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The Bremen Drop Tower is a 140 meter high tower, containing a 120 meter high vacuum
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chamber which we are using to drop experiments under conditions of nearly perfect weightlessness.
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The tower consists of the drop shaft, deceleration chamber, a lot of vacuum pumps, and a catapult
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system which allows us to shoot the experiments from the bottom of the tower to the tip, and
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then falling back again, doubling the microgravity time to nearly 10 seconds, which is very unique.
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Scientists from all over the world, in fields from astrophysics to material science to biology, come to this
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tower to experiment with near zero gravity. Because without the effect of gravity, flames can
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turn into spheres, strange states of matter appear, and things can just get really interesting.
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The Bremen Drop Tower was developed and built 30 years ago. Professor Hans Rath, the founder
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of ZARM and Manfred Fuchs had the idea, and saw the future of Bremen in space sciences
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and industries. To build a lab that can consistently recreate the conditions of weightlessness,
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ZARM engineers have to eliminate the effect of gravity. Gravity is a fundamental force
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which is acting on all kinds of matter. Gravity cannot be eliminated but the effect can be
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eliminated by dropping experiments in free fall. And freely means, without any external
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force acting on the experiment while dropping. We are using a vacuum chamber to avoid air resistance
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during the freefall. And a capsule that can reach velocities up to 165 kilometers per
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hour. Micro in microgravity means that the quality that we are achieving is 1 millionth
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of Earth's gravity. Everyone can experience microgravity by simply jumping off of something. As
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long as the velocity is small and the air resistance is small, the quality of weightlessness
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is quite high.
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Drop Towers have several advantages compared to other microgravity facilities. Other
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facilities might be sounding rockets, satellites, space stations, and also parabola flight on
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planes. The big advantage of drop towers is the accessibility. And the repeatability.
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If one experiment fails, you just try again. On other platforms, this normally is far too
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expensive. The tower runs roughly 250 days a year, with up to 3 drops per day. Depending
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on the experiment, scientists can choose between two different flight campaigns. First is
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drop mode, a straight free fall for 4.7 seconds of microgravity. Here we are at the tip of
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the tower in 120 meters height. While the experiment is still hanging every motion of
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the drop tube is leading to a rotational motion of the drop capsule, which again would lead
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to centrifugal forces during flight time, which you want to avoid. So if you watch
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closely. What you can see here is the effect of mechanical decoupling. The outer structure
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is moving, but the inner structure of the vacuum chamber is almost still. The mechanical
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decoupling of the drop tube allows us to drop experiments even as high wind loads as we have today.
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The second drop style at the tower utilizes a special catapult system. We are
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just entering the catapult cellar, 12 meters below the vacuum chamber. The catapult mainly
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consists of the tube and the piston, the pressure tanks and the hydraulics below. The great
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advantage is we can double the microgravity time to nearly ten seconds.
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Without the catapult, a normal drop tower would have to be 500 meters high to
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achieve the same time. Before each catapult flight, the experiment capsule is lowered
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to this point. Here it is standing for a while, and then when shot. These six valves are opened
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in zero point two seconds and a several hundred liters of oil are rushing through these tubes. It
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is accelerated with 30 gs, 30 times Earth's gravity to fly it's vertical parabola. And
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believe or not... The whole catapult system is not standing on the ground but hanging
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on the ceiling. This was necessary to be able to fine adjust the catapult to optimize the
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flight path of the drop capsule.
