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Science

ESA's Sentinel-2B launch by numbers

There's a palpable sense of superstition ahead of the Sentinel-2B launch in French Guiana. You won't get into the Jupiter control center wearing red - that's the stop color. But so far it's looking good.

Three or four bus loads of us have descended on the Guiana Space Center (CSG) in Kourou, French Guiana. There are heads from the European Space Agency, Airbus, Arianespace, the European Commission and the odd journalist, including me. It's a hot and balmy day: 29 degrees, 79 percent humidity, and a chance of rain. The wind is a bit of a worry. But what does all that matter? It's Monday, March 6, 2017. We're here to witness the launch of Sentinel-2B, Europe's fifth Earth observation satellite, into space.

Here's what you need to know about the satellite and launch in numbers:

The launch

Sentinel-2B is the fourth satellite to be launched by Arianespace, a French multinational, commercial launch service provider. The launch name for the Sentinel-2B mission is VV09.The satellite will be positioned on a sun-synchronous (SSO) polar orbit at 786 kilometers, opposite to its sister satellite, Sentinel-2A. Together they will cover the entire Earth's surface every five days.

The Sentinel program

There are total of six Sentinel satellite "families." Sentinels 1A and 1B have been in orbit since April 2014 and April 2016, respectively. Both were launched by a Soyuz rocket. Sentinel-2A was launched by a Vega rocket in June 2015. And Sentinel-3A was launched in February 2016 by a Rockot vehicle.

The mission

Satellite launches are a precise science, with only some room for estimates. The launcher will carry a payload of "approximately" 1,208 kilograms. And there is a chance the launch will have to be postponed. But other than that, most other things are as exact as can be.

-  ESA scheduled lift-off for Sentinel-2B for Monday, March 6, at exactly 10:49 p.m. (0149 UTC) local time in French Guiana.

-  The mission duration is 57 minutes and 57 seconds.

-  After lift-off, the powered stage of Vega's first three stages will last 6 minutes and 32 seconds.

-  Following the first phase, the launcher's third stage will separate from the upper composite. The upper composite includes the AVUM upper stage, a payload adapter and the satellite. The lower three stages will fall into the sea - or, at least, they will if the wind doesn't blow them back to the coast and the local villages. That's why the wind speed is relevant.

-  Then the upper stage ignites its engine for the first time. It will operate for about seven minutes, followed by a ballistic phase of about 40 minutes.

-  The upper stage then ignites its engine for a second time for approximately two minutes before releasing the Sentinel-2B satellite about one minute after the engine shuts down.

-  The satellite will have an inclination of 98.57 degrees.

Designed for a limited life:

Sentinel-2B's so-called design life is 7 years and three months. But that could be pushed to about 12 years. It has enough fuel for an extended life.

But all things - good and bad - come to an end. The last bit of fuel is reserved for Sentinel-2B, and all other satellites in the Copernicus program, to be de-orbited and burnt up in the Earth's atmosphere within 25 years. The Americans (including people from Google and NASA) are looking into reprogramming certain satellites, once their original purpose has run its course, for them to become part of an interplanetary internet. But, the Sentinel satellites have been designed for a particular purpose, Sentinel-2 director Bianca Hoersch told DW, making it hard for them to be re-commissioned in other areas.

The Sentinel-2B satellite was build by a consortium led by Airbus. Its total mass at launch is 1,130kg. Its dimensions are 3.3m x 2.3m x 1.7m, which is fairly small when you think about what it's got to do. Sentinel-2B state-of-the-art optical instruments - a 290 kilometer swath, a spatial resolution of 10 meters, 13 spectral bands… that's way more than the eye can see. It will deliver data on coastal regions, monitor land mass, vegetation, soil types and habitats.

Two new satellites, Sentinel-2C and 2D are under construction by Airbus DS in Friedrichshafen, Germany. The idea is for them to replace Sentinels 2A and 2B. The plan is to launch the new satellites in 2020 and 2021.

Countdown:

10, 9, 8, 7, … Thunderbirds are go! No, sadly, countdown is not just a case a 10 simple seconds. In fact, this launch has been in preparation for the past two months, since Sentinel-2B arrived at the European spaceport. The final countdown starts 9 hours and 10 minutes before lift-off. Then, hour by hour, various vital units are activated, such as the Multifunctional Unit (MFU), Inertial Reference System (IRS), telemetry, and the Safeguard Master Unit (SMU). At 4 hours and 40 minutes out the onboard computer is activated. At 1 hour and 15 minutes out the transponders and receptors are activated. The launcher system is ready 50 minutes prior to lift-off. Then a final weather report is filed 10 minutes out. And four minutes before lift-off the synchronized system starts. Then, and only then, … is it time for lift-off.

Infografik The VEGA launcher ENG
Infografik ESA Raumstation Französisch-Guayana ENG

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