Modified Acceleration and Consumable Fuel

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Errol_Summerlin
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Re: Modified Acceleration and Consumable Fuel

Post by Errol_Summerlin »

chuck_starchaser wrote:Can't. There's a reason why sky-scrapers 20 kilometers high don't exist. They can't be accelerated by the ground against 1G gravity. Same applies to a structure in space. Worse, because buildings on the ground don't sport maneuvering jets.
don't exist "yet". The build them higher every day...and with sufficient amounts of materials a pyramid could be built arbitrarily high. The ancient egyptians built these giant pyramids without steel rebarb reinforced concrete. Nobody builds pyramids because they take up too much real estate on the ground. But in space, who cares. Its these long skinny ships that will have this problem, especially with torque from maneuvering jets. These things sway noticeably in a stiff breeze. Imagine what thrusters will do to them. Like I said, I think that every hull should have a maximum acceleration associated with it based on the constraint of structural integrity, but by devoting some mass and space inside the ship toward structural integrity(which would incidentally make the ship more difficult to destroy and more massive...slowing it down, one should be able to improve the maximum acceleration. This would be rather inefficient though since the structural integrity increases the mass...which means you need more power just to get to where you were before structural integrity upgrade...and then more power to get up to the new maximum. With only so much space for structural integrity modules and thrust production modules and the need to leave some space for cargo. There would be significant tradeoffs for a benefit that can be tweaked as needed (in terms of the numbers) to produce the desired effect. Thus, by making structural integrity expensive in terms of space and mass, making a 5 kilometer ship that accelerates like a lear jet could be made impossible or possible depending on player feedback. This choice, to me, seems to provide the most flexibility for mod developers as well as for this game.
but even if I'm wrong and we have materials 1000 times stronger in the future, what does that do for us in terms of gameplay? Nothing. Because if you see a 5 kilometer long ship and it accelerates like a lear-jet, you (the player) will simply assume that it is roughly the size of a lear-jet. Why? Because kilometer-sized structures accelerating at multi-G accelerations are totally outside our experience AND imaginative capacity.
Well, most of this game is outside our experience but I don't think that it is outside our imaginative capacity. It is not outside the realm of the physically plausible either. A tetrahedron structure (thanks) several kilometers long could probably handle 1g accelerations if it were well reinforced and you allow for advancements in structural engineering without stretching the imagination too much. In terms of game play. It allows a scenario where one ship is the cargo and engines ship. It gets it acceleration high enough that it can keep up with its escorts. Or it gives captains that ferry cargo in relatively safe areas an option to increase their profit margin a little by speeding up the transport of goods (though the benefits of this would be dubious since extra engines and structural integrity would take up space that could have been used as cargo space. As for player assumptions about the size of a ship, I don't see how that is relevant. Information available from the radar or targeting information will tell you the ship's size. And when you see 15 giant thrusters on the back, the output from which obliterates a small interceptor that happened to be flying behind it when the engines ignited, players will understand that this ship is designed for high speed cargo hauling. Another thing to keep in mind here is the benefits of having engines that accelerate at 1G....no need for "artificial gravity". To me, artificial gravity is completely unphysical. There is only one way to get artificial gravity...accelerate at G...either through centrifugal force on a spinning space station or by by having engines that produces thrust 9.8 times the mass of the spaceship. For ships that do extended duty in space without docking, 1g accelerations would be necessary to prevent bone degradation and muscular atrophy. For me anyway, immersiveness is the most critical part of any sim game. My feeling is that 1G should be the standard acceleration for most capital ships(The bigger ones will need more engines and structural integrity reinforcements to do this), with emergency acceleration up to maybe 3Gs. It isn't feasible to go much higher since the crew won't be strapped down in a nice cushioned chair with artificial pumps for blood to continue to flow during 10G acceleration maneuvers...unless you invent magical inertial dampeners as well that have no basis in reality.


