Newtonian Aurora

[Steve Walmsley (OP)]

Steve, I don't think your math is as good as within 10%. Here's a quick example: the delta-v necessary for a 90-degree course change. In your system, that'd be a delta-v equal to 90% of the velocity, right? What would be necessary in reality is a delta-v of 141% (square root of two, basically).

At 180 degrees, of course, the math is simple... you're costing 180% v rather than 200% v, so you're only off by about 11% there. The smaller the angle, the worse the margin of error gets; at 1%, you charge 1% rather than the real 1.74%.

I take it your current coordinate system is based on speed and angle, rather than x and y vectors?

EDIT: sloanjh got here before me, I just figured I'd crunch the numbers and toss them into a spreadsheet to make sure I wasn't miscalculating.

Thanks for running the numbers. Based on your math and John's, I guess a flat 1.5% per degree would be a reasonable compromise between reality, playability and ease of player understanding.

Yes, fleets now have a heading and velocity and movement is based on that. They don't have a facing in the combat sense however. I don't want to get that tactical.

Steve

[Gidoran]

Will missiles start off at the same velocity as the ship that launches them? So you could do things like whip a missile up to . 1 c or something by charging in to a system, aiming it at the enemy, and letting it use its fuel mostly for maneuvering?

[sloanjh]

Thanks for running the numbers. Based on your math and John's, I guess a flat 1.5% per degree would be a reasonable compromise between reality, playability and ease of player understanding.

Given that this is a computer game, I'm curious why you think a flat rate would be more playable than just having the computer calculate the cost.  (Don't take this as a disagreement - I'm just wondering.)  It seems to me like most of the movement orders should be set up such that the player tells the computer where the fleet should be and when, and then the computer manages the course calculation.  And by "where and when" I really mean a whole host of conditions, such as "least time intercept", "least time zero-zero intercept", "lowest fuel zero-zero intercept within time deltaT", ....  The computer would then just use the appropriate formula.

One thing that will vastly change the interface/complexity: will the ships have enough fuel to do continuous max-burns for an interplanetary trip, or will they only be able to do a short burn then coast most of the way.  The second one is a lot more in line with the deltaV thing above - the first one means solving quadratic equations....

John

[jseah]

Could I humbly ask that fuel and reaction mass be divided?

Reaction mass could simply be virtually anything your engine throws out the back.  Obviously, engine designs will vary depending on the reaction mass used, so each engine design could have another line:

eg.
Reaction mass - H2O
Reaction mass - Inert Gas


This would reduce the massive amounts of fuel needed to the amount of power needed by your engines.  Sorium could simply be something that makes fusion power easily feasible, and that drives the engine.  

Would make ice asteroids and gas giants sources of reaction mass at which ships could easily fill up again, say with a maintenance module/facility.  Some extra mass dedicated to sorium storage would then allow ships to hop from one reaction-mass point to another so as not to need massive fuel tanks to go all the way.  

Also have to second sloanjh's suggestion that the computer work out paths. 

[sloanjh]

Could I humbly ask that fuel and reaction mass be divided?

Reaction mass could simply be virtually anything your engine throws out the back.  Obviously, engine designs will vary depending on the reaction mass used, so each engine design could have another line:

eg.
Reaction mass - H2O
Reaction mass - Inert Gas

This is a really good idea if you want to be realistic.  Not so much because of the "different fuels" issue, but because of the interplay between engine mass, fuel mass, and reactor mass.

The way a reaction engine works is that you "burn" fuel in an engine to provide energy to throw "reaction mass" out the back end at some exhaust velocity to generate delta-momentum = mass thrown*velocity thrown.  This is what's behind the fundamental difference between airplanes and rockets - the airplane doesn't have to carry its reaction mass - it uses its wings to thrown air downwards, and in the engine it uses the core to drive high-bypass fans to throw more air backwards more slowly than if the fans weren't there.  If you go through the equations, this means that airplanes want LOW exhaust velocity, because that gets the most delta-momentum per delta-energy (fuel) (because kinetic energy = momentum^2/(2*mass)).  Rockets, on the other hand, need to carry their reaction mass along with them, and pay for accelerating it before it's used.  This causes reaction mass consumption to be exponential in the final velocity, btw, in the case where most of your ship is reaction mass.  Since you're carrying the reaction mass along, you want to squeeze as much delta-momentum as possible out of each unit of it, so you want HIGH exhaust velocity.  Rockets like a titan use combustion products as the reaction mass, while ion engines use a reactor or solar cells for the energy source and heavy ions as reaction mass.  So there's a whole host of tech line possibilities:

* exhaust velocity
* fuel efficiency (how much energy is in one mass-unit of fuel)
* engine efficiency (how many mass units of engine it takes to process one mass-unit of fuel)
* fuel type (does the fuel get thrown overboard like rockets or kept on as deadweight e.g. reactor-mass, or is it solar powered)

One more thing to emphasize: if most of the mass of your ship is going to be fuel, you need to use the rocket equation, which says IIRC that the cost in reaction mass will be exponential, i.e. deltaV is something like log(TotalMassInitial/TotalMassFinal).

