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Old 12-27-2020, 04:00 PM   #11
AlexanderHowl
 
Join Date: Feb 2016
Default Re: Cinematic Rocket Delta-V Rules

You could just as easily have fuel/coolant requirements for inertialless boost drives and get the same sense of drama while avoiding civilization killing reaction or reactionless rockets. For example, you could rule that inertialless boost drives require 1 fuel tank worth of coolant per engine component for every week of operations, meaning that anyone who skips refueling is going to have a really bad time of it.
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Old 12-27-2020, 04:09 PM   #12
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by Jinumon View Post
IDK. I feel like that can be a lazy way of looking at it. I think the impetus of keeping a ship in repair, cargo in the bay, and fuel in the tank can be a great source of drama and story threads, even in a cinematic game.
Sure, but the point is that there's a wide variety of cinematic rockets (so you need to decide what you're emulating), and they were not generally designed with any particular concern about what is realistic, or even makes sense. For example, anime jump jets don't normally run out of fuel but only allow leaps rather than sustained flight, generally with no explanation as to why they work this way.
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Old 12-27-2020, 04:11 PM   #13
Varyon
 
Join Date: Jun 2013
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by AlexanderHowl View Post
You could just as easily have fuel/coolant requirements for inertialless boost drives and get the same sense of drama while avoiding civilization killing reaction or reactionless rockets. For example, you could rule that inertialless boost drives require 1 fuel tank worth of coolant per engine component for every week of operations, meaning that anyone who skips refueling is going to have a really bad time of it.
This is largely my approach for my Harpyias setting - pseudovelocity boost drives for travel, but rather than fuel I have extremely high-energy capacitors that get drained (due to the rate of drainage and a shortage of energy-generating options, vessels typically need to dock with a fueling station or similar to recharge, which gives the same effect of burning through fuel). Combat is markedly different, with real velocities and pseudoatmospheric flight involved, but the vessels are slow, comparable to WWII aircraft (and weapons are rather short-ranged as well). That's a pretty heavy-superscience setting (not so much in terms of how many such technologies exist, but how prevalent the ones that do exist are), however, which may not be what the OP is looking for.
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Old 12-27-2020, 04:34 PM   #14
Stormcrow
 
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Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by Jinumon View Post
I don't know about how others feel, but personally as a player I get sort of irked if my GM simply declares something like "you're out of fuel" or "a part on your ship breaks" solely for the purpose of creating tension.
If players get to bend reality in the name of cinematics, so do GMs. A vehicle breaking down at exactly the worst moment is very cinematic, and so should be part of the GM's toolkit.
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Old 12-27-2020, 05:10 PM   #15
Jinumon
 
Join Date: Mar 2013
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by AlexanderHowl View Post
You could just as easily have fuel/coolant requirements for inertialless boost drives and get the same sense of drama while avoiding civilization killing reaction or reactionless rockets. For example, you could rule that inertialless boost drives require 1 fuel tank worth of coolant per engine component for every week of operations, meaning that anyone who skips refueling is going to have a really bad time of it.
I've actually done this in the past by having reactionless drives that only function if supplied by a Fuel Cell power plant, so you simply have a "time we can keep the engine on" as opposed to having to calculate delta-V. I think it's a perfectly legitimate middle-ground if that's what you're going for. I tend to like a little more crunch in my games is all.

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Originally Posted by Anthony View Post
Sure, but the point is that there's a wide variety of cinematic rockets (so you need to decide what you're emulating), and they were not generally designed with any particular concern about what is realistic, or even makes sense. For example, anime jump jets don't normally run out of fuel but only allow leaps rather than sustained flight, generally with no explanation as to why they work this way.
Fair point.

