FallingPhoenix
Mongoose
The topic title pretty much says it. I'm curious as to the reasoning behind this...
Why are reaction drives bigger than maneuver drives?
- Thread starter FallingPhoenix
- Start date
Because they are basically giant rocket boosters that are attached to the craft, or taking up space in the ship. they need the space to generate and focus the reaction in order to drive the ship and have the mechanisms so that it can move the ship in the directions you want it to go
ShawnDriscoll
Cosmic Mongoose
Old tech will be bigger than new tech, no matter what higher tech level builds it.
ShawnDriscoll said:
Yeah, not so much. You can use "new" tech to build and "old" tech device, making it smaller and more efficient (and cheaper in some instances, though not always).
But to more directly answer your question, reaction drives would have additional machinery requirements. If you look at how rockets work, there is a great deal of turbo-pumps, piping and other things you don't actually see because they are buried in the rocket. While we don't have the technology behind how maneuver drives work, there is the underlying idea that it's a direct conversion of energy into thrust. This mean you need to provide only wiring to get power to your thruster systems - no piping, no pumps, much less infrastructure required. Which would provide for a smaller Dton footprint.
Reynard
Emperor Mongoose
Remember also that reaction engines are brute force power and require a lot of reinforcement and control while reactionless gravitic maneuver drive push and pull forces not trying to tear a ship apart plus it's a different motive physics lending to much greater efficiency of space. Somewhat akin to a car with an Internal combustion engine, transmission and drive train versus an all electric car with motors as part of each wheel with the majority of space taken by batteries.
Reynard said:
That shouldn't make a difference. The amount of energy put out by a 1G reaction drive is the same as that put out by a 1G gravitic drive - insofar as the ship itself is concerned. The efficiency comes from how much energy is required to generate it, but the net output remains the same across any drive type.
Reynard
Emperor Mongoose
Oh it does make a difference between a device producing an efficient motive force without external energy production and riding a tube blasting a god awful column of hellfire that wants to get lose but for one mistake in structure and control. Reaction drives are not subtle. They're big and bulky for a reason. Traveller favors the maneuver drive but doesn't ignore the rocket. Neither does it make a rocket pretty.
I like the idea you can find quaint places just achieving space travel, maybe even star travel because of quirks in development, using old time low grade sources of propulsion such as reaching a backwater country in your jet then traveling about using the locals' biplane or zeppelin.
I like the idea you can find quaint places just achieving space travel, maybe even star travel because of quirks in development, using old time low grade sources of propulsion such as reaching a backwater country in your jet then traveling about using the locals' biplane or zeppelin.
I do concede that an electrically-powered drive should have a smoother ramp-up to full speed, but with just a little bit of engineering and precision, once your ship begins to accelerate it's going to be the same. At lower specific energy levels, a hydrazine thruster is quite gentle. Nobody has every scaled up say a F-1 Saturn V engine pumping out 1million lbs of thrust for long term in the vacuum of space. I wish somebody would though....
It would be like comparing a liquid-fueled rocket to an airliner. The feel of the rocket is different to start, but once the are both in the air and running at steady power the amount of force they exert is the same. The engineering part comes in via building stabilizers into the hull to offset the vibrations. And that could account for some extra mass, but it shouldn't be a terribly large amount. Not to mention that with higher tech and materials you could build more effecient rocket thrusters that would help eliminate some of the extra.
'Tis an interesting question though.
It would be like comparing a liquid-fueled rocket to an airliner. The feel of the rocket is different to start, but once the are both in the air and running at steady power the amount of force they exert is the same. The engineering part comes in via building stabilizers into the hull to offset the vibrations. And that could account for some extra mass, but it shouldn't be a terribly large amount. Not to mention that with higher tech and materials you could build more effecient rocket thrusters that would help eliminate some of the extra.
'Tis an interesting question though.
In terms of a Reaction Drive it's actually less about it being bigger than a Manoeuver Drive and more about it taking up more space. Stick with me for a second it will make sense.
A reaction drive may not actually be bigger, but the space for it's rocket boosters will take up a whole lot more space on the external displacement.
A reaction drive may not actually be bigger, but the space for it's rocket boosters will take up a whole lot more space on the external displacement.
In terms of a Reaction Drive it's actually less about it being bigger than a Manoeuver Drive and more about it taking up more space. Stick with me for a second it will make sense.
A reaction drive may not actually be bigger, but the space for it's rocket boosters will take up a whole lot more space on the external displacement.
