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TVIW: Caveats for Long-Duration Missions

When he opened the Tennessee Valley Interstellar Workshop in Oak Ridge last week, Les Johnson told the audience that sessions would begin and end on time. Punctuality is a trait that I assume works well in Johnson’s day job at Marshall Space Flight Center, and it certainly was appreciated in Oak Ridge, where the delays and overruns that mar so many conferences just didn’t occur. That kept the pace brisk and the presenters solidly on topic throughout.


That sense of pace and direction is making TVIW into one of my favorite gatherings. Today I’m going to run through some of the presentations from the first day, beginning with the multidisciplinary note with which I closed yesterday’s post. What we gain by keeping a wide range of background in play among the presenters is a chance to spot hidden assumptions, some of which can prove deadly when not properly evaluated. Monday’s TVIW talks helped clarify what we’ve learned about the human presence in space and just how much we have yet to determine.

Image: Les Johnson calls the first session into order in Oak Ridge.

Problems of Survival in Deep Space

Biologist Robert Hampson (Wake Forest School of Medicine) was a familiar face when he took the podium on Monday morning, having appeared at the last TVIW in Huntsville. What Dr. Hampson brings to the table is a rich background in the neurosciences that includes research into cognition, behavior and learning.

All of these come into play when we’re talking about the issues astronauts will face when dealing with long-duration spaceflight. In Huntsville, Hampson had outlined our need for a biomedical research laboratory in weightless conditions, so that we could do the kind of detailed research into artificial gravity that we need before we can think about how to provide it on a mission. The Oak Ridge talk followed up on the idea, explaining the need for a livable habitat where access to vacuum and solar radiation is readily available. A further option would be to place it outside Earth’s magnetosphere to study radiation in that environment and how to mitigate it.

We tend to shrug off the gravity problem by assuming that we can create a rotating habitat, but the ‘tin cans on a string’ notion — two segments joined by a tether — leaves unanswered the question of how long the tether should be and how fast the rotation. The speed of rotation turns out to be critical because while the vestibular system can adapt to linear velocity, angular momentum is perceived as acceleration. Vertigo can be the result of a sudden head turn.

Moreover, all the work we’ve done in zero-g aboard vehicles like the International Space Station has led only to marginal results. Microcravity causes physiological changes that can range from loss of calcium to fluid retention to a reduction in muscle mass and a decrease in the volume and pumping capacity of the heart. Only gravity has the ability to resolve these problems, which is why we need the space lab to explore what forms artificial gravity can take. Hampson said that if astronauts took an extended zero-g mission to Mars, they might be unable to function upon arrival because of Mars’ own gravity, even though it is a paltry 38 percent of that found on Earth.

The lab design resulting from Hampson’s research would allow research subjects and scientists to live in an eight-deck space divided into two four-deck structures connected by a tether, an installation that contained both a human and animal lab, with each of the two segments creating about 1000 square feet of research space. Another significant issue for study here: The degradation of memory, found on Earth in those with radiation therapy for cancer, that can likewise be produced by an overdose of radiation in space. The ideal, then, would be to place the biomedical laboratory at the Earth-Moon L2 point outside the magnetosphere, where all these issues can be studied in the best environment for microbiological and biochemical tests.

Human Prospects on Mars

Oak Ridge National Laboratory’s Fred Sloop also delved into the question of gravity’s effects, noting the huge role that evolution under 1 g has played in the development of our physiology. We’re already talking about private colony missions to places like Mars, but we have to overcome the factors Hampson talked about as well as the embrittlement of bone in zero-g, which can cause as much bone loss for an astronaut in a single month as a menopausal woman loses in a year. Bone demineralization appears most strongly in the pelvis, said Sloop, and with loss of bone we get calcium phosphate released into the body, along with calcium oxalate.

The result: The formation of kidney stones. We also see that extended microgravity causes muscle atrophy, with muscle mass down to 70 percent of preflight after 270 days in orbit. Fluid shifts occur as bodily fluids distribute to the upper portion of the body, a shift that can involve cardiovascular changes and a decrease in blood volume as the red blood cell count drops. The injury potential upon re-entry is significant, for on a long-duration mission, the spine can lengthen more than 7 centimeters. Changes in cognition and mental imagery can impair function.

Sloop believes that despite mechanical countermeasures — MIT, for example, is studying a ‘skin suit’ that mimics a 1 g load on bone and muscle — the best recourse will be artificial gravity created by rotation. “We need to find out what the minimum gravity to retain physiological health really is,” Sloop added. “Is 1 g necessary, or can we get by with less? Mars gravity at .38 g may be sufficient for long-term colonists once they have arrived, but at this point we don’t really know.” In space, a nominal design for a 1 g habitat rotating at 4 rpms with a rotational radius of 56 meters may work, but will it ward off these ills over a 30-month mission to Mars?