Ditto. Neither kinesthetically believable, nor of any gameplay value; unless you're talking about boosting accel from 0.02 G to 0.023 G, or something like that.
Well, I am not saying what the numbers should be, but I think there should be a mechanism built into the engine that allows players to customize their ships to create capital ships with more acceleration than usual if they properly reinforce the hull to handle the stress and have enough thrust. The exact numbers could be determined through player feedback. If the structural integrity cost is too high in terms of mass and volume, then players won't ever buy it, and they will continue to complain at how slow capital ships are and they can't do anything about it.
Well, I'm not the lead guy for vegastrike; not sure there is one anymore; but the matter of antimatter was considered a long many years ago, and abandoned for fusion. And I can't say I disagree with the decision. Problem with antimatter is storage, as you probably know already.
Having said that, it once occurred to me that a new "chemistry" might perhaps be conceivable, where matter and antimatter are bonded in a stable fashion and grown into chrystals. It would have to be some matter crystal structure with cavities featuring a lot of negative charges pointing inwards, where a single anti-hydrogen or anti-deuterium nucleus fits suspended.
But anyhow, in the vegastrike universe ships' power comes from fusion; and I once argued we needed a specification for the fusion fuel, but that never happened. I'd argue for Helium 3.
But in any case, what makes it really easy to sweep aside the fuel and propulsion problems is the fact that we have a much bigger problem to solve first: Getting rid of excess heat.
[\quote]

Well, this one of those rare times when I feel an assumption regarding technical advancements is necessary in order to keep the game realistically plausbile (i.e. don't break any fundamental laws of physics) while still keeping game play fun. Fusion is terribly inefficient in terms of energy per kilogram of fuel(<7*10^14 J/Kg). Even if you neglect the mass of the fusion reactor, you get less than 1% of the rest mass of the reactants liberated in the form of energy. It does provide a convenient propellant though which I will discuss later(the products of the reaction that are not involved in any further fusion reactions). Anti-matter annihilation has a theoretical limit of 9*10^16 J/Kg. That means you need 100 times less fuel to get the same energy output.

Consider a fusion reactor that has fuel equivalent to 1% the mass of the ship. Assume that the 7*10^14 Joules of energy is pumped directly into the roughly kilogram mass of reaction products which then impart all their momentum to the ship...a perfectly efficient process. That gives an exhaust velocity of 3.72e7 m/s. These are mildly relativistic particles so we must use the relativistic rocket equation, but the effective exhaust velocity is 3.75e7. With 1% of the ship as fuel, this gives deltaV=3.76*10^5 m/s...less than the maximum speed of a dostoevsky.

Now consider an anti-matter power plant produces 9*10^16 Joules/Kg with an exhaust velocity of c if it directly utilizes the resulting gamma-rays as propellant. deltaV=3.02*10^6 m/s. While the fusion reactor is more energy efficient in terms of power to thrust ratio by about an order of magnitude, the power/Kg of the anti-matter engine is more efficient by 2 orders of magnitude. This doesn't even include how useful the extra energy efficiency is for weapons and other ship systems.

Furthermore, consider the typical accelerations involved in this game. 10g accelerations. By noting that deltam is small, we can assume the mass (and therefore the acceleration resulting from the thrust) is roughly constant and equate a*t=deltaV to give us a measure of how long you can thrust before running out of fuel. For fusion, roughly 1 hour of 10g acceleration. For anti-matter, 8 hours of 10g acceleration.

Other possibilities include a mass of propellant heated by the energy output of one of the two power plants above that can be used to improve the power to thrust ratio. Essentially, by taking the power generated by the 1% of ship mass that is fuel, and using that power to energize a larger mass of propellant and expel that larger mass at a lower speed, you can reduce the power requirements to get the desired thrust, or, get more thrust for the same power output. For example, consider a ship with 1% of the ship mass in anti-matter fuel and 49% of the ship mass in a propellant. So now, the 9*10^16 Joules of energy is distributed among 49 kilograms of propellant giving each unit of propellant gamma factor of (1+1/49). Then, thrust=gamma*v*dm/dt=(1+1/49) is now 9.95c, about a factor of 10 increase, but our ship is now twice as heavy as our unladen swallow reducing the gains somewhat. The acceleration is anywhere from 5-10 times what it was before, and the deltaV is also increased. There is some magic ratio for these things that gives you the amounts of fuel, propellant, and ship that produce the maximum acceleration, but no matter what you pick for a propellant, more energy/kg is always better.

