[Spaceships] Reactionless Drives, Pseudovelocity, and NOT breaking a setting (much)

[vicky_molokh]

Greetings, all!

It's not my first attempt, and not my first request for aid either. I think I learned some things from the previous attempts and previous advice, and perhaps I'll have better luck this time.

So, I want to a coherent stat-up of how reactionless drives (and, by necessity, pseudovelocity) work in a setting. I know they're TL^, and that means that the best I can hope for is to minimize the damage to the setting in the process. So far, setting-breaking consequences that I would like to avoid the most:

• Hypervelocity kinetic-kill applications. This pretty much necessitates invoking Pseudovelocity.
• Perpetual Motion Machines. This seems to mean, at a minimum, that changes in potential energy due to lifting off from a planet must come from actual, real energy of capacitors aboard the ship that power the reactionless engine and that whatever displacement-velocity that can be achieved in excess of the amount of energy pumped through KE=½×mv² has to be pseudovelocity.

Relativity is an acceptable casualty, and in fact an etheric/hyperdynamic cosmos with some sort of frame-dragging by highly-massive celestial bodies is a suitable outcome. I'm not quite sure how much trouble the setting gets into due to breaks in conservation of momentum (angular and/or linear), but I realise that this is hard to avoid if invoking PV.

The intended effectiveness range of the drives is roughly 1G of 'pseudo+real' acceleration at 1 Power Point of 'normal' work, though I'm guessing that there might be a need to make a drive consume more power while pulling out of a gravity well (as per the potential energy delta relative to the well . . . I think that should be affordable, but I'm not sure yet).

What other things need to be done and adjusted in order to make it a reasonably playable technology that doesn't break settings?

Thanks in advance!

[RogerBW]

My mental model of pseudo-velocity drive is something like 2300AD's stutterwarp, or the drive used in Poul Anderson's Polesotechnic League stories.

In that case, the energy cost of moving from point A to point B needs to vary with gravitational potential difference. If you move your 100-ton ship "up" by 100 metres from Earth's surface, that costs you the same 100MJ or so that you would have needed to feed into an electric motor (though the inefficiency level will be different).

So the standard perpetual motion setup, where you jump something upwards and let it fall down, is circumvented.

In game terms what this will mean is that outward acceleration drops off sharply when you're in any sort of gravity well. It may even be that ships can't use this drive near planets at all, and need rockets or something else for surface-to-orbit.

Is this a useful starting point?

[johndallman]

Originally Posted by vicky_molokh

What other things need to be done and adjusted in order to make it a reasonably playable technology that doesn't break settings?

Pesudovelocity drives usually seem to work by means of rapid short-distance teleports. You need to consider what the movement speed is during the teleport, the maximum rate of the teleports and their maximum distance. These considered together will give you a limiting speed for the drive.

[vicky_molokh]

Originally Posted by RogerBW

My mental model of pseudo-velocity drive is something like 2300AD's stutterwarp, or the drive used in Poul Anderson's Polesotechnic League stories.

In that case, the energy cost of moving from point A to point B needs to vary with gravitational potential difference. If you move your 100-ton ship "up" by 100 metres from Earth's surface, that costs you the same 100MJ or so that you would have needed to feed into an electric motor (though the inefficiency level will be different).

So the standard perpetual motion setup, where you jump something upwards and let it fall down, is circumvented.

In game terms what this will mean is that outward acceleration drops off sharply when you're in any sort of gravity well. It may even be that ships can't use this drive near planets at all, and need rockets or something else for surface-to-orbit.

Is this a useful starting point?

Well, that is in fact one of the starting points in the OP, that is, "at a minimum, that changes in potential energy due to lifting off from a planet must come from actual, real energy of capacitors aboard the ship". It's a thought in the right direction, but I'm not yet sure what are the less-obvious implication for the world based on such a postulate, aside from avoiding gravitic perpetual motion.

Originally Posted by johndallman

Pesudovelocity drives usually seem to work by means of rapid short-distance teleports. You need to consider what the movement speed is during the teleport, the maximum rate of the teleports and their maximum distance. These considered together will give you a limiting speed for the drive.