A Historical Perspective on Colonization

You can see why rushing a deep-space mission under the assumption that we have sufficient experience in nearby space would be a mistake. But the issues aren’t solely biological. Sam Lightfoot (South Georgia State College) tackled the assumptions we bring with us when we attempt to colonize new lands, as revealed in historical precedent. The first colony planted by the Spanish in the United States was not St. Augustine but an attempt in the barrier islands of Georgia by the conquistador Lucas Vazquez de Ayllon, who landed in the area in 1526.

Allyon thought he had brought what he needed — after all, he had tools, livestock and weapons — but many of the tools proved unsuited to the environment. Allyon’s horses did not adapt well in the humid, sandy islands, and European methods of farming failed. The colony’s maps were incomplete and inaccurate, water was in short supply and disease became rampant. Unwilling to exploit local food resources, the colonists refused to eat wheat. Their housing disintegrated because they were using wattle and daub techniques suited for the dry climate of Spain.

Allyon, whose colony had to be evacuated back to Havana, was one of a string of failures whose colonization efforts have been all but forgotten. Pánfilo de Narváez made even Allyon’s attempt look good. Equally unprepared for the actual conditions he found, de Narváez took over 300 conquistadores with him, a group with few skills adapted to local conditions. Only four of his men would survive the colonization attempt, walking up the length of Florida and making their way somehow to Mexico City. In sharp contrast, Hernando de Soto was able to survive because he brought equipment suited to the terrain, along with flexibility in leadership.

The lessons are clear enough, and even more stark when we consider that the next wave of human colonization will be in an environment far more unyielding, and much more difficult to reach and resupply, than even the conquistadores had to contend with. I took away from these multidisciplinary sessions the need to question our most basic assumptions. Fred Sloop’s point about Mars’ gravity stands out: We don’t really know whether humans living at 0.38 g will be able to survive over the long haul. Such basic questions drive the need for research into areas we have found difficult to explore with the existing space infrastructure in low Earth orbit.

More tomorrow as I turn to issues not just of planetary but interstellar migration, looking at presentations that covered everything from beamed sails to ‘worldship’ habitats and the possibilities for space drives. Can we imagine a day when artificial intelligence and additive manufacturing produces the space infrastructure we need in decades rather than centuries? The Tennessee Valley Interstellar Workshop was an opportunity to talk about issues like these not only in the sessions but in informal dinner conversation. More about the proceedings tomorrow.


Comments on this entry are closed.

  • Alex Tolley November 18, 2014, 12:08

    It is nothing less than scandalous that we still don’t have any real handle on what g conditions humans need to survive. There has been next to nothing studied. Nasa has does everything but examine this seriously. Simple experiments like mice in rotating wheels could have been done decades ago, in Skylab for instance. I recall that the Stanford Taurus design for a space colony was partially defined on what was thought to be acceptable rotational movement. But this was back in the mid-1970’s. 40 years have elapsed with no appreciable knowledge improvement. I’ve little doubt that pilots can tolerate all sorts of rotational movement and even non-pilots could behaviorally adapt. However it seems to me that the ‘tin cans on a string’ approach is considered too risky a design and is therefore nixed by the engineers (and they may be right). However that doesn’t mean that the rotational approach isn’t sound, just that we need to determine what would be the best way to build such a structure – between minimalist tethers and the massive 2001 style space station V.

    Back in 1975 I wrote a dissertation for my bachelor’s degree concerning this issue, using early Skylab medical data. Since then we have added enormously to the literature on zero-g effects on physiology. But nothing of importance on mitigation with fractional g. We are still speculating with minimal data to guide us. Some of the rotational radius issues could be studied on Earth, if we accept that the study environment would have to be greater than 1 g. Not such a problem if the subject is physically supported.

    Sorry if this is sounding like a rant, but I have been frustrated at the lack of even minimal progress for decades.

  • NS November 18, 2014, 12:51

    While considering the experience of expeditions like de Soto’s, we shouldn’t forget their effect on the peoples they encountered. De Soto described numerous settlements. A French expedition a few decades later found the same areas utterly depopulated — diseases accidentally introduced by de Soto’s expedition had annihilated the native American population. We ourselves may not encounter ETI in the near future. It’s certainly possible that we will visit worlds with native life that may be as vulnerable in some ways to us as the native Americans were to de Soto.

  • Ron S November 18, 2014, 12:54

    It may be decades yet until we are able to establish long-duration (self-sustaining) habitats in space or other planets. By then it is conceivable that physiological knowledge will progress to the point where we can instruct the body to behave as if gravity were 1g.

    Bodies tend to allocate energy and resources to where it’s needed and to remove/reuse from where it’s not needed. That’s what happens in microgravity. Being able to discover and manipulate the responsible “signal” could solve a multitude of technical issues with habitat construction.

