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The Bremen Drop Tower

zarm.uni-bremen.de

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Re: The Bremen Drop Tower

#21

Post by kgabis »

MengerSponge wrote: post #5
Boothroid wrote: post #3

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

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 a…

Wouldn't it be easier to add some rope pulling the capsule to compensate for the air resistance? Or would it add too much "noise" because of the imperfections of such system?

Re: The Bremen Drop Tower

#22

Post by blywi »

ethagknight wrote: post #17
MengerSponge wrote: post #6

Earlier quoted context omitted.

There are plenty of very good reasons: zero-G planes are only mostly zero-g. They fly a parabolic trajectory, so their body actually rotates about the center of mass while flying. Also, their weightlessness is not as well controlled as a drop tower's. The cost you've listed is for a single passenger. You know what's more expensive to build and operate than a pressure controlled tube on the ground? A pressure controll…

While there are good reasons for a drop tower over an airplane, namely experiments requiring more precise control, I’m not remotely convinced that the Bremen tower was cheaper to build and operate than a Vomit Comet. For one, a 146m tall tower for which ZARM broke ground in 1988 and inaugurated the catapult in 2004; that sounds incredibly expensive. NASA uses old 727s, long out of production so a cost is difficult to…

The tower has actually been in operation since September 1990. So the time needed for construction was just 2 years and not 16 years. For the first years it was operating as a simple drop tower, without a catapult. The catapult was added later in 2004. Construction costs according to German Wikipedia were more than 24 million DM (12.2 million euros), with a further 4.2 million euros for the catapult. They are doing on average about 400 drops per year. The time in micro-gravity is 4.74 sec for a simple drop and 9.3 sec with the catapult. (source: Wikipedia) According to my estimations this amounts to about 18.72 hours of micro-gravity in 24 years.

That's still expensive, but not outrageously so.

Re: The Bremen Drop Tower

#23

Post by nawitus »

ethagknight wrote: post #17
MengerSponge wrote: post #6

Earlier quoted context omitted.

There are plenty of very good reasons: zero-G planes are only mostly zero-g. They fly a parabolic trajectory, so their body actually rotates about the center of mass while flying. Also, their weightlessness is not as well controlled as a drop tower's. The cost you've listed is for a single passenger. You know what's more expensive to build and operate than a pressure controlled tube on the ground? A pressure controll…

While there are good reasons for a drop tower over an airplane, namely experiments requiring more precise control, I’m not remotely convinced that the Bremen tower was cheaper to build and operate than a Vomit Comet. For one, a 146m tall tower for which ZARM broke ground in 1988 and inaugurated the catapult in 2004; that sounds incredibly expensive. NASA uses old 727s, long out of production so a cost is difficult to…

Even if the planes were inexpensive, maintenance and flight costs are high.

Re: The Bremen Drop Tower

#24

Post by morsch »

GuB-42 wrote: post #4

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 yo…

Does anybody know why they are limited to three experiments a day?

According to Wikipedia, they need 90 minutes to evacuate the tower before every experiment. Does an individual experiment involve multiple (dozens? hundreds?) of falls?

I'm assuming they have a long list of people who want to book time in the tower.

Re: The Bremen Drop Tower

#25

Post by Boothroid »

revelation wrote: post #7
Boothroid wrote: post #3

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

Now you just need to retrofit a zero-gravity environment into the disused mineshaft..

So then something akin to a vacuum chamber in a freefall miner's lift then? Surely cheaper than evacuating the whole chamber.

Re: The Bremen Drop Tower

#26

Post by dredmorbius »

ganonm wrote: post #12
lucb1e wrote: post #8

Earlier quoted context omitted.

> 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?

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…

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.

Re: The Bremen Drop Tower

#27

Post by ballenf »

kgabis wrote: post #21
MengerSponge wrote: post #5

Earlier quoted context omitted.

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 a…

Wouldn't it be easier to add some rope pulling the capsule to compensate for the air resistance? Or would it add too much "noise" because of the imperfections of such system?

I was thinking a electromagnetic rail controlled by precise sensors combined with very powerful gyroscope would also work. Probably still need to evacuate some of the air.

Re: The Bremen Drop Tower

#28

Post by dredmorbius »

SomeStupidPoint wrote: post #11
lucb1e wrote: post #8

Earlier quoted context omitted.

> 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?

I think they're implying that if you want to test to effects of microgravity, you don't want something like 14 psi of air pressure happening at the same time, because interactions with the air flows might confound whatever you're trying to test. The station is likely better in terms of gravity , but in terms of test conditions , you're somewhat limited by the astronauts being there.

High-quality vacuum is fairly readily available at the ISS.

Re: The Bremen Drop Tower

#29

Post by bronson »

kgabis wrote: post #21
MengerSponge wrote: post #5

Earlier quoted context omitted.

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 a…

Wouldn't it be easier to add some rope pulling the capsule to compensate for the air resistance? Or would it add too much "noise" because of the imperfections of such system?

Sure, the rope could pull an evacuated chamber, inside of which another chamber could fall without much noise. (assuming you could handle the velocity and stretch in that much rope. thrusters are probably easier)

The longest vertical shaft you're likely to find is around 3km, which gives you a little over 20 seconds of freefall and a couple seconds of violent deceleration.

But the problem is, you're dealing with acceleration squared. The Bremen tower already does almost half that time (9.3s with the slingshot), so it's probably not a big enough difference to warrant the effort and travel.

Re: The Bremen Drop Tower

#30

Post by pavel_lishin »

Boothroid wrote: post #25
revelation wrote: post #7

Earlier quoted context omitted.

Now you just need to retrofit a zero-gravity environment into the disused mineshaft..

So then something akin to a vacuum chamber in a freefall miner's lift then? Surely cheaper than evacuating the whole chamber.

If that vacuum chamber is falling through air, then it's not in freefall.
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