WEBVTT
Kind: captions
Language: en

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If you want to test a scientific experiment
in zero-g, you've got a few options.

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You could send it to the
International Space Station,

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but thats expensive, and, let's be honest,
it's unlikely to happen

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unless you've got a few friends
at a space agency.

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You could package it up into a small Cubesat
and launch it,

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but that's still pretty expensive.

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You could take it along on a zero-g flight,

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and strap yourself into a plane that's accelerating
towards the ground

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at just the right speed to cause weightlessness.

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But that's still a lot of hassle, and a lot
of expense, and a lot of fuel burned.

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But fortunately, there is another option.

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This is the Drop Tower at the
University of Bremen in Germany.

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Inside is an enormous vacuum chamber: and
for the last 90 minutes,

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powerful pumps have been have been removing
all the air from inside,

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turning it into a near-vacuum that's perfect
for freefall experiments.

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And there's a drop capsule
about ready to go.

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In this experiment, I try to study the charge
separation process through tribocharging,

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the effect that causes static electricity.

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During the microgravity, glass beads are released
into a capacitor.

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In microgravity, you have enough time to trace
your particles,

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and you can observe other interesting effects

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that aren't observable in normal gravity.

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Acceleration due to gravity on Earth is roughly
10 metres per second per second,

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and without air resistance to slow things
down,

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that drop capsule is going to start moving
very quickly indeed.

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In the first second after release, the drop
capsule goes 10 metres.

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Next second, 20.

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Next second, 30.

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Next second, 40,

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and then we've used up pretty much all the
height there is.

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To get just one more second's worth of freefall,
you'd have to build this tower half as high

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again.

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Unless you do something really clever, and
start by going up.

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The experiments are installed into a drop
vehicle.

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That's the experiment itself,

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it's all the measurement and diagnostic tools,

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it's the computer controlling it.

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We throw it upwards with up to almost 30g
for 200ms,

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and then into zero-g for almost ten seconds,
then.

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And the deceleration, finally, by the end
of the experiment

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has a value of about 35 to maximum 50g.

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It should be very accurate, because you can
imagine,

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if the energy is too large, we would hit the
ceiling,

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we would destroy our vacuum containment,

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which is the most delicate element we have
in our house.

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We almost perfectly balance the centre of
gravity to the vertical axis of the capsule

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by adjusting some counterweights at appropriate
locations in the capsule.

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The experiments are in fluid mechanics, it's
in combustion,

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it's in fluid handling, it's in biotechnology,

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it's in physics and astrophysics, it's in
fundamental physics.

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So almost any disciplines.

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It's a little counterintuitive, but the capsule
really is weightless:

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all the way up and all the way down.

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The forces acting on it remain the same,

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even as it changes direction relative to us.

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So here we go.

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Launch time.

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The slingshot will fire, and in the nine seconds
that the capsule's in freefall,

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an eight-metre-deep pit filled with polystyrene
pellets

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will slide in over the catapult to catch the
capsule.

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Hopefully!

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Thanks to everyone at the University of Bremen,
at the Drop Tower,

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and to the researchers who were testing here
today!

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Pull down the description for links about
them and about their work.