Well, a multi-teleport still means a mass moves with an observed velocity without absorbing a corresponding amount of kinetic energy. I'd like to see what sort of collateral damage results from that, and how it can be minimised. Notably, what consequences do we get from bending or breaking momentum-conservation, perhaps.

[Ulzgoroth]

Originally Posted by vicky_molokh

Notably, what consequences do we get from bending or breaking momentum-conservation, perhaps.

One of the basic points of pseudovelocity is that you don't need to break momentum conservation, because pseudovelocity moves you without actually involving momentum.

EDIT: Which actually gives me the thought that 'inertialess' technology along the lines of the Lensman books might give you results usefully similar to pseudovelocity without actually using reactionless drives.

[Fred Brackin]

Originally Posted by Ulzgoroth

One of the basic points of pseudovelocity is that you don't need to break momentum conservation, because pseudovelocity moves you without actually involving momentum.

EDIT: Which actually gives me the thought that 'inertialess' technology along the lines of the Lensman books might give you results usefully similar to pseudovelocity without actually using reactionless drives.

Yep, though you can update the technobabble. I'd try something like "a thin bubble of hyperspatial medium surrounds the ship and de-couples it from the universe's inertia-gravitic frame of reference.".

I'd also have objects in drive bubbles stop when encountering normal masses but rather slide past them frictionlessly.

While you are de-coupled you interact with the hyper-dimension and use that for propulsion and maneuvering while becoming limited to a maximum speed based on hyper-drag. Probably whatever maximum speed gives you the travel times you want.

I think the last time I did this I settled on 2 million miles an hour. This made it 1 day to Mars on close approach and 2 days to near the sun. I had jump points (or rather entry points for jump lines) be near solar masses rather than way out past Pluto

Sending ships way the heck out into the outer solar system has all sorts of implications for defending solar systems and long range stealth kinetic strikes even using hard science drives.

The thing about the de=-coupler drive is that when you de-couple your potential energy is "lost" (or it would be if potential energy was real which it isn't in the present tense). When you re-couple you get a new set of potential energy "normal" to the nearest frame-dragging body. All energy "lost" or "gained" comes from or goes to that universal inertial-gravitic reference frame.

There is no "intrinsic" velocity either. That goes away and you get anew one when the drive shuts down. This cuts way down on bookkeeping.

As to Perpetual motion machines" the universe is full of things that have potential energy compared to planets and there is little to no good way to harness that.

All you need to prevent the creation of perpetual motion machines is to make them inferior in cost per unit of output to other possible power sources. Most of the proposed designs for potential energy harvesters I have seen would be terribly expensive and give poor yield per unit of mass or volume.

You could say hydroelectric dams are efficient but that's because you don't pay anything for the energy that goes into raising the water vapor to a higher location. It wouldn't really matter economically if you could violate conservation of energy while raising your mass to be harvested if it still cost money.

So even if a thing is technically sort of possible it wont affect your setting if there's no sane reason to do it.

As to those micro-jump drives they are reactionless and do accumulate kinetic energy but I wouldn't call them pseudovelocity or especially not hyperdynamic in the way Star Wars is.

[Johnny1A.2]

Originally Posted by Ulzgoroth

One of the basic points of pseudovelocity is that you don't need to break momentum conservation, because pseudovelocity moves you without actually involving momentum.

EDIT: Which actually gives me the thought that 'inertialess' technology along the lines of the Lensman books might give you results usefully similar to pseudovelocity without actually using reactionless drives.

Not really.

The Bergenholm is a setting breaker, if applied in ways Smith carefully doesn't talk about, but which players might well tend to do. For ex, you can use the Bergenholm to turn an ordinary construction brick into a WMD, and a very powerful one at that. Yet Boskone never tries to blow up Prime Base with a construction brick.

The best way to get around the velocity problem, IMHO, is to assume that the trip happens outside normal spacetime entirely.

[Fred Brackin]

Originally Posted by Johnny1A.2

Not really.

The Bergenholm is a setting breaker, if applied in ways Smith carefully doesn't talk about, but which players might well tend to do. For ex, you can use the Bergenholm to turn an ordinary construction brick into a WMD, and a very powerful one at that. Yet Boskone never tries to blow up Prime Base with a construction brick.

Nah, not a construction brick that's much too small. Even if you run it up to near C inert on a precisely chosen intrinsic and then render it free all you've got is something that will blow up as soon as it hits atmosphere.