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Originally Posted by Stormcrow View Post
If players get to bend reality in the name of cinematics, so do GMs. A vehicle breaking down at exactly the worst moment is very cinematic, and so should be part of the GM's toolkit.
Agree to disagree on this one. Then again, I don't generally give my players the tools to "bend reality" or, if I do, they come with very specific mechanics that say just how much and how often you can influence the plot. They also often come with give-and-take sort of circumstances, like "Okay, you get to turn that hit into a graze, but now I as the GM get to decide when you fail a roll, as per the Unluckiness disadvantage, once." All that said, these kinds of rule-bending mechanics are always worked out ahead of time and my players are always aware of exactly what might happen if they exploit them too much. It's a sort of in-game contract with each other. I know a lot of people are comfortable just saying "it's my game, rule zero, if you don't like it you can get out," but I feel like the best games reserve that kind of arbitration for only the most dire of circumstances.

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Old 12-27-2020, 05:41 PM   #16
Anthony
 
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Location: Berkeley, CA
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by Jinumon View Post
I've actually done this in the past by having reactionless drives that only function if supplied by a Fuel Cell power plant, so you simply have a "time we can keep the engine on" as opposed to having to calculate delta-V. I think it's a perfectly legitimate middle-ground if that's what you're going for. I tend to like a little more crunch in my games is all.
It's worth asking yourself what cinematic means to you, and whether it's what you actually want out of a game. It sounds like you want unrealistic but not cinematic.
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Old 12-27-2020, 10:18 PM   #17
GURPS Fox
 
Join Date: Jun 2020
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by Varyon View Post
Looking at Spaceships, if you want around 12 G's with water as the reaction mass, you're looking at superscience. TL9+ Nuclear Thermal Rockets do come close, however - using water as the reaction mass, they've got 1.5 G each, for a maximum of 9 G with 6 systems (total 3/10ths of the vessel's mass). With 10 fuel tanks of water (half the vessel's mass), you'll get 2.1 mps delta-V which isn't going to get you much of anywhere fast. You can arbitrarily multiply the delta-V by whatever factor you'd like for your cinematic rockets, of course. Another option might be to allow for high-thrust, like the various fusion reaction engines have access to - this is double acceleration, half delta-V, or 3 G per system (18 G max) and a total of 1.05 mps delta-V when using water; again, you'll need to markedly increase delta-V for this to work out.

If you're willing to go to some limited superscience, the TL 10^ Fusion Torch is an option. Using water, and again with half the vessel's mass in fuel, you're looking at 1.5 G per system and 70 mps delta-V at TL 10^, 210 mps delta-V at TL 11^, and 700 mps delta-V at TL 12^. High-thrust is canonically an option here, for double acceleration (3 G per system) and half delta-V (35, 105, 350 mps, respectively). As an example of what you can manage, let's go with the worst-case - high-thrust water at TL 9^. To go from Earth orbit to Mars orbit, first you've got to burn 2.1 mps to break orbit. You've got 33.9 mps left to play with, but you need to account for both acceleration and deceleration. Deceleration is 0.93 mps less than acceleration (you just need to slow down to orbital velocity, not to a dead stop). If we use all but 0.93 mps delta-V (leaving a little room for error, and making the math easier), that means we accelerate to 16.95 mps, cruise for a while, then burn another 16.02 mps to slow down to orbital velocity. If we accelerate at a comfortable 1 G (we only need the high acceleration for combat), this takes around 45 minutes (12 G would take around 4 minutes), during which time we travel 0.00025 AU, which is pretty much a rounding error compared to the 1.5 AU between Earth and Mars, so we'll ignore it for the next calculation. Traveling 1.5 AU at 16.95 mps takes a bit over 95 days (95 days, 5 hours, 16 minutes, and 48 seconds), then another ~45 minutes to slow down to 0.93 mps. You're probably going to want higher delta-V. One option might be to have an adjustable drive - it only suffers the halved delta-V when used in high-thrust mode (such as in combat). I'll leave it to you to work out the math on that and the other delta-V's (although IIRC, Pyramid #3/79 comes with a spreadsheet that can do most of the work for you).
Thank you for this information.
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Originally Posted by Jinumon View Post
This may be a somewhat unpopular opinion, but when dealing with cinematic or superscience propulsion systems, I actually find it's easier and more efficient to work backwards.

