Don’t space travel. You’ll go blind.

Lately space science has made a slightly disturbing discovery. Space travel makes you go blind. Really.

It’s a bit of a surprise, given that in other ways science has found solutions for most of the biomedical problems of free fall and, along the way, learned an awful lot about osteoporosis, which is a spinoff of incalculable benefit. The eyesight thing is also kind of ironic given that back before the space age began, when there was no experience of how humans might behave in free fall, aero-medical specialists had all kinds of worries about what might happen.

A manned rocket arriving near Mars, possibly. A graphic I made using Kerbal Space Program.

The fears of 1950s doctors were manifest. Maybe heart function would disrupt. Who knew? They didn’t even know whether humans could eat or drink in absence of being pulled down by gravity. One outcome was that aircraft were sent off on special parabolic trajectories, snatching a few seconds of free-fall at a time, during which hapless test subjects gulped down ‘space food’ in an effort to find out whether anything could be swallowed in free-fall (and usually threw them straight back up because these flights were a fast way to make people airsick – there are reasons why they were called ‘vomit comets’).

The good news? It turned out that swallowing is a muscular process, and this was already known – it’s called peristalsis, and yes, humans can swallow even if upside down (but don’t try this at home, folks).

enroute public domain
On the way to Mars, concept for 1981 flight,via NASA.

There were still dire bio-medical predictions that, well, maybe you could survive a few minutes or hours. But what about two or three days? Or three or four? Or fourteen – the time required for a lunar flight. All this had to be proven step-wise, on both sides of the Iron Curtain, by sending men up on flights which – from this perspective – were as much bio-medical research as anything else. One of the more heroic was Gemini VII – in which Jim Lovell and Frank Borman spent fourteen days orbiting Earth with about as much space between them as the front seats of a Volkswagen Beetle. That was their living room, bedroom, dining room, kitchen and, inevitably toilet. Waste liquids were ejected into space in a spray of liquid that froze and caught the sun (‘urion’, quipped Wally Schirra, on another mission), while solids were bagged and stored. As you can imagine, this meant that by about Day 4 or 5 they were living inside what amounted to a commode.

That research continues today. One of the main functions of the International Space Station is as a test lab for studying prolonged free-fall exposure – something that has had huge direct outcomes in, as I say, understanding how osteoporosis works and how to alleviate it.

The thing is that, while we know that humans won’t die even after months or a year in free fall, there’s one major gotcha that nobody thought of in the early days and which exercise can’t fix.

Free-fall makes you functionally short-sighted, often to an absurd degree.

ROMBUS in Mars orbit: Phil Bono’s 1960s scheme for the Red Planet to exploit the capacity of his colossal re-usable rocket system. Here the Mars Excursion Module backs away for landing. Public domain, NASA.

Here’s how it works. Our systems evolved in gravity, meaning that they’re optimised to expect body fluids to be pulled downwards. Everything (such as one-way flapper valves in the main leg arteries) is optimised on the basis of a one-way pull – down. But that doesn’t happen in free fall, and the result is that astronauts end up with fluids accumulating in the upper body – hence the slightly puffy look many astronauts gain after even a short time in space.

The problem is that this fluid accumulation also occurs internally, behind the eye, and over time it flattens the eyeball – destroying clarity of vision by affecting focal length. Eyesight on some astronauts has dropped from 20/20 down to levels approaching the US definition of legal blindness (20/100 on the eye chart) in one case. Furthermore, although this alleviates on return to Earth, it doesn’t entirely reverse and some astronauts have been left with permanent visual impairment.

What this implies is that astronauts might arrive around Mars after an eight-month Hohmann-orbit transfer (the practical one with today’s tech) with eyesight so degraded they can’t even read their instruments. And that’s a worry. The only real answer is to provide artificial gravity – for example, by spinning the spacecraft – which is another hurdle because it requires specific equipment that adds mass and complexity.

My take is that we need better propulsion systems. Something that can lob a spacecraft to Mars in a month or less, for instance. That’s going to mean some fairly esoteric tech – I’m thinking not just VASIMIR-type enhanced electric drives but maybe even something more capable, like a nuclear-fluorescent system. Whatever we use, it’ll have to be reliable, because at the velocities that implies, you’d be on a one-way trip out of the solar system if you couldn’t fire the motor for a braking burn. The problem, as always, would be the cost – literally astronomical – and then maintaining funding for such a project over the generation or more it might take to bring it to reality.