  • Alex Tolley November 18, 2014, 17:21

    @Ron S


    It may be possible, but I would doubt it. You cannot easily substitute physical effects with chemical ones. For example, chemical gradients cannot easily be made without the underlying physical force underlying it. OTOH, some effects can be mitigated, e.g. inner ear balance disturbance can be prevented with drugs/training.

    However, gravity also solves a lot of issues as well, not just physiological. It keeps things in place, provides useful forces that we are well adapted to, not least of which is going to the toilet. Rather than designing for zero-g, just design in the g and use off the shelf tools.

    Partial g is more interesting. Clarke speculated that low g would enhance lifespan. More likely it doesn’t, although we just don’t know which processes might gain and which lose under lower g loads (we cannot bed-rest subjects for a life time to test the idea). But we could test mice in centrifuges to get some clues.

    When/if we do these studies, we need an environment that separates out gravity and radiation. Studies on various space stations did not do that, so that is hard to be certain whether micro-g or radiation is the key variable to observed changes.

  • Al Jackson November 18, 2014, 17:38

    This triggers a bee in my bonnet.
    From the beginning the ISS had been criticized for not doing enough science.
    It has not done as much physical science as was planned but that’s budget stuff.
    However the amount of zero g medical knowledge learned has been invaluable and continues. It’s kind of a ‘piggy back free’ since one gets the data for every crew now. However there is a lot by design. Something new is learned all the time, changes in the eye being one of the latest ones. The Centrifuge Accommodations Module was canceled in 2005 due to budget problems, sigh. NanoRacks Centrifuge is, I think, on the ISS this year. So there is a small centrifuge there, but need a bigger one, Well… don’t think there will be a manned Mars expedition for some while so still time to do the artificial gravity research.

  • william November 18, 2014, 19:32

    I find this extremely amusing that the subjects in question are dealing with practical matters related to just near interplanetary spaceflight. I read Robert Zubrin’s ‘Case for Mars’ a few years ago and I recall how dismissive he was concerning all the particular expected worries that might be encountered on a mission. Apparently he must’ve downplayed it a little too much, since there is are a lot of unresolved issues concerning manned flight.
    One thing that is always been of some concern with regards to these missions to other planets and colonization is the question of what happens to humans that have long-term occupancy on any given planetary body. For people who were born in such weak gravity there is a possibility they could never ever make a trip to Earth because their cardiovascular system and bone structure could not support them against the unanticipated Earth’s gravity.

    In the long run, it’s possible that when colonization becomes a permanent part of the human expansion into other worlds, they will literally create new types of human beings that have not been seen before and have no direct connection with the physiology of their forbearers.
    I just wish to close by saying that I’m pleased we didn’t start off with solar sailing as the first topic of the day.

  • william November 18, 2014, 19:39

    Oh I forgot; do you know if there is online recorded video of the conference ?

  • Paul Gilster November 18, 2014, 22:18

    Video will be available soon and when it is, I will post the link.

  • Rangel November 18, 2014, 22:21

    The problem is: After more than 4 decades, why are we still don’t know how much gravity the human body required to work properly (at least an aproximation)?

    Not even a reduced centrifuge attached to the ISS to study low-G effects on mices and other animals. I know there is plans for put that on the ISS, but it could be done a long time ago.

    I am at same time satisfied with the space program and its advanced as i am disappoint in some questions, like that one, we could really already be testing partial-G effects on humans. What about a low-cost inflatable torus to the ISS? And i hope what we couldn’t learn from the ISS the future chinese space station help us to clarify.

    It seems that we will learn about the effect of moon’n gravity by practice before we research on it, since there are many countries willing to do manned landings in the 2020’s, Russia will build a base for longer stays on the moon and Japan is interested as well to build a base there, as is China a decade later. it seems Russia vision for a lunar base will be the the first that fit long stays like the ISS now, so it will help us to answer the question of low gravity, at least for the 1.66g range.

    Let’s not forget the start of the year-long stays on the ISS starting next year, it will tell us a lot about long-term zero-G (pretty useful for more info about the effects on a long travel to Mars).

  • Andrew Palfreyman November 18, 2014, 22:55

    We’ve needed a 1g rotating space station for decades. If we want to answer the Mars question, let’s build a suitable “2nd floor” at 0.38 gee for that. Two birds with one stone.

    And I agree that it’s scandalous that we still don’t have full details on extended lower gee living.

  • mike3 November 19, 2014, 1:19



    Correct. We don’t know enough about Mars, for example, yet, to be sure it has no native life, much less what an interaction of native and Terran life would do. This is why I advocate the telepresence solution for Mars: don’t go to the surface just yet, but use rovers controlled from orbit to explore, at least at first. By putting humans in orbit around Mars, you eliminate the light speed limit which frustrates control from Earth, allowing for far more research to be done in a given amount of time. One could add additional features to the rover that would gather up much greater amounts of data than could be transmitted easily over interplanetary distances as well.

