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Astronaut Challenge

10/13/2006 2:41 AM

Suppose you are 'space-walking' in the 'vacuum' of space, just below the ISS and facing it, i.e., with your back towards Earth. You are not in contact with the ISS and have no angular momentum relative to it.

You now want to look at planet Earth, but the cumbersome space suit prevents you from just craning your neck to do so. How do you reorient yourself so that you can look at Earth without touching the ISS or using the suit's thrusters?

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#1

Re: Astronaut Challenge

10/13/2006 4:10 AM

I suppose it would depend on what I had with me. If I had anything I could rotate like a tool on the end of a tether I would try to get it spinning like you would do with a lasoo. This would be harder without typical gravity but still possible. It should act like a gyroscope. Once spinning, pulling against it should allow you to rotate. A test of the principle would be to sit in a swivel chair while holding a rotating bicycle wheel, now try to tilt the wheel and you spin around in the chair. Another method, once it is spinning, release it. Once the tether reaches its end it should create a torque that will eventually spin you toward earth provided it was released in any direction other than toward the ISS and it is attached anywhere other than your center of mass. Alternatively, if I had no tether I would extend 1 arm out to my side and quickly bend at the elbow drawing my hand to my chest which should be reasonably close to my center of mass. If I had a tool to hold in my hand it might get me rotating a bit quicker.

slo

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#2

Re: Astronaut Challenge

10/13/2006 5:51 AM

Rotating your arms from the shoulder in the same direction would turn you around a horizontal axis as a reaction to the rotation, I'm sure. I think. Maybe?...

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#3

Re: Astronaut Challenge

10/13/2006 8:27 AM

Flatulence.

Okay, the real answer. SAFER. The backpacks in the spacesuit (you did remember to pack that, didn't you?) contains compressed nitrogen gas designed for maneuvering in space (mostly if you get untethered from the spacecraft without an MMU).

Since you are not allowed to do that, I think you can effectively do a summersault by moving your arms and/or legs (tucking the legs and extending them and swinging the arms). I am not sure I can describe the action because it is going to be a coordinated effort to do it. However, I think the secret is the leg extension because you need change the body length to control the rotation. It is similar to a skater doing a spin where they extend and retract their arms in an act of conservation of momentum.

This doesn't need to be done fast. In fact, you want to do things very slowly in space.

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#4

Re: Astronaut Challenge

10/13/2006 11:03 PM

Some students at MIT and their professor figured out how cats always land on their feet. My daddy told me when I was a kid that if I could figure that out I would really have something. Did I listen? Nooooo. Which is why I kicked myself when I read this. These guys are going to be (probably already are) rich! Here's how it works and how you can rotate yourself without inducing spin. Very useful for satellites and spacecraft or perhaps humans who want to see earth. Some of you were close. What you do is extend your arms and twist the upper and lower halves of your body one direction. Next, retract your arms and twist back the other way. Because the angular momentum is different due to the change in the length of your "lever arms" you have repositioned yourself on one axis. And yes, if you want to get picky maybe because or the in-out movement of the arms you are off and slightly spinning on some other axis but maybe with practice and using your legs just right you can learn to cancel that effect.

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#5
In reply to #4

Re: Astronaut Challenge

10/13/2006 11:50 PM

Quoting rcapper: "Some students at MIT and their professor figured out how cats always land on their feet... these guys are going to be (probably already are) rich!"

Yep, and the cats figured that out some millions of years earlier! That's probably way cats are mostly rich...

I guess they use their tails and body twists? If that will work inside a bulky and restrictive space suit, I'm not too sure, though!

Jorrie

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#7
In reply to #5

Re: Astronaut Challenge

10/14/2006 1:16 AM

I've never seen a space suit up close but maybe if you can move your arms and legs you could make it work. Even a small index can be repeated to achieve the desired rotation.

I couldn't find the original reference but here is an article describing it and it is in context to the challenge:

http://www.eetimes.com/issue/mn/showArticle.jhtml;jsessionid=NJOFPACOJP13WQSNDLPSKH0CJUNN2JVN?articleID=22104537&_requestid=501610

If that link doesn't work try this one but you'll have to register (free) if you're not already.

http://www.eetimes.com/register/articleLogin.jhtml;jsessionid=MBEFOSY5KS1SWQSNDLRSKH0CJUNN2JVN?_requestid=504642

Or here is the article:

Portland, Ore. — The National Aeronautics and Space Administration's "weightless wonder" aircraft will be the testbed this week for a robot that exhibits catlike motion in free fall. The work could one day lead to designs that eliminate the need for retrorockets, gas jets and gyroscopes in satellites and other spacecraft.

