Choosing 4E Spaceship Propulsion
 

I'm looking for some experienced advice and criticism, since I can't seem to decide on a crucial worldbuilding detail. My group and I have played a few sessions in a nondescript space opera setting some time ago, and we've enjoyed it enough to want to continue. I've decided to thoroughly flesh-out the setting before we start again, going with the Sci-Fi kitchen-sink approach, and then taking out elements that don't fit the tone. Now, we've agreed to keep it (relatively) light-hearted and adventurous, with very high TLs (around TL 11 mostly), rayguns, space pirates, interstellar kingdoms, psionic powers, that sort of thing, but we also wanted to establish some ground rules and keep it consistent. Less space-fantasy and more far-future-tech advanced enough to be miraculous.

However, the question of space travel (both interplanetary and interstellar) is giving me headaches. I can't seem to find a compromise between gritty enough to be interesting, and handwaved enough to be unobtrusive. I only managed to narrow it down to a few prerequisites and key issues:

1) My players expressed the wish for non-instant stardrive, something like Star Trek warp or Star Wars hyperdrive, but we haven't decided on the speed yet. I personally think silly quantum probability jumps would be a lot of fun. They'd be allowed to visit about 300-500 parsecs, and I'd like to avoid communication- or travel-times over 6 months.

2) I'm not quite sure how "connected" I want my star systems to be. Should inter-system jumps/hyperdrive be unavailable? If we're going for a theme of frontiersmanship and a dispersed, decentralized humanity, what would be more suitable?

3) I'd like it if there was some fuel consumption or resource management to anchor the PCs more closely to planets and space stations. However, we've already introduced advanced technologies, including artificial gravity, which should eventually lead to a bias or diametric drive, if not something even more advanced. Would that suit a space opera better, and am I just giving my players unnecessary busywork?

4) I've considered speed-of-plot interplanetary travel, but I can't really justify an abstraction like "1 AU per day" in 4E Spaceships rules, or use it in Spaceships combat. 3-4 days for an Earth-Mars voyage (or its equivalent) sound about right for pacing purposes, but it requires such ludicrous velocities that it begs the question why I'm even bothering with realism.

5) I wouldn't want to have just one type of engine, purely for diversity's sake. I'd prefer there to be a difference between sluggish (1G or below) long-range ships and snappy orbital ships or combat drones that can't maintain thrust for more than ~30 minutes or so.

6) A minimum of plausibility would be welcome, even barely-coherent technobabble. I had to suppress most of my hard-sci-fi instincts for this setting, and think more in terms of drama and emotional weight, but I believe some consistency can't really hurt as long as it doesn't interfere with gameplay. I've been scouring tvtropes for fictional examples to copy, but I've got nothing so far. Maybe you guys know of some speculative propulsion system that I could use.

I may wrong on all of the above - if you think something else would represent the tone of the setting better, feel free to correct me. So, what do you base your tech choices on? Has anyone run into a similar problem? What would, in your opinion, best suit a space opera? I'd appreciate any advice you can give, much obliged.

Re: Choosing 4E Spaceship Propulsion
 

Consider making it hyperspace like in Babylon-5. They had hyperspace where ships moved at the same speed but things were much closer together, I think, JMS never really did specify more then needed (ships moved at the speed of plot - but you can make them move more consistantly).

Then add in Hyperspace storms (watch an episode of B5, just think of Hyperspace as having storms, not hard to visualize), so going through will take longer.

Finally add in Fold Faults from Macross Frontier, normally a fold (warp, jump, etc..) takes X time for Y distance, but going through a fault takes MUCH longer, weeks instead of days for instance.

Finally finally, do not try to pin it down, just say that hyperspace exists, that there are storms and faults, both come and go according to the following observed pattern (whatever pattern suits your needs) but that the big heads in the science fields can't explain WHY it works - only how...

Re: Choosing 4E Spaceship Propulsion
 

The traditional ways of solving this problem are:

Pick a technology, on the basis of what you find appealing and/or plausible, elaborate it a bit for the sake of realistic variations, and then let it shape your plots.