So,provided my math is right, it seems to me that the "base" thrusters should be when the thrusters use the direct products of the power plant (fusion or anti-matter) that produces energy. These power sources may have sufficient fuel that, for the purposes of the game, they can be considered infinite(anti-matter clearly better for this), but there isn't really any feasible "infinite" power source(yeah, solar is too weak for this game...too much energy output). Consider 1% of the ship mass as anti-matter, but reduce the acceleration it produces by a factor 40...down to .25g as you suggested earlier in the thread. Then it lasts 320 hours before running out...virtually infinite unless you are too poor to replenish it when you dock. Then in addition to fuel, players could have "booster" which is really a propellant gas expelled in great quantities but at lower speeds than the typical products of these processes resulting in increased thrust and even better "fuel" efficiency if the propellant is inexpensive compared to fuel (which it should be).

Finally, with regards to the propellant, I think that it would be interesting to make the "propellant" be just about anything. After all, it doesn't matter what is from a theoretical perspective. If you can get the energy from the power plant into the liquid,gas, or solid, and shoot it out the rear of your space craft, you are golden. This allows players to "scoop" booster juice from planetary atmospheres or even, in an emergency, use cargo as booster juice. It would add an interesting tactical option. Fighters that typical function in deep space may not use boosters as much as those that function near planets. Or planetary craft which depend more on boosters might be able to have smaller power plants.
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Re: Modified Acceleration and Consumable Fuel

Post by chuck_starchaser »

The problem with antimatter remains: Where do you carry a kilo of antimatter? You might say "it's just a game", but I betcha any money if we make the ships antimatter-powered there will be people asking how the hell we do that, at the forum, all the time.
Anyhow, with regards to accelerations, the problem is you're trying to solve a problem we want to stay a problem. We don't WANT high accelerations anymore. We're sick of them, and of all models looking like little toys. Because I'm telling you: Myself, and most new players, look at Clydesdale cargo ship, and we assume it's about 100 meters long; maybe 200 meters on the outside. Well, officially it is about two kilometers top to bottom; and well over five kilometers long. And I'm telling you that if I take on the job of making it look its size by remodeling and retexturing it, it will look like an obscenely expensive, 100 meter sized scaled toy model. Why? Because at 10 or 20 G's, you hit the gas and in 2 or 3 seconds you've passed it; and there's NOTHING in our range of daily experience that gets close to that. We can maybe imagine 2 G's, with great concentration effort; but we can't imagine 10 or 20.
So, we are sick of this stupid paradigm of having ridiculous accelerations that all they do is make ships and stations look like toys.
So, I brought up all the problems with acceleration: thermal, structural, etceteras, in order to further support the motion to bring accelerations down. You are arguing for the opposite: defending high accelerations. I'm sure you are doing so with the best of intentions; but just know that you're stepping hard on my toes.
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Re: Modified Acceleration and Consumable Fuel

Post by klauss »

And if stepping on chuck's toes isn't enough, you're stepping hard on a very important gameplay issue: WOW - what you should say when you look at a clydesdale.

Doesn't happen.

Because of ridiculous accelerations.

I spent more time flying around than I did ever before while debugging cubemaps ;) and now I can tell that SPEC also goes against that WOW feeling, because it's just another form of ludicrous acceleration.

I believe we must set the no-spec zone around stations bigger, so you must approach them from a nice comfy distance. The same with capital ships.

Anyway, high accelerations, even if we could explain them, I don't think we want them. They're not part of our daily life, our mind can't comprehend them (at the intuitive level), so they kill this WOW part of the experience that I'd really like VS to have.

Let me add, constant prolongued acceleration isn't on our daily experiences either, and well against intuitiveness. We don't freefall. Ever, except just before we die (because we fell off a plane or something like that). That's why bungee jumping, skydiving and those things are so fun, they're totally alien to us, they mean death in our instinctual brains, and only our conscious brain knows we'll end up cheating death (with the bungee, the parachute, etc...). But merely visual stimuli doesn't cut it to produce the feeling, so the feel of freefall in a game is impossible... what you get when accelerating constantly over a long time is just to expose the artificial nature of the game.

