7
$\begingroup$

I want to create to create a ship that does NOT rely on rotational gravity to have a constant downward force on everything. The people built a g-force generator that does NOT induce gravity, just a force.

So, can a gravity generator that uses energy to accelerate objects towards the generator work?

If there is a 100 joules of energy that supplied to the generator, it could accelerate a 1 kg object down under 1 $m/s^2$ for 200 seconds. This situation does not regard efficiency or the mass of the generator itself for simplicity. The mathematics are based on energy, mass, and velocity ($E = 1/2 \cdot M \cdot V^2$).

Remember, this would be in the void of space. Would this be possible under real physics or would I have to implement a fifth force for this to happen? If it can happen, could it have an inverse square relationship with distance like real gravity?

It can work in any way possible if there is one, but the generator has to work regardless of acceleration of the generator itself. For example, the generator works whether it has a total acceleration of 0 $m/s^2$ or 100,000 $m/s^2$. It can work combined with other generators or actual gravitational pulls.

$\endgroup$
  • 1
    $\begingroup$ Not sure how to answer this. You don't explain how the generator is supposed to work. $\endgroup$ – elPolloLoco Mar 27 at 15:08
  • 1
    $\begingroup$ "If there is a 100 joules of energy that supplied to the generator, it could accelerate a 1 kg object down under 1 m/s^2 for 200 seconds. This situation does not regard efficiency or the mass of the generator itself for simplicity. The mathematics are based on energy, mass, and acceleration (E = .5*M*A^2). " I am pretty sure this is wrong: the energy is 0.5 * M *velocity^2 (not A^2). 1kg accelerated at 1m/s^2 for 200s has velocity 200m/s, so 20000 J. $\endgroup$ – maria_c Mar 27 at 15:28
  • $\begingroup$ Even assuming such a system could exist, it definitely couldn't work the same under 100000 km/s/s unless it could somehow also generate antigravity. $\endgroup$ – jdunlop Mar 27 at 15:28
  • $\begingroup$ Momentum. Remember that the conservation of momentum is independent of the conservation of energy -- and actually in mechanics energy is not a conserved quantity. (The conservation of energy comes from thermodynamics.) One kilogram accelerated at 1 m/s² for 200 s gets a momentum of 200 kg·m/s which must come from somewhere. As for the question as asked: as far as we know, gravitational mass and inertial mass are one and the same thing, and there is no other thing just like them. (And we know for certain that there is no fifth force which manifests at accessible energies.) $\endgroup$ – AlexP Mar 27 at 16:40
  • $\begingroup$ @AlexP That sentence in parentheses is the reason I asked. $\endgroup$ – Pyrania Mar 27 at 18:07
11
$\begingroup$

You could simulate gravity using electrostatic attraction.

I cannot run the numbers you provided, but electrostatic attraction can be strong in proportion to the charges involved. It is the same principle that causes cat hair to be stuck to a rubbed balloon. It would work even better in space because space is dry and charge could not leak off into the humid air. In an atmosphere, charge can equilibrate across a space full of gas by breaking the gas down into glowing conductive plasma - this is a spark. In space there will be no equilibrating unless the charged surfaces come into contact with each other, and you can prevent that by coating your spacefarers in nonconductive full body skin tight latex suits.

Using charge for attraction in space is not purely zany. NASA has a scheme for an "E-glider" - a spacecraft which makes use of these electrostatic forces around asteroids to maneuver. Unlike gravity which only pulls stuff together, charge is more versatile and can be greater or lesser, positive or negative. In the example the charged vehicle maneuvers relative to the asteroid using manipulation of charge.

https://www.nasa.gov/feature/e-glider-active-electrostatic-flight-for-airless-body-exploration

E-glider

There was no mention of the skintight latex suits in this NASA article, but I feel they were strongly implied. The spaceships will need latex suits too.

$\endgroup$
  • $\begingroup$ Yes! This is the kind of thing I was looking for! $\endgroup$ – Pyrania Mar 27 at 15:50
  • 1
    $\begingroup$ the OP wanted a "gravity-like" force. A key property of Gravity is that it cannot be shielded against. This method relying on electrostatic forces seems be possible to shield against, e.g. Faraday cages? $\endgroup$ – maria_c Mar 27 at 15:54
  • 2
    $\begingroup$ Another key property of gravity is that is only attractive, and never repulsive. Another key property of gravity is that is does not produce sparks... $\endgroup$ – AlexP Mar 27 at 16:45
  • $\begingroup$ The problem with electrostatics is that if you need to get anywhere near 1g of acceleration, you will need very high voltages. One mistake, and your passengers get vaporized by the discharge. $\endgroup$ – Ryan_L Mar 27 at 17:10
  • $\begingroup$ @maria_c Perhaps I should change gravity-like to force-like. Forces that work in reverse like electrostatics I want, but do not need. $\endgroup$ – Pyrania Mar 27 at 18:09
10
$\begingroup$

Those already exist, they are called rockets.

When astronauts take off from Earth they are iften faced with high G forces (up to 8g if I recall correctly). That is not coming from rotation, nor from the Earth.

In fact, if you wish to go anywhere far from here, a constant rocket acceleration might provide you with some comfort. A constant 1g from the engine will keep your bo es healthy and take you to other star systems relatively quickly.

