
The Bremen Drop Tower - Tomte
https://www.zarm.uni-bremen.de/drop-tower.html
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novium
There's a great Tom Scott video about the tower
[https://www.youtube.com/watch?v=4aCMDQsx740](https://www.youtube.com/watch?v=4aCMDQsx740)

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Tomte
Oh, and there's a user's manual!

[https://www.zarm.uni-
bremen.de/fileadmin/images/droptower/do...](https://www.zarm.uni-
bremen.de/fileadmin/images/droptower/downloads/Users_Manual_0611.pdf)

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GuB-42
How does it compare to zero-G planes (vomit comet)? These planes can provide
much more than 10 seconds of weightlessness, do it a dozen of times per flight
without exceeding 2g of acceleration. Much bigger volume, much bigger payload,
people can use it, it looks better in every aspect. By comparison, the drop
tower can do three 10-second experiments per day, and the
acceleration/deceleration look quite violent.

If you want to get in and have a trip, it costs around $5-10k. So judging by
this price, it doesn't seem that the expense is high enough to justify
building an apparatus that looks quite expensive.

I'm sure that there is a very good reason for drop towers to exist, I just
don't know which one.

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owenversteeg
I think 10 seconds is long enough for most purposes.

Let's say the drop tower is open 9am-7pm Monday-Friday, so 10 hours a day, for
5 days a week, and 50 weeks a year. That's 2500 hours of drop time a year.
Let's say the building can be expected to last 100 years (probably lasts much
longer, it's solid concrete after all) and cost 20 million dollars to build.
Thus, you get 250k hours of drop time for $20MM, so each hour of drop time
costs $80.

[edit] whoops, turns out it's only operational for 30 seconds a day! That
makes the price go up about a factor of 1000, so the cost is now roughly $80k
per hour.

Let's say you have a vacuum chamber (usually required for zero-g experiments)
that takes up 3 seats, and you pick the cheapest zero-G flight I could find at
$5000 for one flight, 15 periods of 20-30 seconds of weightlessness each
(let's say avg 25 seconds.) That's $15,000 for 375 seconds, or 0.104 hours. So
your hourly price is $144,230.

With the revised math, the tower still wins, $80k to $144k, but I'm surprised
it can only drop three times a day.

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lfam
> Let's say the drop tower is open 9am-7pm Monday-Friday, so 10 hours a day,
> for 5 days a week, and 50 weeks a year. That's 2500 hours of drop time a
> year. Let's say the building can be expected to last 100 years (probably
> lasts much longer, it's solid concrete after all) and cost 20 million
> dollars to build. Thus, you get 250k hours of drop time for $20MM, so each
> hour of drop time costs $80.

The drop tower does not allow things to be dropped for 10 hours each day.
There are only 3 drops per day, so each day gives <30 seconds of drop time.

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jessriedel
One of the applications for these sorts of microgravity conditions is the
creation of large quantum superpositions, especially doing interferometry
(roughly, double-slit experiments) with Bose-Einstein condensates.

[https://physics.aps.org/articles/v6/23](https://physics.aps.org/articles/v6/23)

~~~
horstbort
Hey, that's my experiment! :-) So great to see that here on HN.

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Boothroid
I would think many countries have disused mineshafts that might be good
candidates for a far longer drop

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MengerSponge
It isn't sufficient to just have a deep hole in the ground. You need a vacuum
too!

I had to poke around to find this: "Before the experiment, 18 high-performance
pumps make sure that the drop tube is almost free of air containing only one
ten thousandth of the normal air pressure. Due to the vacuum, the air
resistance is so low that the Bremen Drop Tower can provide one of the best
quality of microgravity - in some aspects even better than on the
International Space Station (ISS)"

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lucb1e
> in some aspects even better than on the International Space Station (ISS)

Woa, does anyone know in what way this tower provides less gravity than the
space station?

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ganonm
The centre of mass of the ISS follows a fixed orbit round the earth (to first
order approximation that is, occasional thrust is required to maintain this
trajectory). Moving away from the centre of mass, by definition, puts you into
a slightly different orbit. This perturbed orbit has a different trajectory
and orbital speed. This will manifest itself as very small reactionary forces
relative to the ISS structure, in other words what you and me call gravity. In
plain English, except for at the exact centre of mass position within the ISS
(Or any point exactly on the trajectory traced by it) objects will appear to
drift.

In the microgravity tower, translations within the experimental container will
not result in divergent trajectories, so no drift will occur.

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dredmorbius
I think you've just answered for me why the ISS is effectively flat and two-
dimensional rather than three. Also this strongly suggests that the station
has a spin moment corresponding to its orbital period, about 90 minutes.

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alfa02
Great to see this on hacker news. I can see the tower from my office.

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maj0rhn
It's a Johnny-come-lately. Every day going to work I used to drive by the
"Shot Tower" in downtown Baltimore, USA (it's still there, I'm not), built in
1828 to make various types of spherical ammunition, including cannonballs.
Wikipedia lists some even older shot towers. The Baltimore tower was for many
years the tallest structure in America.

[https://en.wikipedia.org/wiki/Shot_tower](https://en.wikipedia.org/wiki/Shot_tower)

~~~
DangerousPie
Shot tower != drop tower tough. I'm not familiar with shot towers, but based
on the wiki page they just seem to be tall towers that are used to produce
ammunition.

Drop towers are used to conduct scientific experiments and require a lot of
precise engineering to work properly. So for example they need to have a
double-wall to keep the inner tube still, and have vacuum pumps to remove air
from the inside.