The robot, thus far tested only under less-than-ideal conditions in a university lab, rotates without angular momentum by changing the length of parts of its body while rotating them in opposite directions, much as a falling cat does. A successful NASA test of the concept could transform all space gear now based on gyroscopes — including satellites, the space station and the space shuttle — by enabling precise, vernier-like orientation control with zero angular momentum.

Managing that momentum is the bane of space navigation today. The law of conservation of angular momentum dictates that when an object rotates in one direction, there must be an equal and opposite rotation in the other direction. The law complicates almost every space-based maneuver, introducing unwanted spin that must be compensated for with retrorockets or gas jets.

In devising the concept, project leader Gregory Ojakangas, a physics professor at Drury University (Springfield, Miss.), borrowed from a species that flouts the rules of angular momentum. "When you drop a cat upside down, it always lands on its feet, with no spin. It doesn't paddle the air — that would impart spin — it just expands its upper body and rotates it, then contracts its upper body and rotates in the opposite direction," said Ojakangas. "In that sense, ours is not a new idea; nature has been doing it for I don't know how many millions of years."

This week, the catlike robot will be put to the test over the Gulf of Mexico in a Boeing KC-135a Stratotanker aircraft — the plane NASA calls the weightless wonder — which simulates the effect of weightlessness in space.

When an astronaut friend of Ojakangas' described to the physicist how his catlike motions while weightless enabled him to ratchet around without spinning, seemingly violating the law of conservation of angular momentum, the professor hit on an idea. Ojakangas researched the physical laws governing the physiological traits that let cats eliminate spin, then proposed the robot idea as a class project to a group of students.

The resultant robot has a bottom part that always counterrotates with the top part, thereby canceling angular momentum, and yet the different weights extended from the top and bottom allow for a net rotation without spin. The students have tested the robot in the lab by hanging it from a long wire, but twists in the wire have introduced unwanted angular momentum that have foiled the team's ability to take precise measurements. Ojakangas' team will test its theory more reliably with the robot aboard the NASA flight.

"It's a curious little device, and potentially a way of turning satellites without any net spin, without gyroscopes and without gas jets or any kind of propulsion," said Ojakangas

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#8
In reply to #7

Re: Astronaut Challenge

10/14/2006 4:54 AM

Rcapper said: "I couldn't find the original reference but here is an article describing it and it is in context to the challenge:"

Fascinating stuff! One cool space cat.

But, will it work for a human body in a spacesuit? One can fling your arms out somewhat, but how much you can twist you body inside the suit, we will have to ask an astronaut that's done it.

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#10
In reply to #8

Re: Astronaut Challenge

10/14/2006 7:34 AM

Well clearly we aren't making progress toward what your thinking Jorrie. If I were a female astronaut perhaps I would take out my compact and just look in the mirror but I doubt that's what you had in mind either. By the way here are a couple more references and it was Drury University not MIT as I had thought. I found the reference to the original web site but it had been taken down. I did print the math they had posted there if anyone is interested I can scan it and put it up.

http://www.drury.edu/multinl/story.cfm?ID=10475&NLID=246

http://www2.drury.edu/physics/ataglance/zero_g_ratchet.html

I suppose if I lacked the body mobility required to do the cat maneuver I could swing a hammer or other implement. You didn't exclude using some tool or maybe to throw something to generate a turn and then throw something the other way to stop. I doubt a human would be able to judge the force and timing to effect accurate positioning that way. I know, I would radio NASA to put an image up on my heads up video that projects onto the inside of my face shield. Surely they have this, no?

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#6

Re: Astronaut Challenge

10/14/2006 12:22 AM

Cats land feet down, toast lands butter side down, hmm.....

If I could tape some toast, butter side up to a cat's back...........

Eureeka!

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#9

Re: Astronaut Challenge

10/14/2006 7:07 AM

I like the answers about waving arms and legs to gain motion and I am sure it would work - perhaps only too well.

I remember reading many years ago in a science fiction story (it might have been Arthur C Clarke) that an astronaut drifted way into space because he had no means of independant propulsion - and waving his arms and legs made it worse - although he could get some motion - he could not point himself in the right direction.