    With this, we could do enough science to more definitively settle the life question, which would then inform our decisions about what to do regarding colonization, if any.

    Using a telepresence system could also be cheaper than a surface landing.

    It would be a shame if there were life on Mars, and we ruined it by being too crass. The scientific and moral value of something like that is simply too great to play fast and loose.

    The same goes with even more potentially-habitable places, such as Europa. “Fortunately” for any native life, there is a whole lot of radiation there, which tends to discourage manned exploration, and encourage unmanned exploration, or telepresence exploration from a greater distance (so would probably have some, but still much less than from Earth, light speed delay).

  • DCM November 19, 2014, 5:32

    It’s true that millions of American Indians who never even saw, maybe never heard of Europeans or Africans were killed by imported diseases but it’s also true that much of Africa was never successfully colonized by outsiders because of the diseases there. We shouldn’t forget it can work both ways.

  • Al Jackson November 19, 2014, 9:42

    Funny you should ask.
    In modern prose science fiction a number of stories about this.
    One of the best, no surprise, is Robert Heinlein’s It’s Great to Be Back! (1947).
    The MacRaes who have been in residence at Luna City for a long time come back to Earth, and they do have their physiological problems, though it’s social reasons that make them come back.
    I don’t know how many stories there where about people with cardiovascular problems benefiting from zero g there have been. Clarke wrote about it. Fritz Leiber had people in zero g colonies living long lives. Carl Sagan’s billionaire benefactor was in orbit for life extension. Seem , for some time, SF got the zero g effects wrong.
    However the effects were worried about long ago, von Braun’s Space Station (1948) had artificial gravity. Station V and Discovery of 2001 : A Space Odyssey had ‘rotational’ gravity.
    Early on it was thought one had to have artificial gravity because people would go mad in long term free fall!

  • ljk November 19, 2014, 10:22

    The only real reason to send humans into space now and definitely in the future is to colonize other worlds and space itself. Machines and computers are getting better each day to the point they will be able to conduct space exploration far more efficiently and with fewer resources and of course no potential for the loss of life.

    So if you want to explore space, use robots with AI. Humans are for colonizing and this assumes we will be able to live on other worlds – or will we have to use biotechnology to modify our descendants as well to exist in places with varying masses and much higher extremes of temperature and radiation? And we may also have to modify humans to want to live in environments where mobility and living space is limited.

    We have been brought up on decades of romanticized visions of brave astronauts and cosmonauts boldly exploring and living on alien worlds but can they? Perhaps more studies of those folks who stay in Antarctica year-round are required, but even they can go outside to breath the air, cold as it is, and they know if something goes wrong a plane or ship can rescue them in a matter of hours or days. They are also no longer isolated even with communications with the rest of humanity. The same cannot be said for those living on Mars or even Luna.

  • Alex Tolley November 19, 2014, 11:53

    OBSERVER: Galileo, you’ve been dropping weights off the top of this tower for years now.
    GALILEO: Yes, it’s been fascinating. I’ve found out all sorts of interesting things about the drop relating to density, shape, height of fall….
    OBS: That’s great, but we asked you to work out how to aim our cannons correctly.
    GAL: Can’t do that. No equipment to fire cannon balls. But why do we need to do that? We could drop balls on the enemy instead. I can drop then so precisely…

  • NS November 19, 2014, 12:49

    To DCM, yes, we’ll have to be sure astronauts protect themselves and that returning astronauts don’t accidentally bring alien organisms back with them. Historically Europe did get hit by diseases from other parts of the world (plague, possibly syphilis). Unlikely as it probably is, we certainly wouldn’t want to encounter something like Martian ebola.

    I like mike3’s idea of thorough remote exploration before any human visitation as well. It also brings up an issue that’s been discussed here before — if we can build comfortable space habitats (with Earth-like gravity etc.) is there any need to colonize planetary surfaces?

  • Alex Tolley November 19, 2014, 13:16

    While I think Zubrin is very dismissive of some risks, such as tolerable radiation levels, I think he does have a point. Some time ago I was watching a documentary on radiation levels. The presenter showed that places like Chernobyl had lower levels than where people live today. It is possible that we are too cautious and conservative regarding this hazard. Radiation has possibly become the boogeyman of space. Of course I am using the term radiation very loosely, and the documentary presenter was just using a Geiger counter and not looking at the subject in any depth. OTOH, some executives almost live on aircraft and there doesn’t seem to be any obvious rise in cancer rates for this group.

    New technology and environments have always resulted in safety questions being asked. “Can a person breathe on a train moving at 35 mph?” “Will the heart explode in zero-g?” These questions now seem foolish, but others, some of which are real issues, have taken their place.

