Good ways to limit space travel?
 

I'm working on a new campaign for my group and need some help. TL9, hard scifi, and somewhat more serious.

The campaign is set in a trinary star system. The two primary sun sized stars orbit each other at ~144 AU, leaving them both enough room for their own set of interesting planets. Further out, at 288 AU is a smaller star orbiting the barycentre of the two larger stars, it also has it's own set of planets.

The plan is to have each of the two primary stars host a separate colonial empire, with the two not hostile, but not exactly friends either.

The third star is supposed to be either mostly or totally unexplored. What I want is for it to be currently inaccessible, and for some technological advance during the game to make it accessible. It's supposed to be a "captured" star, and is much older than the first two. (5 billion years compared to 11.5 billion). I basically intend it to be a Schrödinger's star. Maybe one of the habitable planets used to have a now dead civilization on it, maybe there's bronze age aliens going about their business, maybe there's the remnants of an FTL drive system to be found in that dead civilization if I want to expand the scope of the campaign.

But how would I even do this? My current plan for space travel is to have some as yet undetermined drive allow for constant 1g acceleration, with that providing "gravity". But even if ships need to stop to refuel, what's stopping them from just flying off to the third star, only expending fuel part of the time there and back? Alternatively, if I go to a very hard scifi approach and only have the engines in use at the very start and very end then they can still get to the third star, it just takes longer.

Basically, how do I stop two empires that are currently competing for habitable planets and useful resources from either wanting to or being able to travel to the star to see what goodies are to be gotten? I can't hide the star, I can't really stop anyone from getting there at TL9 if they're willing to take the time, and whatever is stopping both empires needs to have held up for the past 100-200 years. (I'm not certain on how long these two empires have been at TL9 with spaceflight, etc)

Re: Good ways to limit space travel?
 

It is not necessary to make the third star impossible to reach, only to make it to big an investment for the return. Suppose recent engine upgrades can leave more holdspace.

Perhaps scouts had been there before but no attempt has been made to exploit it.


Another possibility. The fuel you use is only sufficient for a one way voyage at that range. The only reason you were able to settle the second star's worlds was that ore deposits were discovered making it possible to refine fuel for the return voyage on site. Once that was done colonies were gradually built. Now unmanned probes have discovered similar ore deposits on the third star's planets.

Re: Good ways to limit space travel?
 

The trouble with it being scouted but unexploited is that it's harder to justify people just not knowing about many of the things I'd like to put there. Alien ruins, alien primitives, would be simple to spot. So either I decide ahead of time on what's there (somewhat defeating the purpose), or it must be something non-obvious to scouts (limiting my options).

As for distance, that just increases the time required. Sure, it might be far enough that to get there takes more than half the fuel, but then all the ship needs to do is not use as much fuel on the way there. Burn at the start to get up to speed, burn while there to slow down, coasting in the middle.

For distance to work the star needs to be REALLY far away. Ideally I want the star to be close enough to get to within at most a year of travel time once whatever limitation on travel there has been lifted.

Re: Good ways to limit space travel?
 

Sustained 1 G is seldom used with the words "TL9" "hard science"and "limited". You probably have to scrap this drive is you want limited space travel in pretty much any way. Sustainable !G would allow for very reasonable STL interstellar travel.

Also, any propulsion system even one that has to be Emergent Superscience that still acts in a Newtonian framework that allows for trips of 144 AU will go twice that far under some sort of circumstances.

You need some sort of non-Newtonian Superscience drive to enforce a hard range limit. Some sort of Jump or hyperdrive that required a target star and did not permit jumps to the middle of nowhere and di not allow for jumps of 288 AU might do the trick. Introduce the 288 AU drive when you desire.

If you drastically shorten the trips in normal space by jumping over most of that 144 AU in the middle you can use a much more hard science drive that could not travel 288 Au in less than decades. If it travelled no faster than our Voyager probes it could take centuries. Hundreds of AU is a long,long _long_ trip for a hard science propulsion system.

Re: Good ways to limit space travel?
 

The 1g thing I my current hacky solution to gravity on spaceships. It is/was my one TL^ thing to tie things together. You do point out the problems with that though so It's probably best to drop it.

