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The Bremen Drop Tower

zarm.uni-bremen.de

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Re: The Bremen Drop Tower

#11

Post by SomeStupidPoint »

lucb1e wrote: post #8
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…

> 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.

Re: The Bremen Drop Tower

#12

Post by ganonm »

lucb1e wrote: post #8
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…

> 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 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.

Re: The Bremen Drop Tower

#13

Post by 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

Re: The Bremen Drop Tower

#14

Post by Luc »

lucb1e wrote: post #8
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…

> 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?

Perhaps the ISS has more vibration from all those life support systems?

Re: The Bremen Drop Tower

#16

Post by DangerousPie »

maj0rhn wrote: post #13

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

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.

Re: The Bremen Drop Tower

#17

Post by ethagknight »

MengerSponge wrote: post #6
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…

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 assign but they were $20mm new, NASA’s planes were probably enroute to the boneyard when they acquired them.

Re: The Bremen Drop Tower

#18

Post by owenversteeg »

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…

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.

Re: The Bremen Drop Tower

#19

Post by uhnuhnuhn »

owenversteeg wrote: post #18
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…

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 h…

According to the video on the linked website, ZARM can do 3 drops a day with 4.7 seconds of microgravity per drop.

Re: The Bremen Drop Tower

#20

Post by lfam »

owenversteeg wrote: post #18
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…

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 h…

> 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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