    There are times when I imagine what would have happened if historical explorers were as cautious as we are. One can imagine Columbus needing to build ocean ship simulators to test whether crew could stand being out of sight of land for weeks on end (The Mars 500 simulator) Or perhaps the rolling motion would be too much for the crew. What about the climate? Would disease be a problem on a ship? (We now know that scurvy did become an issue for ship crews until it was solved by the British Navy). Today, long sea voyages are commonplace.

    We’re seeing the same boogeyman questions today, e.g. “Hampson said that if astronauts took an extended zero-g mission to Mars, they might be unable to function upon arrival because of Mars’ own gravity”. We’ve had astronauts in space for longer than a Mars trip and they can function on Earth after returning. Maybe not immediately on landing, but fairly quickly. Can we not build in some recuperation time, perhaps with automated assistants?

    The issue of rotational radius is well illustrated by responses to the Discovery’s centrifuge in 2001: A Space Odyssey. The “educated” argument is that Coriolis forces would make such a small radius at a minimum uncomfortable to live with, and likely worse. But is that true? We have no information on adaptation to such conditions. We know that ordinary humans can adapt to the motion of sea going ships after a period of adaptation, that may result in temporary nausea. Would behavioral adaptation not occur in rotating vehicles? Such adaptations might include not moving too much, making careful moves in some directions, preparing muscles for forces as you climb to the hub, and so on. We just don’t know. Had any of the rotating space stations been flown we would have at least some idea. If we design world ships, do they need to have radii in terms of kilometers, or will much smaller radii do? In the nearer term, if we design space hotels, what do we need to make it comfortable for our paying tourists. How much g and what radius is acceptable to allow for an enjoyable experience? If Earth tourism development is any guide, conditions on a space station will eventually become as similar to stable dry land as possible. Aircraft fly smoothly in the stratosphere avoiding tropospheric turbulence. Cruise ships are roll stabilized to prevent even temporary nausea upsetting a trip. Space hotels may offer 1 g and undetectable rotational forces in the main living areas.

  • ljk November 19, 2014, 14:04

    Chance to bury your DNA on the moon in a time capsule

    00:01 19 November 2014 by Paul Marks

    It’s like something out of 2001: A Space Odyssey. An artefact buried in the lunar surface conceals a big secret. Only this time, the secret is you…

    A plan to establish a lunar archive containing human DNA and a digital record of life on Earth is being unveiled this week. Called Lunar Mission One, the archive is the brainchild of British space consultant David Iron, who has worked on Skynet, the UK spy satellite network, and Galileo, the European Union’s global positioning system.

    His idea is to charge people £50 or so to place a sample of their DNA, in the form of a strand of hair, in an archive to be buried on the moon, alongside a digital history of as much of their lives as they want to record, in the form of text, pictures, music and video. Iron presented the plan at a space flight conference at the Royal Society in London on 19 November.

    The catch? He needs at least 10 million earthlings to do this if he’s to generate the £500 million the moon shot will need.

    Full article here:


    To quote:

    Another space flight venture plans to send religious artefacts to the moon, as New Scientist reported in May. The Church of England has even told Iron that the plan to store DNA on the moon does not conflict with Christian doctrine. “It is beyond religion,” Iron notes.

    “I’m intrigued. This lunar time capsule might be a lot of fun,” says Roger Launius, a director of the Smithsonian National Air and Space Museum in Washington DC. “The idea of being able to point up at the moon and say ‘there’s a bit of me up there’ will have a lot of appeal.”

    Monica Grady, a scientist working on the Rosetta comet lander mission at the Open University in Milton Keynes, UK, thinks the mission will be an inspiration to schoolchildren who will be asked to contribute ideas for the public archive. “The idea of an ‘ark’ of digital data will spark much discussion,” she says.

    One lofty hope is that the archive can serve as a sort of “backup drive” for human civilisation. But extracting DNA from hair may be challenging, says Alan Cooper at the Australian Centre for Ancient DNA at the University of Adelaide. For long-term storage, he says, DNA from cheek cells or blood would be more stable.

  • Alex Tolley November 19, 2014, 14:28

    @ljk So if you want to explore space, use robots

    I agree. It is often stated than an astronaut could do in minutes what a Mars rover does in a year. However I watched a fascinating talk about how to reduce the time delay issue for robots by using video game techniques to make controlling a rover much more like continuous driving. The idea was that robot exploration could be much faster on Mars. Now how far this could be extended, e.g. Europa was not answered, but clearly with more AI the machine could be much more autonomous and avoid doing stupid things. The same approach was suggested for flying vehicles and that is even easier. The presenters argument was that this was a far better solution to solving the time delay problem than sending astronauts to Mars orbit to control robots from there.

    Robots and AI have Moore’s Law on their side whereas human exploration cannot really change the fundamentals of life support, only propulsion. With the impressive new capabilities for vision processing, plus the new neuromorphic chips offering very low power neural type processing, I can only see that robotic exploration will continually leap forward in capability.