The Jump drive seems like a pretty good solution, though I do still need some sort of sublight drive, or other way to get around the system. Each one has it's most distant planets at 48 AU from the star, so ships still need some way to manage their longest trips being about 48 AU without everyone being geriatric by the time they arrive. Or I remove all of the outposts and colonies too far from the star.

The other thing to consider is Lagrange points. I had intended to put [interesting things] at those points. Trojan planets in the L4 and L5 of the stars, space stations at the L1-L3 points. Though some of them are nicely at half the 144 distance. So maybe the jump drives need to be charged near a star, and then run off of that battery. They can either expend the full charge to jump to another star, or spend half to jump to somewhere else with the ability to jump back. It even nicely solves my in-system travel problem. Jump ships just need to store some charge to be able to get back from the outerplanets so they can charge at the star.

Re: Good ways to limit space travel?
 

Radiation. Assume that radiation shielding was just good enough to make travel between A and B possible, if spectacularly ill-advised, and recent improvements in materials science finally allow shielding good enough to send a manned expedition to C (and make travel between A and B safe enough for the non-deranged or professionally obligated). Failing that, you can define your drive system to be something like 2300AD's stutterwarp: a maximum range of 7.7 ly before it has to discharge accumulated radiation into a gravity well. If it fails to do that, it crisps everyone and everything involved. Maybe the drive only now became efficient enough to operate that long without irradiating the crew and electronics?

Re: Good ways to limit space travel?
 

Maybe use some sort of gateway device like the Mass Relays from Mass Effect? They can fling you to another relay almost instantly, but you need your own propulsion to go anywhere else.

So you have a linked pair between your two inhabited stars and nobody has found a way to the third one. The third star might have a dormant relay, or the players would have to build one when they got there. There could be a lot of questing involved in the new system to try and find the resources or knowledge to make a relay in the first place.

Re: Good ways to limit space travel?
 

Any reasonable set of numbers, using hard science (the only way to go that way is to throw something the other way), 1g acceleration for more than a day or two would require energy sources not much more plausible than teleporting using a Ring of Wishing. I'm getting numbers that look like gigawatt outputs out of a laptop battery, and, just as unbelievable, the ability of the drive to survive that kind of energy density. That's some hot exhaust.

Honestly, if rotating (or counter-rotating, to avoid gyroscopic effects) or just plain living in microgravity doesn't work for you, artificial gravity is probably no more magical than 1g interplanetary travel. It also avoids implications of 1g travel that you are searching for a solution for.

Re: Good ways to limit space travel?
 

If you want to limit travel to the third star, stay away from jump drive and stick with constant 1G acceleration--this model is a great way to keep things theoretically plausible and it provides hard-sci artificial gravity. Using this system makes acceleration and fuel storage/consumption huge factors in any travel.

To keep the third star inaccessible, make refueling difficult. This also keeps things believable; after all, why should refueling be an easy option, especially in the emptiness of interstellar space? Since constant acceleration at 1G would eat up a lot of fuel, just declare that it is an in-system-only option--Maybe just a few AU (an already enormous distance). And make refueling take a long time, requiring lengthy layovers--especially long ones if there is not a fuel depot established. This is related to Jason's suggestion that the fuel would only be enough for 1-way, since there would be no industrial infrastructure to support refueling at the destination. Travel to and fro would require an investment of human resources and decades of construction at the far end.

You could also make the orientation of the planes of the systems to each other work to your refueling advantage. Since most baryonic matter will be found roughly within the disk of the the ecliptic, if the stars had roughly parallel ecliptic planes most refueling stations (presumably servicing spacecraft utilizing the raw materials of asteroids and planets) would likely be no closer to the other system than the stars themselves. So there is no convenient half-way point. As a bonus, this coincidental arrangement provides a fertile field for all kinds of "Intelligent Design" theory subplots.

Re: Good ways to limit space travel?
 

If there was an ancient civilization, maybe one of its defense drones lasted just long enough to destroy the first scout ships, but damaged or destroyed itself in the process. The locals held back until now, with all sorts of theory, fiction, and religious nuttery about the third star/third star people, but someone managed to make the trip and return in one piece with some data. If there's a lowtech society, they could have suffered a tech collapse, so you could place the low tech species on the same planet as the high tech ruins.

Re: Good ways to limit space travel?
 

