distributed evenly across the surface?

What can cause slight changes to this gravitational force? Try mountain ranges, ocean trenches, even the density variations within the Earth's crust and mantle. Then there is also the fact the Earth's rotation can affect gravity variations.

Why is this so important? We have to gain more knowledge about these changes so we can accurately measure ocean circulation and sea levels. After all, climate change may be here to stay for a number of generations. We must study all we can in order to possess the information to know how to anticipate what happens next and how best to prepare for it.

This is a mock-up example of what the gravitational map will look like. It represents the Earth's gravity distribution with an accuracy and spacial resolution never before achieved. ESA

You have to take your hat off to these persevering scientists for the job they did. They figured out how to precisely measure gravitational fluctuations for as much as 160 miles up!

Gravity is closest to the Earth's surface so this cool satellite needed to be as close to the surface as it could. The next problem they faced was the instrumentation on the GOCE satellite had to be stable to measure accurately. What that means is that the ideal situation is for GOCE to be placed in an environment that has as little aerial drag as possible. OK, no aerial drag is what they truly desire but we all know engineers and scientists are actually romantic dreamers of the perfect utopia.

Well, the GOCE team must have had some second-born children in the crowd who knew how to make realistic compromises to get the most bang for their buck. This satellite is like a sleek new aerodynamic car and the propulsion system on this baby is so unique it makes it possible for the satellite to orbit at 158 miles above the Earth. That's lower than most Earth observation satellites. The beauty of this is that at 158 miles above the Earth eliminates most of the aerial drag.

As you have guessed by now, this GOCE satellite is a slamming low-ride, so low it is riding on the very fringes of our atmosphere. The sleek aerodynamic design helps the satellite to polish off any remaining air for drag yet that still isn't enough. It seems like there is always "just one more thing, by the way..."

Ratcheting it up to the next issue they had to resolve was the satellite had to be capable of remaining stable while, are you ready for this? free fall. At this high altitude if the air interferes even a little bit then the data could be wildly skewed - and the mission is so screwed.

Never fear, your favorite creative engineer was here to the rescue. These guys are always thinking. The GOCE satellite was outfitted with the latest sexy space fashionista's trend of the electric ion propulsion engine as thruster. This ion thruster is like a nanny, ready to protect and provide a nudge or two with its thrusters whenever the satellite encounters any drag on the space playground.

So, how long did it take these guys to calibrate this sensitive drama queen of a satellite? Try months! The team started the satellite in a 170 mile orbit above the Earth and gently teased her down to the 158 mile level.

The team is also lucky right now that this project is not experiencing any solar activity, giving perfect atmospheric conditions for the gravity mapping. With the good luck of the lack of solar activity it turns out the initial data coming in to the team has turned out to be even more accurate than they hoped. Read that as geeks gone wild, partying and dancing on their monitors. It's a good day to be a scientist, saving humanity...

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