Sketch out some plots, select technologies and constraints to fit them, and then proceed as above.

Do you have any particular model you're trying to emulate? A few that your write-up reminds me of are: the Lensman series (correct starting point for this is First Lensman), the Honor Harrington series (On Basilisk Station) and The Culture (Consider Phlebas). You clearly want something more rational than Star Trek or Star Wars, so prose fiction is likely to be the best model.

Re: Choosing 4E Spaceship Propulsion
 

Hmmm, I know of Macross Frontier and Babylon 5, but I must admit I haven't seen them yet (and everyone always looks at me suspiciously when I admit that), but I'm sure they have wikia sites where the fans collected technical details.

You're right, I'll let stardrive go unexplained, or just say "quantum this, quantum that", as it's merely a convenience and a necessity of the genre (and you don't need to travel through hyperspace in everyday life). However, more palpable elements like sublight engines and nanofabrication are a bit trickier, since they change the way society looks like from the ground-up.

I like the idea of faults, it gives a strategic dimension to interstellar space. When I was thinking of a jump drive, I discovered that it made star systems more connected to each other than to the individual planets inside those systems, and interstellar distance practically stopped being relevant. I think I'll stick to some sort of hyperdrive, since I don't want a voyage to the nearest system and an enemy's homeworld 500 parsecs away to take the same amount of time/effort.

EDIT:
I've read all of the above, and I think the Honorverse is a good match in aesthetic feel (I initially had the idea of ships with sail-like propulsion ramming each other, but I thought it was a bit too fanciful), but The Culture is closer in terms of technological development (i.e. advanced enough tech to create unrecognisable, immortal, transhuman cultures with few limits and worries), although I backed off from TL12 humanity for fear that the players wouldn't have anything to associate to, or that there wouldn't be tension.

Speaking of the Lensman, I had the idea of making all the ships inertialess. It would prevent the whole "civilian spaceship propulsion = weapons of mass destruction" (e.g. ships would be forbidden from accumulating enough kinetic energy to cause significant damage in the vicinity of a planet/station) and give a good reason for there to be a lot of civilian and corporate ships flying around. Plus, if they can decelerate instantly, it cuts travel time by about 1-3 days on interplanetary distances (1-10 AU), giving me space to use more realistic reaction engines. However, the implications are a bit unclear to me, since I'm no physicist - if hit with a kinetic projectile (missile, gun, gauss), would the ship loose all of its (pseudo) velocity? If so, what would happen if a laser hit them? How would they react to atmospheric reentry (GURPS Spaceships says an inertialess object is merely stopped in place by a collision, and suffers no damage)?

Re: Choosing 4E Spaceship Propulsion
 

Well, with Smithian inertialesness, the velocity an object has is whatever causes the thrust on it to equal the resistance from the medium it's travelling through. Using this for interstellar travel requires entirely discounting relativity, and conservation of energy, which you may not be comfortable with. For coping with projectiles and interstellar debris, it's best to have the inertialessness field extend a little beyond the ship's hull, since that means collisions don't have any effect on the ship - the inertialess objects just get swept along. Your drive exhaust has to be a beam of some kind of radiation, and that has to be immune to the inertialessness effect, or it couldn't produce a reaction.
If radiation isn't affected by inertialessness, lasers work normally.
Well, there's no need for a high-speed reentry. You turn off the thrust, and you stop. You let yourself fall under gravity, still inertialess, and deploy parachutes so that atmospheric drag limits your falling speed to something low.

Something that may suit you a bit better would be the Alderson Drive, from The Mote in God's Eye. This is a typical drive of the kind that does jumps between special points on the edge of star systems, creating in-system travel time, but avoiding the need for huge interstellar velocities.

Re: Choosing 4E Spaceship Propulsion
 

Yeah, I was afraid that might be the case. I wasn't planning on using it for interstellar travel, since even ignoring relativity would produce travel times in years (unless acceleration is something like 500G). It's also problematic that the engine has to be a beam, since it means equipping every ship, including the smallest civilian tramp freighter, with a high-powered laser, which might throw a wrench into the whole "ubiquitous, safe space travel"-thing.