It all ended happily because he was able to detach some external part of his spacesuit to give him something to 'push and pull' against then (with practice) when correctly aligned - to 'throw' it away to give enough momentum to get himself back to the ship. Phew that was close!

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#11

Re: Astronaut Challenge

10/14/2006 12:43 PM

My first choice would be to get both arms swinging in the same direction in a vertical plane (vertical from the perspective of the astronaut: backstroke or crawl would work), and to allow gyroscopic procession to do the work. I'd do that first, because it seems like the most fun, albeit difficult in the space suit. But the arm rotational speed could be very slow and still be effective.

If that failed, then I'd attempt the cat maneuver, which could be done quite slowly and still work.

Failing that, I'd start up one of my power tools with its motor axis aligned so that the counter torque would twist me around.

If that failed, I'd be frustrated, so I'd throw the same tool from one side of my body so that I'd spin around until the tether caught. I'd only get a glimpse of earth, but maybe that would be enough to keep me happy.

I might also try simply sticking out an arm and a leg on one side, in hopes that microgravity imbalance effects acting on my new CG would cause me to rotate. No matter if I went head over heels, or heels over head, or pirouetted, eventually, I'd face earth.

Finally, if all my experiments went haywire, I'd throw my hands up in frustration. (Actually, I'd rotate them forward from the shoulder until they were pointing straight "up".) Then, lo and behold, just as a long jumper must throw his arms back to avoid landing on his back, I'd find that my body would rotate in the opposite direction, heels over head, giving me my view of the home planet.

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#12
In reply to #11

Re: Astronaut Challenge

10/16/2006 9:49 AM

Looks like Ken has all the angles covered!

What is the answer Jorrie?

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#13
In reply to #12

Re: Astronaut Challenge

10/16/2006 10:36 AM

Well STL, since you asked, I have to confess, I do not have the answer! That's why I was hoping a real astronaut would respond. However, I think PlbMak (post #2) had it the simplest and the closest. The arms of a space suit are designed to be quite flexible, although I don't think rotating the arms around the shoulders would be quite possible.

But I think one can quite simply use a bit of shoulder, elbow and wrist to make circles with your hands like when skipping a rope. Conservation of momentum will put you in a slow somersault, which you can stop by 'skipping' the other way (maybe you can just stop 'skipping'?) The legs and arms can also be used to induce roll, but I think it would be much more difficult. In space, it is all about doing it slowly and controlled.

If it was not for the suit, it would have been easy and a lot more fun. We have all seen footage of people playing inside the ISS and also in the 'vomit comet'!

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#15
In reply to #13

Re: Astronaut Challenge

10/16/2006 11:35 AM

Ah, ah, ah, Jorrie! Not the same! Inside the spacecraft (ISS, Shuttle, Soyuz, etc.) as well as an aircraft in free fall (Vomit Comet), there is air, and where there is air there is a reaction mass, albeit very small and fluid, but a mass nevertheless, to "push" against, e.g. "fanning" with your hands, for an "equal and opposite reaction". In the (near) vacuum of space there is (almost) no mass to push against, or to conduct sound waves. That is why:

"In space no one can hear you scream!"

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#16
In reply to #15

Re: Astronaut Challenge

10/16/2006 12:22 PM

Oh no, STL! Now I have to agree with you 1% and disagree 99%! I will state with 89.97% confidence that 99% of the rotational antics in the ISS and the Vomit Comet comes from the same method that the cat employs to land on its feet. The cat says it only gets 1% assistance from the air, so it ignores that.

OK, I don't know about the 1%, but I am very sure that the air plays an absolutely minor role.

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#17
In reply to #15

Re: Astronaut Challenge

10/16/2006 1:26 PM

STL, have you ever seen the girls and guys in the weightless situation with air, (ISS or 'vomit comet') "fanning their hands" to create reaction? I guess not! I agree with Jorrie that this effect is negligible compared to inertial reaction forces. They twist and spike and turn - thats it!

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#18
In reply to #17

Re: Astronaut Challenge

10/16/2006 2:46 PM

Now, wait a minute. I never said that they didn't or couldn't use "gyrations", only that motion, however small, was possible and practical through reaction against air, but not in a vacuum.

In reality from what I have seen of video of those weightless "antics", they usually get their start, spinning, hurtling, somersaults, whatever, from the reaction of pushing off the floor, bulkhead, celing, fixed equipment, etc. I am sure that gyrations also play a role, but much smaller than the initial action/reaction thrust as per Sir Isaac. Now, if they were specifically trying to demonstrate the gyroscopic effect, that would be very different!