I took a crack at this a while back for my own space opera setting (which never got off the ground but that's neither here nor there). Instead of looking at the available options in the various Spaceships books and building a setting around it, I decided on certain standard metrics and then made my own custom propulsion drives based on those metrics. Things like:
  • How long do I want it to take a ship to travel across a star system?
  • How long should a ship be able to burn for on one fuel tank?
  • How many Reaction Engines/Fuel Tanks should be the standard on typical freighters, q-ships, etc?
  • How expensive should it be to refill a fuel tank?
Once you've got a decent amount of answers for these questions, not based on existing drives but based on how easy, fast, and economical you want space travel to be, then you can start assigning numbers to things like:
  • How much delta-V does a single fuel tank provide?
  • How many G of acceleration does a single reaction engine provide?
  • How expensive is a ton of fuel?
I find that when it comes to mechanics, it's more important for them to fit the style of game you want to play rather than adhere strictly to realism. So long as it remains internally consistent and gets you the results you want, who cares, right?

Jinumon
Well, at the core, is a war setting, where there is no peace, only a cease-fire until the next war. Anywhere within the solar system, there are at least two factions fighting it out.

One of the core things of the setting that it is a 'future-history' setting, where things progress, however slowly. Originally, the various factions of humanity used NTRs and nuclear lightbulbs to travel between planets, but due to the fact that peace is no longer a thing in the setting, it was found that the rockets aren't good enough in the D-V department to head to somewhere, fight, and then head out to somewhere else. So the various factions invested in researching ways to improve the delta-v to maximize effectiveness.

This led to a high-efficiency fusion drive similar to Transhuman Space's High-Efficiency Plasma Recombustion Fusion Rocket (HePlaR). They're not Battletech efficient (~40 days at 1G for only 1.6kTons of hydrogen!?!) but they're enough to turn a trip that would take years (Earth to Jupiter) and reduce that to a handful of months... and that is before the invention of the 'Interplanetary Drive' (making a trip that would have taken years to a literal handful of months).
Quote:
Originally Posted by Anthony View Post
It's worth asking yourself what cinematic means to you, and whether it's what you actually want out of a game. It sounds like you want unrealistic but not cinematic.
'Unrealistic' is usually termed 'cinematic' from what I've heard...
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Old 12-28-2020, 03:54 AM   #18
Anthony
 
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Location: Berkeley, CA
Default Re: Cinematic Rocket Delta-V Rules

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Originally Posted by GURPS Fox View Post
'Unrealistic' is usually termed 'cinematic' from what I've heard...
Cinematic is also unrealistic, but unrealistic is broader than that. Cinematic is 'things happen because dramatically appropriate'.
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Old 12-28-2020, 07:01 AM   #19
GURPS Fox
 
Join Date: Jun 2020
Default Re: Cinematic Rocket Delta-V Rules

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Cinematic is also unrealistic, but unrealistic is broader than that. Cinematic is 'things happen because dramatically appropriate'.
Eh, then I've been talking to people who don't want to differentiate.
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Old 12-28-2020, 07:06 AM   #20
AlexanderHowl
 
Join Date: Feb 2016
Default Re: Cinematic Rocket Delta-V Rules

Superscience and magic are unrealistic, but they are not necessarily cinematic (you can have FTL or spell casting in a noncinematic setting). The primary issue with even limited superscience drives in such a setting is that inertia becomes the ultimate weapon. Even at 35 mps per fuel tank, a spacecraft with 10 fuel tanks can reach 490 mps easily, meaning that every ton of remaining mass is equivalent to 68.5 kilotons of TNT, meaning that civilian terrorists can turn a SM+9 merchant ship in a full scaled Tsar Bomba. Even a SM+4 AKV becomes much more valuable as a WMD than as a combatant, as it would be the equivalent of over 340 kilotons of TNT at full speed.
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