Thot

After 15 billion years, I believe it is safe to say it's not going to happen. Waiting for Godot isn't even fun in theater.

Well, the last fundamental breakthrough in physics was almost a century ago. I'd love to be wrong, but it doesn't seem there are big loopholes that allow interstellar travel in this universe or any that is accessible. If our own physics isn't indicator enough, consider this: We have not been visited.

It's not just NASA. It is the universe itself. FTL is probably impossible. Generation ships are probably impossible. Interstellar travel of all kinds probably is impossible. We have to deal with that.

Hm, people claiming about aliens in area 51 aren't exactly reliable sources, but this sure as hell is good gaming inspiration. FTR, NASA does not work on any actual drive. They are in way, way way too early stages for that.

The problem with that is that it utterly changes space combat based on a completely arbitrarily chosen form of space magic. This again doesn't ring very futuristic to me, more like fantasy.

I think the speed of light is an application of a rule , not the rule itself. In other words: Speed of light in a vacuum is the maximum speed this universe will alow, but slowing down light will not decrease the maximum speed the universe allows. Or at least that is what special relativity assumes.

Skyhooks fail for the same reason that other would-be solutions would: Too complicated. AND they also have this issue that they'll wreck the whole planet if something goes wrong. Which it will. You can use present-day technology there. How about just making them live for a million and then some years, and have them just use old-fashioned "poop a little gas out of the rear" drives? They'll probably lie dormant until they reach another star drifting, but they'll arrive. IF you can reach a velocity that is needed to escape the origin solar system.

But then, you don't really need a spaceship, what you need is a self-sufficient habitat moving away from the sun early enough... So IF fusion is possible on a human-useable scale, that is what we'll see. Otherwise, we'll use some leftover uranium and hope it lasts long enough to somehow get to some other star.

If you can accelerate something to that speed, you don't need to accelerate anything to that speed.

Oh, but there can be, just not that far out. Earth orbit, solar orbit at 1 AU, maybe more of the inner system, that offers so much space (literally) that you can spend millennia there.

Science station? Why bother? Send a probe and do the data anlysis from Earth? Industrial? What would you produce out there, and for who? Pirates? Who would they be pirating on out there? Trade station? Who would trade what there?

The only way to do that is to convert it into photons. Lamps aren't putting out a lot of pressure, though.

That was the norm throughout most of human history, especially in warfare. And see Battlestar Galactica for reasons why this might be the only option. You have to make a choice here: Either micrometeorites are bad, or you can easily patch holes. Which is it? Chemical rockets to lift off and maneuver to a certain distance from the planetary body (100,000 km), then FTL into the orbit of another planetary body within range, then land with aerobreaking (which does make sense because it's cheap to take off again with rented rockets) or just dock with a space station at the destination.. Or just gene therapy for anyone willing to go into space. Because that implies they have a lot of resources, which again changes the tone of the campaign completely. And what is the exhaust velocity of those "ion drives"? But the fundamentals of the fundamentals, like fuel consumption, the number one limiting factor in space travel, should somewhat relate to reality in a hard SF setting.

Yes. My misunderstanding was, apparently, to see M-Space as a generic "SF guide for Mythras" instead of a more specific "this is Mythras Star Wars". 5 m/s² is half a G. That's not something worth thinking about. And depending on your setting, there may be reasons to use human pilots over remote controls or Ai brains. We are talking about spaceships with the sturdiness of an airplane at most. If a micrometeorite hits you, you're dead anyway. That would be the landing - or the "we cut our tanks dry" emergency where radiation isn't your biggest concern. Well, for my past campaign, I had to add FTL anyway, so I just decided to set the FTL drive's capabilities in such a way that chemical rockets sufficed. Not to a hereditary class of oligarchs. If I can simply and plausibly make any PC and important NPC in my campaign a spacefarer just by declaring them so, without any other worldly consequences like fortune or fame, that's fine by me. Besides, it doesn't seem to be such a small share of the population who can stand it. I wasn't saying that Ion drives had more delta V than necessary, but that they don't, in practice, have more delta V than chemical rockets. For an ion drive, you need exotic reaction mass like Xenon right now - because it is freaking complicated to use non-noble gases. There is basically no way you can mine xenon from an asteroid. Well, in orbit (at 8 km/s, roughly). Why? Once your are in orbit (and such a behemoth would be built there already), you just slap more fuel tanks onto it until you are at 90% fuel, or even more Add another 9 million tons and you get to 20,000 m/s of delta V. Why would anyone want to build a colony on Ceres? There is nothing there that you cannot find elsewhere closer to the sun. Cassini needed 7 years to get to Saturn. Kickstarted with a liftoff rocket (a Titan IV), and with 2000 m/s on-board delta V. Ion drives and the even less powerful higher Isp drives are not noticeably accelerating, meaning there is no action going on, which is bad for tension at the game table. And they don't seem to give that impressive results in practice anyway. The space probe Dawn had only about 11,000 m/s of delta V. Compared to our Battlerocket Solaria, I can only say: Why bother with the ion thruster, plus the power source, plus the waste heat, plus the extremely rare reaction mass in the form of Xenon?