After several shenanigans involving undetectable speedsters everyone is running a massive overlap on their electros and either free you'll see the mini-bergenholm on the brick detected or the naked brick at near c will be detected by the ionization as it flies through interplanetary medium of normal density.

This is not to say that something rather more elaborate than that wouldn't make a planetary fortress-cracker and I did do away with intrinsic velocity wit my de-coupler drive.

[Ulzgoroth]

Originally Posted by Johnny1A.2

Not really.

The Bergenholm is a setting breaker, if applied in ways Smith carefully doesn't talk about, but which players might well tend to do. For ex, you can use the Bergenholm to turn an ordinary construction brick into a WMD, and a very powerful one at that. Yet Boskone never tries to blow up Prime Base with a construction brick.

It's probably been more than a decade since I read any Smith, so I can't speak to the precise properties of the Bergenholm.

But you probably don't want to simply replicate those anyway, because they're more than a bit ridiculous. A generator that lets you downshift your ship's inertial mass, though, doesn't need to partake of the sillier aspects.

[vicky_molokh]

Originally Posted by Ulzgoroth

One of the basic points of pseudovelocity is that you don't need to break momentum conservation, because pseudovelocity moves you without actually involving momentum.

EDIT: Which actually gives me the thought that 'inertialess' technology along the lines of the Lensman books might give you results usefully similar to pseudovelocity without actually using reactionless drives.

On the contrary, it seems to break conservation of momentums because it 'just moves'. Like this:

Originally Posted by lwcamp

Angular momentum is also a vector (classically, anyway - relativity adds some additional components that are hard to visualize, but I'll just stick with the classical 3-vector version). Angular momentum is defined as the magnitude of the momentum times the perpendicular distance from the observer to the object (in a direction mutually perpendicular to the momentum vector and the direction from the observer to the object). If something isn't moving, it has no angular momentum (assuming no internal motions - a rotating object has angular momentum but not everything with angular momentum needs to be rotating). If something is moving but is headed straight toward you or straight away from you, it also has no angular momentum. The further its distance of closest approach becomes (assuming a straight line trajectory) and the faster it is moving and the more massive it is, the greater its angular momentum. So, consider an observer moving toward the spacecraft, and then have the spacecraft warp away in a direction perpendicular to the direction to the observer. From the observer's point of view the spacecraft starts off with non-zero momentum (it is moving in his reference frame) but zero angular momentum (it is going straight toward him). After the warp we know that it must be going the same speed and direction from conservation of momentum, but now it is not headed straight toward the observer. Consequently it has non-zero angular momentum. Since you can always find a frame of reference that does this, free-form warping violates the conservation of angular momentum and is thus disallowed in general relativity.

How do we get around this? I can think of three ways. First, the spacecraft can dump all of its energy when it turns on its warp drive. Without energy it has no mass and thus neither momentum or angular momentum. It leaves the energy behind in some form - matter or radiation (if it is in the form of radiation, you get the release of 20,000 megatons of energy per ton of spacecraft mass). Then, when it gets to its destination it absorbs as much energy as needed to precipitate the spacecraft out of warp (that is, a 100 ton spacecraft would need to have its warp bubble gobble up 100 tons of mass at its destination in order to release the spacecraft). The spacecraft will end up with the velocity of the mass the warp field gobbled up. Until the spacecraft precipitates out of warp it cannot exchange energy with the rest of the universe (doing so would add or subtract mass to the warp bubble, which would then violate angular momentum conservation). This probably means the spacecraft is flying blind and will have a difficult time finding the mass it needs to exit warp.

Second, you can have a prepared pathway of highly curved spacetime, and all warp travel is along this path. Since the spacetime geometry of the pathway is highly curved, we are outside of the Newtonian limit and angular momentum (and energy and so on) is not localized along the path. This lets you go from one point on the path to another, but you can't warp to places off the path.

Third is that the warp drive emits some sort of radiation which never decays away to the weak field limit. This last possibility is not very good for adventure fiction since strong field gravitational radiation smashing through the universe out to arbitrary distances is rather hard on the setting.

And now I wonder just how bad the second solution is. As in, can the drive itself be the creator of such highly-curved spacetime?