Another thing I was considering is the Mass-Effect-inspired mass cancellation, but I wasn't sure how they justified it in-universe. If you make an entire ship massless, how does its massless reaction mass impart momentum onto it? And if your ship has the mass of a photon, why doesn't it decelerate whenever it hits a stray hydrogen molecule in space? And supposedly, Mass Effect ships have negative mass, which makes things even more confusing and speculative (supposedly, having negative mass would negate time dilation for reasons unknown to me). I'm starting to think a simple shamelessly overpowered rocket would suit me best (e.g. 1G acceleration, 5,000 mps per fuel tank).

Re: Choosing 4E Spaceship Propulsion
 

This sort of thing is generally known as "pseudovelocity" is standard Gurpsese and is a good solution to a number of problems in Space Opera.

I used such a drive in 2 campaigns and it worked well. What I did was declare that the pseudovelocity field was establsihed as soon as you left atmosphere and ships rapidly accelerated to their crusing velocity but did not accelerate any more after that.

I set velocity at c. 1 million miles per hour. This would give you your trip to Mars in 2 to 6 days. Twice that speed would work too. You can actually hit a higher normal space speed with the right sort of drives but I definitely made the PV drive much easier to do than that.

Massive particles and bodies in space did not interact normally with any ship under PV drtive. I described the result as the two sliding past each other frictionlessly rather than any sort of collision.

Tis has the extremely useful side effect of making ships under drive immune to most of the radiation from solar flares and cosmic rays too. Particle beams too. Lasrrs and high energy photons affect ships normally.

Normal KE weapons are utterly useless and 2 objects that are within 10x maas of each other and under drive bounce off each other with each engine needing to make a HT roll or go down (non-catstrophically).

Penalize this roll by at least -2 for each 10x factor and make failure increasingly catastrophic (for the smaller ship only). Anything missile sized explodes but far enough way from a ship to be ineffective. Nukes have to be set off before drive field interaction so only proximity detonation is possible.

Antimatter would still be problematic. I recomend you avoid antimatter.

EMP effects might still be possible and I did leave in a hole where a SEFOP or Explosively Forged Projectile could detonate at the drive field limit and still hit the ship with its' projectile. This is defintely optional. I just left it in so that small ships could attack larger ones with non-nuclear torpedoes.

When you turn on the dirve all of your relative velocity and potential energy (relative to _whatever_) goes "away" and doesn't ever come back. Think of it as beign evenly distributed across all the mass of the universe or anything else that helps.

When the drive shuts down (voluntarily or otherwise) the ship gets a new nrmal space vector normalized tot eh nearest object capable of producing the gravitational effect known as "frame dragging".

In the most common uses this will leave you in orbit (equatorial and prograde) of the nearest planet. If not a planet, a sun follwed by star cluster, galaxy, galsctic cluster and so on.

For FTL I used "jump lines". These from between any stellar bodies (or anythign else with a degenerate matter core) and had a useful length of 3.3 parsecs x the combined masses of the two bodies in terms of solar masses.

Implications of this are that Class M dwarves can almost always be ignored with useful connections being increasingly likely as stellar mass increases. Most binaries can also be ignored as their relative motion ususually measn any "lines" they would form cross and disrupt each other.

Trust me. Ignoring red dwarves and binaries will make your star mapping much easier.

Type A stars tend to form multiple connection points with greater than average length and long trips in such a set up came to be known as "Taking the A Train" in my games.

With the assumptions used in First In, stars with habitabhle planets seldom had direct connections. Usually 3-5 jumps were rnecessary with normla space maneuvering required to go from one line to the next. Pirates were known to hang out in empty systems along Jump routes. That 2 million mph ship usually took about a week to make an average trip.

Having the Jump connection be a line rather than a point also has the useful effect of making it impractical to put mines or station a fleet on top of the Jump exit. Interception before an attacker can reach your mainworld is still normally possible.

There. Hopes that help. More info probably available on request.

