Chris Smith

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Head scans of astronauts have shown signs of raised intracranial pressure affecting their eyes and pituitary glands, new research has revealed.

Writing in the journal Radiology, University of Texas Medical School, Houston radiologist Larry Kramer MRI scanned 27 spacefarers who had each notched up an average of 108 days in orbit.

The imaging showed signs of small cavities in the pituitary glands of three astronauts, flattening of the backs of the eyeballs in six cases, increased fluid around the optic nerves in nine individuals and bulges in the optic discs inside the eye in four cases.

These are features that would normally characterise increased intracranial pressure and they go some way towards explaining the basis for something that NASA has known for a while: that in the aftermath of exposure to microgravity, astronauts have an above-average chance of experiencing vision problems.

In fact, 30% of short-duration space trippers and 60% of longer-duration orbiters report sight loss symptoms.

The researchers speculate that the changes are caused by fluid shifts that occur inside the head in response to chronic microgravity exposure. Fluid that would normally collect in the tissues of the extremeties under the influence of gravity instead builds up inside the head. This is the same reason that astronauts often characteristically become temporarily puffy-faced in space.

But what is intriguing to NASA is not the 60% who do suffer problems but the 40% who don't. Studying them might reveal why they are relatively protected from the problem and lead to ways to protect those at risk, or identify individuals best suited for longer space missions.

Sending someone to Mars is likely to involve a year in space, so solving problems like this will be critical to the success such missions. In the meantime, NASA are proposing to carry out pre- and post-flight MRI scans of their astronauts on Earth and then monitor them in orbit using ulatrasound scans of their eyes.

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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? CliffordK, Tue, 20th Mar 2012

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.  Geezer, Tue, 20th Mar 2012

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?
CliffordK, Wed, 21st Mar 2012

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? Geezer, Wed, 21st Mar 2012

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. graham.d, Wed, 21st Mar 2012

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. Geezer, Wed, 21st Mar 2012

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. CliffordK, Wed, 21st Mar 2012

Why would you say it's a different type of weightlessness Clifford? I think it's exactly the same  Geezer, Wed, 21st Mar 2012

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. CliffordK, Thu, 22nd Mar 2012

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. graham.d, Thu, 22nd Mar 2012

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