Speedy scanner: Earth observation satellite Sentinel-2B ready for ′breakthrough′ launch | Science| In-depth reporting on science and technology | DW | 02.03.2017
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Speedy scanner: Earth observation satellite Sentinel-2B ready for 'breakthrough' launch

At the rate the Americans send satellites into space, you'd be right to ask, is it special anymore? Not very. But the Sentinel-2B satellite launch next week is. It's a "breakthrough" in European technology.

Sometimes it's easy to feel an overbearing sense of lag in Europe. You look to the west and see America, with what seems like a million-and-one satellite or other rocket launches every other day. Most often they involve commercial operators - SpaceX, Orbital ATK, United Launch Alliance...

And then you glance back at the navel of Europe and everything seems so slow, so labored, so uninspired. Regardless of the pros and cons of a commercialized space industry, the American entrepreneurial spirit does seem to drive innovation - and some of it's even good.

But Europe? You may wonder, where has all the inspiration gone? And, dare I say it, the speed too?

Well, all that is changing. European space activities may still be slower and somewhat more considered than in the US. But when the European Space Agency (ESA) launches the Sentinel-2B satellite into space on the night of March 6-7, it will mark a "breakthrough" in Earth observation technology, leaving even the Americans behind in that field. Telecommunications satellites are, admittedly, another order of scale.

"It's a breakthrough certainly in the field of Earth observation and multispectral optical observation, which is Sentinel-2's specialty. We are now the undisputed reference for creating a system with this level of information," says Paolo Labirinti, ESA's assembly integration and test manager for the Sentinel-2 program, speaking from Kourou, French Guiana.

Infografik ESA Raumstation Französisch-Guayana ENG

Sentinel-2's technology was custom-built by Airbus Defense and Space, according to Labirinti, a company with decades of experience. It may be "niche" technology, he says, but it's far more powerful than the Americans' best effort in Earth observation, the Landsat-8.

"Landsat-8 is a very advanced satellite built by the Americans, but it's not as powerful as Sentinel-2 at this stage," says Labirinti.

But he's just as quick to add that Landsat-8 is a reference point for the Europeans and their applications in space, "so I don't want to be unfair to our Landsat-8 partners! They've done so much for the understanding of the Earth."

Higher rates than ever

There's another reason why the Sentinel-2B launch is special. The launch makes the Sentinel-2 constellation complete. With both Sentinel-2A and 2B working in tandem, it will double the rate of data on land coverage and vegetation around the globe.

Currently, Sentinel-2A scans the Earth once every 10 days. Once Sentinel-2B is fully operational, the two together will deliver complete images of the planet about every 5 days. That is the so-called "revisit time" at the Equator. They will be on a polar orbit with a slight inclination of 98.62 degrees.

"That means we're orbiting the north and south poles roughly every 90 minutes at a speed of about 7 kilometers per second," says Sentinel-2 mission manager, Bianca Hoersch.

There will be a gap of about 180 degrees - or a time delay of about 50 minutes - between the Sentinel-2A and 2B, each mapping the planet with a huge 290 kilometer swath.

"They have the same distance, so they fly in a sort of tandem constellation," says Hoersch. "But the Earth rotates at the same time, so one satellite sees one part of the Earth and the second one sees another part 50 minutes later. And that over five days gives you full coverage of the Earth."    

One big Sentinel family

These are just two of a family of Sentinel satellites. Sentinels 1A and 1B are already in orbit, as is Sentinel-3A. They each have their individual focus but also help each other out. For instance, Sentinel-1 delivers radar data for emergency response and things like land deformation. Being a radar instrument, Sentinel-1 is good with clouds. Sentinel-2, on the other hand, is an optical instrument, and not that great with clouds. So Sentinel-1 can provide date from the tropics, where it's often hard to get cloud free images.

But Sentinel-2 is not to be outdone. It sees more than we ever could with our eyes.

"Sentinel-2 has special features. The revisit rate of two satellites every 5 days, the spatial resolution of up to 10 meters, and the 13 spectral bands, a lot of which we didn't have on previous missions," says Hoersch.

The eye would only see four of those bands.

"If you looked with the eye or a camera, you would see the visible light. But on top of that, we're getting information on the near and the mid-infrared, which is information the eye can't see. But it's there and the vegetation on the Earth reflects this in this wavelength," explains Hoersch.

Off to and from Kourou

Sentinel-2B will be sent into space on a Vega small launcher from ESA's spaceport at Kourou, French Guiana.

The launch is scheduled for 10:49 pm local time on Monday, March 6. But it may be postponed by a day, depending on the conditions.

At the time of writing, and depending on whom you ask, the weather forecast for Kourou on Monday is showers to heavy rain and winds of about 13 kilometers per hour. 

"Rain is not so much the problem for the launcher. It's more the winds, and especially high winds at ground level," says Labirinti.

So on the day, they will send balloons from the launcher at different times to monitor the winds. There are several "green lights" they need to achieve, the last being 20 minutes before the launch. Then there's the issue of lightning, which was discovered as early as the Apollo missions 

"Lightning is a concern. We're also concerned about debris from the launcher falling on nearby beaches and villages," says Labirinti. "Debris from the first stages of the launch could fall back to the coast, depending on the winds."

Alas, the weather is impossible to control. But the launch team controls the rest and there's a lot to prepare: they have completed checks on the satellite, and it's been loaded into the upper stage of the Vega launcher, a liquid-propellant called the Attitude Vernier Upper Module (AVUM). Then there's a dress rehearsal of the countdown to get through before the launcher is armed on Saturday. But the checks and tests will continue until Monday… or Tuesday. We'll see.

Follow our coverage of the launch. Zulfikar Abbany will be at the launch site in French Guiana. And DW's Kai Steinecke and Lea Albrecht will be at ESA's control center in Darmstadt.

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