If you want to test a scientific experiment in zero-g, you've got a few options.
You could send it to the International Space Station,
but thats expensive, and, let's be honest, it's unlikely to happen
unless you've got a few friends at a space agency.
You could package it up into a small Cubesat and launch it,
but that's still pretty expensive.
You could take it along on a zero-g flight,
and strap yourself into a plane that's accelerating towards the ground
at just the right speed to cause weightlessness.
But that's still a lot of hassle, and a lot of expense, and a lot of fuel burned.
But fortunately, there is another option.
This is the Drop Tower at the University of Bremen in Germany.
Inside is an enormous vacuum chamber: and for the last 90 minutes,
powerful pumps have been have been removing all the air from inside,
turning it into a near-vacuum that's perfect for freefall experiments.
And there's a drop capsule about ready to go.
In this experiment, I try to study the charge separation process through tribocharging,
the effect that causes static electricity.
During the microgravity, glass beads are released into a capacitor.
In microgravity, you have enough time to trace your particles,
and you can observe other interesting effects
that aren't observable in normal gravity.
Acceleration due to gravity on Earth is roughly 10 metres per second per second,
and without air resistance to slow things down,
that drop capsule is going to start moving very quickly indeed.
In the first second after release, the drop capsule goes 10 metres.
Next second, 20.
Next second, 30.
Next second, 40,
and then we've used up pretty much all the height there is.
To get just one more second's worth of freefall, you'd have to build this tower half as high
again.
Unless you do something really clever, and start by going up.
The experiments are installed into a drop vehicle.
That's the experiment itself,
it's all the measurement and diagnostic tools,
it's the computer controlling it.
We throw it upwards with up to almost 30g for 200ms,
and then into zero-g for almost ten seconds, then.
And the deceleration, finally, by the end of the experiment
has a value of about 35 to maximum 50g.
It should be very accurate, because you can imagine,
if the energy is too large, we would hit the ceiling,
we would destroy our vacuum containment,
which is the most delicate element we have in our house.
We almost perfectly balance the centre of gravity to the vertical axis of the capsule
by adjusting some counterweights at appropriate locations in the capsule.
The experiments are in fluid mechanics, it's in combustion,
it's in fluid handling, it's in biotechnology,
it's in physics and astrophysics, it's in fundamental physics.
So almost any disciplines.
It's a little counterintuitive, but the capsule really is weightless:
all the way up and all the way down.
The forces acting on it remain the same,
even as it changes direction relative to us.
So here we go.
Launch time.
The slingshot will fire, and in the nine seconds that the capsule's in freefall,
an eight-metre-deep pit filled with polystyrene pellets
will slide in over the catapult to catch the capsule.
Hopefully!
Thanks to everyone at the University of Bremen, at the Drop Tower,
and to the researchers who were testing here today!
Pull down the description for links about them and about their work.