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-   -   [Spaceships] Your preferences regarding plausible/playable Reactionless Drives (https://forums.sjgames.com/showthread.php?t=73624)

jason taylor 10-07-2010 12:44 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Actually the idea of using tractor/pressors to move in system sounded cool. It provides an interesting element of weirdness in the movement system that reflects on tactics.

vicky_molokh 10-07-2010 01:09 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by jason taylor (Post 1059836)
What I'd like to know, is whether reactionless drives really get enough plot mileage to justify the bending of normal physics from the authorial stand point. How much do they do that another kind of reaction drive does not? If the idea is to economize space or fuel or reduce heat then ano ther kind of reaction drive can be arranged that does the same thing. FTL is an absolute necessity(space opera never seems to work without FTL, so we just have to live with it). Grav control is very much of a convenience(there are only a few times we really want to think about the yucky consequences of being without gravity for weeks at a time, and anyway it's an extra headache for the props department in a stage rather then literary forum). But why reactionless drive?
Reactionless drives exist to remove the glutonnous fuel requirements of a spaceship. However, for that purpose, it appears that it is sufficient to use an 'omni-tractor' drive. I.e. a contactless reaction drive similar to an EM Tether, but one which pushes against an immense sphere, perhaps as huge as a galaxy. Although it probably involves the assumption that gravitons (or whatever is it that transfers the impulse/kinetic energy/etc.) moves FTL, which seems to be not proven as of now.

jason taylor 10-07-2010 01:18 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by vicky_molokh (Post 1059851)
Reactionless drives exist to remove the glutonnous fuel requirements of a spaceship. However, for that purpose, it appears that it is sufficient to use an 'omni-tractor' drive. I.e. a contactless reaction drive similar to an EM Tether, but one which pushes against an immense sphere, perhaps as huge as a galaxy. Although it probably involves the assumption that gravitons (or whatever is it that transfers the impulse/kinetic energy/etc.) moves FTL, which seems to be not proven as of now.
Exactly. My point is the same purpose can be served by calling it "minimal reaction" or "super efficient" reaction rather then reaction-LESS, and assuming that this is enough to fulfill the fuel efficiency problems.

The analogy being the tremendous amount of energy stored in atoms, that was only recently available, for better or worse.

malloyd 10-07-2010 01:28 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by jason taylor (Post 1059836)
But why reactionless drive?
Well, you need a drive capable of relatively high accelerations for a long time before running out of fuel in order to cut interplanetary travel times down to reasonable levels - i.e. less than months. It is really convenient if you can continuously accelerate for the entire trip without running out of fuel, since that simplifies the math tremendously. Of course you can do that with amazing fuel efficiencies too, that's the concept of conversion drives, or Megatraveller HEPLAR thrusters.

It's also often convenient for the drive exhaust not to be hideously destructive, which is incompatable with the first peformance goal for a realistic reaction exhaust, though of course you can ignore that too.

For games, well, reactionless drives are a handy way to convert settings where fuel consumption and drive exhaust were ignored or unrealistically downplayed (that is, most fiction) to a system that would otherwise insist on tracking them, without making it impossible for the players to recreate something in the story.

David Johnston2 10-07-2010 01:38 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by jason taylor (Post 1059836)
What I'd like to know, is whether reactionless drives really get enough plot mileage to justify the bending of normal physics from the authorial stand point. How much do they do that another kind of reaction drive does not? If the idea is to economize space or fuel or reduce heat then ano ther kind of reaction drive can be arranged that does the same thing.
If you are going to be violating conservation laws anyway, why pretend otherwise?

Anthony 10-07-2010 02:36 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by vicky_molokh (Post 1059851)
Although it probably involves the assumption that gravitons (or whatever is it that transfers the impulse/kinetic energy/etc.) moves FTL, which seems to be not proven as of now.
In fact, we're pretty sure it's not true.

Anthony 10-07-2010 02:44 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by malloyd (Post 1059863)
It is really convenient if you can continuously accelerate for the entire trip without running out of fuel, since that simplifies the math tremendously.
Actually, what's really convenient is a boost drive that just gets up to a fixed velocity quite quickly and then lets you stay at that velocity. Accelerated movement is more complicated than 'measure the distance and multiply by X to determine how long the trip takes'. For in-system travel, a speed of around 250 km/sec (1 AU/week) is convenient and means impact energy is equivalent to 7,500x the object's mass in high explosive.

vicky_molokh 10-07-2010 03:35 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by Anthony (Post 1059919)
In fact, we're pretty sure it's not true.
Gravitons? Who knows. Supposedly time slows to a halt in a singularity, yet singularities emit gravitons, which somehow manage to 'get somewhere' in time. So they seem to be able to jump over the fences that slow down or stop even the mighty photon.

Hmmm. I wonder if some sort of tachion-like matter be used as a way of conserving momentum/mass-energy in a pseudo-reactionless (but not pseudospeed) drive.

sir_pudding 10-07-2010 03:48 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by vicky_molokh (Post 1059964)
Gravitons? Who knows. Supposedly time slows to a halt in a singularity, yet singularities emit gravitons, which somehow manage to 'get somewhere' in time. So they seem to be able to jump over the fences that slow down or stop even the mighty photon.
.
This a problem with any model of gravity that requires particles. I think it's becoming increasingly clear that "gravitons" probably don't exist.

Anthony 10-07-2010 04:40 PM
Re: [Spaceships] Your preferences regarding plausible/playable Reactionless Drives
 
Quote:
Originally Posted by vicky_molokh (Post 1059964)
Gravitons? Who knows. Supposedly time slows to a halt in a singularity, yet singularities emit gravitons, which somehow manage to 'get somewhere' in time. So they seem to be able to jump over the fences that slow down or stop even the mighty photon.
Black holes can also have electromagnetic charge and thus engage in electromagnetic interactions, which we know are moderated by photons.


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