These don't exist in a binary system with more-or-less equal masses. You need the smaller mass to be less than ~1/25 of the larger mass for the equilateral points (L4-L5) to be stable. The co-linear Lagrange points (L1-L3) do exist, but stable orbits around them (halo or Lissajous) will be extremely difficult to find and maintain.

I would assume that both systems were colonized from somewhere else at nearly the same time, not one from the other. That gives you a space race to drive development, even if it isn't strictly economical. If your default drive is space sails (photon or magnetic), your "breakthrough" could be the fielding of laser/maser or particle beam boosters.

Your target world could have an optically thick atmosphere that limits attempts to map its surface from the original colony systems.

Re: Good ways to limit space travel?
 

Maybe when the higher ups saw the oddities reported by scouting robots they concocted a convenient lie layered with half truths about the impossibility of getting there/getting information from there, and began a fnord space program to rush into the potential riches and claim monopoly.

Re: Good ways to limit space travel?
 

If the 3rd star is a captured wanderer, its orbit isn't likely to be circular. Give it an eccentric orbit that has only just brought it close enough to be reachable.

Re: Good ways to limit space travel?
 

I second this. Whatever probables actuarial artificial gravity would introduce into the setting wouldn't be that much more outrageous then whatever allows these 1g drives to operate.

Re: Good ways to limit space travel?
 

Possible scenario:

Ships which will make that trip are very expensive, and neither empire can afford to just throw them away.

The third star is sending more radiation in the band usually used for communication, making it impossible to maintain contact with ships within (some distance) of it.

The first several ships sent to explore were lost. No data came back showing what happened or why. They're just gone. Neither empire is willing to send more because then the other will have an advantage in material.

Now, a new communications array has been invented which should allow communication (at light speed). So now there's reasonable expectation that at least data will come back.

Who would be crazy enough to go out on this ship knowing the previous expeditions were lost? The most likely scenario is that this ship will suffer the same unknown fate as the prior ships. But the brave crew will go down in history as the discoverers of... whatever is there.

Maybe the communication system was invented and then rapidly stolen by the other empire and now both are racing to be the first to send their suicide squad to discover what's there.

Re: Good ways to limit space travel?
 

I think I'm probably going to use the jump drive option.

The trouble with the constant 1g is that if something is out of range for the sup to constantly burn during the trip, then all it needs to do is not constantly burn. Do it for half/one quarter/etc the time and you still arrive just fine.

The radiation idea is good, both the lethality and the interference with communications, it was actually what I was imagining. The jump drive option just happens to solve the second issue of in-system travel without the 1g drive. It also has less of a "footprint" than the radiation thing, which might raise other issues.

Don't exist at all? Or do they have the same instability that the L1 through L3 normally have? The plan is for two 1.2 solar mass stars and one 0.6 solar mass star. I don't suppose there's some other set of gravitationally stable points to use?

The plan is actually to have the larger of the two systems (It kinda just happened during system generation, I ended up with several more orbits to fill on the first of the two 1.2 solar mass stars) be home to this campaign's "Earth". During TL8 a colony ship was sent to the second star where a second habitable planet was found. In the vein of the British colonization of Canada the colony continued to get more or less reliable support to help it grow. It also achieved independence in the same way Canada did around late TL8, early TL9. The difference is that now the mother government is sort of regretting letting go so easily. The first star is home to a Representative Democracy with heavy corporate influence. It's in-system (in-star?) outposts and colonies each with a corporate government. The second star is home to an Athenian Democracy, transitioning more and more towards a Cybercracy, limited only by how powerful they can build their computers. The idea is that the mother government has a much better developed industrial base, with a lot more natural resources. The cybercracy on the other hand has fewer resources (though not a massive shortage), but have gotten better at using them effectively and are somewhat more advanced.

===

As a total aside, the Space book is really great. I got pretty much all of the inspiration from the setting as I was rolling up the three star's planetary systems. I got one large system with a bunch of good resource rolls, that later in generation got a lot of Standard or Delayed rolls for TL. The second system had fewer bodies, but got very good rolls during TL generation. No Delayed and most of the Advanced. Finally I got a third star that has a gas giant in the habitable zone (Using eccentric gas giant layout) with a whole bunch of habitable moons.