  • Ole Burde November 19, 2014, 16:01

    ”…..but the ‘tin cans on a string’ notion — two segments joined by a tether — leaves unanswered the question of how long the tether should be and how fast the rotation. ” …I believe Gerald O’Neal , In his classic work ‘The new Frontier’ made som intelligent asumptions about what the minimum rotating period should be , in order to make a ”tin can” comfortably habitable for 90% of an arbitrary population .
    What I dont get , is why it should be so important to know the the exact minimum length of the tether . Tethers are relatively cheap and lightweigt stuff, why not just make it an adjustable length with plenty of spare cable to be reeled in or out ? Such a system should be capable of rotating any two habitats of comparable mass , of reeling in and out , and of spinning up or down to a standstill in a few minutes . Sensible engineering points to a solution where the rotation mekanism is a separate system , whith its own energy suply ,dataprocessing , gyroscopes and perhabs smalscale rocket engines as a backup . Even for an asteroid mission , it would make sense to divide the spacecraft into two halves , more or less ,. that could be rotated for most of the time . In such a rotating double-habitat , one of the reasons for using expensive high accelerations would disappear .
    The rotation system as a whole , if build flexible enough , could be reused many times by different combinations of habitats .

  • ljk November 19, 2014, 18:14

    Let us see what the pioneers of space colonies had to say…

    NASA SP-413

    Space Settlements: A Design Study

    Edited by

    Richard D. Johnson, NASA Ames Research Center
    Charles Holbrow, Colgate University

    Authored by the participants of



    This site links to other books on the subject here:


    If you want it as one document in PDF format:


  • kamal ali November 20, 2014, 3:45

    I too am completely at a loss to understand
    why NASA et al do not put more
    emphasis on minimum gravity research.
    It’d be great to use the ISS to
    do some decent centrifuge experiments.
    If anyone can shed light on why they would
    be so expensive or difficult, please enlighten me.
    Seems to me that 3 primary axes on which
    to push for Mars are minimum-G generation,
    radiation mitgation and propulsion. I dont see a
    well thought-out ladder of increasing goals
    along these axes being sought out. Why is that?
    Can NASA not lobby for a budget for radiation
    mitigation and use that to bolster deep space
    probes so that besides reaching their targets,
    they can also do radiation experiments en route?
    If any of you can give me insights into why
    this is not happening, please enlighten me
    (I’m guessing $ but maybe there’s more).

  • Alex Tolley November 20, 2014, 12:54

    @Ole Burde – you make a good point about the flexibility of tethers. Fixing teh radius is obviously of concern with circular structures like the Bernal Sphere or Stanford Torus. But if you can live with a tether, at least for experimental purposes, one should be able to test different configurations.

    I would imagine that with a tether, you would still want a flexible, pressurized tube to allow movement between the 2 cans. Perhaps multiple tethers connecting the cans and surrounding the tube would provide the necessary safety. You would want the cans to be big enough to test various phenomena of the rotating structure.

    I think that the cans on a tether idea might be sufficient for early journeys, but that circular structures are the way to go for more mature structures, including hollowed/inflated asteroids.

  • Rob Hampson November 21, 2014, 1:09

    Paul – I want to thank you for an excellent synopsis of the talks at TVIW. I do want to add a few points to the discussion here: with respect to “fooling” the human body into making the adaption to micro-gee – medical science *does* have drugs which slow loss of calcium, muscle degeneration, and reduced cardiac capacity. However, to date, those treatments have not proven to be effective at halting the physiological changes induced by micro-gee. An issue of concern is the conversion of muscle fibers from slow-twitch (sustained effort and endurance) to predominantly fast-twitch (brief bursts of effort). An illustration is a weight lifter who can *lift* weights, but cannot hold them. Since the very act of standing in a 1-G field requires slow-twitch muscle, it is a critical effect on astronauts. With respect to the effect of degeneration during the voyage on Mars explorers, experience with the ISS astronauts have show that it takes several weeks to recover strength after return to normal gravity. The fear of physiologists like myself is that astronaut explorers would arrive at their destination after a 6 month (or longer journey) and be unable to explore the surface since they would have to allow time to recover – but that there would be no work, no construction, no exploration and no way of responding to emergencies during that recovery period (and no assistance from other humans already present – as there is on Earth for returning ISS crew).

    Finally, there is a critical gap in micro-centrifuge studies with mice and full-scale livable rotating habitats for humans – namely, studies on quadrupeds will have limited applicability to understanding artificial gravity on bipeds. Humans stand upright, with our vital organs in line with the long bones of the body. Mice, rats, even the smaller monkey species (which could conceivably be housed on the ISS) do not. I was asked about the discarded plan for a short-radius centrifuge to be attached to the ISS that would allow astronauts to sleep in 0.5-1.0 G – wouldn’t that forestall the degradation? Perhaps, but the problem with short-radius rotation is that the difference in perceived gees (and coriolis forces) would be significant to a standing human. Lying down would reduce the differential, but then the advantage of G-force in line with the long bones of the body (spine, legs, arms) – and on the pelvis – would be lost.

