Engineering Artificial Gravity

Yesterday I introduced R B Harkess and his new book to this blog and as you will have gathered I commented on some sections of its earlier manuscript. There was a scene where he really played around artificial gravity in a serious way, but instinct told me that it was somehow inconsistent. yes, I did say INSTINCT and yes there is such a thing as engineering instinct.

End result was I asked the Harkess person to let me think about the whole scene and how the artifical gravity could be made to work…

One good general rule of engineering is keep things simple. Amongst other things it makes the devices easy to build and easy to repair. It has other advantages for science fiction writers… it makes things easy to explain and as Harkess says, helps with the flow of writing.

The main problem with gravity is that it radiates outwards in all directions. This can lead to an overspill in that force where the author does not want it. So we need a material that can block gravity going in certain directions. We also of course need a gravity generation mechanism. And this is really all that is needed in terms of invention… the rest can be engineered… seriously.

I’m going to take the rest of this by simple steps so as to make it easy to understand and apologise immediately for what might appear to be baby-speak.

If you have a gravity generating substance, lets call it gragen (for want of inventing a name) sitting at the bottom of a long test tube made of the gravity blocking material (lets call this substance gravbloc), where would you experience gravity outside the test tube from the gragen? The answer is only when you have line of sight to the gragen i.e. directly over the test tube mouth and a smidgen off the main line of the test tube. The gravbloc has to be a gravity absorber (as opposed to gravity reflector) as otherwise you will get gravity reflected at various angles off the gravbloc near the top of the test tube, which in turn will cause spillage in many directions.

Now what happens when you put a set of test tubes next to each other with their open ends all pointing in the same direction? You get an area above the test tubes that experience gravity and a quickly diminishing field at the edges.

Let’s now miniaturise the test tubes into a layer of carpet say… You have the gravity immediately above you and not to the sides, except for a small overspill. Even that overspill can be reduced by adding small ‘winglets’ of gravbloc rising up out of the sides of the path.

The difficulties with this is that gravity goes on into distance above the carpet. However, if this carpet is inside a building all that is needed is to have this gravity absorbing material in the ceiling facing the carpet. If it is in open air, then by the time the gravity reaches other structures, it will be very much weaker and therefore barely noticeable. Remember gravity is proportional to one over the distance squared.

As for where the energy of absorbing gravity goes to – well given that the crack is open to the atmosphere, you might like the underfloor heating from the path!

Simples as the meerkats would say… (for those not familiar we have a series of adverts in the UK using cute meerkat puppets).


9 thoughts on “Engineering Artificial Gravity

  1. Most sci fi has used rotating parts on space ships to create gravity. Not being a physicist, I don’t know how plausible it is.

    1. Hello,
      True they use rotating parts to give the feel of gravity, only it’s centrifugal (though some people mistakenly call it centripetal) force. This is not the gravitational force that is normally associated with mass. I hope this helps.

  2. Hello!
    I was sent here via Twitter, (RBHarkness), because I’m trying to world-build a space station that could support several million people, and right now Gravity is the factor I’m pondering.

    Just for curiosity’s sake, I was interested in your description of gravity as though it gives off Gravity-Rays, like light? (Line-of-sight and all.) I had always thought it emanated, like heat. And yes, while I am technically interested, I am not a science major.

    So, anyways, space station. I had originally thought to have a gravity generator, and then I realized that I have no idea how Gravity works and that would be weird, and then I thought I’d have the spine of the station massively reinforced, and then I thought about the mass required to get gravity, and then again I realized that I don’t know how gravity works, so I should stop and go with centrifugal force. I take it that is plausible?

    1. Hello Jazz,
      That Harkess person gets everywhere… in the nicest possible sense I hasten to add.

      I’ll try and answer your queries in simple terms and apologise if you already know some of this…

      What I did in my blog was to have a material that neutralised gravity make up the carpet and designed the carpet so that gravity could only act in the direction where there was no material i.e. using miniature long test tubes stacked side by side. This also assumes that at the bottom of these test tubes there is sufficient mass or gravitational generative material to exert the force. The basic concepts of a gravity blocking and gravity generating materials are pure science fiction at the moment.

      Now the laws of physics strictly speaking tell us how things will react in given circumstances. They do not tell us what it is or why they work. I don’t think anyone truly understands what the forces of nature (gravity, electromagnetism, weak nuclear force, strong nuclear force) are. So you are not alone in not understanding, just one of the few who actually realise they don’t.

      Let’s stick Newtonian ordinary physics. Gravity is associated with mass. If you have point mass in space, the effect of gravity will be felt radially outwards. The gravitational strength is proportional to one over the distance squared. So its strength drops off the further away you are. Gravity is also proportional to the mass of the object exerting the gravitational force. In other words the more mass the more gravity.

      If you go for having ordinary mass to produce gravity, you either end up with something quite big or something radioactive (as currently all known heavy particles are radioactive).

      However, work is going on the extend the periodic table list of elements and there is a belief that further up the table a region of stable (non-radioactive) elements exist. If those could be manufactured, then you would have your dense mass. So having a core for your satellite using this material is a possibility. I would however, suggest you manufacture this material in space as it would require an awful of energy to pull this material from a planet such as Earth.

      So a spine with this material could work, providing your spine isn’t too long. Otherwise the pull in gravity would vary over space station.

      The centrifugal force concepts are dealt with very well by three authors: Arthur C Clarke – Rendezvous with Rama; Hal Clements – A Matter of Gravity; and Larry Niven – Ringworld, though you will also need to read the sequel Ringworld Engineers, which effectively corrected a subtle technical flaw in Ringworld.

      I hope this helps… if you have any further queries, please get back to me.

      1. That’s fascinating, thank you! I did not know about the postulated stable heavy materials, I’ll store that away. I think for this story I’ll go with centrifugal force, to avoid gravity well issues with shipping. I mean, what’s the point of having a space station that’s just as difficult to dock with/get away from as a planet?

        I do have one more question. Do you know off-hand what the necessary rate of rotation on a centrifugal station is to simulate one g?

  3. Hello Jazz,

    I’m afraid I’m going to have to resort to equations to answer your question and all I can do is hope you’ll be able to follow me.

    As you may have guessed the answer is not all that simple. But basically you are asking what is the rate of rotation required in order to make acceleration due to the centrifugal force the same as that due to gravity on Earth – which is 9.806 metres per second squared.

    Well first off, it depends on what distance you are from the centre of rotation. Let this distance by denoted by r. Let the rate of rotation be denoted by w. This should be in units of radians per second. The equation you require is

    9.806 = r . w . w

    where the dot denotes multiplication.

    Note r has to be in metres.

    Good luck with your story.

  4. If you had asked this question a year ago, I would have said no, I can’t be certain.
    Now I’m certain that it is only a matter of time and putting in the effort to make the gragen and gravbloc work, and the rest is as I noted in my post.
    What’s changed you may ask?
    Let’s just say as a result of exploring follow-on ideas for my novel, I gained some insights into technology and how it could be made to work. And yes, I’m in the process of writing a novel a spinoff of one of those technologies… yes I did say one and that’s more than a novel’s worth, believe me!

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