Re: Good ways to limit space travel?
 

The treaty that ended some previous hostilities included not setting up new colonies, including the other star. The "no expansion" part of the treaty ends during the campaign. Now you don't even have to invoke some sort of weirdness!

Re: Good ways to limit space travel?
 

You really cannot have long term 1g drives in hard science TL9. A small fraction like 0.001g is much more likely as you are really energy limited when you want to make your reaction mass last long enough for maximum total speed.

And really with hard science there is nothing likely stopping things from traveling to the further star, it will just take longer.

So I would go by the one miracle rule and add something like a pseudo velocity drive that is limited in operation duration until it needs to discharge in high enough gravity, with the third star being further away than the maximum. Also have the alternative engines be really poor. Thus your options are along the lines of: Take few weeks to get to star B or a decade to star C.. so no one bothered as there was something more important to spend the money on. Then when you want it you could allow a breakthrough in the technology to allow for the travel.. or perhaps a discovery of large enough objects in an oort cloud type thing to allow discharging the dive on the way(making travel to other star be: accelerate at the oort cloud, wait, accelerate,decelerate to the target star system).

Re: Good ways to limit space travel?
 

You'll have to think through the implications of a jump drive, then. For instance, unless it is limited in drastic ways any ship can escape combat by jumping, so all combats must be mutually agreed upon. I.e. both sides have to want combat. It's hard to trap and destroy a weaker force.

Is there a reason that you picked 288AU as a distance for the third companion star? There are trinary systems where the third orbits much farther than that. 1000AU might solve your problem.

Or, I'd say, drop the 1g reactionless drive and use jump gates. This has a number of advantages from your point of view. (Other than that reactions drives offend me, of course.) One is that it introduces good handwavium: the gates are wormholes that you have to first grow to size and then you have to ship one massive end of it across real space to make the gate. This is expensive and time consuming. Obviously, shipping them smaller distances is less onerous so you might have only one or two long wormholes between the two near companion stars but several smaller ones within each system. Have the stronger empire have a Gibraltar-like extraterritorial outpost in the weaker empire's system or something- it makes for interesting politics. Perhaps they control the gate between the two stars? And everyone (players) groks wormholes. Another advantage is that these gates create natural chokepoints for trade and combat. A final advantage is that it explains why the 1000AU system is only now being explored: someone finally got around to shipping a wormhole there through slow-space. Or alternatively, create great upheaval in your campaign by developing a jump drive! Suddenly these gates are obsolete! Either way, though, there still probably would have been unmanned probes to the distant star. I don't think there's any way around that. It might take them a century to get there, though, using conventional drives, so the data available now might be old TL7 stuff- not a lot of detail, but a few damned shocking images in secret files somewhere...

For shipboard gravity use spin of some sort.

I agree with making one star much smaller than the other, among the two developed systems. You could make one a small red dwarf with a single planet in the goldilocks zone, but it was such a great garden world that the initial colonization effort ages ago chose it despite the very short year. So now that is the older, more established empire, with almost every airless rock in the system colonized. Then the younger system is a larger star with a wide goldilocks zone with two or even three planets in it, but none are "just right" and needed some development, so it was colonized later from the older colony at the smaller star. This explains the "Gibraltar" outposts in the newer larger system, and creates political strife in that while the older empire might be more advanced somehow the newer empire is larger and more populous with greater potential resources. At TL9 no one is doing semicore mining so the smaller older empire might even be approaching a resource-constrained environment, especially if it is poor in asteroids and other small exploitable bodies. When you have to land on a big rock (i.e. a planet) to do any mining then gravity is a bitch. This creates an almost early-UK-USA vibe. There might be more than one "Gibraltar". To make it really interesting have one such be the Old Empire's biggest source of some sort of unobtanium, whereas the New Empire thinks that the entire larger star system should manifestly belong to them!

Re: Good ways to limit space travel?
 

Don't exist at all. An object at L4 or L5 is orbiting the primary (larger) mass, with just enough perturbation from the secondary to keep it fixed in place (in a co-rotating coordinate system). If the secondary is too large, the object essentially "doesn't know" which mass to orbit and wanders around instead.

Your system will have long-term stable restricted four-body (three stars + object) orbits, but they won't be confined to particular points in space. In fact, they probably wander around all three stars, taking tens or hundreds of thousands of years to make the circuit.