$\endgroup$
  • 1
    $\begingroup$ But would start causing real problems with impacts very quickly, and problems with relativistic mass increases at about the half-year mark. $\endgroup$ – jdunlop Mar 27 at 15:26
  • 2
    $\begingroup$ If you can build a constant boost drive that will run a half year, the relativistic effects won't be insoluble. For one, any reaction mass you might be using will be similarly affected. Impacts, now, that takes some technology... $\endgroup$ – Zeiss Ikon Mar 27 at 15:43
  • 2
    $\begingroup$ Fueling and safely maintaining the 1g acceleration are definitely difficult; but compared to other non-rotational methods of artificial gravity, this seems like one of the most logical. If relativistic speeds were really such a concern; you could always just accelerate in the other direction with 1g, slowing you back down a bit while maintaining the force. You would just need some method to flip the craft (or just the interior space) in the opposite direction so that 1g still pointed the same way for the passengers. $\endgroup$ – JMac Mar 27 at 19:30
  • $\begingroup$ @jdunlop, relativistic mass increases is not a problem, because you totally don't care how much heavier the stars and galaxies around you become! Remember, you are always in your own reference frame and there you are not moving at all, less so at relativistic speeds. $\endgroup$ – Jan Hudec Mar 27 at 20:52
  • $\begingroup$ Relativistic mass increase is more of a solution than a problem, folks. The more kinectic energy you can pack on a slab, the smoother diplomacy getd with other powers. $\endgroup$ – Renan Mar 27 at 21:15
9
$\begingroup$

There's a reason why the centripetal gravity ring is so popular

Here's your spaceship:

terrible spaceship drawing

Note: I am not an artist.

You start by accelerating weights

enter image description here

If you accelerate a 1 $kg$ weight downwards at 1 $ms^{-2}$, you'll exert a force of 1 $N$ on it. Now, that 1 $N$ gets distributed across the mass of the entire spaceship. Let's say it weighs 50,000 $kg$. This means that the acceleration will be 0.00002 $ms^{-2}$, roughly 2 millionths of Earth's gravity. You won't even notice that.

In order to provide Earth gravity to a spaceship that big (which is a realistic size for what you're looking for), you'll need 500,000 $N$ – the equivalent of launching a 500,000 $kg$ mass down at 1 $ms^{-2}$ (which is rather impractical, since it weighs more than your ship) or launching a 100 $kg$ mass down at 5000 $m s^{-2}$.

Now you're accelerating your whole ship

You're now launching a huge mass at a huge speed downwards. As Renan mentioned in his answer, this is starting to look like a rocket engine. But the problem remains: now that you've sent that thing flying downwards, you're not getting it back. You've just lost 100 $kg$ and your gravity has ended as quickly as it began.

So you need to continuously launch huge masses at huge speeds. This is going to have the side effect of pushing you in the other direction, really fast. In fact, to get 10 $ms^{-2}$ of pseudo-gravitational acceleration, you need to accelerate at 10 $ms^{-2}$ upwards.

enter image description here

So unless you want your gravity generator to fling the ship around (...it's literally a rocket engine!), you'll have to flip the ship around and go the other way for a while. That way, you spend a few minutes accelerating one way, then have a short zero-g break while you rotate, and then spend a few minutes accelerating the other way. Don't try this while docking.

enter image description here

And now you're swinging back and forth

So you ideally want to avoid the zero-g period while you flip the ship. So you keep the gravity generator (aka rocket engine) on the bottom of the ship and leave it running while you turn. So you spin around in a spiral pattern, always accelerating upwards relative to the people.

You want to make the spiral as circular as possible, because a perfect circle wouldn't change the trajectory of the ship, whereas anything else would. So you add side thrusters and spin around in a controlled circle, spending equal time accelerating in every direction.

And now you're orbiting a point.

Your main issue now is that you're throwing out all this mass and not getting anywhere. Bear in mind that you have to carry all these weights with you everywhere you go just to have gravity.

So instead of constantly launching the weights, you keep one big weight, heavier than the ship (maybe it's a fuel tank or something), and tie the spaceship to it using a long cable. That way, the spaceship swings around the weight like a sling, creating the same circular effect, but you don't burn any fuel.

enter image description here

But your ship pulls on the weight in the middle, and swings it from side to side. So for balance, you put another equally heavy ship on an equally long cable on the other side. Now it's like a 2-bladed ceiling fan: the symmetry prevents it from wobbling.

enter image description here

Now, you probably see my point. If you don't want your generator to fling you chaotically around space, the best solution is a rotating centripetal gravity system. I know that's not what you asked for, but your gravity generator is literally a rocket engine. If you want gravity while the ship isn't burning its engines, you need one of these:

enter image description here

$\endgroup$
  • $\begingroup$ Rather than a 2nd ship, you can just note that the center of the ship and the weight is part way along the cable. And ... done. $\endgroup$ – Yakk Mar 27 at 19:27
  • $\begingroup$ @Yakk Yeah, but I haven't put the main forward engine at the center of mass: it's still on the ship. You want your point thrust source to not be wobbling around, and we can't mount it on the cable, so we'll put it on the big fuel tank in the middle and slap on a counterweight. $\endgroup$ – Adrian Hall Mar 27 at 19:55
  • 1
    $\begingroup$ Note: I am quite an accomplished artist. - Fixed that for you. Drawings are great. $\endgroup$ – JPhi1618 Mar 27 at 20:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.