I can imagine some workaround by incredibly sophisticated magnetic field shapes. But there simply is no option whatsoever to get rid of the limitations of reaction mass. Because they are real. We could build such ships right now. Elon Musk's SpaceX is beginning to. They do seem to be as close to the real thing as we'll ever be. Then of course everything is different. But it doesn't look like it. You don't need FTL in order to have a space setting. Actually, that IS doable. With some 5000 m/s of delta v and an acceleration of 0.5g (similar to most atmospheric fighter jets today), you could do 20 minutes of constant burning. If you limit yourself to relatively low speeds, that can be enough to do traditional dogfighting. Only for half an hour or so (as you don't burn CONSTANTLY), but that's good enough for a carrier vs carrier battle. Even in the best case that will just add to your overall waste heat. No, storing enough H2 around you is actually an option. And as you need that for your rocket anyway... but sure, a magnetic field would be convenient. Of course. That is what real space travel is: Some chemical rockets and lots of orbit calculations. As a chemist, you will surely know how important it is to quantify such statements. The amount of energy for a high Isp drive is... unsettling. I never claimed it wasn't hard, just that other drives are even harder. The beauty of the chemical rocket is that it carries its power in its fuel, and that takes most of that out of the rear end of your spacecraft with it. Yes, you need really large amounts of fuel for high delta V, but it seems to be easier to just accept that and have a very large tank than to build overcomplicated drives that never quite achieve what you design them for. We live under the tyranny of the rocket equation, and this is not going to change. Not at all. NASA has done tests with it - some people cannot stand it, yes, but others can. For my campaign, I just assumed all relevant characters had passed that test. Well, all that effort to just get some 10,000 m/s of delta V when you could as well just put more fuel on your spaceship... seems wasted. You could do that computation (based on E=1/2m*v²), but by putting it in terms of energy, you are making things complicated because of the rocket equation. Let's just imagine a rocket ship, let us call it the Battlerocket Solaria. Without fuel, it is about as massive as a Nimitz class aircraft carrier, so about 100,000 tons.We want our Battlerocket Solaria to have significant delta V, so we give it a fuel tank with 900,000 tons of fuel. Therefore, the starting mass (fully loaded) is 1,000,000 tons. With a H2/O2 rocket, that will give us: Delta V=4462*LN(1,000,000/100,000) which equals 10,274 m/s of total Delta V. How big the engine is that we use this fuel with is irrelevant for that, but we'll probably equip our Battlerocket Solaria with missiles and fighters for armament, so the mothership won't need to be terribly agile. The Saturn V rocket's engine had a thrust of 33,851 kN. let us give our battlerocket three of those, so we have about 100,000 kN of hrust. When the Battlerocket Solaria is fully loaded, her engines will accellerate her at 1 m/s², which goes up to 10m/s² when the tanks are almost dry. She could do this for about 2,000 seconds non-stop - but you'd never do that, of course.

Well, Traveller CAN do chemical rockets and other reaction thrusters. M_space doesn't seem to have that option at all. Sure, but there is no had physical barrier preventing tech to solve these issues. Reaction mass is different in that you cannot work around the need for it. Slow motion is boring? No. Reactionless thrusters as depicted in Traveller and M-Space are flat-out impossible, full stop. The only way it IS possible is with photons as your reaction mass, and that requires amounts of energy no foreseeable spaceship will ever have accessible. Even then, thrust would be so low that they'd not be worth it, except for interstellar voyages. Every joule of energy you produce eventually becomes waste heat. You can get rid of some by putting it in the reaction drive's exhaust, but that is necessarily imperfect. Worked fine for all the deep space probes any group of humans has sent out, with few exceptions. V follows from delta V. A chemical rocket can at most have an impact velocity of something like 10km/s. Bad for the house or block it hits, but rather unimpressive on the city. Not so with a fusion rocket that gives you 200.000 km/s of delta V... But you forgot more than half of the drive here: The power source. The additional cooling. The reaction mass that needs to be cooled even more. No, I am saying that high Isp-drives are even more complicated than chemical rockets, and we hit a limit there, too. See above: It is not about the efficiency of the power source. You will always have 100% of your stored energy as waste heat EVENTUALLY, except for that which you put out of your engine. Photovoltaics is great technology, but it won't power a multi-GW-spaceship. And that's what you need for high Isp ships.. Only by your ability to build stable hulls that can handle the acceleration stress. The size of a single rocket engine is limited, yes, but you can just use multiple engines. That wasn't my point. If you have gyro core (or just two countering centrifugges, all you need is the ability to create rotation (like a common motor), wihtout having to spend any delta V. Judging by the time and effort put into their development without having anything terribly impressive to show for yet, I would say yes. The amount of sail surface needed for that to be noticeable on a timescale relevant for manned space flight is prohibitive. And I had hoped someone had done the groundwork already.