The Lagrange points are very much a special case in astrodynamics, although one that turns up fairly frequently in real life.

Re: Good ways to limit space travel?
 

Just as a note this won't work at all (and the OP seems to understand that). One of the wonders of constant acceleration is that travel time is not linear with distance. It increases as the square root of the linear distance.

As a handy rule of thumb to remember a accel and decal trip of 1 AU takes about 3 days or 72 hours. A trip of 144 AU is of course, 144x as far in linear distance but only 12x as long in trip time at constant acceleration. So 36 days.

A trip 2x as far as that only takes 1.41 times as long rather than 2x as long. even if it absolutely is not possible to fit more fuel onto the ship than that 144 AU trip requires at 1G you can go farther by accelerating slower.

The square factor works with slower speeds as well so accelerating at 0.5G makes the trip last 1.41x as long. Traveling 2x as far still only takes 1.41x as long too. So if you can go 144 AU in 36 days at 1G you can go 288 AU in 72 days at 0.5 G on exactly the same amount of fuel.

If an alien cae and offered us a 0.01G constant acceleration drive I'd jump at it. You'd be accelerating 100x more slowly but trip time would only increase by a factor of 10. Only 3 weeks to Mars at close approach instead of the 6 months current planning is talking about.

As another note, refueling one ship from another ship or a space station requires matched velocities and mid voyage velocities for a constant 1G ship can be quite high. For that 36 day/1G trip they are around 5% of c. So there won't be a lot of refueling halfway through the trip unless you use a Bussard ramjet perhaps.

Re: Good ways to limit space travel?
 

You probably could, but you wouldn't. Instead, you'd do the acceleration and deceleration at 1g, and spend the time in the middle drifting.

Re: Good ways to limit space travel?
 

Back of the envelope calculations say "no" but it's a close thing. Accelerating at half speed adds 15 days to the trip and accelerating at full speed and drifting adds 16.6.

I'd probably find 51 days at half G more comfortable than 17G days of 0G. I believe the plumbing would still work then and it absolutely would not work at 0G.

Re: Good ways to limit space travel?
 

If your calculations are telling you that you can complete your trip faster while moving slower at every point along the way, there's something wrong with your calculations.

If your spaceships are not designed to function in freefall, you're going to have a very hard time parking them.

Re: Good ways to limit space travel?
 

<shrug>Do the math yourself. Don't just yell at people who do about what happened when they did the math. I did nothing more than see how long it would take to cross 144 AU at a constant 5% of c and add that to the 36 days of acceleration.

As to parking, if I had 1 G capability I'd normally be landing and not parking.

This is starting to be a sidetrack.

Re: Good ways to limit space travel?
 

Swap out your contant-with-fuel-1g drive for one that also requires the presence of a functional gravity well to operate. That way, the drive simply fails (or slows down unacceptably) past a certain distance from the primary stars.

Re: Good ways to limit space travel?
 

...Seriously, actually doing the math is unnecessary to show why your conclusion cannot be correct.

But fine. 0.5 g accelerating over 72 AU (to the mid-point) takes a little more than 24 days and gets up to a bit over 10 million m/s (3.4% of c). So that's our fairly terrifying half-delta-V. And actually, this paragraph is entirely unnecessary to my point, though I'll use it at the end to deliver actual trip times.

Doubling the acceleration means spending half that time covering half the distance, and then covering the second half of the distance drifting at maximum speed. The maximum speed is twice the average speed of the continuously accelerating ship, so that takes a quarter of the aforementioned time. All told, 3/4ths the time, roughly 18 days, to the mid point, and of course the same from the mid-point to the destination. For a little more precision, it comes to 36.4 days, vs 48.5 at reduced thrust.

Trip time formula if you want to do it out:

1 G isn't enough to take off or land unless you're doing it aerodynamically.

Re: Good ways to limit space travel?
 

In that case, just make jump drives require jump gates. The first ship(s) there will be the very long expensive mission(s) to build the first jump gate in 3rd-star's system.

The radiation was a good idea. The lose-contact-with-any-probe-sent was a good idea. The highly eccentric orbit was a good idea. You have options, which is nice; one or more could be in effect.

Agreed.