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#14

Re: Astronaut Challenge

10/16/2006 10:42 AM

Wait til a piece of space garbage comes flying along, and then put your hand in front of it. :)

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#19

Re: Astronaut Challenge

10/16/2006 2:58 PM

I think if you punch hard, and fast, and retract slow and easy, you would turn, due to the inertial impulse, off-center from your body's center. It may be hard to punch in a space suit, but it should be possible to create a difference between the outward motion, and the corresponding return. This is, I think, just a variation of the other physics already outlined, of turning your upper torso at a different rate than your lower. I do think it is possible produce a uni-directional inertial impulse. See

http://www.open.org/davidc/

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#20
In reply to #19

Re: Astronaut Challenge

10/16/2006 3:34 PM

That doesn't work unless you are scooting on you butt on the floor. Friction overcomes the low impulse (slow) movement. When you do the math, integrate F=ma over time the effect is equal in both directions. If you want to see all the stuff that doesn't work in this regard just google "inertial engine" its worth it for the entertainment value!

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#21
In reply to #20

Re: Astronaut Challenge

10/16/2006 4:53 PM

hmm.. I think you are right. I was just sitting here in my office chair... punching.. and not moving...

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#22
In reply to #21

Re: Astronaut Challenge

10/16/2006 11:48 PM

In the end, remember, it's still a requirement of Newton that momentum and angular momentum be conserved. Punching only causes a tiny turn while the fist is in motion. When the punch stops, so does the rotation.

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#23
In reply to #22

Re: Astronaut Challenge

10/17/2006 11:23 AM

Also remember that as you punch, the reaction is caused by the fact that you are accelerating your fist and forearm. When you come to the end of your punch stroke, you decelerate your fist and forearm to avoid a shoulder separation. Whatever rotation you gain from the acceleration, you reverse in the deceleration. (This assumes you are doing this in space, without any slip-stick effects... although punching sometimes qualifies as slapstick. )

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#24
In reply to #23

Re: Astronaut Challenge

10/17/2006 3:23 PM

Not really. You experience movement of both extremities in inverse proportion to their mass and then they stop. You don't get movement again until you retract your fist and then you are exactly where you started. I doesn't matter how fast you move in either direction the effect is the same as long as you move on the same path the same distance.

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#25
In reply to #24

Re: Astronaut Challenge

10/17/2006 3:45 PM

Ken and rcapper,

I think Ken is confusing velocity and displacement. And Jorrie called it anyway when he said that "Punching only causes a tiny turn while the fist is in motion. When the punch stops, so does the rotation."

Ken said that, "Whatever rotation you gain from the acceleration, you reverse in the deceleration." NOT true. Whatever velocity you gain from acceleration, you reverse in deceleration. If initial velocity was zero, final velocity will be zero. You have still gained a displacement in rotation, and, as long as your mass does not change, momentum is conserved, just as Jorrie said.

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#26
In reply to #25

Re: Astronaut Challenge

10/17/2006 4:16 PM

Gadzooks! You're right STL and rcapper. I'm going to have to get to bed earlier from now on. Or maybe it's something I ate for breakfast... Or maybe all this spinning around has made me dizzy.

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#27
In reply to #26

Re: Astronaut Challenge

10/17/2006 8:36 PM

It's ok Ken. It's just good to know that I'm not the only one that occasionally rushes to say something without thinking it through. With so many eyes on us, not much goes un-noticed. Part of the fun maybe.

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#28

Re: Astronaut Challenge

07/15/2008 1:09 PM

You don't have to reorient yourself to face the Earth. The spacewalk suits have a small mirror on one wrist and you just need to look in that to see behind you.

The Compact wins.

The mirror was placed to allow the astronauts to look behind them for things like the arm and debris and has been used to view earth. There may be a movie of one of the first spacewalks on the ISS that shows an astronaut looking in the wrist mirror.

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#29
In reply to #28

Re: Astronaut Challenge

07/15/2008 1:33 PM

Hi Kaboom, you're right, but the objective of the exercise was obviously to find out how an astronaut could reorient him/herself in free space.

Jorrie

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#30
In reply to #29

Re: Astronaut Challenge

07/15/2008 2:07 PM

NASA during the Gemini program did tests on the ways to reorient ones self in space in a suit at pressure and found that, though do able was not an easy thing to be done and thus added the mirror.