    Hence, we need to have a radius of at least tens of meters for the astronauts to comfortably stand and walk in the centrifuge. With radius comes two trade-offs – (1) longer radius requires fewer RPMs to effect 1 G, but (2) longer radius means higher linear velocity at the ends with the 1 G force. The big unknown is how the vestibular (balance) system will adapt to the coriolis forces of the rotating habitat.

    Solution – let’s build the lab and find out.

    Again, thank you Paul for the summary and the chance to interact with your readers!

  • drs November 21, 2014, 3:24

    “It is often stated than an astronaut could do in minutes what a Mars rover does in a year.”

    Almost always left out is the cost. Spirit and Opportunity cost $800 million together, less than one Shuttle launch. Curiosity $2.5 billion. Up to $1.8 billion of the latter was apparently development cost; what if we produced 20 rovers at a time? What’s the realistic cost of a manned Mars mission including return capability, and how many rovers could that buy?

  • Ole Burde November 21, 2014, 12:34

    Alex Toley : The easiet and cheapest way forward is mostly to make a relatively simple eksperiment capable of delivering a lot of NEW information. Having two existing space modules ( they could be worn out sattelites ! ) spun up to 1G connected by a relatively simple tethersystem would do exatly that , deliver a lot of new information .
    The question to be answered first , is whether a cable system is possible at all . Any one of many aparently simple engineering problems might open up a ‘pandoras box’ full of snakes . Nothing like it has ever been done before , and that in itself is a god reason to aproach the problem cautiously.
    How Astronauts exactly would move from one to the other , or how and if they would enter the moving system through its center of gravity , should not be part of the first configuration of our experiment . Good engineering in the development stage never waste money trying to heap too many variables into a single experiment … this can perhabs best be understood by examining the gigantic and wastefull failures resulting from the opposite asumptions : The long line of failed NASA projects trying to build a successor to the spaceshuttle …those guys didn’t have to proove the possibility of an airbreathing rocket motor in an independent experiment-line , they just KNEEW they could do it , and invested billions in building any number of components for the spaceplane as a whole . The sad failure of Biosphere 1 falls into the same category…HYBRIS !

  • Paul Gilster November 21, 2014, 15:31

    Rob Hampson writes:


    And thank you, sir, for taking the time to add these helpful insights. It was a real pleasure seeing you again — I remember you were at Huntsville last time. Your work in the ‘C for Commo’ workshop was tremendously productive.

  • Alex Tolley November 21, 2014, 16:05

    @Ole Burde – I hear you, KISS. Oversimplifying can also have its problems. For example, if one can is ruptured (like Mir), the crew would ideally need to get to the other can for safety – but a simple tether would require an EVA made extra hazardous by the forces. I’d want the 2 cans to offer redundancy for safety, otherwise one might just as well be a simple counterweight.

    @Rob Hampton – you make some good points about the differences between mice and humans, but these are no different in principle from any animal model. Whether 2 legged or 4, physiological effects of g on bone loss, muscle strength, etc should be indicative. They may not apply exactly, but the point is that we haven’t even done the basics yet after all this time. I like your finishing point: Solution – let’s build the lab and find out.. Yes!

  • Eniac November 23, 2014, 0:19

    The cans on a string model is a very good one, as it will add little extra cost to a station, and avoids moving parts. Since it would likely be impossible to dock directly with the cans, though, we would need a dock at the hub and some kind of funicular vehicle to transport crew and cargo up and down. Or, on second thought, elevators. Should not be too difficult: The load-carrying cables make excellent rails.

    When we think about bigger space stations, I tend to think the beautiful wheels and cylinders from the stories and movies will be rare. Rather, we will see organic growth where more cans are added at the hub, and then the hub extended axially, such that when grown large the whole thing will have the appearance of a giant cylindrical brush. A city in space, with the buildings hanging out from a central rotating axis rather than standing on flat ground. A web of pedestrian bridges will be built between the buildings to avoid having to go through the hub so much. The view from those, if they have windows, should be gorgeous.

  • Eniac November 23, 2014, 18:07

    For those lamenting the dearth of research on human ability to withstand low gravity, I would suggest that we now have proof that humans can withstand more than 1 year of zero gravity without being substantially harmed, and that they can remain productive throughout that entire time. By actual having done it. If this is not real, solid evidence, I do not know what is. No mini-centrifuge with mice in it will produce data even remotely as useful, nor will a human scale model the expense of which would likely dwarf the entire ISS budget. Just saying.

