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