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Experiments range from fundamental physics like quantum
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mechanics, up to more applied sciences like fire safety devices on space stations. Today
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we have a very interesting experiment in our drop tube. I'm working now in granular
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metasciences. And, my position is a researcher at the German center for aerospace research
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in Cologne. We would like to develop new measurement methods to analyze sand remotely on moon or
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asteroids. Because we cannot just take a sample, bring it here and investigate it. Right now,
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we are refurbishing the experiment. We circulate water through a sample and measure light scattering
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properties. Light scattering is exactly what it sounds like; shining a light on a sample
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and measuring how fast it fluctuates to reveal a material's inner structure. Dr. Born
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and his team can leverage this technique to reveal the dynamic motion of particles on
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planetary surfaces one day. But to get there, they have to start with something a bit simpler,
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like water. This tower is for us the only place on earth where air bubbles and sand
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particles move in the same way because they're not affected by gravity. We had the last days
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some problem with the experiment routines we checked until late night and it worked
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properly, so I think we have a good chance for a good day for good experiments.
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The experiment capsule has a diameter of 80 centimeters and is between 1.5 and 2.5 meters long. At
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the bottom we have a battery pack and service module which is a computer to automize the
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experiment and to log the data. The possibilities can range from simple temperature or pressure
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sensors, up to high speed cameras with up to 1,000 frames per second. And the rest of
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the volume and space is left for the experiment. What you can see from here is the piston the big
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black piece of carbon fiber. The experiment is placed on top of the piston, standing on
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just this small space.
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Once the experiment capsule is installed, pumps switch on to suck
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the air out and create a vacuum. These are our vacuum pumps. We're just starting to
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evacuate our drop tube. This will take about 90 minutes before we can drop the experiment
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or shoot the catapult.
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We want to create scattering from spherical air bubbles and
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today we hope to see for the first time that they really form perfect spheres in microgravity.
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We are ready to fly, so I will ask Lisa now to set up everything in action.
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So we saw in the
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live video from our sample cell that we had air bubbles in the cell and they really stopped
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flowing. Such that you have no buoyancy anymore basically they just stop and you can have
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a look at them in microgravity. And this is what we were actually aiming for so it worked,
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and yeah, we are very excited about that. If we have a working set-up, we can change some
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parameters. On different planets, you have different gravity intensities. If we are able
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to show how things work in microgravity, we might draw conclusions to different gravity
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regimes at some point. If you want to investigate the soil on Mars you have to have a method
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that can remotely investigate packing density or flow behavior. All the rovers we sent
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to space so far they went to a so-called stationary operation mode because they just got stuck
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in sand. So it would be really great to have a sensor in front of the rover which measures
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the extent of the sand starting to flow. And then we can say, stop, no we cannot drive
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on the sand, we need to drive somewhere else. We start with something simple and then we successively
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increase complexity and see if we can take the theory along.
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After the flight, the capsule entered the deceleration container here and then we reflooded the drop
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tube for about 30 minutes, fished for the experiment, and now we are taking it out again. Even
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though the deceleration container is 8 meters in height, it takes approximately 3 meters
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to decelerate the capsule from 140 kilometers per hour to 0. The cone shape of the capsule
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limits the deceleration to up to 40 G to shield the experiments from too hard accelerations. And
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also to help break the capsule's fall. The deceleration is achieved using tiny polystyrene
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balls. The noise that you are hearing is the recycling of our polystyrene balls that were
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compacted due to the deceleration of the experiment. We are sucking the polystyrene balls out at
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the bottom and lifting it up to the top again and throw them in again.
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Now the experiment
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is opened and the outer shell is removed which remains in the drop tube, and the experiment
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is handed over to the scientists to prepare the next flight.
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The existing Bremen drop
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tower is limited in repetition, mainly by the time that it takes to evacuate this 1,700
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cubic meters of air out of the drop shaft. We've been asking scientists what they need and
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what they would want for future drop towers. And they've said 100x more experiments per day.
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What I am standing on is our new Gravitower Bremen, which is actually under construction.
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The idea of this new kind of drop tower is that we avoid the vacuum chamber by putting a slider
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around the experiment, which allows us to repeat experiments all day long. We hope
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to take it in to normal operation at the end of this year. Then it is open to scientists from
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all over the world. Giving scientists an even more efficient portal to microgravity will create new
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opportunities to test ambitious space hardware and speed up the pace of scientific discovery,
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one drop at a time.