  • Alex Tolley November 24, 2014, 11:55

    No one is arguing about the data for zero gravity. The deleterious effects are well known, especially bone loss which takes months if not years to fully recover from back on Earth.

    What we need to know is what partial g is satisfactory so that constant exercise is unneeded, recovery time minimal to get on with exploration of a world, and that developmental issues (e.g. having children) is not impaired so that we can colonize. Maybe the answer is that we need a full 1 g. But we just don’t have any data.

  • Eniac November 26, 2014, 0:03

    Alex: I guess what I am saying is that we have learned that the deleterious effects of zero gravity appear no worse than those associated with playing football or working in a mine, both activities that have been prosperously maintained for a long time here on Earth. Bone loss, chronic traumatic encephalopathy, or chronic obstructive pulmonary disease, take your pick.

    Having learned this is a key result of manned space activity so far, and not something we should ignore by stating that “we don’t have any data”.

  • Michael November 26, 2014, 14:32

    Bone loss in a low gravity environment such as Mars might be tolerable provided they do some heavy lifting. Power lifters on earth have higher than normal bone densities and they only lift for short periods, no more than a few minutes per day.


  • Alex Tolley November 26, 2014, 15:57

    @Eniac – you can always avoid mining and football. Even coal miners with “black lung” can mine for decades before they die. We don’t even know if you can survive in 0 g that long. I don’t think we would want to live in 0 g, except for short trips and sports activities. But whether lunar or Martian gravity is enough is completely unknown. Having lots of data about up to 1 year in 0 g is like saying we have lots of data about complete inactivity, but nothing about minimum exercise levels to maintain a healthy life. It is an extreme that isn’t sustainable.

  • Eniac November 27, 2014, 15:44


    Are you saying there are not people maintaining healthy lives without exercise? I think you are wrong….

    Zero g is not an extreme. It is the absence of a condition that is incidental to life, a condition that life strains against, and could do without. Since it is ever-present on Earth, though, we might expect all sorts of incidental problems when it is gone. By now we know such problems, although they do exist, are not life threatening or incapacitating for humans, for as long as we have been able to test. Zero g is a minor factor, compared with, say, the absence of air or increased radiation levels. The latter we also might be able to tolerate, but the former we really have to do something about. Which is why we have pressure vessels, airlocks, and other equipment far more researched and engineered than gravity. Basic life support comes first, comfort and long-term health will be taken care of in time as we really start moving out.

  • Skotch Vail November 30, 2014, 3:02

    Micro-gravity is a disaster for humans and creates ever more complicated engineering requirements to keep folks functioning.

    For a long while I’ve wanted centauri-dreams to pick up the subject of artificial gravity vessels, since it seems one the absolutely required steps to getting to the stars. I figured it hasn’t been covered much previously because it was not strictly an interstellar subject and therefore to small an issue to discuss here.

    Obviously the first test need not be a reusable space station. The simplest approach would be a disposable habitat with a counterweight and cable in between, in low earth orbit. If the rotational speed and cable length could be adjusted then we would learn most of what we need to know. Is moon gravity livable, is mars gravity livable?

    No need for central hubs, elevators, passage tubes, or anything in the second vessel save for sufficient mass. Keep it simple and get it done.

    This experiment has already been done, The Gemini 11 mission produced artificial gravity via a 36-meter tether but the 0.00015 g produced for a very short period was not useful for what we need to know.

    I would love to see more discussion about this here. Unlike many of the concepts that are decades or centuries away, this could be done now, and creating political pressure to get this done, away from the ISS, needs to come from somewhere.

  • Michael November 30, 2014, 16:35

    There is also the possibility of using the linear acceleration/deceleration phase to produce gravity. Say 1 g for several hours and none or reduced g during a sleep cycle and so on.

  • Eniac December 3, 2014, 23:42

    Skotch Vail


    Having a dead counterweight is a good idea. However, I don’t see how you can dock with a station without a central hub and transportation between it and the habitat. Without docking, experiments would be restricted to the short time it takes for the habitat to run out of provisions, which is probably not what you have in mind.

  • Michael December 4, 2014, 15:47

    Nasa has been looking into vibration systems to mimic gravity effects on the body of animals, it could be a possible solution to the physiological effects of low gravity.


  • Mark Zambelli December 15, 2014, 11:02

    Over on the Atomic Rockets website there is a page dealing with artificial gravity ( http://www.projectrho.com/public_html/rocket/artificialgrav.php ) where I found this java calculator by Ted Hall… http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm . Tweak the inputs to see how much coriolis force etc would need to be endured. Thought it was pertinent to link to it here.

    I used to think the biggest hurdle (wihout a second, counter-rotating compartment) would be steering, but it looks like steering would be perfectly fine albeit counter-intuitive with the requirement for thrusting at 90 degrees to what you would expect if you weren’t flying a huge gyroscope. This also shares some of the issues associated with controlling spin-stabilised light/mag-sails.