There are tricks to get the feeling of mechanical acceleration though. Cars, they can accelerate quite a bit, but in my experience I have to feel the mechanical effort, or my mind doesn't believe it. So, to get that feeling I was experimenting one day, and came up with "cockpit shake" for SPEC drive. It gets the message to your brain that your ship is doing a great effort to get that acceleration.

So, care must be taken and tricks must be employed if you want to have uncommon movement in a game, to aid suspension of disbelief.
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Re: Modified Acceleration and Consumable Fuel

Post by Errol_Summerlin »

chuck_starchaser wrote:The problem with antimatter remains: Where do you carry a kilo of antimatter? You might say "it's just a game", but I betcha any money if we make the ships antimatter-powered there will be people asking how the hell we do that, at the forum, all the time.
Anyhow, with regards to accelerations, the problem is you're trying to solve a problem we want to stay a problem. We don't WANT high accelerations anymore. We're sick of them, and of all models looking like little toys. Because I'm telling you: Myself, and most new players, look at Clydesdale cargo ship, and we assume it's about 100 meters long; maybe 200 meters on the outside. Well, officially it is about two kilometers top to bottom; and well over five kilometers long. And I'm telling you that if I take on the job of making it look its size by remodeling and retexturing it, it will look like an obscenely expensive, 100 meter sized scaled toy model. Why? Because at 10 or 20 G's, you hit the gas and in 2 or 3 seconds you've passed it; and there's NOTHING in our range of daily experience that gets close to that. We can maybe imagine 2 G's, with great concentration effort; but we can't imagine 10 or 20.
So, we are sick of this stupid paradigm of having ridiculous accelerations that all they do is make ships and stations look like toys.
So, I brought up all the problems with acceleration: thermal, structural, etceteras, in order to further support the motion to bring accelerations down. You are arguing for the opposite: defending high accelerations. I'm sure you are doing so with the best of intentions; but just know that you're stepping hard on my toes.
Magnetic containment...positrons are charged. Consider fusion...you have insane temperatures and pressures inside the fusion core and you contain the reaction with magnetic fields, but whatever pressure is inside there is the same as the amount of magnetic pressure you have to apply to contain it. In other words, you need insanely strong magnetic fields that can adjust to counter plasma instabilities to control a fusion reaction.

For positrons, it is actually far more simple to contain them. They are not particularly energetic, and, in fact, could be laser-cooled to ridiculously low temperatures so that tiny magnetic fields could contain them. Releasing their energy just involves creating a "hole" in your magnetic field that allows some flux of positrons to enter the chamber where your propellant is and heat it. controlling the flow of positrons would be detail work in magnetic field manipulation, but eminently doable... especially if they are super-cooled. In terms of containment, positron containment is far easier than fusion temperature plasma containment.

The real problem for anti-matter is creation of it and getting it inside a perfect vacuum magnetic containment unit. But is is fairly easy to imagine a solution to this. LHC produces anti-matter particles quite often as a result of ridiculously high energy collisions between atomic particles. The trouble is that the LHC is only a partial vacuum. Thus, anti-matter particles almost immediately find some matter to interact with and annihilate. In fact, most of the time, the only evidence they ever existed is the characteristic energy of the gamma ray resulting from the annihilation. Now, imagine LHC built in interplanetary space near earth with only 2 particles per centimeter cubed...or in our local interstellar bubble .07 particles per cubic centimeter. These are very impressive vacuums in which positrons would have mean free paths large enough that they could be successfully diverted by electro-magnetic fields into magnetic containment units virtually free of matter to react with. Thus, the problems of creation and storage of anti-matter is solved, at least conceptually. The technology would take some work, but the solution is, IMO, good enough for believability.

With regards to cap ship accelerations, don't misunderstand me. I like the numbers you have. The wow factor is very important to me as well. I am just finding the accelerations hard to justify in terms of the physics. I want to justify them, but I am finding it difficult.