Re: Choosing 4E Spaceship Propulsion
 

A 1G reactionless engine will make almost all interplanetary travel measured in days (e.g., from earth to mars with multiple engines) to weeks (e.g., one side of the system to the other on a single engine). Even limiting reactionless to the TL7^ 0.1G rotary reactionless engine still gives you some interplanetary travel times measured only in days with few journeys requiring more than a couple months.

If jump gates (that jump either directly to a jump gate in another system, or into hyperspace where you can travel in parsecs per day) can only be built outside of stellar and planetary gravitational influence (e.g., past Neptune's orbit), then interplanetary travel will always be easier than interstellar travel and planets within a system will find it easier to trade and travel within the system, but interstellar travel won't be necessarily out of the question.

If reactionless engines are limited to 1G per spacecraft system (e.g., super reactionless isn't allowed or hasn't been developed), but superscience reaction engines are allowed, then interplanetary/interstellar travel will use reactionless engines but short-distance travel/combat will use reaction engines. There are a number of reaction engine choices at TL11^ -- for example, the Super Fusion Torch pulls 50G per engine and lasts 25 minutes per tank per engine, while a High-Thrust Super Antimatter Plasma Torch consuming antimatter-boosted water can pull 600G per engine but lasts only 16 seconds per tank per engine -- so there's a lot of room for design choices. Even some non-superscience engines might be advantageous over a 1G reactionless engine in a short dogfight: for example, a TL10 High-Thrust External Pulsed Plasma engine pulls 4G per engine and lasts 2.6 minutes per tank per engine.

Re: Choosing 4E Spaceship Propulsion
 

Oooh, more feedback, yum!
This sounds just about right, but I'm not sure how a fixed speed (if I understood correctly, PV ships have no acceleration, they instantly achieve ~300 mps or so, and come to a full stop just as fast) would work in spaceship combat, especially the tactical variant discussed in Spaceships 3.

This would greatly simplify things, but with the multitude of different cultures and alien species I plan on having, it would be a bit weird if everyone used lasers and only lasers. It also makes ramming/boarding infeasible.

I also remembered another reason not to have inertialess drives - the traditional Gundam justification for spaceships with arms/manipulators was that they could change orientation by rotating their limbs, due to conservation of angular momentum, which allows fine microgravity manoeuvring. I kinda wanted ships with robotic arms, and this gave me a good reason, except an inertialess "space mecha" wouldn't be affected by it.

OOOooh, I like this option! So, these lines would be like highways/tunnels between stars? You just approach one, even at 10 AU from the star, and you can hitch a ride? And every line connects to only two stars, so you have to switch lines at each system on long journeys? Sounds kinda cool, it averts the whole fixed-gate-problem where you can count on every jumpgate having an armada around it which basically leads to a tightly-controlled universe with no room for pirates.

These numbers look pretty good for interplanetary travel and combat, though I'd rather keep the difference in acceleration between high- and low-performance drives below 30G (otherwise it's difficult to choose a space turn-length and distance scale), so I might have to tweak the numbers a bit (e.g. a 20-25G Fusion Torch with double the delta-v/fuel tank).

I know from experience that using a combination of reaction/reactionless engines, both firing simultaneously during interplanetary travel adds another step to calculating travel time and delta-v consumption. Is it possible that a reactionless drive would somehow neutralize reaction drives active at the same time? Without the whole inertialess thing, it doesn't seem like something that would be intuitive to my players. :P

Re: Choosing 4E Spaceship Propulsion
 

You're thinking of boost drives, which are a very specific variant of pseudovelocity drives. PV drives normally only have the game effect that they don't have much velocity for collision purposes, rendering missiles less destructive.

Boost drives are covered in Spaceships 7, including necessary modifications to the tactical combat system.
Notably, Smith didn't do it that way; two inertialess ships that collided would simply stick together, with their velocity determined by wherever their jets were pointing, and whovever's were more powerful. But neither ship would be damaged by the collision.

You could declare that they interfere with one another, and using both simultaneously is contraindicated (though you may want to keep it as a possibility, for when the extra acceleration is worth the risk).