There was a site years ago, at the beginning of the internet for the public, that actually had the contortions required to turn a body in space. The main idea was to rotate the hips in the suit in one direction and the throw the arms in the opposite to produce a spin. Reverse the operation to cancel the spin when oriented correctly. The problem was instead of a longitudinal spin only you also imparted a minor horizontal spin and began to tumble slowly. The problem manifested when the astronauts didn't move their arms in a level plane.

While the suit is at pressure for a spacewalk the legs have very little movement since they have no articulated joints (basically a bag in the shape of legs). The arms have shoulder and wrist joints with a slightly more flexible elbow area. The inside of the elbow joint isn't as stiff as the wrest of the arm due to the way the material is placed. Like a cat you're moving your body by creating a net difference in motion between two portions of the same body, Basically you throw one part of the body a bit slower than the other part. The friction from the bodies muscles actually imparts the spin not the outside atmosphere.

How's that for an answer

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#31
In reply to #30

Re: Astronaut Challenge

07/15/2008 10:52 PM

Hi Kaboom, good answer! To some extent already answered in the many replies above, but a good summary.

Jorrie

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#32
In reply to #31

Re: Astronaut Challenge

07/17/2008 10:55 AM

I did a bit of rechecking and it was the Apollo spacewalk's. It was on the same mission as the hand held air jet manoeuvring system, the grandfather of the MMU we have today.

On a side note sort of, Why don't they slow down the reentry vehicle to subsonic before entering the atmosphere to remove atmospheric heating on reentry?

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#33
In reply to #32

Re: Astronaut Challenge

07/18/2008 4:41 AM

Hi Kaboom, you asked: "Why don't they slow down the reentry vehicle to subsonic before entering the atmosphere to remove atmospheric heating on reentry?"

Too much energy to counter and little fuel left! You would need about 2/3 of the energy that it took to launch the vehicle in order to "stop it" in space - and then you had to lift all that fuel into orbit in the first place!

If Earth was airless like the Moon, that would have been a big problem! The Moon is luckily much lighter than Earth, so not such a big problem there.

Jorrie

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#34
In reply to #33

Re: Astronaut Challenge

07/22/2008 10:46 AM

There has to be a better, more efficient, way to get into and out of space without burning millions of tons of fuel.

The way I see it the getting to space isn't very hard, it's the getting into orbit that takes all the fuel. IF you can get to space just by flying to the edge THEN burn your fuel to get your required orbit and speed you should end up with a savings in fuel, shouldn't you?

Yes at some point you will need to supplement the Oxygen for the engines to fly up to space but once high enough the difference between your orbiting needs in the Stratosphere and the Troposphere should be a sufficiently large savings.

How about this for all to churn some grey matter on:

Using a vehicle about the proportions and capacity of an A380.

-How much fuel would it take to get into space (above the stratosphere) with conventional engines?

-How much fuel would then be needed to achieve an orbit for the ISS?

-How much payload would be left?

-What is the difference in cost to fly by shuttle and by plane?

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#35
In reply to #34

Re: Astronaut Challenge

07/22/2008 1:23 PM

Hi Kaboom, you wrote: "The way I see it the getting to space isn't very hard, it's the getting into orbit that takes all the fuel. IF you can get to space just by flying to the edge THEN burn your fuel to get your required orbit and speed you should end up with a savings in fuel, shouldn't you?"

The problem is that normally aspirated jet engines (even scramjets) can get you up to about 30 km (~100,000 ft), which is just 10% of where you want to be for orbit. I know they count "space" from some 100 km altitude up, but you cannot really orbit there - still too many air molecules. So, your rocket engines must lift you all the way from 30 km to 300 km AND then give you the orbital speed as well.

Ignoring air resistance, the potential energy required to lift a payload to 100 km is ~9 times more than to 30 km and then another ~9 times more to get to 300 km. Then add another ~10 times that for orbital kinetic energy and you can see the problem. It takes more than 800 times the energy to orbit at 300 km than to fly at 30 km altitude.

Orbit via shuttle vs. airplane? The shuttle can, the plane can't!

Jorrie

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#36
In reply to #35

Re: Astronaut Challenge

07/29/2008 9:46 AM

Bummer, I heard somehwere the Russians were looking into this approach for their version of a shuttle but once the Americans launched theirs the Russians stopped trying to fly part way. I don't know how accurate the information I heard was but it does sound plausible.

I guess we have to get a really really really big balloon filled with Helium and launch from there :)

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