With increased size comes increased volume for fuel, engines, and proellant. So, while a big giant megaton ship would use much more fuel and propellant than a 1 ton ship, it can still accelerate just as fast if it uses enough energy and fuel. I am dubious of the structural engineering argument because, if you use an appropriate shape, a pyramid for example. Any time you scale up the size of the object, you scale up the area over which it is distributed as well. However, now that I think about it, the mass goes as scale factor (r) cubed, and the area over which it is distributed only goes as r^2...but even if this problem did occur, you could always just expand the base of the ship without increasing its height and build short fat capital ships with thrusters spread out evenly over the bottom solving that problem. They might have serious issues with torque, but that isn't the matter at hand. The heat dissipation argument kind of works. If heat dissipation is your limiting factor, heat dissipation goes up as the surface area which goes as r^2, but the mass (and hence the power requirements) go up as r^3 and it would make a nice pretty m^(-1/3)[or 1/r if the ships are all spheres] type of relationship value for accelerations if your ship's are spheres and heat dissipation is what is limiting power production. But, then you might imagine some weird ship designs that have a whole lot of surface area (for heat dissipation) and little volume. Think of something like a long central pipe that goes through the center's of 10 discs, but each disc is separated by some space.

Anyway, I am perfectly ok with the accelerations you guys decided on, and I don't mean to step on your toes, but in order to suspend MY disbelief, I have to make sense of it in terms of the physics. I never have understood why capital ships were always big and slow in space sim games. It always seemed to me that it was another one of those leftovers from terrestrial thinking that went up into space with us just like using drag in space. I wanted you to prove that it made sense physically is all. It, of course, feels right, but I can't shake the feeling that it is just my terrestrial experiences that shape what "feels" right.

And about my desire to allow you to spec your big ship to improve its acceleration, well, that is all part of what modders will do afterwards and as long as the engine has the capability, what particular are available in the game is just a wish list. Never-the-less, I think it could be very interesting to have these upgrades so long as their trade-offs were big enough so that you can't tweak out your cap ship to out-accelerate an interceptor...but maybe to out-accelerate a slightly smaller ship giving your opponents a bit of a surprise.

I agree about increasing size of no-spec zones. That also provides more opportunity for pirating ARRRR!.
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Re: Modified Acceleration and Consumable Fuel

Post by klauss »

Errol_Summerlin wrote:Anyway, I am perfectly ok with the accelerations you guys decided on, and I don't mean to step on your toes, but in order to suspend MY disbelief, I have to make sense of it in terms of the physics. I never have understood why capital ships were always big and slow in space sim games. It always seemed to me that it was another one of those leftovers from terrestrial thinking that went up into space with us just like using drag in space. I wanted you to prove that it made sense physically is all. It, of course, feels right, but I can't shake the feeling that it is just my terrestrial experiences that shape what "feels" right.
Ships have to maneuver. Propulsion doesn't go only forward, it must go backwards and sideways. It must be able to receive torque just as well for turning and docking. I bet turning is the biggest issue... pushing forward is rather trivial.
In essence, the engineering problem is trivial only if you fail to consider it.
I bet you can find more problems than solutions if you do think it through in breadth.
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Re: Modified Acceleration and Consumable Fuel

Post by Errol_Summerlin »

Oh, well perhaps this is the communication problem. I was specifically considering going in only one direction. I don't think anybody expects their cap ship to spin like a top a bitch or dodge incoming enemy fire with their lateral thrusters. I understood the issue to be that if you decrease cap ship accelerations, getting places takes forever. Skyscrapers can't handle much torque. They have to consider wind sheer dangerous, but they can handle 1g in the vertical direction because they were built to handle it. I am thinking the same thing for cap ships. While small ships may buzz around like hummingbirds thrusting in all directions equally well, cap ships would need to limit themselves to large acceleration in one direction(still not as large as smaller ships, but enough so that the travel times are not so disparate).
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Re: Modified Acceleration and Consumable Fuel

Post by klauss »

Actually, we're also talking about fighter accelerations. 30g accelerations in some ships make them feel like mosquitoes instead of fighters.
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Re: Modified Acceleration and Consumable Fuel

Post by chuck_starchaser »