John

[jseah]

^I was mainly trying to allow Titan to be a refueling source.  You can scoop some helium from Saturn and deposit on Titan or you can Titan's ice. 

Also lends some tactical depth as ice asteroids or planets as well as gas giants become refueling sources for reaction mass that limit the delta-v of your ship. 
While reactor fuel is what limits the life of your ship, and that needs a population and refineries. 

[Charlie Beeler]

The need tp seperate engine fuel and reaction mass will only be needed if Steve goes with a thrust/reaction drive.  It is entirely possible he plans to use a field manitulation model (ala Weber's "wedge" in the Honor-verse) that does not use reaction thrust.

Grub for pondering

[jseah]

The equations about burning fuel and delta-v heavily imply a reaction drive. 

Field manipulation and reactionless drives have whatever physics you want to give them.  Weber's wedge in particular applies an acceleration and according to many instances in the series, bringing things into the wedge does not slow down the ship at all. 

[Charlie Beeler]

So far the only thing I see is that inertia, and a host of important baggage, is replacing the current inertialess movement system.  Whether "conventional" reaction thrust or some yet to be determined thust model based on handwavium and unobtainium that generates a field to influence acceleration and course change is as yet unknown. 

My only point is that reaction thrust should not be assumed at this stage.

[jseah]

Fair enough.  I only proposed it as a possible solution to the "ships need too much fuel" problem. 

The key points are:
Reaction mass, that makes your ship go, can be easily gotten.  IE. full refueling where you have a minor base, no refineries needed. 
Reactor fuel, that makes your lights stay on, need to be provided by industry. 

[sloanjh]

So far the only thing I see is that inertia, and a host of important baggage, is replacing the current inertialess movement system.  Whether "conventional" reaction thrust or some yet to be determined thust model based on handwavium and unobtainium that generates a field to influence acceleration and course change is as yet unknown. 

My only point is that reaction thrust should not be assumed at this stage.

I just went and actually read closely Steve's initial post, and the rocket equation still applies even if it's a reactionless drive, if you define a equivalent exhaust velocity that I suspect is thrust/fuelBurnRateInMassPerTime.  So dV should be Veff*ln(M0/M1).  The fuel source, exhaust velocity, engine mass etc. can be abstracted into the engine mass fuel efficiency that Steve already has, if you define "fuel" as "power source + reaction mass, as appropriate".  One thing this brings up is that I'm assuming that the mass == volume simplification would be thrown out: mass should == volume - volumeOfFuelAlreadyBurned at the very least (unless the new inertia is volume-based rather than mass based due to some foible of a handwavonium reactionless engine).

John

PS - Just to be clear, I'm not at all invested in which direction Steve decides these things, I'm just trying to point out the Newtonian physics where applicable.

[seinwave]

Will Aurora II use these physics?

[Din182]

Will Aurora II use these physics?

It will be more of a spinoff of the original for the people who want more realism.

[DAW69]

If Steve wanted to simplify things then the argument could be made (handwaving time) that Aurora drives are variants of matter-anti-matter drives.   In this case the actual mass of the fuel is trivial compared to the mass of a ship.   The volume could be thought of as the size of the magnetic confinement magic required to contain anti-matter.   But then again I'm lazy.

[Steve Walmsley (OP)]

Will missiles start off at the same velocity as the ship that launches them? So you could do things like whip a missile up to . 1 c or something by charging in to a system, aiming it at the enemy, and letting it use its fuel mostly for maneuvering?

Yes, missiles will start with the velocity of the ship that launched them, so you could use the above tactic. I will be looking at a lot closer at kinetic weapons because with the potential speeds involved kinetic weapons could be deadly. In fact, I will probably be redesigning a significant part of beam weapons mechanics to allow much longer range. In the past, anything above 5 light seconds was impossible on the basis that ships ignoring the effects of inertia could instantly change course. With ships generally following far more predictable courses, beam weapons and kinetic weapons could be fired at great distances and tracked on the map over time like missiles. Ships will be able to make themselves more difficult targets by expending an amount of fuel to make minor course changes or minor changes in velocity but these would use a lot of fuel if they were used as a matter of course (and would make the ship detectable to thermal sensors) so different levels of evasion would likely be employed based on the potential threat. As a counter-counter, kinetic weapons might fire a slowly spreading cloud of small but high speed projectiles. I will also look at point defence being able to intercept kinetic projectiles. All the above is thinking out loud at the moment so it may change when I get down to the coding.

Steve