Any thoughts?

Copyright © Matthew Wright 2018


10 thoughts on “Don’t space travel. You’ll go blind.

  1. It seems that even with better (faster) propulsion systems, flights would have to be severely restricted to within mars orbit, Matthew – hopefully someone will invent artificial gravity (forget magnetism).
    Only other answer would be our old favourite, genetically modified humans 😎

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  2. That is quite a disadvantage. Our bodies have evolved for approximately 1g of gravity. The solution would be a spacecraft with artificial gravity. The problem of course, is that artificial gravity exists only in the realms of science fiction. For now. In science fiction, artificial gravity (or cancellation of gravity) or “paragravity” is sometimes present in spacecraft that are neither rotating nor accelerating. At present, there is no confirmed technique that can simulate gravity other than actual mass or acceleration. It is interesting that of all of the problems that could have arisen from prolonged spaceflight, that fluid in the eye would be a major concern.

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    1. Yes, who’d have guessed that one? It’s underscored the importance of checking these things out in low earth orbit first. Spinning the spacecraft is probably the way to go, but that has its own problems with Coriolis effects on a short axis (I think ‘Discovery’s carousel was too small even though it was 40 feet diameter). It’d be nice if artificial gravity of the sci-fi ‘this is actually in a movie studio’ variety was possible – but as Scotty put it, ye canna change the laws of physics!

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  3. Your post made me rethink something I’ve thought about for awhile, and should already have seen the inherent flaw in that thought. Here’s the thought: Imagine an x-y graph. Let the x-axis represent some variation of propulsion efficiency in terms of delta-v (as long as we’re using some form of reaction propulsion), and the y-axis increasing efficiency of life support. Then the more efficient the propulsion is, the less efficient life support needs to be.

    Well…maybe. You made me think about two things in succession: first, there’s a minimum level of efficiency for life support that depends on the mission of the vessel. If you’re a fast courier, say, going from base to base, maybe you can get along with the absolute minimum, say, air recycling and a relief tube. OK, for female astronauts that might have to be modified.

    What I didn’t think of was that, for a long-range exploration vessel, “going boldly where no man has gone before,” you have to have the best available efficiency in both categories.

    And this post then made me think that “life support” might mean more than an on-board ecosystem, but also include some form of artificial gravity…so that, at the end of the trip, you can be sure you got where you intended to go!

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    1. I hadn’t thought of that – you’re right! Artificial gravity should be considered part of the life-support (because, in effect, it is, medically). The challenge then is actually producing it – I guess a spinning habitat is the obvious answer, but the greater triumph would be figuring out a way of doing it without violating General Relativity. In that regard I’ve seen research recently into a way of explaining quantum effects that actually works with GR – the schtik is that individual particles may not necessarily obey causality (I think this was played with in 1991 but never explored much). Probably that won’t change how we understand gravity to work, but on the other hand pulling at a loose thread in a theory usually creates outcomes that aren’t predicted, so maybe there will be an answer to that and, with it, sci-fi style artificial gravity without centripetal force.

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      1. I have a friend who thinks artificial gravity of the non-spin sort would open up the entire solar system from the POV of making asteroids colonizable. I’m trying to keep an eye on the research being done on gravity as an “emergent” field.

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        1. I think it might too, because it would mean gravity has polarity and could be harnessed as a drive system. Heinlein pretty much envisaged that with his Horst-Conrad impeller drive, which seemed to be associated with an anomalous artificial gravity. Of course he didn’t explain the physics too closely… In the real world I suspect a new theory of gravity will emerge in a while – not dislodging Einstein but offering a different way of explaining the phenomenon. Whether that then allows us to have polar gravity or not is another matter… but it would be nice…

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  4. I’m thinking we won’t even attempt a significant presence on Mars until we can get there in a month or so. So maybe in the near term, eyesight may not be a factor. And any Mars colony won’t be practical until we have a space-based industry.

    We need to be able to construct starships in orbit, not sending extremely expensive launches up a little bit at a time. Once we have that space-based industry building ships, I think constructing a vessel with a centripetal gravity wheel with living quarters will be less problematic. That’s not to say developing that space industry won’t be difficult, just a necessary step.

    We could make genetic enhancements that fix the eyeball problem, but unless we get an orbital industry established and start mining materials on the Moon, we won’t be traveling very far in space anyway.

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