Errol_Summerlin wrote:Oh, well perhaps this is the communication problem. I was specifically considering going in only one direction. I don't think anybody expects their cap ship to spin like a top a bitch or dodge incoming enemy fire with their lateral thrusters. I understood the issue to be that if you decrease cap ship accelerations, getting places takes forever.
The problem of trips taking forever currently doesn't exist; but in any case, IF we want a genuine space experience, with true distances, true sizes, true forces, true accelerations... travel should take forever. So, for the sake of gameplay we need to lie. We agree. Now, the question is where or what do we lie about? I prefer one big lie to many small lies; and the one big lie here is SPEC, so might as well make it as big as it needs to be. I don't like the paradigm of stretching the truth all over the place, like making planetary distances 1/10 th of what they really are, allowing accelerations 10 times greater that what's feasible, ignoring waste heat problems, etceteras. So my plan is for injecting truth everywhere that there's lies, and then collecting all the cheating necessary into a single package called "spec".

(((And I think the best lie for spec, --MUCH simpler and cleaner than "space compression", "tunneling", "Alcubierre", "subspace", "hyperspace", "wormholes", and all the FTL sci-fi buzzwords--, is to base spec on "inertial mass reduction" or "mass hiding"; because no matter what you do to get around Relativity, you still need big engines and many months to get up to C, never mind 97 C... But if we somehow were able to reduce mass by ratio N, conservation of momentum would dictate our speed has to go up by N as well; so with a new buzzword "inertial mass hiding" we not only get around Einstein ((if we somehow inject N into the formula)), but we can explain our acceleration to multi-c as an energy-neutral operation.)))
(((((Furthermore, if we make "mass hiding" work only for inertia, but NOT for gravitation, we'd have something that allows realistic orbits and "slingshot" maneuvers around planets; only happening in a smaller time-frame. It would be equivalent to "time-compression" without the acceleration of time.)))))
Skyscrapers can't handle much torque. They have to consider wind sheer dangerous, but they can handle 1g in the vertical direction because they were built to handle it. I am thinking the same thing for cap ships. While small ships may buzz around like hummingbirds thrusting in all directions equally well, cap ships would need to limit themselves to large acceleration in one direction(still not as large as smaller ships, but enough so that the travel times are not so disparate).
I've thought about this many times, and perhaps we could implement it; --but NOT to allow 1G to capships; I'm thinking maybe 0.2 G fwd, 0.03 G in other directions--; and what we'd need to implement this is a smarter autopilot that turns around 180 at mid trip to deccelerate. But let's discuss this after the physics rework.
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Re: Modified Acceleration and Consumable Fuel

Post by shenle »

Okay, so sionce fuel is now consummable, don't you think it's time to implement a way to replenish it too? I haven't seen any fuel for sale anywhere. :)

(yes, a repair will replenish fuel but I guess sometimes you might just want to stop at the pump, not the body shop...)
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Re: Modified Acceleration and Consumable Fuel

Post by chuck_starchaser »

I've no idea what it would take to implement; probably Python work, not sure.
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Re: Modified Acceleration and Consumable Fuel

Post by TBeholder »

Deus Siddis wrote: there is economical access to such things as antimatter, so wouldn't chemical rockets in general be obsolete?
Having a hydraulic press doesn't make hammers obsolete. And aside of chuck_starchaser's argument on non-triviality of advanced thrusters, "chemical rockets" is a stretchable term.
For example, a chemical thruster may be augmented with a plasma thruster stage (in VS terms - Type 0 afterburner?). Especially if its fuel is salted with Lithium - like in explosives-powered MHD generators. Generally, plasma thrusters seem to be the most convenient choice for ships, though - once we have fusion to not worry about energy and warpdrive to cut on travel times and stretch the delta-V leash. That, or direct fusion, but having a fusion reactor on each thruster node got to introduce specific limitations too.

Generally, at least ship/atmospheric, ship/space (cruising), ship/space (maneuverable) and missile/space are different enough that requirements to engines are vastly different.