I don't quite see why this is a reply to the sentence you quoted immediately before that? It's extremely fundamental, in contrast to the other things you mention, as it limits the ship's core ability (velocity change) significantly and cannot be explained away without violating major physics laws, unlike with waste heat, for instance (because at least there are radiator concepts that could theoretically work up to some point; rectionless thrusters are flat out impossible if we are not talking about lamps photon drives). But there are issues with higher specific impulse drives that, at close distance, look quite significant, to sy the least. 1. If you do the math for the waste heat, you find that your crew is boiled, or with some thrusters, the ship is melted, regardless of what kind of cooling system you imagine. 2. Their accellerations are so incredibly low that crews don't notice them. Which also means it takes a boring amount of time to get to any desired speed. 3. Too much delta V in the hands of basically any civilian tramp freighter captain mean every doofus owns a weapon of mass destruction. Chemical rockets don't really pose that problem. 4. All the higher specific impulse drives are incredibly complicated, which means expensive and prone to failure. Do you really want spacecraft to be a privilege of the top 0.001% in your interstellar empire? 5. What is the power source? I don't quite see how the nature of the missile changes the fact that the ships basically don't move, so there is no maneuvering, merely a quite boring ECM battle which ends the moment one side is hit. They are all viable, depending on the size of the ship. You can do rotation with a gyro core or similar installations, no need to spend delta V on that (though the total amount you'd spend wouldn't be high anyway). No issues with renting a rocket for "assisted initial velocity", but ion drives are complicated, extremely low thrust and power hungry. See above. Right now, the big money is on chemical rockets. For unmanned ships with unlimited time and as long as there is no FTL (which seems likely, though), perhaps.

But that is for the FTL side of things. That's "magic" anyway, so one can easily make up any number one likes. Which is cool, but not helping with the question.

Well, one could argue that a generic SF RPG should include support for more than one type of SF setting. Besides, it doesn't only lack chemical rocket fuel but also fusion rocket fuel, antimatter rocket fuel, even just reactor fuel for the average magic space drives. I had hoped someone might have done some work there. No problem if that isn't within the system's abilities, I'll just import a design system from another source. Hydrogen, methane, kerosene or hydrazine, combined with liquid oxygen. Enough to give a ship a few thousand m/s of delta v. If you want faster travel than what this will allow for, use the FTL drive. If you don't have one, coast a lot, and do swing-by maneuvers, and possibly use the Oberth effect to your benefit. Of course, in such a universe, space battles are boring artillery duels with little to no actual tactics once the shooting starts. There are centrifugal artificial gravity system ideas that do work better, like rotating the entire ship along one axis, or enclosed centrifuges that are encased in stationary armor on the outside, or even using tethered fuel tanks as counterweights to rotate around a common center of mass with the main ship (this is particularly useful for ships in the classic "player ship size" range). As your chemical rocket ships ( I maintain they are the most likely ship to ever actually be built in significant numbers) coast a lot anyway, having to stop rotation for a while while changing course isn't a big deal, because you won't do that often.

That was indeed my impression, but that's disappointing. Fuel is THE big issue with spacecraft. Well, then I'll just have to use GURPS Spaceships, converted to metric. The stats will work with BRP with only slight conversion, I believe.

Given the heating and power problems all the alternatives produce, chemical rockets still are the best option for almost any application , even IF we ever solve the fusion problem on the ground. For a campaign of mine, I created an entire galactic setting where even the most advanced civilizations use chemical rockets, because the advantages of all the other systems aren't just worth the complications - but that was with a different system. (And yes,that implies renting rockets to lift you into space at the spaceports.) But yes, it's terribly hard to do space travel. That's a given. Anyway, does anyone have stats for fuel tanks (be they for chemical drives, fusion rockets, ion engines or whatever) for use in M-Space? I can do the math myself, but before I spend time on that, I'll rather check out what all the other people did. Or do you guys just wing it? (But then, why bother with a spacecraft design system at all?)

M-Space has spaceship construction rules, but they do seem to be lacking fuel tanks... which is particularly sad if you wish to use chemical rockets or even hard SF reaction drives in your setting. Has anyone done any work on this in order to get good numbers of Delta V and fuel percentage out of the M-Space spaceship construction system?

Thanks for the hint!

A bit outside the box, but it makes sense... I've added a plant to my setting whose sap eats away the drinker's magic points. Thanks!

For punishing the most evil (by the rulers' definition) people! Thanks for this idea!