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

[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?

[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.

[Johnny1A.2]

Originally Posted by Fred Brackin

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.

That's not how you'd do it. With the Bergenholm, what you'd do is take a brick or a rock or a ball of cotton, put on a ship, and let that ship accelerate inert until it's pressing against c, relative to Prime Base. That wouldn't be hard for ships like those of the later Lensman books. It doesn't matter if it takes a week to do it.

Then, when you've got a velocity of .99c or .999c relative to Prime Base, then you turn on the Bergenholm. Now you transport the thing to Prime Base, making very sure to keep it constantly inertialess. You take it to Earth and sneak it near whatever your target is.

Then you turn off the Bergenholm, either with a timer, a remote, or a suicide bomber, and watch the film of the multi-megaton fireball on the evening news.

Note that this technique can be used on any scale. Any given 'free' cargo could actually have a megadisaster intrinsic velocity, there's nothing to indicate this until you turn off the Bergenholm. You could weaponize any shipment of anything that way.

Granted active Bergenholms are themselves detectable by sensors, but all that tells you is that there's an active Bergenholm. That's not even unusual on most Civilized worlds, especially near military facilities and space ports. Spacecraft usually inert in space, but they use Bergenholm-equipped space armor, etc, all the time on the ground. Nor is it improbable that an active Bergenholm could be shielded from sensors anyway.

[dataweaver]

Hmm… gravitational acceleration can be defined as the gradient of the potential energy field. With or without pseudovelocity, a ship will have to navigate the potential energy field; and that can result in the ship's real velocity changing in response to the gravity fields. For instance, a ship that engages its PV drive to go 180˚ around the sun will find when the PV drive is deactivated that its real velocity will have rotated 180˚ as well. Likewise, dropping down the gravity well will result in potential energy converting into real kinetic energy, and your overall speed will have increased as if you had fallen down the well rather than pseudo-flying down it.

How would that affect things?

[Ulzgoroth]

Originally Posted by Johnny1A.2

That's not how you'd do it. With the Bergenholm, what you'd do is take a brick or a rock or a ball of cotton, put on a ship, and let that ship accelerate inert until it's pressing against c, relative to Prime Base. That wouldn't be hard for ships like those of the later Lensman books. It doesn't matter if it takes a week to do it.

Then, when you've got a velocity of .99c or .999c relative to Prime Base, then you turn on the Bergenholm. Now you transport the thing to Prime Base, making very sure to keep it constantly inertialess. You take it to Earth and sneak it near whatever your target is.

Then you turn off the Bergenholm, either with a timer, a remote, or a suicide bomber, and watch the film of the multi-megaton fireball on the evening news.

Not sure that the use of the inertialess capability is contributing much to the relativistic bombardment problem. The ability to drive a payload to near-c speeds without using the Bergenholm is the foundation of what you're doing...

[Fred Brackin]

Originally Posted by Johnny1A.2

That's not how you'd do it. With the Bergenholm, what you'd do is take a brick or a rock or a ball of cotton, put on a ship, and let that ship accelerate inert until it's pressing against c, relative to Prime Base. That wouldn't be hard for ships like those of the later Lensman books. It doesn't matter if it takes a week to do it.

.

A month if you use the 11Gs Velantians build for when inert. You'd need 40-50Gs for a week.

Even regular Patrol ships may have more thrust than they can stand to use while inert. It could well be that the 5Gs most Patrol ships can pull while inert is because of organic limits and not propulsion,. There's no benchmark I can think of that would tell you how fast a drone ship could accelerate.

I'm not even sure you can run a bergenholm inside another bergenholm and your carrying ship and that ship would have to match intrinsics with Earth before it would be allowed to land.

There's probably a customs inspection by spy-ray or sense of perception is not physical boarding just to make sure the hold isn't full of duodec which would make your multi-megaton fireball without bergenhom tricks.

You'd have to be satisfied with blowing up the Port of New York anyway. Nobody but the Patrol lands at Prime Base, No more than commercial jetliners land at Andrews AFB.