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Author Topic: Does long-term microgravity endanger eyesight?  (Read 6231 times)

Offline thedoc

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Does long-term microgravity endanger eyesight?
« on: 15/03/2012 21:07:26 »
Head scans of astronauts have shown signs of raised intracranial pressure affecting their eyes and pituitary glands, new research has revealed.

Read the whole story on our website by clicking here

  
« Last Edit: 15/03/2012 21:07:26 by _system »


 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #1 on: 20/03/2012 21:54:19 »
Certainly there needs to be more research into the subject.  Could the issues be simulated with rats?  Perhaps rats that are already being used for other experiments?

However, vision problems, as well as muscle and bone loss are reasons why NASA should implement an artificial gravity component in the International Space Station.  Unfortunately the Centrifuge Accommodations Module was cancelled.

What was the definition of "Short Duration Space Trippers" that still have a 30% chance of eye problems?
 

Offline Geezer

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Re: Does long-term microgravity endanger eyesight?
« Reply #2 on: 20/03/2012 22:18:00 »
Why do we have to perpetuate the myth of "microgravity"? Astronauts in Earth orbit are experiencing pretty much the same gravity as the rest of us. What is different for them is that they are weightless because there is nothing to prevent their continuous free-fall.
 
I'm probably fighting a losing battle on this, but I think it's a bit irresponsible to use a term that can easily mislead a lot of people. "Microgravity" implies there is hardly any gravity at all, and that is simply not the case here. 
 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #3 on: 21/03/2012 00:40:30 »
I do think that Zero-G is just as good of a term.
Wikipedia does have a good explanation of Micro Gravity, including the gravity experienced at different distances from the Earth and Sun.

One might use the term, orbital freefall, or at least explain that Zero-G in Earth orbit is due to orbital freefall. 

While a spaceship that is coasting away from Earth will still experience gravity from the sun and planets, the occupants will still experience a zero-G environment as they are falling at the same speed as their craft.

However, the term Zero-G does explain the phenomenon that the astronauts are experiencing.  The explanation becomes much more wordy if one uses Zero-G due to Orbital Freefall...  does that really help anybody?  I suppose it helps students understand that space doesn't truly have an absence of gravity...  if they don't already know it.

It sounds like the vision problems are related to time in space.  However, have they confirmed that similar problems do not occur with fighter pilots experiencing high G forces?  Also, what is the long-term prognosis for the astronauts that have experienced this problem with vision?
 

Offline Geezer

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Re: Does long-term microgravity endanger eyesight?
« Reply #4 on: 21/03/2012 01:11:47 »
Zero-G is complete bollocks rather inaccurate too, but possibly less offensive than microgravity.
 
I wonder how these things come about. Is it because some newspaper writer initially coins the phrase, then a bunch of scientists (who really should know better) start jabbering on about it?
 

Offline graham.d

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Re: Does long-term microgravity endanger eyesight?
« Reply #5 on: 21/03/2012 08:34:55 »
Geezer, I note you have a "thing" about this :-) Don't you think we should embrace the concepts of General Relativity and say that a force due to accelerated motion is just as much a real force as that produced in any other way (e.g centrifugal force) and, likewise, the cancellation of gravity by being in free-fall can also be considered as "Zero-G". I sense you were taught the evils of ever using the phrase "centrifugal force" at school (as was I), but I don't think it is beyond people's imagination to understand the basic concepts of GR and to be taught that this force is (in every sense) a real force for the person experiencing it. In fact, it may be more educational than the convoluted denial of its existence.
 

Offline Geezer

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Re: Does long-term microgravity endanger eyesight?
« Reply #6 on: 21/03/2012 17:39:12 »
How did you guess that?!?
 
My objection is purely to the terminology because it can easily cause people with little scientific background (and even some with a a fair amount of scientific background) to assume that there is no gravitational effect on objects in orbit.
 
We don't (at least I don't) talk about being in "microgravity" or "zero-G" every time our feet leave the ground, but the condition is exactly the same.
 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #7 on: 21/03/2012 18:00:24 »
I would agree that "microgravity" is the wrong term for the gravity experienced in LEO.  According to the wikipedia page above, the gravity in LEO is about 9 m/s2, hardly "micro". 

On a voyage from here to Jupiter, one would truly experience the microgravity, but again, a person's sensation of gravity would be entirely dependent on the acceleration profile of the spaceship.  If coasting, one would notice the spaceship slowly decelerating, but one would still be free floating in the ship (zero-G).

Yep, Michael Jordan experiences a few moments of zero-G before smacking into the floor after each jump, although it is not the same type of weightlessness.
 

Offline Geezer

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Re: Does long-term microgravity endanger eyesight?
« Reply #8 on: 21/03/2012 18:36:18 »
Yep, Michael Jordan experiences a few moments of zero-G before smacking into the floor after each jump, although it is not the same type of weightlessness.

Why would you say it's a different type of weightlessness Clifford? I think it's exactly the same  :)
 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #9 on: 22/03/2012 04:02:29 »
I suppose the main difference between the basketball player and the astronaut is that for the astronaut, the frame of reference (international space station) is falling at the same rate they are falling, and thus they have zero acceleration with respect to their reference frame.  Not even any extra wind resistance.

For the basketball player, their reference frame, the gymnasium, is stationary with respect to the Earth, and thus the BB player's movement is dictated by the frame with gravity slamming him into the floor.

Obviously a skydiver also experiences freefall, but feels wind resistance during the freefall.
 