A reaction drive may not actually be bigger, but the space for it's rocket boosters will take up a whole lot more space on the external displacement.
on factor in using a reaction drive..HEAT... turning fuel into thrust means exciting it to higher energy levels..usually by heating it up...with a handy fusion reactor you can use a simple expedient of channeling hydrogen, or even water, through the core and turning it into plasma. That takes a bit of plumbing, and insulation, to prevent the drives from turning the interior of the ship into an oven., or melting components to slag.
a lot of the complexity of a rocket is cooling it, and containing a barely controlled explosion of super-hot gasses for more than a nano second. that means heavier materials, and a plumbers nightmare of piping and conduits.
a lot of the complexity of a rocket is cooling it, and containing a barely controlled explosion of super-hot gasses for more than a nano second. that means heavier materials, and a plumbers nightmare of piping and conduits.
wbnc said:
The reaction is taking place in a vacuum of space. Yes, there will be heat, but the heat would be contained within the nozzles and projected out. We also have no idea what form of fusion is being used in the power plants. Are they heating up plasma, containing it within a field and then converting the heat into electricity? Or is it a cold-fusion style reaction that produces very little heat? Thing is we don't know. But we already do know that there's a lot of hand wavium going on in the tech tree. Who's to say they can't easily manufacture materials that would 100% reflect the heat within the rocket nozzles, or have some sort of magical insulating material only millimeters thick that doesn't absorb any heat?
Most of the complexity of rockets today is not in cooling - it's in the machinery that pressurizes, pumps and ignites the fuel. You really don't want any issues or leaks when messing with liquid oxygen and your fuel of choice. An F-1 Saturn V engine is pretty big - about 18ft tall. But nearly all of that (about 12 feet) is the engine nozzle, not the engine portion itself.
phavoc said:
I.m not discounting the problem of containing and directing fuel flow as a source of extra volume....just suggesting another factor.
Ask any one who builds model rockets about a burn through. Or Goddard, or Von Braun...Heat is a major issue in any sort of rocket. because in order for a rocket to work, fuel has to be excited and expanded...the more excited,the hotter it gets.
the fuel delivery system is the cooling system of liquid fueled rockets. I am not sure how they handle cooling in solid fuel rockets...but in liquid fueled rockets they cool the body of the engine the cryogenic hydrogen is pumped though channels in the body, and around the exhaust nozzles...otherwise it melts down in short order. The system hasn't changed much since the V-2 rocket....
http://www.braeunig.us/space/propuls.htm
If you are using a charged gasses, you can use an electrical field to channel the gasses away from the exhaust cone. But if you are using simple physical constraints then the gasses directly contact the material of the cone. that results in rapid heating. The metal of the exhaust cone would reach temperatures where most metal lose strength in seconds when exposed to rocket exhaust...except for the fact that cryogenic gas is being channeled through or around it.
another problem....
vacuum doesn't aid in cooling, it inhibits it...there is no medium to absorb the heat from an object and carry it away. Even heavy insulation would build up heat faster than it could be radiated away....that's why vacuum bottles are used for cryogenic gas storage.
https://en.wikipedia.org/wiki/Cryogenic_storage_dewar
Since we are only able to predict a technology based on what is already known....it would seem that the same problems would occur with any significantly advanced engine...physics, and natural laws, having a really poor attitude towards letting you ignore them.
you could layer super ceramics, and aero-gels around a rocket to trap the heat for long periods, but that takes up space, and makes the tonnage of a reaction engine larger...which is one reason I say that along with the fuel systems, gimble mounts, and other hardware an electrically driven directed system doesn't need...cooling has to be considered as part of the issue.
Any super heat resistant alloy would turn up in armor as well if it existed... making lasers and plasma weapons about as useful as a spud-gun against a battleship. So since lasers and plasma weapons are in use, it's not likely anyone has cracked the thermal insulation problem.
FallingPhoenix
Mongoose
Given that the regular maneuver drives are completely fictional, it seems to me it's completely up to what sort of feel you're going for as to what size they are.
My thought is that if someone wants a setting using jump drives and reaction drives, you really need the reaction drives to be smaller and/or pretty fuel efficient to make viable craft that also use jump drives.
Then again, maybe the current sizes mean you could do the "jump ship" and "drop ship" thing a la Battletech...maybe I'll have to try that...
If we're going to start talking about heat, though, then we have to start talking about massive radiators for any ship with a fusion drive, laser weapons, etc.
Ooh! Maybe Traveller ships can give low power to their jump drives and radiate all the heat into jump space!
My thought is that if someone wants a setting using jump drives and reaction drives, you really need the reaction drives to be smaller and/or pretty fuel efficient to make viable craft that also use jump drives.
Then again, maybe the current sizes mean you could do the "jump ship" and "drop ship" thing a la Battletech...maybe I'll have to try that...
If we're going to start talking about heat, though, then we have to start talking about massive radiators for any ship with a fusion drive, laser weapons, etc.
Ooh! Maybe Traveller ships can give low power to their jump drives and radiate all the heat into jump space!