Missile propulsion systems got to be reasonably easy (anything with Tritium is straight out) and safe (most fission schemes are out) both to store and kickstart, compact, strong (most of fuel-efficient stuff need not apply) and cheap. Which means for shorter active times plasma-augmented chemical thrusters are just fine.
Though again, there can be other good options, depending on the purpose (assumed scenario of usage varies all the way from "short-range intercept of a maneuverable target" to "slow target, mostly-ballistic projectile"). Up to and including MagBeam assisted launch. :twisted:
nphillips wrote:But I like the idea of expendable fuel for controlling the ship. So, my modification of the idea is to keep the ship's computer in control of ion thrusters that provide standard y/p/r, but the maximum acceleration for all ships using these thrusters would be less than 0.25G. For higher accelerations, the pilot can activate these boosters.
In other words, you want delta-V to matter even after making it mostly irrelevant for long-range travel (via warp drives)?
Even without wasting fusion fuel on exhaust (like it's assumed now), once you get back to Newtonian physics, delta-V and thus lots of propellant are needed to do just about anything immediately noticeable.
It's that simple. Acceleration as actively as dogfight, jousting or frantic dodging maneuvers require (as opposed to steering within degrees, stretched to hours) means great force - lift-off grade thrust, not ion lights. Now look at the table. Engines that are efficient and have good thrust tend to want paricularly exotic fuel, be inherently huge (as in, kilometer-long) or have "little" drawbacks like leaking "hot" isotops into exhaust. Thus expect thrusters that give good force (and thus acceleration) to be less efficient in spending lots of propellant you need to accelerate for momentum such maneuvering implies.
Here we go.

The only good choices for a maneuverable ship seem to be, unsurprisingly, plasma (preferrably variations of MHD, rather than just advanced plasmatrons) and almost-raw fusion reactor exhaust - and assumption that we'd have routinely useable fusion power in itself means enough of control over plasma to make both variants even better than that. And unless fusion reactors get very compact and quick-starting (then again, maybe we can afford keeping the containment fields hot in maneuvering mode?), they still won't fit for maneuver thrusters.
chuck_starchaser wrote:But anyhow, in the vegastrike universe ships' power comes from fusion; and I once argued we needed a specification for the fusion fuel, but that never happened. I'd argue for Helium 3.
Probably, depending on the assumptions. There aren't too many viable variants.
The main choice is whether to have neutrons or not. Neutronic reactions are easier to burn and cheap fuel-wise, but require to, well, handle neutrons - which means either tons of absorbing materials that go into waste, or some sort of (non-EM) containment field, that adds both to equipment and to ignition energy cost (and thus latency), since it should be fully powered before igniting the reaction. Tritium makes neutronic reactions look more lucrative, but it's also unstable. He-3 spontaneously appearing in the fuel system is still good; need to adjust reactor for current T/He-3 rate and/or separate them and extra radiation shielding for every tank, manometer and capillar aren't prohibitive, but no great fun either.
Conversely, charged particles are obviously easy to utilize (both for thrust and extraction of energy) via EM forces rather than collision heat exchange. Thus aneutronic reactions are generally preferrable if we want the reactor to be compact and efficient overall.
Look e.g. here or here. Available reactions are:
  • p + B-11 → 3 He-4; LC=497 (times harder to ignite than D+T)
  • p + Li-6 → He-4 + He-3; bad cross-section and low output give LC=1486 - worse. May be a part of He-3/p cycle with two below, once that becomes easy - but it's still not for compact reactors, let alone reactor-thrusters.
  • He-3 + He-3 → He-4 + 2 p; can't find LC nor even cross-section data, but compared to D+He-3 (LC 16, second best after D+T), energy 12.9:18.3, electron penalty 2/4:2/3, 2x for single reagent - 1.05x better subtotal, so unless cross-section is very low, it got to be good.
  • He-3 + Li-6 → 2 He-4 + p; no data either, but with energy is 0.92x of D+He-3 and 0.6x from electrons - unless cross-section is huge, it doesn't look great.
If a "hot ions - cold electrons" solution is available via plasma tricks, it would improve LC, though no more than 6x, 4x, 4x and 5x respectively.
So most likely yes.
"Two Eyes Good, Eleven Eyes Better." -Michele Carter
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