Offline graham.d

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Re: Does long-term microgravity endanger eyesight?
« Reply #10 on: 22/03/2012 13:44:21 »
I am guessing you have a specific meaning for LEO Clifford. If you were aboard a Low Earth Orbiting satellite then you would experience no gravity (except some very slight tidal force) providing, as the name suggests, it was in a stable orbit. From the frame of someone on the earth the satellite would be experiencing 9m/s/s as that would be the centripetal acceleration due to the earth's gravity.
 

Offline Airthumbs

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Re: Does long-term microgravity endanger eyesight?
« Reply #11 on: 23/03/2012 04:05:42 »
I am all with Geezer, get rid of the confusing nonsense such as micro gravity.  It really just confuses things!  Free-fall would be a much better description?
 

Offline Geezer

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Re: Does long-term microgravity endanger eyesight?
« Reply #12 on: 23/03/2012 08:35:15 »
If you were aboard a Low Earth Orbiting satellite then you would experience no gravity (except some very slight tidal force) providing, as the name suggests, it was in a stable orbit. From the frame of someone on the earth the satellite would be experiencing 9m/s/s as that would be the centripetal acceleration due to the earth's gravity.

Graham,

I think you can only use that argument in the absence of an obvious gravitational field. In this case both the astronaut and the spacemobile are obviously in a gravitational field that is almost as strong as that at the Earth's surface, so they are clearly both accelerating at 9m/s/s (in free-fall).

You can't use two frames at the same time to analyze a system. You either have to describe it with respect to the terrestrial observers frame, or the astronaut's frame, but not both simultaneously at the same time, or even concurrently.
 

Offline imatfaal

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Re: Does long-term microgravity endanger eyesight?
« Reply #13 on: 23/03/2012 09:45:36 »
It's all a bit horses for courses - Geezer; I think is correct.  But the term free-fall whilst understood by some - will always have public connotations of hitting something at the end (I know orbits decay - but that's not the point).  For the great unwashed gravity is what stops us floating off - and those pictures of guys in the ISS seem to be just floating off; therefore they are in zero gravity.  Dumbing down is a terrible thing - but sometimes it does make things easier.  My favourite explanation is that they are constantly falling towards earth and always missing
 

Offline graham.d

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Re: Does long-term microgravity endanger eyesight?
« Reply #14 on: 23/03/2012 10:57:00 »
Well, I really don't know many non-scientists who bother to try to understand the idea that centifugal force (for example) is not a "real" force so that the term should never be used. It is my opinion that they are actually right and more in tune the the concepts of GR. It is right to explain the mechanisms and how it comes about as viewed from a stationary frame of reference, but it is also true if something looks like a force and feels like a force, then it is a force, and there is nothing to stop it having a convenient name.

I will have to disagree on this one though I accept that this view is different from the last 60 years of physics teaching in schools.
 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #15 on: 23/03/2012 12:08:42 »
After beating a dead horse into the ground...  perhaps it is time to get back to the original topic of eye problems related to travelling in space, and changes in CSF, with the conclusion that these eye and pituitary problems are due to the Zero-G environment aboard the spacecraft.

Astronauts are also subjected to brief periods of high G forces, and I believe they are subjected to an atmosphere of perhaps ˝ atm and enriched oxygen.  I would hope they could come up with an animal model, and perform tests on the animals to get to the bottom of this. 

And, it is time to start building centrifugal modules for the international space station for the work and time not requiring zero-G.  One of the issues with a centrifugal module would be sealing the joint.  It would be easiest to build it as double-walled, with a non rotating outer hull, and a rotating inner segment.
 

Offline graham.d

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Re: Does long-term microgravity endanger eyesight?
« Reply #16 on: 23/03/2012 12:36:02 »
This horse is not dead - it's just resting :-)

The problems in the eye (at least some of them) may result from higher than normal blood pressure in the upper body for extended periods, and the lower atmospheric pressure would make that worse especially for the exterior capilliaries. The higher BP arises because the human body is adapted for persons standing in a normal gravity for a lot of time each day. The result is that the arteries and veins are adapted to have a reduced pressure in the upper body and a higher one in the lower body. Obviously people can lie down for long periods (I know I do) without problems, so it cannot be that dramatic an effect.

Actually, as far as I am aware, the Mir Space station has its living quarters at sea level atmospheric pressure. The only reason to have an oxygen rich low pressure was to reduce the weight for take off and I can't think of a good reason to have to have this conditio in an orbiting space staion. The US had that terrible disaster many yaers ago because of the high oxygen levels being a disaster in the event of a fire. I don't think the Russians ever adopted this system.

Whats wrong with the Arthur C Clarke/ Stanley Kubrick type of space station as depicted in the film 2001 (and, to be fair) in lots of previous space comics)? Another, more primitive system, would be just to counter balance the lived-in section with a weight on the end of a tether and have the whole thing rotating about the C of G.
 

Offline CliffordK

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Re: Does long-term microgravity endanger eyesight?
« Reply #17 on: 23/03/2012 13:04:36 »
Thanks,
I see notes on the NASA page that the pressure in the ISS is about 1atm.
Well the pressure is just the same as here on the ground, 14.7 psi. And the composition is just the same as air.

Perhaps the low pressure I had heard about was that it was easier to engineer space suits for low pressure.  So, if one had many space walks, then rather than compressing/decompressing for a spacewalk, they would make the living accommodations also at low pressure.

Part of the point of running experiments in space is to have Zero-G, so one wouldn't want the entire station rotating, but part of the time would likely be best spent under normal gravity (computer time, exercising, sleeping, etc).  Unless there would be a risk of something like "gravity bends" from frequent changes in gravity.
 

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Re: Does long-term microgravity endanger eyesight?
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